Allergy Eyes<\/h1>\r\n<\/div>\r\nEyes that are red, watery, and itchy are typical of an allergic reaction known as allergic rhinitis. Commonly called hay fever, allergic rhinitis is an immune system reaction, typically to the pollen of certain plants. Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes, it responds to harmless foreign substances as though they were pathogens. This is the basis of allergies like hay fever.\r\n\r\nAllergies<\/h1>\r\n<\/div>\r\nAn\u00a0[pb_glossary id=\"4877\"]allergy[\/pb_glossary]<\/strong>\u00a0is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless [pb_glossary id=\"2704\"]antigen[\/pb_glossary]. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.\r\nAllergens<\/h2>\r\nAny antigen that causes an allergy is called an\u00a0[pb_glossary id=\"4999\"]allergen[\/pb_glossary].<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.\r\n\r\n\r\n[h5p id=\"640\"]\r\n\r\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em>\r\n\r\n<\/div>\r\nPrevalence of Allergies<\/h2>\r\nThere has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.\r\n\r\nOne explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.\r\nHow Allergies Occur<\/h2>\r\nThe diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.\r\n\r\n[caption id=\"attachment_5000\" align=\"aligncenter\" width=\"341\"]![\"17.3](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/512px-Mast_cells-2.jpg\")
Figure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em>[\/caption]\r\nTreating Allergies<\/h2>\r\nThe symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with [pb_glossary id=\"5469\"]antihistamines<\/span><\/strong>[\/pb_glossary]<\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span>\r\nTreating Anaphylaxis<\/h3>\r\nThe most severe allergic reaction is a systemic reaction called\u00a0[pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary].<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.\r\n\r\n[caption id=\"attachment_5003\" align=\"alignnone\" width=\"745\"]![\"17.6.4](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Signs_and_symptoms_of_anaphylaxis-2.png\")
Figure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em>[\/caption]\r\nImmunotherapy for Allergies<\/h3>\r\n[caption id=\"attachment_5005\" align=\"alignleft\" width=\"303\"]![\"17.6.5](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Allergy-Tests-2.jpg\")
Figure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em>[\/caption]\r\n\r\nAnother way to treat allergies is called\u00a0[pb_glossary id=\"5004\"]immunotherapy[\/pb_glossary],<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.\r\n\r\nAutoimmune Diseases<\/span>\r\n\r\n[pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary]<\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, [pb_glossary id=\"5539\"]B cells<\/span>[\/pb_glossary]<\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to [pb_glossary id=\"5799\"]pathogen<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span>\r\n\r\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.\r\n\r\nAt a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.\r\nCommon Autoimmune Diseases<\/h2>\r\nAn estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary] and [pb_glossary id=\"5007\"]multiple sclerosis[\/pb_glossary]. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys [pb_glossary id=\"2590\"]insulin[\/pb_glossary]-secreting islet cells in the [pb_glossary id=\"3197\"]pancreas[\/pb_glossary]. In the case of multiple sclerosis, the immune system attacks and destroys the [pb_glossary id=\"3028\"]myelin sheaths<\/span>[\/pb_glossary]<\/span>\u00a0that normally insulate the [pb_glossary id=\"5901\"]axon<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0of <\/span>[pb_glossary id=\"2984\"]neuron<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span>\r\n\r\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include [pb_glossary id=\"5008\"]rheumatoid arthritis[\/pb_glossary] and [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary] (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.\r\n\r\n[caption id=\"attachment_5010\" align=\"aligncenter\" width=\"549\"]![\"Figure](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/1024px-Symptoms_of_SLE-2.png\")
Figure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em>[\/caption]\r\nTreatment for Autoimmune Diseases<\/h2>\r\nNone of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.\r\n\r\nImmunodeficiency<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary]<\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.\r\nCauses of Immunodeficiency<\/h2>\r\nDozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0[pb_glossary id=\"5012\"]primary immunodeficiency[\/pb_glossary]<\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked [pb_glossary id=\"2479\"]recessive[\/pb_glossary] [pb_glossary id=\"2381\"]mutation[\/pb_glossary] that interferes with normal B cell and T cell production.\r\n\r\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0[pb_glossary id=\"5013\"]secondary immunodeficiency[\/pb_glossary]<\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:\r\n\r\n \t- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\r\n \t
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\r\n \t
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\r\n \t
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\r\n \t
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\r\n<\/ul>\r\n\r\n
Focus on HIV<\/h1>\r\n<\/div>\r\nHuman immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary])<\/strong> is the most common cause of immunodeficiency in the world today. HIV infections of human hosts are a relatively recent phenomenon. Scientists think that the virus originally infected monkeys, but then jumped to human populations. most likely from a bite, probably sometime during the early to mid-1900s. This most likely occurred in West Africa, but the virus soon spread around the world. HIV was first identified by medical researchers in 1981. Since then, HIV has killed almost 40 million people worldwide, and its economic toll has also been enormous. The hardest hit countries are in Africa, where the virus has infected human populations the longest, and medications to control the virus are least available.\u00a0 In 2016, over 63,000 Canadians were living with HIV.\r\nHIV Transmission<\/h2>\r\nHIV is transmitted through direct contact of [pb_glossary id=\"3538\"]mucous membranes<\/span>[\/pb_glossary]<\/span> or body fluids such as blood, semen, or breast milk. As shown in Figure 17.6.7, transmission of the virus can occur through sexual contact or the use of contaminated hypodermic needles. It can also be transmitted from an infected mother\u2019s blood during late pregnancy or childbirth, or through breast milk after birth. In the past, HIV was also transmitted occasionally through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way.<\/span>\r\n\r\n[caption id=\"attachment_5014\" align=\"aligncenter\" width=\"500\"]![\"17.6.7](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/HIV-transmission-2.jpg\")
Figure 17.6.7 HIV may be transmitted in all of the ways shown here: through sexual activities, from mother to child (in utero, during childbirth, through breastmilk), and by sharing needles.<\/em>[\/caption]\r\nHIV and the Immune System<\/h2>\r\nHIV infects and destroys [pb_glossary id=\"5537\"]helper T cells<\/span>[\/pb_glossary]<\/span>, the type of [pb_glossary id=\"4832\"]lymphocyte<\/span>s<\/span>[\/pb_glossary]<\/span> that regulate the immune response. This process is illustrated in the diagram in Figure 17.6.8. The virus injects its own DNA into a helper T cell and uses the T cell\u2019s \u201cmachinery\u201d to make copies of itself. In the process, the helper T cell is destroyed, and the virus copies go on to infect other helper T cells. HIV is able to evade the immune system and keep destroying helper T cells by mutating frequently so its surface antigens keep changing, and by using the host cell\u2019s membrane to hide its own antigens.<\/span>\r\n\r\n[caption id=\"attachment_5015\" align=\"aligncenter\" width=\"500\"]![\"17.6.8](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/HIV-life-cycle-2.jpg\")
Figure 17.6.8 This diagram shows how HIV infects and destroys helper T cells.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"5016\"]Acquired immunodeficiency syndrome[\/pb_glossary] (AIDS)<\/strong> may result from years of damage to the immune system by HIV. It occurs when helper T cells fall to a very low level and opportunistic diseases occur. Opportunistic diseases are infections and tumors that are rare, except in people with a damaged immune system. The diseases take advantage of the \u201copportunity\u201d presented by people whose immune system cannot fight back. Opportunistic diseases are usually the direct cause of death for people with AIDS.\r\nTreating HIV\/AIDS<\/h2>\r\nFor patients who have access to HIV medications, infection with the virus is no longer the death sentence\u00a0that it once was. By 1995, combinations of drugs called \u201chighly active antiretroviral therapy\u201d were developed. For some patients, these drugs can reduce the amount of virus they are carrying to undetectable levels. However, some\u00a0level\u00a0of virus always hides in the body\u2019s immune cells, and it will multiply again if a patient stops taking the medications. Researchers are trying to develop drugs to kill these hidden viruses, as well. If their efforts are successful, it could end AIDS.\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nEpiPens\u00ae and their sole manufacturer (pharmaceutical company Mylan) were featured in headlines in 2016, but not for a good reason. The media\u00a0outburst\u00a0was triggered by a drastic price hike in EpiPens\u00ae \u2014 and Mylan\u2019s apparent greed.\r\n\r\n[caption id=\"attachment_5017\" align=\"alignleft\" width=\"290\"]![\"17.6.9](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Epipen-by-Stock-Catalog-on-flickr-e1592884964782-2.jpg\")
Figure 17.6.9 An Epipen\u00ae is a hypodermic device that administers a dose of epinephrine, used for the emergency treatment of an acute allergic reaction.<\/em>[\/caption]\r\n\r\nEpiPens\u00ae are auto-injectable syringes preloaded with a measured dose of epinephrine, a drug that can rapidly stop a life-threatening anaphylactic response to an allergen. Using the device is easy and does not require any special training. The injector just needs to be jammed against the thigh, which can be done through clothing or on bare skin. Each year, doctors write millions of prescriptions for EpiPens\u00ae. Many people with severe allergies always carry two of the devices with them, just in case they experience anaphylaxis, although most of them never need to use them. Other people with severe allergies have literally had their lives saved multiple times by EpiPens\u00ae when they had anaphylactic reactions. Even when the devices haven\u2019t been used, they must be replaced each year due to expiration of the epinephrine.\r\n\r\nYou might think that EpiPens\u00ae would be relatively inexpensive, given their life-saving potential. As recently as 2009, a two-pack of EpiPens\u00ae cost about $100. However, in just seven years, the cost of the same two-pack of EpiPens\u00ae skyrocketed by an incredible 400%! By 2016, the cost was $600 or more. Mylan apparently raised the price for the sole purpose of increasing profits. The company also raised prices significantly on many other drugs. The price hike in EpiPens\u00ae alone was certainly profitable. In 2015, the sale of EpiPens\u00ae earned Mylan $1 billion. Mylan\u2019s CEO took home almost $19 million the same year, which was an increase of more than 600% over her prior salary.\r\n\r\nNews coverage of the price hike in EpiPens\u00ae began in the summer of 2016 after a price increase in May of that year. Both private citizens and elected officials expressed outrage over the price increase, especially when coupled with the gluttonous profits of the company and its CEO. By late August, Mylan responded to the backlash by offering discount coupons for EpiPens\u00ae. A few days later, the company promised to introduce a cheaper, generic version of the device. Analysts quickly determined that selling a generic version would allow Mylan to make more money on the product than reducing the price of the name-brand device, which they still declined to do. By September of 2016, Mylan was being investigated for antitrust violations\u00a0related\u00a0to sales of EpiPens\u00ae to public schools in New York City.\r\n\r\nThe Mylan\/EpiPen\u00ae story may still be making the news. But whatever its outcome, the story has already added fuel to public and private debates about important ethical issues\u00a0\u2014\u00a0issues such as the excessive costs of life-saving drugs and the huge profits of big pharma. What is the most recent news on EpiPens\u00ae and Mylan? If you are interested, you can check the headlines online to find out. What are your views on the ethical issues they raise?\r\n\r\n17.6 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless antigen. Any [pb_glossary id=\"2704\"]antigen[\/pb_glossary] that causes allergies is called an [pb_glossary id=\"4999\"]allergen[\/pb_glossary]. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\r\n \t
- The prevalence of allergies has been increasing for decades, especially in developed countries, where they are much more common than in developing countries. The hygiene hypothesis posits that this has occurred because humans evolved to cope with more pathogens than we now typically face in our relatively sterile environments in developed countries. As a result, the immune system \u201ckeeps busy\u201d by attacking harmless antigens.<\/li>\r\n \t
- Allergies occur when [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]. On subsequent exposures to the allergen, the mast cells immediately release [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]\u00a0that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with [pb_glossary id=\"5469\"]antihistamines[\/pb_glossary]\u00a0that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called [pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary], is a medical emergency that is usually treated with injections of epinephrine. [pb_glossary id=\"5004\"]Immunotherapy[\/pb_glossary] for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary] occur when the immune system fails to recognize the body\u2019s own molecules as self and attacks them, causing damage to tissues and organs. A family history of autoimmunity and female gender are risk factors for autoimmune diseases.<\/li>\r\n \t
- In some autoimmune diseases, such as [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary], the immune system attacks and damages specific body cells. In other autoimmune diseases, such as [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary], many different tissues and organs may be attacked and injured. Autoimmune diseases generally cannot be cured, but their symptoms can often be managed with drugs or other treatments.<\/li>\r\n \t
- [pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary] occurs when the immune system is not working properly, generally because one or more of its components are inactive. As a result, the immune system is unable to fight off pathogens or cancers that a normal immune system would be able to resist.<\/li>\r\n \t
- [pb_glossary id=\"5012\"]Primary immunodeficiency[\/pb_glossary] is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. [pb_glossary id=\"5013\"]Secondary immunodeficiency[\/pb_glossary] occurs because of some event or exposure experienced after birth. Possible causes include aging, certain medications, infections with pathogens, and other disorders, such as obesity or malnutrition.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]), which infects and destroys helper T cells. HIV is transmitted through mucous membranes or body fluids. The virus may eventually lead to such low levels of helper T cells that opportunistic infections occur. When this happens, the patient is diagnosed with [pb_glossary id=\"5016\"]acquired immunodeficiency syndrome[\/pb_glossary] (AIDS). Medications can control the multiplication of HIV in the human body \u2014 but they don't eliminate the [pb_glossary id=\"4283\"]virus[\/pb_glossary] completely.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"641\"]<\/li>\r\n \t
- How does immunotherapy for allergies work?<\/li>\r\n \t
- What are autoimmune diseases?<\/li>\r\n \t
- Identify two risk factors for autoimmune diseases.<\/li>\r\n \t
- Autoimmune diseases may be specific to particular tissues, or they may be systemic. Give an example of each type of autoimmune disease.<\/li>\r\n \t
- What is immunodeficiency? Compare and contrast primary and secondary immunodeficiency. Give an example of each.<\/li>\r\n \t
- What is the most common cause of immunodeficiency in the world today? How does this affect the immune system?<\/li>\r\n \t
- Distinguish between HIV and AIDS.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/-q7Fz7NIMWM\r\nWhy do people have seasonal allergies? - Eleanor Nelsen, TED-Ed, 2016.<\/p>\r\nhttps:\/\/youtu.be\/0TipTogQT3E\r\n
Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, TED-Ed, 2015.<\/p>\r\nhttps:\/\/youtu.be\/pJa6KVLwl9U\r\n
The Boy in the Bubble | Retro Report | The New York Times, 2015.<\/p>\r\nhttps:\/\/youtu.be\/Mjr9h_QmdeM\r\n
Why Are Peanut Allergies Becoming So Common? Seeker, 2014.<\/p>\r\nhttps:\/\/youtu.be\/RiMSmDBvgto\r\n
What Are Tonsil Stones? | Gross Science, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 17.6.1<\/strong>\r\n\r\nOedema<\/a> by Championswimmer<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.2<\/strong>\r\n\r\n \t- Medical (latex) gloves<\/a> from pngimg.com is used under a CC BY-NC 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/) license.<\/li>\r\n \t
- House dust mites (5247996458)<\/a> by Gilles San Martin<\/a> from Namur, Belgium on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\r\n \t
- \u00a0Honey bee macro<\/a> by Karunakar Rayker<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/li>\r\n \t
- Peanuts<\/a> by Karolina Grabowska<\/a> on Pexels<\/a> is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Photo of dog and grey cat<\/a> by ERC4N51<\/a> on pxhere is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Tags: Pollen Allergy Spring<\/a>\u00a0by Castagnari53<\/a> on Pixabay<\/a>, is used under the Pixabay License<\/a> (https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\nFigure 17.6.3<\/strong>\r\n\r\n512px-Mast_cells<\/a> by National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute<\/a> (p.29) is in\u00a0the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.4<\/strong>\r\n\r\nSigns_and_symptoms_of_anaphylaxis<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\n\r\nFigure 17.6.5<\/strong>\r\n\r\nAllergy Tests<\/a> by Dan Pupius<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 17.6.6<\/strong>\r\n\r\n1024px-Symptoms_of_SLE<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons\u00a0is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\nFigure 17.6.7<\/strong>\r\n\r\nHIV transmission<\/a>\u00a0by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n
![\"\"](\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/logo_ck12.png\")
\u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span>![\"CK-12](\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/icon_licence.png\" "\\"CK-12")
<\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 17.6.8<\/strong>\r\n\r\nHIV life cycle<\/a> by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 17.6.9<\/strong>\r\n\r\nEpipen by Stock Catalog on flickr<\/a> by Stock Catalog<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\nReferences<\/h2>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 8 HIV may be transmitted in all of the ways shown here [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nBrainard, J\/ CK-12 Foundation. (2016). Figure 9 This diagram shows how HIV infects and destroys helper T cells [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nCBS News. (2016, August 16). Rising cost of potentially life-saving EpiPen puts pinch on families [online article]. CBS Interactive Inc. https:\/\/www.cbsnews.com\/news\/allergy-medication-epipen-epinephrine-rising-costs-impact-on-families\/<\/p>\r\n
Gross Science. (2015, June 29). What are tonsil stones? | Gross Science. YouTube. https:\/\/www.youtube.com\/watch?v=RiMSmDBvgto&feature=youtu.be<\/p>\r\n
H\u00e4ggstr\u00f6m, M. (2014). Medical gallery of Mikael H\u00e4ggstr\u00f6m 2014.\u00a0WikiJournal of Medicine<\/i>\u00a01<\/b>\u00a0(2).\u00a0DOI:10.15347\/wjm\/2014.008.\u00a0ISSN\u00a02002-4436<\/p>\r\n
National Institute of Allergy and Infectious Diseases (NIAID). (n.d.). Severe combined immunodeficiency (SCID) [online article]. National Institute of Health (NIH). https:\/\/www.niaid.nih.gov\/diseases-conditions\/severe-combined-immunodeficiency-scid<\/p>\r\n
National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute (U.S.). (2003, September). Understanding the immune system and how it works [NIH Publication No. 03-5423]. Scholar Works<\/em> - \u00a0Indiana University. https:\/\/scholarworks.iupui.edu\/handle\/1805\/748<\/p>\r\n[The] New York Times. (2015, December 15). The boy in the bubble | Retro Report | The New York Times. YouTube. https:\/\/www.youtube.com\/watch?v=pJa6KVLwl9U&feature=youtu.be<\/p>\r\n
Seeker. (2014, October 3). Why are peanut allergies becoming so common? YouTube. https:\/\/www.youtube.com\/watch?v=Mjr9h_QmdeM&feature=youtu.be<\/p>\r\n
Summary: Estimates of HIV incidence, prevalence, and Canada's progress on meeting the 90-90-90 HIV targets 2016. (2018, July). Public Health Agency of Canada. https:\/\/www.canada.ca\/content\/dam\/phac-aspc\/documents\/services\/publications\/diseases-conditions\/summary-estimates-hiv-incidence-prevalence-canadas-progress-90-90-90\/pub-eng.pdf<\/p>\r\n
Swetlitz, I., Silverman, E. (2016, August 25). Mylan may have violated antitrust law in its EpiPen sales to schools, legal experts say [online article]. STATNews.com. https:\/\/www.statnews.com\/2016\/08\/25\/mylan-antitrust-epipen-schools\/<\/p>\r\n
TED-Ed. (2016, May 26). Why do people have seasonal allergies? - Eleanor Nelsen. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=-q7Fz7NIMWM&feature=youtu.be<\/p>\r\n
TED-Ed. (2015, March 16). Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, https:\/\/www.youtube.com\/watch?v=0TipTogQT3E&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\n![\"17.6.1](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Oedema-2.jpg\")
Figure 17.6.1 Oh m-eye!<\/em><\/figcaption><\/figure>\n\nAllergy Eyes<\/h1>\n<\/div>\n
Eyes that are red, watery, and itchy are typical of an allergic reaction known as allergic rhinitis. Commonly called hay fever, allergic rhinitis is an immune system reaction, typically to the pollen of certain plants. Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes, it responds to harmless foreign substances as though they were pathogens. This is the basis of allergies like hay fever.<\/p>\n
\nAllergies<\/h1>\n<\/div>\n
An\u00a0allergy<\/a><\/strong>\u00a0is a disorder in which the immune system makes an inflammatory response<\/a> to a harmless antigen<\/a>. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.<\/p>\nAllergens<\/h2>\n
Any antigen that causes an allergy is called an\u00a0allergen<\/a>.<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.<\/p>\n\n\n<\/div>\n<\/div>\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em><\/p>\n<\/div>\nPrevalence of Allergies<\/h2>\n
There has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.<\/p>\n
One explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.<\/p>\n
How Allergies Occur<\/h2>\n
The diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.<\/p>\nFigure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em><\/figcaption><\/figure>\nTreating Allergies<\/h2>\n
The symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with antihistamines<\/span><\/strong><\/a><\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span><\/p>\nTreating Anaphylaxis<\/h3>\n
The most severe allergic reaction is a systemic reaction called\u00a0anaphylaxis<\/a>.<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.<\/p>\nFigure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em><\/figcaption><\/figure>\nImmunotherapy for Allergies<\/h3>\nFigure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em><\/figcaption><\/figure>\nAnother way to treat allergies is called\u00a0immunotherapy<\/a>,<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.<\/p>\nAutoimmune Diseases<\/span><\/p>\nAutoimmune diseases<\/a><\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, B cells<\/span><\/a><\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to pathogen<\/span>s<\/span><\/a><\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span><\/p>\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.<\/p>\n
At a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.<\/p>\n
Common Autoimmune Diseases<\/h2>\n
An estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are type I diabetes<\/a> and multiple sclerosis<\/a>. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys insulin<\/a>-secreting islet cells in the pancreas<\/a>. In the case of multiple sclerosis, the immune system attacks and destroys the myelin sheaths<\/span><\/a><\/span>\u00a0that normally insulate the axon<\/span>s<\/span><\/a><\/span>\u00a0of <\/span>neuron<\/span>s<\/span><\/a><\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span><\/p>\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include rheumatoid arthritis<\/a> and systemic lupus erythematosus<\/a> (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.<\/p>\nFigure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em><\/figcaption><\/figure>\nTreatment for Autoimmune Diseases<\/h2>\n
None of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.<\/p>\n
\nImmunodeficiency<\/h1>\n<\/div>\n
Immunodeficiency<\/a><\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.<\/p>\nCauses of Immunodeficiency<\/h2>\n
Dozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0primary immunodeficiency<\/a><\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked recessive<\/a> mutation<\/a> that interferes with normal B cell and T cell production.<\/p>\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0secondary immunodeficiency<\/a><\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:<\/p>\n\n- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\n
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\n
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\n
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\n
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\n<\/ul>\n\n
Focus on HIV<\/h1>\n<\/div>\n
Human immunodeficiency virus (
Allergies<\/h1>\r\n<\/div>\r\nAn\u00a0[pb_glossary id=\"4877\"]allergy[\/pb_glossary]<\/strong>\u00a0is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless [pb_glossary id=\"2704\"]antigen[\/pb_glossary]. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.\r\nAllergens<\/h2>\r\nAny antigen that causes an allergy is called an\u00a0[pb_glossary id=\"4999\"]allergen[\/pb_glossary].<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.\r\n\r\n\r\n[h5p id=\"640\"]\r\n\r\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em>\r\n\r\n<\/div>\r\nPrevalence of Allergies<\/h2>\r\nThere has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.\r\n\r\nOne explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.\r\nHow Allergies Occur<\/h2>\r\nThe diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.\r\n\r\n[caption id=\"attachment_5000\" align=\"aligncenter\" width=\"341\"] Figure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em>[\/caption]\r\nTreating Allergies<\/h2>\r\nThe symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with [pb_glossary id=\"5469\"]antihistamines<\/span><\/strong>[\/pb_glossary]<\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span>\r\nTreating Anaphylaxis<\/h3>\r\nThe most severe allergic reaction is a systemic reaction called\u00a0[pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary].<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.\r\n\r\n[caption id=\"attachment_5003\" align=\"alignnone\" width=\"745\"] Figure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em>[\/caption]\r\nImmunotherapy for Allergies<\/h3>\r\n[caption id=\"attachment_5005\" align=\"alignleft\" width=\"303\"] Figure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em>[\/caption]\r\n\r\nAnother way to treat allergies is called\u00a0[pb_glossary id=\"5004\"]immunotherapy[\/pb_glossary],<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.\r\n\r\nAutoimmune Diseases<\/span>\r\n\r\n[pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary]<\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, [pb_glossary id=\"5539\"]B cells<\/span>[\/pb_glossary]<\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to [pb_glossary id=\"5799\"]pathogen<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span>\r\n\r\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.\r\n\r\nAt a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.\r\nCommon Autoimmune Diseases<\/h2>\r\nAn estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary] and [pb_glossary id=\"5007\"]multiple sclerosis[\/pb_glossary]. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys [pb_glossary id=\"2590\"]insulin[\/pb_glossary]-secreting islet cells in the [pb_glossary id=\"3197\"]pancreas[\/pb_glossary]. In the case of multiple sclerosis, the immune system attacks and destroys the [pb_glossary id=\"3028\"]myelin sheaths<\/span>[\/pb_glossary]<\/span>\u00a0that normally insulate the [pb_glossary id=\"5901\"]axon<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0of <\/span>[pb_glossary id=\"2984\"]neuron<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span>\r\n\r\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include [pb_glossary id=\"5008\"]rheumatoid arthritis[\/pb_glossary] and [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary] (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.\r\n\r\n[caption id=\"attachment_5010\" align=\"aligncenter\" width=\"549\"] Figure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em>[\/caption]\r\nTreatment for Autoimmune Diseases<\/h2>\r\nNone of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.\r\n\r\nImmunodeficiency<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary]<\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.\r\nCauses of Immunodeficiency<\/h2>\r\nDozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0[pb_glossary id=\"5012\"]primary immunodeficiency[\/pb_glossary]<\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked [pb_glossary id=\"2479\"]recessive[\/pb_glossary] [pb_glossary id=\"2381\"]mutation[\/pb_glossary] that interferes with normal B cell and T cell production.\r\n\r\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0[pb_glossary id=\"5013\"]secondary immunodeficiency[\/pb_glossary]<\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:\r\n\r\n \t- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\r\n \t
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\r\n \t
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\r\n \t
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\r\n \t
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\r\n<\/ul>\r\n\r\n
Focus on HIV<\/h1>\r\n<\/div>\r\nHuman immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary])<\/strong> is the most common cause of immunodeficiency in the world today. HIV infections of human hosts are a relatively recent phenomenon. Scientists think that the virus originally infected monkeys, but then jumped to human populations. most likely from a bite, probably sometime during the early to mid-1900s. This most likely occurred in West Africa, but the virus soon spread around the world. HIV was first identified by medical researchers in 1981. Since then, HIV has killed almost 40 million people worldwide, and its economic toll has also been enormous. The hardest hit countries are in Africa, where the virus has infected human populations the longest, and medications to control the virus are least available.\u00a0 In 2016, over 63,000 Canadians were living with HIV.\r\nHIV Transmission<\/h2>\r\nHIV is transmitted through direct contact of [pb_glossary id=\"3538\"]mucous membranes<\/span>[\/pb_glossary]<\/span> or body fluids such as blood, semen, or breast milk. As shown in Figure 17.6.7, transmission of the virus can occur through sexual contact or the use of contaminated hypodermic needles. It can also be transmitted from an infected mother\u2019s blood during late pregnancy or childbirth, or through breast milk after birth. In the past, HIV was also transmitted occasionally through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way.<\/span>\r\n\r\n[caption id=\"attachment_5014\" align=\"aligncenter\" width=\"500\"] Figure 17.6.7 HIV may be transmitted in all of the ways shown here: through sexual activities, from mother to child (in utero, during childbirth, through breastmilk), and by sharing needles.<\/em>[\/caption]\r\nHIV and the Immune System<\/h2>\r\nHIV infects and destroys [pb_glossary id=\"5537\"]helper T cells<\/span>[\/pb_glossary]<\/span>, the type of [pb_glossary id=\"4832\"]lymphocyte<\/span>s<\/span>[\/pb_glossary]<\/span> that regulate the immune response. This process is illustrated in the diagram in Figure 17.6.8. The virus injects its own DNA into a helper T cell and uses the T cell\u2019s \u201cmachinery\u201d to make copies of itself. In the process, the helper T cell is destroyed, and the virus copies go on to infect other helper T cells. HIV is able to evade the immune system and keep destroying helper T cells by mutating frequently so its surface antigens keep changing, and by using the host cell\u2019s membrane to hide its own antigens.<\/span>\r\n\r\n[caption id=\"attachment_5015\" align=\"aligncenter\" width=\"500\"] Figure 17.6.8 This diagram shows how HIV infects and destroys helper T cells.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"5016\"]Acquired immunodeficiency syndrome[\/pb_glossary] (AIDS)<\/strong> may result from years of damage to the immune system by HIV. It occurs when helper T cells fall to a very low level and opportunistic diseases occur. Opportunistic diseases are infections and tumors that are rare, except in people with a damaged immune system. The diseases take advantage of the \u201copportunity\u201d presented by people whose immune system cannot fight back. Opportunistic diseases are usually the direct cause of death for people with AIDS.\r\nTreating HIV\/AIDS<\/h2>\r\nFor patients who have access to HIV medications, infection with the virus is no longer the death sentence\u00a0that it once was. By 1995, combinations of drugs called \u201chighly active antiretroviral therapy\u201d were developed. For some patients, these drugs can reduce the amount of virus they are carrying to undetectable levels. However, some\u00a0level\u00a0of virus always hides in the body\u2019s immune cells, and it will multiply again if a patient stops taking the medications. Researchers are trying to develop drugs to kill these hidden viruses, as well. If their efforts are successful, it could end AIDS.\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nEpiPens\u00ae and their sole manufacturer (pharmaceutical company Mylan) were featured in headlines in 2016, but not for a good reason. The media\u00a0outburst\u00a0was triggered by a drastic price hike in EpiPens\u00ae \u2014 and Mylan\u2019s apparent greed.\r\n\r\n[caption id=\"attachment_5017\" align=\"alignleft\" width=\"290\"] Figure 17.6.9 An Epipen\u00ae is a hypodermic device that administers a dose of epinephrine, used for the emergency treatment of an acute allergic reaction.<\/em>[\/caption]\r\n\r\nEpiPens\u00ae are auto-injectable syringes preloaded with a measured dose of epinephrine, a drug that can rapidly stop a life-threatening anaphylactic response to an allergen. Using the device is easy and does not require any special training. The injector just needs to be jammed against the thigh, which can be done through clothing or on bare skin. Each year, doctors write millions of prescriptions for EpiPens\u00ae. Many people with severe allergies always carry two of the devices with them, just in case they experience anaphylaxis, although most of them never need to use them. Other people with severe allergies have literally had their lives saved multiple times by EpiPens\u00ae when they had anaphylactic reactions. Even when the devices haven\u2019t been used, they must be replaced each year due to expiration of the epinephrine.\r\n\r\nYou might think that EpiPens\u00ae would be relatively inexpensive, given their life-saving potential. As recently as 2009, a two-pack of EpiPens\u00ae cost about $100. However, in just seven years, the cost of the same two-pack of EpiPens\u00ae skyrocketed by an incredible 400%! By 2016, the cost was $600 or more. Mylan apparently raised the price for the sole purpose of increasing profits. The company also raised prices significantly on many other drugs. The price hike in EpiPens\u00ae alone was certainly profitable. In 2015, the sale of EpiPens\u00ae earned Mylan $1 billion. Mylan\u2019s CEO took home almost $19 million the same year, which was an increase of more than 600% over her prior salary.\r\n\r\nNews coverage of the price hike in EpiPens\u00ae began in the summer of 2016 after a price increase in May of that year. Both private citizens and elected officials expressed outrage over the price increase, especially when coupled with the gluttonous profits of the company and its CEO. By late August, Mylan responded to the backlash by offering discount coupons for EpiPens\u00ae. A few days later, the company promised to introduce a cheaper, generic version of the device. Analysts quickly determined that selling a generic version would allow Mylan to make more money on the product than reducing the price of the name-brand device, which they still declined to do. By September of 2016, Mylan was being investigated for antitrust violations\u00a0related\u00a0to sales of EpiPens\u00ae to public schools in New York City.\r\n\r\nThe Mylan\/EpiPen\u00ae story may still be making the news. But whatever its outcome, the story has already added fuel to public and private debates about important ethical issues\u00a0\u2014\u00a0issues such as the excessive costs of life-saving drugs and the huge profits of big pharma. What is the most recent news on EpiPens\u00ae and Mylan? If you are interested, you can check the headlines online to find out. What are your views on the ethical issues they raise?\r\n\r\n17.6 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless antigen. Any [pb_glossary id=\"2704\"]antigen[\/pb_glossary] that causes allergies is called an [pb_glossary id=\"4999\"]allergen[\/pb_glossary]. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\r\n \t
- The prevalence of allergies has been increasing for decades, especially in developed countries, where they are much more common than in developing countries. The hygiene hypothesis posits that this has occurred because humans evolved to cope with more pathogens than we now typically face in our relatively sterile environments in developed countries. As a result, the immune system \u201ckeeps busy\u201d by attacking harmless antigens.<\/li>\r\n \t
- Allergies occur when [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]. On subsequent exposures to the allergen, the mast cells immediately release [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]\u00a0that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with [pb_glossary id=\"5469\"]antihistamines[\/pb_glossary]\u00a0that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called [pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary], is a medical emergency that is usually treated with injections of epinephrine. [pb_glossary id=\"5004\"]Immunotherapy[\/pb_glossary] for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary] occur when the immune system fails to recognize the body\u2019s own molecules as self and attacks them, causing damage to tissues and organs. A family history of autoimmunity and female gender are risk factors for autoimmune diseases.<\/li>\r\n \t
- In some autoimmune diseases, such as [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary], the immune system attacks and damages specific body cells. In other autoimmune diseases, such as [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary], many different tissues and organs may be attacked and injured. Autoimmune diseases generally cannot be cured, but their symptoms can often be managed with drugs or other treatments.<\/li>\r\n \t
- [pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary] occurs when the immune system is not working properly, generally because one or more of its components are inactive. As a result, the immune system is unable to fight off pathogens or cancers that a normal immune system would be able to resist.<\/li>\r\n \t
- [pb_glossary id=\"5012\"]Primary immunodeficiency[\/pb_glossary] is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. [pb_glossary id=\"5013\"]Secondary immunodeficiency[\/pb_glossary] occurs because of some event or exposure experienced after birth. Possible causes include aging, certain medications, infections with pathogens, and other disorders, such as obesity or malnutrition.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]), which infects and destroys helper T cells. HIV is transmitted through mucous membranes or body fluids. The virus may eventually lead to such low levels of helper T cells that opportunistic infections occur. When this happens, the patient is diagnosed with [pb_glossary id=\"5016\"]acquired immunodeficiency syndrome[\/pb_glossary] (AIDS). Medications can control the multiplication of HIV in the human body \u2014 but they don't eliminate the [pb_glossary id=\"4283\"]virus[\/pb_glossary] completely.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"641\"]<\/li>\r\n \t
- How does immunotherapy for allergies work?<\/li>\r\n \t
- What are autoimmune diseases?<\/li>\r\n \t
- Identify two risk factors for autoimmune diseases.<\/li>\r\n \t
- Autoimmune diseases may be specific to particular tissues, or they may be systemic. Give an example of each type of autoimmune disease.<\/li>\r\n \t
- What is immunodeficiency? Compare and contrast primary and secondary immunodeficiency. Give an example of each.<\/li>\r\n \t
- What is the most common cause of immunodeficiency in the world today? How does this affect the immune system?<\/li>\r\n \t
- Distinguish between HIV and AIDS.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/-q7Fz7NIMWM\r\nWhy do people have seasonal allergies? - Eleanor Nelsen, TED-Ed, 2016.<\/p>\r\nhttps:\/\/youtu.be\/0TipTogQT3E\r\n
Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, TED-Ed, 2015.<\/p>\r\nhttps:\/\/youtu.be\/pJa6KVLwl9U\r\n
The Boy in the Bubble | Retro Report | The New York Times, 2015.<\/p>\r\nhttps:\/\/youtu.be\/Mjr9h_QmdeM\r\n
Why Are Peanut Allergies Becoming So Common? Seeker, 2014.<\/p>\r\nhttps:\/\/youtu.be\/RiMSmDBvgto\r\n
What Are Tonsil Stones? | Gross Science, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 17.6.1<\/strong>\r\n\r\nOedema<\/a> by Championswimmer<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.2<\/strong>\r\n\r\n \t- Medical (latex) gloves<\/a> from pngimg.com is used under a CC BY-NC 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/) license.<\/li>\r\n \t
- House dust mites (5247996458)<\/a> by Gilles San Martin<\/a> from Namur, Belgium on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\r\n \t
- \u00a0Honey bee macro<\/a> by Karunakar Rayker<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/li>\r\n \t
- Peanuts<\/a> by Karolina Grabowska<\/a> on Pexels<\/a> is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Photo of dog and grey cat<\/a> by ERC4N51<\/a> on pxhere is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Tags: Pollen Allergy Spring<\/a>\u00a0by Castagnari53<\/a> on Pixabay<\/a>, is used under the Pixabay License<\/a> (https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\nFigure 17.6.3<\/strong>\r\n\r\n512px-Mast_cells<\/a> by National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute<\/a> (p.29) is in\u00a0the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.4<\/strong>\r\n\r\nSigns_and_symptoms_of_anaphylaxis<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\n\r\nFigure 17.6.5<\/strong>\r\n\r\nAllergy Tests<\/a> by Dan Pupius<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 17.6.6<\/strong>\r\n\r\n1024px-Symptoms_of_SLE<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons\u00a0is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\nFigure 17.6.7<\/strong>\r\n\r\nHIV transmission<\/a>\u00a0by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 17.6.8<\/strong>\r\n\r\nHIV life cycle<\/a> by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 17.6.9<\/strong>\r\n\r\nEpipen by Stock Catalog on flickr<\/a> by Stock Catalog<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n
References<\/h2>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 8 HIV may be transmitted in all of the ways shown here [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nBrainard, J\/ CK-12 Foundation. (2016). Figure 9 This diagram shows how HIV infects and destroys helper T cells [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nCBS News. (2016, August 16). Rising cost of potentially life-saving EpiPen puts pinch on families [online article]. CBS Interactive Inc. https:\/\/www.cbsnews.com\/news\/allergy-medication-epipen-epinephrine-rising-costs-impact-on-families\/<\/p>\r\n
Gross Science. (2015, June 29). What are tonsil stones? | Gross Science. YouTube. https:\/\/www.youtube.com\/watch?v=RiMSmDBvgto&feature=youtu.be<\/p>\r\n
H\u00e4ggstr\u00f6m, M. (2014). Medical gallery of Mikael H\u00e4ggstr\u00f6m 2014.\u00a0WikiJournal of Medicine<\/i>\u00a01<\/b>\u00a0(2).\u00a0DOI:10.15347\/wjm\/2014.008.\u00a0ISSN\u00a02002-4436<\/p>\r\n
National Institute of Allergy and Infectious Diseases (NIAID). (n.d.). Severe combined immunodeficiency (SCID) [online article]. National Institute of Health (NIH). https:\/\/www.niaid.nih.gov\/diseases-conditions\/severe-combined-immunodeficiency-scid<\/p>\r\n
National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute (U.S.). (2003, September). Understanding the immune system and how it works [NIH Publication No. 03-5423]. Scholar Works<\/em> - \u00a0Indiana University. https:\/\/scholarworks.iupui.edu\/handle\/1805\/748<\/p>\r\n[The] New York Times. (2015, December 15). The boy in the bubble | Retro Report | The New York Times. YouTube. https:\/\/www.youtube.com\/watch?v=pJa6KVLwl9U&feature=youtu.be<\/p>\r\n
Seeker. (2014, October 3). Why are peanut allergies becoming so common? YouTube. https:\/\/www.youtube.com\/watch?v=Mjr9h_QmdeM&feature=youtu.be<\/p>\r\n
Summary: Estimates of HIV incidence, prevalence, and Canada's progress on meeting the 90-90-90 HIV targets 2016. (2018, July). Public Health Agency of Canada. https:\/\/www.canada.ca\/content\/dam\/phac-aspc\/documents\/services\/publications\/diseases-conditions\/summary-estimates-hiv-incidence-prevalence-canadas-progress-90-90-90\/pub-eng.pdf<\/p>\r\n
Swetlitz, I., Silverman, E. (2016, August 25). Mylan may have violated antitrust law in its EpiPen sales to schools, legal experts say [online article]. STATNews.com. https:\/\/www.statnews.com\/2016\/08\/25\/mylan-antitrust-epipen-schools\/<\/p>\r\n
TED-Ed. (2016, May 26). Why do people have seasonal allergies? - Eleanor Nelsen. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=-q7Fz7NIMWM&feature=youtu.be<\/p>\r\n
TED-Ed. (2015, March 16). Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, https:\/\/www.youtube.com\/watch?v=0TipTogQT3E&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 17.6.1 Oh m-eye!<\/em><\/figcaption><\/figure>\n\nAllergy Eyes<\/h1>\n<\/div>\n
Eyes that are red, watery, and itchy are typical of an allergic reaction known as allergic rhinitis. Commonly called hay fever, allergic rhinitis is an immune system reaction, typically to the pollen of certain plants. Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes, it responds to harmless foreign substances as though they were pathogens. This is the basis of allergies like hay fever.<\/p>\n
\nAllergies<\/h1>\n<\/div>\n
An\u00a0allergy<\/a><\/strong>\u00a0is a disorder in which the immune system makes an inflammatory response<\/a> to a harmless antigen<\/a>. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.<\/p>\nAllergens<\/h2>\n
Any antigen that causes an allergy is called an\u00a0allergen<\/a>.<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.<\/p>\n\n\n<\/div>\n<\/div>\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em><\/p>\n<\/div>\nPrevalence of Allergies<\/h2>\n
There has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.<\/p>\n
One explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.<\/p>\n
How Allergies Occur<\/h2>\n
The diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.<\/p>\nFigure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em><\/figcaption><\/figure>\nTreating Allergies<\/h2>\n
The symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with antihistamines<\/span><\/strong><\/a><\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span><\/p>\nTreating Anaphylaxis<\/h3>\n
The most severe allergic reaction is a systemic reaction called\u00a0anaphylaxis<\/a>.<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.<\/p>\nFigure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em><\/figcaption><\/figure>\nImmunotherapy for Allergies<\/h3>\nFigure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em><\/figcaption><\/figure>\nAnother way to treat allergies is called\u00a0immunotherapy<\/a>,<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.<\/p>\nAutoimmune Diseases<\/span><\/p>\nAutoimmune diseases<\/a><\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, B cells<\/span><\/a><\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to pathogen<\/span>s<\/span><\/a><\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span><\/p>\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.<\/p>\n
At a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.<\/p>\n
Common Autoimmune Diseases<\/h2>\n
An estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are type I diabetes<\/a> and multiple sclerosis<\/a>. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys insulin<\/a>-secreting islet cells in the pancreas<\/a>. In the case of multiple sclerosis, the immune system attacks and destroys the myelin sheaths<\/span><\/a><\/span>\u00a0that normally insulate the axon<\/span>s<\/span><\/a><\/span>\u00a0of <\/span>neuron<\/span>s<\/span><\/a><\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span><\/p>\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include rheumatoid arthritis<\/a> and systemic lupus erythematosus<\/a> (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.<\/p>\nFigure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em><\/figcaption><\/figure>\nTreatment for Autoimmune Diseases<\/h2>\n
None of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.<\/p>\n
\nImmunodeficiency<\/h1>\n<\/div>\n
Immunodeficiency<\/a><\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.<\/p>\nCauses of Immunodeficiency<\/h2>\n
Dozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0primary immunodeficiency<\/a><\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked recessive<\/a> mutation<\/a> that interferes with normal B cell and T cell production.<\/p>\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0secondary immunodeficiency<\/a><\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:<\/p>\n\n- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\n
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\n
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\n
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\n
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\n<\/ul>\n\n
Focus on HIV<\/h1>\n<\/div>\n
Human immunodeficiency virus (
Prevalence of Allergies<\/h2>\r\nThere has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.\r\n\r\nOne explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.\r\nHow Allergies Occur<\/h2>\r\nThe diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.\r\n\r\n[caption id=\"attachment_5000\" align=\"aligncenter\" width=\"341\"] Figure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em>[\/caption]\r\nTreating Allergies<\/h2>\r\nThe symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with [pb_glossary id=\"5469\"]antihistamines<\/span><\/strong>[\/pb_glossary]<\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span>\r\nTreating Anaphylaxis<\/h3>\r\nThe most severe allergic reaction is a systemic reaction called\u00a0[pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary].<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.\r\n\r\n[caption id=\"attachment_5003\" align=\"alignnone\" width=\"745\"] Figure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em>[\/caption]\r\nImmunotherapy for Allergies<\/h3>\r\n[caption id=\"attachment_5005\" align=\"alignleft\" width=\"303\"] Figure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em>[\/caption]\r\n\r\nAnother way to treat allergies is called\u00a0[pb_glossary id=\"5004\"]immunotherapy[\/pb_glossary],<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.\r\n\r\nAutoimmune Diseases<\/span>\r\n\r\n[pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary]<\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, [pb_glossary id=\"5539\"]B cells<\/span>[\/pb_glossary]<\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to [pb_glossary id=\"5799\"]pathogen<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span>\r\n\r\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.\r\n\r\nAt a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.\r\nCommon Autoimmune Diseases<\/h2>\r\nAn estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary] and [pb_glossary id=\"5007\"]multiple sclerosis[\/pb_glossary]. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys [pb_glossary id=\"2590\"]insulin[\/pb_glossary]-secreting islet cells in the [pb_glossary id=\"3197\"]pancreas[\/pb_glossary]. In the case of multiple sclerosis, the immune system attacks and destroys the [pb_glossary id=\"3028\"]myelin sheaths<\/span>[\/pb_glossary]<\/span>\u00a0that normally insulate the [pb_glossary id=\"5901\"]axon<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0of <\/span>[pb_glossary id=\"2984\"]neuron<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span>\r\n\r\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include [pb_glossary id=\"5008\"]rheumatoid arthritis[\/pb_glossary] and [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary] (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.\r\n\r\n[caption id=\"attachment_5010\" align=\"aligncenter\" width=\"549\"] Figure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em>[\/caption]\r\nTreatment for Autoimmune Diseases<\/h2>\r\nNone of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.\r\n\r\nImmunodeficiency<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary]<\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.\r\nCauses of Immunodeficiency<\/h2>\r\nDozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0[pb_glossary id=\"5012\"]primary immunodeficiency[\/pb_glossary]<\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked [pb_glossary id=\"2479\"]recessive[\/pb_glossary] [pb_glossary id=\"2381\"]mutation[\/pb_glossary] that interferes with normal B cell and T cell production.\r\n\r\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0[pb_glossary id=\"5013\"]secondary immunodeficiency[\/pb_glossary]<\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:\r\n\r\n \t- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\r\n \t
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\r\n \t
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\r\n \t
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\r\n \t
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\r\n<\/ul>\r\n\r\n
Focus on HIV<\/h1>\r\n<\/div>\r\nHuman immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary])<\/strong> is the most common cause of immunodeficiency in the world today. HIV infections of human hosts are a relatively recent phenomenon. Scientists think that the virus originally infected monkeys, but then jumped to human populations. most likely from a bite, probably sometime during the early to mid-1900s. This most likely occurred in West Africa, but the virus soon spread around the world. HIV was first identified by medical researchers in 1981. Since then, HIV has killed almost 40 million people worldwide, and its economic toll has also been enormous. The hardest hit countries are in Africa, where the virus has infected human populations the longest, and medications to control the virus are least available.\u00a0 In 2016, over 63,000 Canadians were living with HIV.\r\nHIV Transmission<\/h2>\r\nHIV is transmitted through direct contact of [pb_glossary id=\"3538\"]mucous membranes<\/span>[\/pb_glossary]<\/span> or body fluids such as blood, semen, or breast milk. As shown in Figure 17.6.7, transmission of the virus can occur through sexual contact or the use of contaminated hypodermic needles. It can also be transmitted from an infected mother\u2019s blood during late pregnancy or childbirth, or through breast milk after birth. In the past, HIV was also transmitted occasionally through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way.<\/span>\r\n\r\n[caption id=\"attachment_5014\" align=\"aligncenter\" width=\"500\"] Figure 17.6.7 HIV may be transmitted in all of the ways shown here: through sexual activities, from mother to child (in utero, during childbirth, through breastmilk), and by sharing needles.<\/em>[\/caption]\r\nHIV and the Immune System<\/h2>\r\nHIV infects and destroys [pb_glossary id=\"5537\"]helper T cells<\/span>[\/pb_glossary]<\/span>, the type of [pb_glossary id=\"4832\"]lymphocyte<\/span>s<\/span>[\/pb_glossary]<\/span> that regulate the immune response. This process is illustrated in the diagram in Figure 17.6.8. The virus injects its own DNA into a helper T cell and uses the T cell\u2019s \u201cmachinery\u201d to make copies of itself. In the process, the helper T cell is destroyed, and the virus copies go on to infect other helper T cells. HIV is able to evade the immune system and keep destroying helper T cells by mutating frequently so its surface antigens keep changing, and by using the host cell\u2019s membrane to hide its own antigens.<\/span>\r\n\r\n[caption id=\"attachment_5015\" align=\"aligncenter\" width=\"500\"] Figure 17.6.8 This diagram shows how HIV infects and destroys helper T cells.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"5016\"]Acquired immunodeficiency syndrome[\/pb_glossary] (AIDS)<\/strong> may result from years of damage to the immune system by HIV. It occurs when helper T cells fall to a very low level and opportunistic diseases occur. Opportunistic diseases are infections and tumors that are rare, except in people with a damaged immune system. The diseases take advantage of the \u201copportunity\u201d presented by people whose immune system cannot fight back. Opportunistic diseases are usually the direct cause of death for people with AIDS.\r\nTreating HIV\/AIDS<\/h2>\r\nFor patients who have access to HIV medications, infection with the virus is no longer the death sentence\u00a0that it once was. By 1995, combinations of drugs called \u201chighly active antiretroviral therapy\u201d were developed. For some patients, these drugs can reduce the amount of virus they are carrying to undetectable levels. However, some\u00a0level\u00a0of virus always hides in the body\u2019s immune cells, and it will multiply again if a patient stops taking the medications. Researchers are trying to develop drugs to kill these hidden viruses, as well. If their efforts are successful, it could end AIDS.\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nEpiPens\u00ae and their sole manufacturer (pharmaceutical company Mylan) were featured in headlines in 2016, but not for a good reason. The media\u00a0outburst\u00a0was triggered by a drastic price hike in EpiPens\u00ae \u2014 and Mylan\u2019s apparent greed.\r\n\r\n[caption id=\"attachment_5017\" align=\"alignleft\" width=\"290\"] Figure 17.6.9 An Epipen\u00ae is a hypodermic device that administers a dose of epinephrine, used for the emergency treatment of an acute allergic reaction.<\/em>[\/caption]\r\n\r\nEpiPens\u00ae are auto-injectable syringes preloaded with a measured dose of epinephrine, a drug that can rapidly stop a life-threatening anaphylactic response to an allergen. Using the device is easy and does not require any special training. The injector just needs to be jammed against the thigh, which can be done through clothing or on bare skin. Each year, doctors write millions of prescriptions for EpiPens\u00ae. Many people with severe allergies always carry two of the devices with them, just in case they experience anaphylaxis, although most of them never need to use them. Other people with severe allergies have literally had their lives saved multiple times by EpiPens\u00ae when they had anaphylactic reactions. Even when the devices haven\u2019t been used, they must be replaced each year due to expiration of the epinephrine.\r\n\r\nYou might think that EpiPens\u00ae would be relatively inexpensive, given their life-saving potential. As recently as 2009, a two-pack of EpiPens\u00ae cost about $100. However, in just seven years, the cost of the same two-pack of EpiPens\u00ae skyrocketed by an incredible 400%! By 2016, the cost was $600 or more. Mylan apparently raised the price for the sole purpose of increasing profits. The company also raised prices significantly on many other drugs. The price hike in EpiPens\u00ae alone was certainly profitable. In 2015, the sale of EpiPens\u00ae earned Mylan $1 billion. Mylan\u2019s CEO took home almost $19 million the same year, which was an increase of more than 600% over her prior salary.\r\n\r\nNews coverage of the price hike in EpiPens\u00ae began in the summer of 2016 after a price increase in May of that year. Both private citizens and elected officials expressed outrage over the price increase, especially when coupled with the gluttonous profits of the company and its CEO. By late August, Mylan responded to the backlash by offering discount coupons for EpiPens\u00ae. A few days later, the company promised to introduce a cheaper, generic version of the device. Analysts quickly determined that selling a generic version would allow Mylan to make more money on the product than reducing the price of the name-brand device, which they still declined to do. By September of 2016, Mylan was being investigated for antitrust violations\u00a0related\u00a0to sales of EpiPens\u00ae to public schools in New York City.\r\n\r\nThe Mylan\/EpiPen\u00ae story may still be making the news. But whatever its outcome, the story has already added fuel to public and private debates about important ethical issues\u00a0\u2014\u00a0issues such as the excessive costs of life-saving drugs and the huge profits of big pharma. What is the most recent news on EpiPens\u00ae and Mylan? If you are interested, you can check the headlines online to find out. What are your views on the ethical issues they raise?\r\n\r\n17.6 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless antigen. Any [pb_glossary id=\"2704\"]antigen[\/pb_glossary] that causes allergies is called an [pb_glossary id=\"4999\"]allergen[\/pb_glossary]. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\r\n \t
- The prevalence of allergies has been increasing for decades, especially in developed countries, where they are much more common than in developing countries. The hygiene hypothesis posits that this has occurred because humans evolved to cope with more pathogens than we now typically face in our relatively sterile environments in developed countries. As a result, the immune system \u201ckeeps busy\u201d by attacking harmless antigens.<\/li>\r\n \t
- Allergies occur when [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]. On subsequent exposures to the allergen, the mast cells immediately release [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]\u00a0that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with [pb_glossary id=\"5469\"]antihistamines[\/pb_glossary]\u00a0that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called [pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary], is a medical emergency that is usually treated with injections of epinephrine. [pb_glossary id=\"5004\"]Immunotherapy[\/pb_glossary] for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary] occur when the immune system fails to recognize the body\u2019s own molecules as self and attacks them, causing damage to tissues and organs. A family history of autoimmunity and female gender are risk factors for autoimmune diseases.<\/li>\r\n \t
- In some autoimmune diseases, such as [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary], the immune system attacks and damages specific body cells. In other autoimmune diseases, such as [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary], many different tissues and organs may be attacked and injured. Autoimmune diseases generally cannot be cured, but their symptoms can often be managed with drugs or other treatments.<\/li>\r\n \t
- [pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary] occurs when the immune system is not working properly, generally because one or more of its components are inactive. As a result, the immune system is unable to fight off pathogens or cancers that a normal immune system would be able to resist.<\/li>\r\n \t
- [pb_glossary id=\"5012\"]Primary immunodeficiency[\/pb_glossary] is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. [pb_glossary id=\"5013\"]Secondary immunodeficiency[\/pb_glossary] occurs because of some event or exposure experienced after birth. Possible causes include aging, certain medications, infections with pathogens, and other disorders, such as obesity or malnutrition.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]), which infects and destroys helper T cells. HIV is transmitted through mucous membranes or body fluids. The virus may eventually lead to such low levels of helper T cells that opportunistic infections occur. When this happens, the patient is diagnosed with [pb_glossary id=\"5016\"]acquired immunodeficiency syndrome[\/pb_glossary] (AIDS). Medications can control the multiplication of HIV in the human body \u2014 but they don't eliminate the [pb_glossary id=\"4283\"]virus[\/pb_glossary] completely.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"641\"]<\/li>\r\n \t
- How does immunotherapy for allergies work?<\/li>\r\n \t
- What are autoimmune diseases?<\/li>\r\n \t
- Identify two risk factors for autoimmune diseases.<\/li>\r\n \t
- Autoimmune diseases may be specific to particular tissues, or they may be systemic. Give an example of each type of autoimmune disease.<\/li>\r\n \t
- What is immunodeficiency? Compare and contrast primary and secondary immunodeficiency. Give an example of each.<\/li>\r\n \t
- What is the most common cause of immunodeficiency in the world today? How does this affect the immune system?<\/li>\r\n \t
- Distinguish between HIV and AIDS.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/-q7Fz7NIMWM\r\nWhy do people have seasonal allergies? - Eleanor Nelsen, TED-Ed, 2016.<\/p>\r\nhttps:\/\/youtu.be\/0TipTogQT3E\r\n
Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, TED-Ed, 2015.<\/p>\r\nhttps:\/\/youtu.be\/pJa6KVLwl9U\r\n
The Boy in the Bubble | Retro Report | The New York Times, 2015.<\/p>\r\nhttps:\/\/youtu.be\/Mjr9h_QmdeM\r\n
Why Are Peanut Allergies Becoming So Common? Seeker, 2014.<\/p>\r\nhttps:\/\/youtu.be\/RiMSmDBvgto\r\n
What Are Tonsil Stones? | Gross Science, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 17.6.1<\/strong>\r\n\r\nOedema<\/a> by Championswimmer<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.2<\/strong>\r\n\r\n \t- Medical (latex) gloves<\/a> from pngimg.com is used under a CC BY-NC 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/) license.<\/li>\r\n \t
- House dust mites (5247996458)<\/a> by Gilles San Martin<\/a> from Namur, Belgium on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\r\n \t
- \u00a0Honey bee macro<\/a> by Karunakar Rayker<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/li>\r\n \t
- Peanuts<\/a> by Karolina Grabowska<\/a> on Pexels<\/a> is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Photo of dog and grey cat<\/a> by ERC4N51<\/a> on pxhere is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Tags: Pollen Allergy Spring<\/a>\u00a0by Castagnari53<\/a> on Pixabay<\/a>, is used under the Pixabay License<\/a> (https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\nFigure 17.6.3<\/strong>\r\n\r\n512px-Mast_cells<\/a> by National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute<\/a> (p.29) is in\u00a0the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.4<\/strong>\r\n\r\nSigns_and_symptoms_of_anaphylaxis<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\n\r\nFigure 17.6.5<\/strong>\r\n\r\nAllergy Tests<\/a> by Dan Pupius<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 17.6.6<\/strong>\r\n\r\n1024px-Symptoms_of_SLE<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons\u00a0is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\nFigure 17.6.7<\/strong>\r\n\r\nHIV transmission<\/a>\u00a0by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 17.6.8<\/strong>\r\n\r\nHIV life cycle<\/a> by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 17.6.9<\/strong>\r\n\r\nEpipen by Stock Catalog on flickr<\/a> by Stock Catalog<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n
References<\/h2>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 8 HIV may be transmitted in all of the ways shown here [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nBrainard, J\/ CK-12 Foundation. (2016). Figure 9 This diagram shows how HIV infects and destroys helper T cells [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nCBS News. (2016, August 16). Rising cost of potentially life-saving EpiPen puts pinch on families [online article]. CBS Interactive Inc. https:\/\/www.cbsnews.com\/news\/allergy-medication-epipen-epinephrine-rising-costs-impact-on-families\/<\/p>\r\n
Gross Science. (2015, June 29). What are tonsil stones? | Gross Science. YouTube. https:\/\/www.youtube.com\/watch?v=RiMSmDBvgto&feature=youtu.be<\/p>\r\n
H\u00e4ggstr\u00f6m, M. (2014). Medical gallery of Mikael H\u00e4ggstr\u00f6m 2014.\u00a0WikiJournal of Medicine<\/i>\u00a01<\/b>\u00a0(2).\u00a0DOI:10.15347\/wjm\/2014.008.\u00a0ISSN\u00a02002-4436<\/p>\r\n
National Institute of Allergy and Infectious Diseases (NIAID). (n.d.). Severe combined immunodeficiency (SCID) [online article]. National Institute of Health (NIH). https:\/\/www.niaid.nih.gov\/diseases-conditions\/severe-combined-immunodeficiency-scid<\/p>\r\n
National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute (U.S.). (2003, September). Understanding the immune system and how it works [NIH Publication No. 03-5423]. Scholar Works<\/em> - \u00a0Indiana University. https:\/\/scholarworks.iupui.edu\/handle\/1805\/748<\/p>\r\n[The] New York Times. (2015, December 15). The boy in the bubble | Retro Report | The New York Times. YouTube. https:\/\/www.youtube.com\/watch?v=pJa6KVLwl9U&feature=youtu.be<\/p>\r\n
Seeker. (2014, October 3). Why are peanut allergies becoming so common? YouTube. https:\/\/www.youtube.com\/watch?v=Mjr9h_QmdeM&feature=youtu.be<\/p>\r\n
Summary: Estimates of HIV incidence, prevalence, and Canada's progress on meeting the 90-90-90 HIV targets 2016. (2018, July). Public Health Agency of Canada. https:\/\/www.canada.ca\/content\/dam\/phac-aspc\/documents\/services\/publications\/diseases-conditions\/summary-estimates-hiv-incidence-prevalence-canadas-progress-90-90-90\/pub-eng.pdf<\/p>\r\n
Swetlitz, I., Silverman, E. (2016, August 25). Mylan may have violated antitrust law in its EpiPen sales to schools, legal experts say [online article]. STATNews.com. https:\/\/www.statnews.com\/2016\/08\/25\/mylan-antitrust-epipen-schools\/<\/p>\r\n
TED-Ed. (2016, May 26). Why do people have seasonal allergies? - Eleanor Nelsen. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=-q7Fz7NIMWM&feature=youtu.be<\/p>\r\n
TED-Ed. (2015, March 16). Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, https:\/\/www.youtube.com\/watch?v=0TipTogQT3E&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 17.6.1 Oh m-eye!<\/em><\/figcaption><\/figure>\n\nAllergy Eyes<\/h1>\n<\/div>\n
Eyes that are red, watery, and itchy are typical of an allergic reaction known as allergic rhinitis. Commonly called hay fever, allergic rhinitis is an immune system reaction, typically to the pollen of certain plants. Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes, it responds to harmless foreign substances as though they were pathogens. This is the basis of allergies like hay fever.<\/p>\n
\nAllergies<\/h1>\n<\/div>\n
An\u00a0allergy<\/a><\/strong>\u00a0is a disorder in which the immune system makes an inflammatory response<\/a> to a harmless antigen<\/a>. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.<\/p>\nAllergens<\/h2>\n
Any antigen that causes an allergy is called an\u00a0allergen<\/a>.<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.<\/p>\n\n\n<\/div>\n<\/div>\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em><\/p>\n<\/div>\nPrevalence of Allergies<\/h2>\n
There has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.<\/p>\n
One explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.<\/p>\n
How Allergies Occur<\/h2>\n
The diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.<\/p>\nFigure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em><\/figcaption><\/figure>\nTreating Allergies<\/h2>\n
The symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with antihistamines<\/span><\/strong><\/a><\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span><\/p>\nTreating Anaphylaxis<\/h3>\n
The most severe allergic reaction is a systemic reaction called\u00a0anaphylaxis<\/a>.<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.<\/p>\nFigure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em><\/figcaption><\/figure>\nImmunotherapy for Allergies<\/h3>\nFigure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em><\/figcaption><\/figure>\nAnother way to treat allergies is called\u00a0immunotherapy<\/a>,<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.<\/p>\nAutoimmune Diseases<\/span><\/p>\nAutoimmune diseases<\/a><\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, B cells<\/span><\/a><\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to pathogen<\/span>s<\/span><\/a><\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span><\/p>\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.<\/p>\n
At a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.<\/p>\n
Common Autoimmune Diseases<\/h2>\n
An estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are type I diabetes<\/a> and multiple sclerosis<\/a>. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys insulin<\/a>-secreting islet cells in the pancreas<\/a>. In the case of multiple sclerosis, the immune system attacks and destroys the myelin sheaths<\/span><\/a><\/span>\u00a0that normally insulate the axon<\/span>s<\/span><\/a><\/span>\u00a0of <\/span>neuron<\/span>s<\/span><\/a><\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span><\/p>\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include rheumatoid arthritis<\/a> and systemic lupus erythematosus<\/a> (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.<\/p>\nFigure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em><\/figcaption><\/figure>\nTreatment for Autoimmune Diseases<\/h2>\n
None of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.<\/p>\n
\nImmunodeficiency<\/h1>\n<\/div>\n
Immunodeficiency<\/a><\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.<\/p>\nCauses of Immunodeficiency<\/h2>\n
Dozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0primary immunodeficiency<\/a><\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked recessive<\/a> mutation<\/a> that interferes with normal B cell and T cell production.<\/p>\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0secondary immunodeficiency<\/a><\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:<\/p>\n\n- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\n
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\n
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\n
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\n
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\n<\/ul>\n\n
Focus on HIV<\/h1>\n<\/div>\n
Human immunodeficiency virus (
Figure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em>[\/caption]\r\nTreating Allergies<\/h2>\r\nThe symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with [pb_glossary id=\"5469\"]antihistamines<\/span><\/strong>[\/pb_glossary]<\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span>\r\nTreating Anaphylaxis<\/h3>\r\nThe most severe allergic reaction is a systemic reaction called\u00a0[pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary].<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.\r\n\r\n[caption id=\"attachment_5003\" align=\"alignnone\" width=\"745\"] Figure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em>[\/caption]\r\nImmunotherapy for Allergies<\/h3>\r\n[caption id=\"attachment_5005\" align=\"alignleft\" width=\"303\"] Figure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em>[\/caption]\r\n\r\nAnother way to treat allergies is called\u00a0[pb_glossary id=\"5004\"]immunotherapy[\/pb_glossary],<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.\r\n\r\nAutoimmune Diseases<\/span>\r\n\r\n[pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary]<\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, [pb_glossary id=\"5539\"]B cells<\/span>[\/pb_glossary]<\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to [pb_glossary id=\"5799\"]pathogen<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span>\r\n\r\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.\r\n\r\nAt a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.\r\nCommon Autoimmune Diseases<\/h2>\r\nAn estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary] and [pb_glossary id=\"5007\"]multiple sclerosis[\/pb_glossary]. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys [pb_glossary id=\"2590\"]insulin[\/pb_glossary]-secreting islet cells in the [pb_glossary id=\"3197\"]pancreas[\/pb_glossary]. In the case of multiple sclerosis, the immune system attacks and destroys the [pb_glossary id=\"3028\"]myelin sheaths<\/span>[\/pb_glossary]<\/span>\u00a0that normally insulate the [pb_glossary id=\"5901\"]axon<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0of <\/span>[pb_glossary id=\"2984\"]neuron<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span>\r\n\r\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include [pb_glossary id=\"5008\"]rheumatoid arthritis[\/pb_glossary] and [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary] (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.\r\n\r\n[caption id=\"attachment_5010\" align=\"aligncenter\" width=\"549\"] Figure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em>[\/caption]\r\nTreatment for Autoimmune Diseases<\/h2>\r\nNone of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.\r\n\r\nImmunodeficiency<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary]<\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.\r\nCauses of Immunodeficiency<\/h2>\r\nDozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0[pb_glossary id=\"5012\"]primary immunodeficiency[\/pb_glossary]<\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked [pb_glossary id=\"2479\"]recessive[\/pb_glossary] [pb_glossary id=\"2381\"]mutation[\/pb_glossary] that interferes with normal B cell and T cell production.\r\n\r\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0[pb_glossary id=\"5013\"]secondary immunodeficiency[\/pb_glossary]<\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:\r\n\r\n \t- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\r\n \t
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\r\n \t
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\r\n \t
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\r\n \t
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\r\n<\/ul>\r\n\r\n
Focus on HIV<\/h1>\r\n<\/div>\r\nHuman immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary])<\/strong> is the most common cause of immunodeficiency in the world today. HIV infections of human hosts are a relatively recent phenomenon. Scientists think that the virus originally infected monkeys, but then jumped to human populations. most likely from a bite, probably sometime during the early to mid-1900s. This most likely occurred in West Africa, but the virus soon spread around the world. HIV was first identified by medical researchers in 1981. Since then, HIV has killed almost 40 million people worldwide, and its economic toll has also been enormous. The hardest hit countries are in Africa, where the virus has infected human populations the longest, and medications to control the virus are least available.\u00a0 In 2016, over 63,000 Canadians were living with HIV.\r\nHIV Transmission<\/h2>\r\nHIV is transmitted through direct contact of [pb_glossary id=\"3538\"]mucous membranes<\/span>[\/pb_glossary]<\/span> or body fluids such as blood, semen, or breast milk. As shown in Figure 17.6.7, transmission of the virus can occur through sexual contact or the use of contaminated hypodermic needles. It can also be transmitted from an infected mother\u2019s blood during late pregnancy or childbirth, or through breast milk after birth. In the past, HIV was also transmitted occasionally through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way.<\/span>\r\n\r\n[caption id=\"attachment_5014\" align=\"aligncenter\" width=\"500\"] Figure 17.6.7 HIV may be transmitted in all of the ways shown here: through sexual activities, from mother to child (in utero, during childbirth, through breastmilk), and by sharing needles.<\/em>[\/caption]\r\nHIV and the Immune System<\/h2>\r\nHIV infects and destroys [pb_glossary id=\"5537\"]helper T cells<\/span>[\/pb_glossary]<\/span>, the type of [pb_glossary id=\"4832\"]lymphocyte<\/span>s<\/span>[\/pb_glossary]<\/span> that regulate the immune response. This process is illustrated in the diagram in Figure 17.6.8. The virus injects its own DNA into a helper T cell and uses the T cell\u2019s \u201cmachinery\u201d to make copies of itself. In the process, the helper T cell is destroyed, and the virus copies go on to infect other helper T cells. HIV is able to evade the immune system and keep destroying helper T cells by mutating frequently so its surface antigens keep changing, and by using the host cell\u2019s membrane to hide its own antigens.<\/span>\r\n\r\n[caption id=\"attachment_5015\" align=\"aligncenter\" width=\"500\"] Figure 17.6.8 This diagram shows how HIV infects and destroys helper T cells.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"5016\"]Acquired immunodeficiency syndrome[\/pb_glossary] (AIDS)<\/strong> may result from years of damage to the immune system by HIV. It occurs when helper T cells fall to a very low level and opportunistic diseases occur. Opportunistic diseases are infections and tumors that are rare, except in people with a damaged immune system. The diseases take advantage of the \u201copportunity\u201d presented by people whose immune system cannot fight back. Opportunistic diseases are usually the direct cause of death for people with AIDS.\r\nTreating HIV\/AIDS<\/h2>\r\nFor patients who have access to HIV medications, infection with the virus is no longer the death sentence\u00a0that it once was. By 1995, combinations of drugs called \u201chighly active antiretroviral therapy\u201d were developed. For some patients, these drugs can reduce the amount of virus they are carrying to undetectable levels. However, some\u00a0level\u00a0of virus always hides in the body\u2019s immune cells, and it will multiply again if a patient stops taking the medications. Researchers are trying to develop drugs to kill these hidden viruses, as well. If their efforts are successful, it could end AIDS.\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nEpiPens\u00ae and their sole manufacturer (pharmaceutical company Mylan) were featured in headlines in 2016, but not for a good reason. The media\u00a0outburst\u00a0was triggered by a drastic price hike in EpiPens\u00ae \u2014 and Mylan\u2019s apparent greed.\r\n\r\n[caption id=\"attachment_5017\" align=\"alignleft\" width=\"290\"] Figure 17.6.9 An Epipen\u00ae is a hypodermic device that administers a dose of epinephrine, used for the emergency treatment of an acute allergic reaction.<\/em>[\/caption]\r\n\r\nEpiPens\u00ae are auto-injectable syringes preloaded with a measured dose of epinephrine, a drug that can rapidly stop a life-threatening anaphylactic response to an allergen. Using the device is easy and does not require any special training. The injector just needs to be jammed against the thigh, which can be done through clothing or on bare skin. Each year, doctors write millions of prescriptions for EpiPens\u00ae. Many people with severe allergies always carry two of the devices with them, just in case they experience anaphylaxis, although most of them never need to use them. Other people with severe allergies have literally had their lives saved multiple times by EpiPens\u00ae when they had anaphylactic reactions. Even when the devices haven\u2019t been used, they must be replaced each year due to expiration of the epinephrine.\r\n\r\nYou might think that EpiPens\u00ae would be relatively inexpensive, given their life-saving potential. As recently as 2009, a two-pack of EpiPens\u00ae cost about $100. However, in just seven years, the cost of the same two-pack of EpiPens\u00ae skyrocketed by an incredible 400%! By 2016, the cost was $600 or more. Mylan apparently raised the price for the sole purpose of increasing profits. The company also raised prices significantly on many other drugs. The price hike in EpiPens\u00ae alone was certainly profitable. In 2015, the sale of EpiPens\u00ae earned Mylan $1 billion. Mylan\u2019s CEO took home almost $19 million the same year, which was an increase of more than 600% over her prior salary.\r\n\r\nNews coverage of the price hike in EpiPens\u00ae began in the summer of 2016 after a price increase in May of that year. Both private citizens and elected officials expressed outrage over the price increase, especially when coupled with the gluttonous profits of the company and its CEO. By late August, Mylan responded to the backlash by offering discount coupons for EpiPens\u00ae. A few days later, the company promised to introduce a cheaper, generic version of the device. Analysts quickly determined that selling a generic version would allow Mylan to make more money on the product than reducing the price of the name-brand device, which they still declined to do. By September of 2016, Mylan was being investigated for antitrust violations\u00a0related\u00a0to sales of EpiPens\u00ae to public schools in New York City.\r\n\r\nThe Mylan\/EpiPen\u00ae story may still be making the news. But whatever its outcome, the story has already added fuel to public and private debates about important ethical issues\u00a0\u2014\u00a0issues such as the excessive costs of life-saving drugs and the huge profits of big pharma. What is the most recent news on EpiPens\u00ae and Mylan? If you are interested, you can check the headlines online to find out. What are your views on the ethical issues they raise?\r\n\r\n17.6 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless antigen. Any [pb_glossary id=\"2704\"]antigen[\/pb_glossary] that causes allergies is called an [pb_glossary id=\"4999\"]allergen[\/pb_glossary]. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\r\n \t
- The prevalence of allergies has been increasing for decades, especially in developed countries, where they are much more common than in developing countries. The hygiene hypothesis posits that this has occurred because humans evolved to cope with more pathogens than we now typically face in our relatively sterile environments in developed countries. As a result, the immune system \u201ckeeps busy\u201d by attacking harmless antigens.<\/li>\r\n \t
- Allergies occur when [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]. On subsequent exposures to the allergen, the mast cells immediately release [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]\u00a0that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with [pb_glossary id=\"5469\"]antihistamines[\/pb_glossary]\u00a0that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called [pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary], is a medical emergency that is usually treated with injections of epinephrine. [pb_glossary id=\"5004\"]Immunotherapy[\/pb_glossary] for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary] occur when the immune system fails to recognize the body\u2019s own molecules as self and attacks them, causing damage to tissues and organs. A family history of autoimmunity and female gender are risk factors for autoimmune diseases.<\/li>\r\n \t
- In some autoimmune diseases, such as [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary], the immune system attacks and damages specific body cells. In other autoimmune diseases, such as [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary], many different tissues and organs may be attacked and injured. Autoimmune diseases generally cannot be cured, but their symptoms can often be managed with drugs or other treatments.<\/li>\r\n \t
- [pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary] occurs when the immune system is not working properly, generally because one or more of its components are inactive. As a result, the immune system is unable to fight off pathogens or cancers that a normal immune system would be able to resist.<\/li>\r\n \t
- [pb_glossary id=\"5012\"]Primary immunodeficiency[\/pb_glossary] is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. [pb_glossary id=\"5013\"]Secondary immunodeficiency[\/pb_glossary] occurs because of some event or exposure experienced after birth. Possible causes include aging, certain medications, infections with pathogens, and other disorders, such as obesity or malnutrition.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]), which infects and destroys helper T cells. HIV is transmitted through mucous membranes or body fluids. The virus may eventually lead to such low levels of helper T cells that opportunistic infections occur. When this happens, the patient is diagnosed with [pb_glossary id=\"5016\"]acquired immunodeficiency syndrome[\/pb_glossary] (AIDS). Medications can control the multiplication of HIV in the human body \u2014 but they don't eliminate the [pb_glossary id=\"4283\"]virus[\/pb_glossary] completely.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"641\"]<\/li>\r\n \t
- How does immunotherapy for allergies work?<\/li>\r\n \t
- What are autoimmune diseases?<\/li>\r\n \t
- Identify two risk factors for autoimmune diseases.<\/li>\r\n \t
- Autoimmune diseases may be specific to particular tissues, or they may be systemic. Give an example of each type of autoimmune disease.<\/li>\r\n \t
- What is immunodeficiency? Compare and contrast primary and secondary immunodeficiency. Give an example of each.<\/li>\r\n \t
- What is the most common cause of immunodeficiency in the world today? How does this affect the immune system?<\/li>\r\n \t
- Distinguish between HIV and AIDS.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/-q7Fz7NIMWM\r\nWhy do people have seasonal allergies? - Eleanor Nelsen, TED-Ed, 2016.<\/p>\r\nhttps:\/\/youtu.be\/0TipTogQT3E\r\n
Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, TED-Ed, 2015.<\/p>\r\nhttps:\/\/youtu.be\/pJa6KVLwl9U\r\n
The Boy in the Bubble | Retro Report | The New York Times, 2015.<\/p>\r\nhttps:\/\/youtu.be\/Mjr9h_QmdeM\r\n
Why Are Peanut Allergies Becoming So Common? Seeker, 2014.<\/p>\r\nhttps:\/\/youtu.be\/RiMSmDBvgto\r\n
What Are Tonsil Stones? | Gross Science, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 17.6.1<\/strong>\r\n\r\nOedema<\/a> by Championswimmer<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.2<\/strong>\r\n\r\n \t- Medical (latex) gloves<\/a> from pngimg.com is used under a CC BY-NC 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/) license.<\/li>\r\n \t
- House dust mites (5247996458)<\/a> by Gilles San Martin<\/a> from Namur, Belgium on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\r\n \t
- \u00a0Honey bee macro<\/a> by Karunakar Rayker<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/li>\r\n \t
- Peanuts<\/a> by Karolina Grabowska<\/a> on Pexels<\/a> is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Photo of dog and grey cat<\/a> by ERC4N51<\/a> on pxhere is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Tags: Pollen Allergy Spring<\/a>\u00a0by Castagnari53<\/a> on Pixabay<\/a>, is used under the Pixabay License<\/a> (https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\nFigure 17.6.3<\/strong>\r\n\r\n512px-Mast_cells<\/a> by National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute<\/a> (p.29) is in\u00a0the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.4<\/strong>\r\n\r\nSigns_and_symptoms_of_anaphylaxis<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\n\r\nFigure 17.6.5<\/strong>\r\n\r\nAllergy Tests<\/a> by Dan Pupius<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 17.6.6<\/strong>\r\n\r\n1024px-Symptoms_of_SLE<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons\u00a0is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\nFigure 17.6.7<\/strong>\r\n\r\nHIV transmission<\/a>\u00a0by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 17.6.8<\/strong>\r\n\r\nHIV life cycle<\/a> by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 17.6.9<\/strong>\r\n\r\nEpipen by Stock Catalog on flickr<\/a> by Stock Catalog<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n
References<\/h2>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 8 HIV may be transmitted in all of the ways shown here [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nBrainard, J\/ CK-12 Foundation. (2016). Figure 9 This diagram shows how HIV infects and destroys helper T cells [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nCBS News. (2016, August 16). Rising cost of potentially life-saving EpiPen puts pinch on families [online article]. CBS Interactive Inc. https:\/\/www.cbsnews.com\/news\/allergy-medication-epipen-epinephrine-rising-costs-impact-on-families\/<\/p>\r\n
Gross Science. (2015, June 29). What are tonsil stones? | Gross Science. YouTube. https:\/\/www.youtube.com\/watch?v=RiMSmDBvgto&feature=youtu.be<\/p>\r\n
H\u00e4ggstr\u00f6m, M. (2014). Medical gallery of Mikael H\u00e4ggstr\u00f6m 2014.\u00a0WikiJournal of Medicine<\/i>\u00a01<\/b>\u00a0(2).\u00a0DOI:10.15347\/wjm\/2014.008.\u00a0ISSN\u00a02002-4436<\/p>\r\n
National Institute of Allergy and Infectious Diseases (NIAID). (n.d.). Severe combined immunodeficiency (SCID) [online article]. National Institute of Health (NIH). https:\/\/www.niaid.nih.gov\/diseases-conditions\/severe-combined-immunodeficiency-scid<\/p>\r\n
National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute (U.S.). (2003, September). Understanding the immune system and how it works [NIH Publication No. 03-5423]. Scholar Works<\/em> - \u00a0Indiana University. https:\/\/scholarworks.iupui.edu\/handle\/1805\/748<\/p>\r\n[The] New York Times. (2015, December 15). The boy in the bubble | Retro Report | The New York Times. YouTube. https:\/\/www.youtube.com\/watch?v=pJa6KVLwl9U&feature=youtu.be<\/p>\r\n
Seeker. (2014, October 3). Why are peanut allergies becoming so common? YouTube. https:\/\/www.youtube.com\/watch?v=Mjr9h_QmdeM&feature=youtu.be<\/p>\r\n
Summary: Estimates of HIV incidence, prevalence, and Canada's progress on meeting the 90-90-90 HIV targets 2016. (2018, July). Public Health Agency of Canada. https:\/\/www.canada.ca\/content\/dam\/phac-aspc\/documents\/services\/publications\/diseases-conditions\/summary-estimates-hiv-incidence-prevalence-canadas-progress-90-90-90\/pub-eng.pdf<\/p>\r\n
Swetlitz, I., Silverman, E. (2016, August 25). Mylan may have violated antitrust law in its EpiPen sales to schools, legal experts say [online article]. STATNews.com. https:\/\/www.statnews.com\/2016\/08\/25\/mylan-antitrust-epipen-schools\/<\/p>\r\n
TED-Ed. (2016, May 26). Why do people have seasonal allergies? - Eleanor Nelsen. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=-q7Fz7NIMWM&feature=youtu.be<\/p>\r\n
TED-Ed. (2015, March 16). Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, https:\/\/www.youtube.com\/watch?v=0TipTogQT3E&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 17.6.1 Oh m-eye!<\/em><\/figcaption><\/figure>\n\nAllergy Eyes<\/h1>\n<\/div>\n
Eyes that are red, watery, and itchy are typical of an allergic reaction known as allergic rhinitis. Commonly called hay fever, allergic rhinitis is an immune system reaction, typically to the pollen of certain plants. Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes, it responds to harmless foreign substances as though they were pathogens. This is the basis of allergies like hay fever.<\/p>\n
\nAllergies<\/h1>\n<\/div>\n
An\u00a0allergy<\/a><\/strong>\u00a0is a disorder in which the immune system makes an inflammatory response<\/a> to a harmless antigen<\/a>. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.<\/p>\nAllergens<\/h2>\n
Any antigen that causes an allergy is called an\u00a0allergen<\/a>.<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.<\/p>\n\n\n<\/div>\n<\/div>\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em><\/p>\n<\/div>\nPrevalence of Allergies<\/h2>\n
There has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.<\/p>\n
One explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.<\/p>\n
How Allergies Occur<\/h2>\n
The diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.<\/p>\nFigure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em><\/figcaption><\/figure>\nTreating Allergies<\/h2>\n
The symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with antihistamines<\/span><\/strong><\/a><\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span><\/p>\nTreating Anaphylaxis<\/h3>\n
The most severe allergic reaction is a systemic reaction called\u00a0anaphylaxis<\/a>.<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.<\/p>\nFigure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em><\/figcaption><\/figure>\nImmunotherapy for Allergies<\/h3>\nFigure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em><\/figcaption><\/figure>\nAnother way to treat allergies is called\u00a0immunotherapy<\/a>,<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.<\/p>\nAutoimmune Diseases<\/span><\/p>\nAutoimmune diseases<\/a><\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, B cells<\/span><\/a><\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to pathogen<\/span>s<\/span><\/a><\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span><\/p>\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.<\/p>\n
At a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.<\/p>\n
Common Autoimmune Diseases<\/h2>\n
An estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are type I diabetes<\/a> and multiple sclerosis<\/a>. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys insulin<\/a>-secreting islet cells in the pancreas<\/a>. In the case of multiple sclerosis, the immune system attacks and destroys the myelin sheaths<\/span><\/a><\/span>\u00a0that normally insulate the axon<\/span>s<\/span><\/a><\/span>\u00a0of <\/span>neuron<\/span>s<\/span><\/a><\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span><\/p>\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include rheumatoid arthritis<\/a> and systemic lupus erythematosus<\/a> (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.<\/p>\nFigure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em><\/figcaption><\/figure>\nTreatment for Autoimmune Diseases<\/h2>\n
None of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.<\/p>\n
\nImmunodeficiency<\/h1>\n<\/div>\n
Immunodeficiency<\/a><\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.<\/p>\nCauses of Immunodeficiency<\/h2>\n
Dozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0primary immunodeficiency<\/a><\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked recessive<\/a> mutation<\/a> that interferes with normal B cell and T cell production.<\/p>\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0secondary immunodeficiency<\/a><\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:<\/p>\n\n- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\n
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\n
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\n
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\n
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\n<\/ul>\n\n
Focus on HIV<\/h1>\n<\/div>\n
Human immunodeficiency virus (
Figure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em>[\/caption]\r\nImmunotherapy for Allergies<\/h3>\r\n[caption id=\"attachment_5005\" align=\"alignleft\" width=\"303\"] Figure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em>[\/caption]\r\n\r\nAnother way to treat allergies is called\u00a0[pb_glossary id=\"5004\"]immunotherapy[\/pb_glossary],<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.\r\n\r\nAutoimmune Diseases<\/span>\r\n\r\n[pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary]<\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, [pb_glossary id=\"5539\"]B cells<\/span>[\/pb_glossary]<\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to [pb_glossary id=\"5799\"]pathogen<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span>\r\n\r\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.\r\n\r\nAt a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.\r\nCommon Autoimmune Diseases<\/h2>\r\nAn estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary] and [pb_glossary id=\"5007\"]multiple sclerosis[\/pb_glossary]. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys [pb_glossary id=\"2590\"]insulin[\/pb_glossary]-secreting islet cells in the [pb_glossary id=\"3197\"]pancreas[\/pb_glossary]. In the case of multiple sclerosis, the immune system attacks and destroys the [pb_glossary id=\"3028\"]myelin sheaths<\/span>[\/pb_glossary]<\/span>\u00a0that normally insulate the [pb_glossary id=\"5901\"]axon<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0of <\/span>[pb_glossary id=\"2984\"]neuron<\/span>s<\/span>[\/pb_glossary]<\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span>\r\n\r\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include [pb_glossary id=\"5008\"]rheumatoid arthritis[\/pb_glossary] and [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary] (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.\r\n\r\n[caption id=\"attachment_5010\" align=\"aligncenter\" width=\"549\"] Figure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em>[\/caption]\r\nTreatment for Autoimmune Diseases<\/h2>\r\nNone of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.\r\n\r\nImmunodeficiency<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary]<\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.\r\nCauses of Immunodeficiency<\/h2>\r\nDozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0[pb_glossary id=\"5012\"]primary immunodeficiency[\/pb_glossary]<\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked [pb_glossary id=\"2479\"]recessive[\/pb_glossary] [pb_glossary id=\"2381\"]mutation[\/pb_glossary] that interferes with normal B cell and T cell production.\r\n\r\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0[pb_glossary id=\"5013\"]secondary immunodeficiency[\/pb_glossary]<\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:\r\n\r\n \t- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\r\n \t
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\r\n \t
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\r\n \t
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\r\n \t
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\r\n<\/ul>\r\n\r\n
Focus on HIV<\/h1>\r\n<\/div>\r\nHuman immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary])<\/strong> is the most common cause of immunodeficiency in the world today. HIV infections of human hosts are a relatively recent phenomenon. Scientists think that the virus originally infected monkeys, but then jumped to human populations. most likely from a bite, probably sometime during the early to mid-1900s. This most likely occurred in West Africa, but the virus soon spread around the world. HIV was first identified by medical researchers in 1981. Since then, HIV has killed almost 40 million people worldwide, and its economic toll has also been enormous. The hardest hit countries are in Africa, where the virus has infected human populations the longest, and medications to control the virus are least available.\u00a0 In 2016, over 63,000 Canadians were living with HIV.\r\nHIV Transmission<\/h2>\r\nHIV is transmitted through direct contact of [pb_glossary id=\"3538\"]mucous membranes<\/span>[\/pb_glossary]<\/span> or body fluids such as blood, semen, or breast milk. As shown in Figure 17.6.7, transmission of the virus can occur through sexual contact or the use of contaminated hypodermic needles. It can also be transmitted from an infected mother\u2019s blood during late pregnancy or childbirth, or through breast milk after birth. In the past, HIV was also transmitted occasionally through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way.<\/span>\r\n\r\n[caption id=\"attachment_5014\" align=\"aligncenter\" width=\"500\"] Figure 17.6.7 HIV may be transmitted in all of the ways shown here: through sexual activities, from mother to child (in utero, during childbirth, through breastmilk), and by sharing needles.<\/em>[\/caption]\r\nHIV and the Immune System<\/h2>\r\nHIV infects and destroys [pb_glossary id=\"5537\"]helper T cells<\/span>[\/pb_glossary]<\/span>, the type of [pb_glossary id=\"4832\"]lymphocyte<\/span>s<\/span>[\/pb_glossary]<\/span> that regulate the immune response. This process is illustrated in the diagram in Figure 17.6.8. The virus injects its own DNA into a helper T cell and uses the T cell\u2019s \u201cmachinery\u201d to make copies of itself. In the process, the helper T cell is destroyed, and the virus copies go on to infect other helper T cells. HIV is able to evade the immune system and keep destroying helper T cells by mutating frequently so its surface antigens keep changing, and by using the host cell\u2019s membrane to hide its own antigens.<\/span>\r\n\r\n[caption id=\"attachment_5015\" align=\"aligncenter\" width=\"500\"] Figure 17.6.8 This diagram shows how HIV infects and destroys helper T cells.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"5016\"]Acquired immunodeficiency syndrome[\/pb_glossary] (AIDS)<\/strong> may result from years of damage to the immune system by HIV. It occurs when helper T cells fall to a very low level and opportunistic diseases occur. Opportunistic diseases are infections and tumors that are rare, except in people with a damaged immune system. The diseases take advantage of the \u201copportunity\u201d presented by people whose immune system cannot fight back. Opportunistic diseases are usually the direct cause of death for people with AIDS.\r\nTreating HIV\/AIDS<\/h2>\r\nFor patients who have access to HIV medications, infection with the virus is no longer the death sentence\u00a0that it once was. By 1995, combinations of drugs called \u201chighly active antiretroviral therapy\u201d were developed. For some patients, these drugs can reduce the amount of virus they are carrying to undetectable levels. However, some\u00a0level\u00a0of virus always hides in the body\u2019s immune cells, and it will multiply again if a patient stops taking the medications. Researchers are trying to develop drugs to kill these hidden viruses, as well. If their efforts are successful, it could end AIDS.\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nEpiPens\u00ae and their sole manufacturer (pharmaceutical company Mylan) were featured in headlines in 2016, but not for a good reason. The media\u00a0outburst\u00a0was triggered by a drastic price hike in EpiPens\u00ae \u2014 and Mylan\u2019s apparent greed.\r\n\r\n[caption id=\"attachment_5017\" align=\"alignleft\" width=\"290\"] Figure 17.6.9 An Epipen\u00ae is a hypodermic device that administers a dose of epinephrine, used for the emergency treatment of an acute allergic reaction.<\/em>[\/caption]\r\n\r\nEpiPens\u00ae are auto-injectable syringes preloaded with a measured dose of epinephrine, a drug that can rapidly stop a life-threatening anaphylactic response to an allergen. Using the device is easy and does not require any special training. The injector just needs to be jammed against the thigh, which can be done through clothing or on bare skin. Each year, doctors write millions of prescriptions for EpiPens\u00ae. Many people with severe allergies always carry two of the devices with them, just in case they experience anaphylaxis, although most of them never need to use them. Other people with severe allergies have literally had their lives saved multiple times by EpiPens\u00ae when they had anaphylactic reactions. Even when the devices haven\u2019t been used, they must be replaced each year due to expiration of the epinephrine.\r\n\r\nYou might think that EpiPens\u00ae would be relatively inexpensive, given their life-saving potential. As recently as 2009, a two-pack of EpiPens\u00ae cost about $100. However, in just seven years, the cost of the same two-pack of EpiPens\u00ae skyrocketed by an incredible 400%! By 2016, the cost was $600 or more. Mylan apparently raised the price for the sole purpose of increasing profits. The company also raised prices significantly on many other drugs. The price hike in EpiPens\u00ae alone was certainly profitable. In 2015, the sale of EpiPens\u00ae earned Mylan $1 billion. Mylan\u2019s CEO took home almost $19 million the same year, which was an increase of more than 600% over her prior salary.\r\n\r\nNews coverage of the price hike in EpiPens\u00ae began in the summer of 2016 after a price increase in May of that year. Both private citizens and elected officials expressed outrage over the price increase, especially when coupled with the gluttonous profits of the company and its CEO. By late August, Mylan responded to the backlash by offering discount coupons for EpiPens\u00ae. A few days later, the company promised to introduce a cheaper, generic version of the device. Analysts quickly determined that selling a generic version would allow Mylan to make more money on the product than reducing the price of the name-brand device, which they still declined to do. By September of 2016, Mylan was being investigated for antitrust violations\u00a0related\u00a0to sales of EpiPens\u00ae to public schools in New York City.\r\n\r\nThe Mylan\/EpiPen\u00ae story may still be making the news. But whatever its outcome, the story has already added fuel to public and private debates about important ethical issues\u00a0\u2014\u00a0issues such as the excessive costs of life-saving drugs and the huge profits of big pharma. What is the most recent news on EpiPens\u00ae and Mylan? If you are interested, you can check the headlines online to find out. What are your views on the ethical issues they raise?\r\n\r\n17.6 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless antigen. Any [pb_glossary id=\"2704\"]antigen[\/pb_glossary] that causes allergies is called an [pb_glossary id=\"4999\"]allergen[\/pb_glossary]. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\r\n \t
- The prevalence of allergies has been increasing for decades, especially in developed countries, where they are much more common than in developing countries. The hygiene hypothesis posits that this has occurred because humans evolved to cope with more pathogens than we now typically face in our relatively sterile environments in developed countries. As a result, the immune system \u201ckeeps busy\u201d by attacking harmless antigens.<\/li>\r\n \t
- Allergies occur when [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]. On subsequent exposures to the allergen, the mast cells immediately release [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]\u00a0that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with [pb_glossary id=\"5469\"]antihistamines[\/pb_glossary]\u00a0that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called [pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary], is a medical emergency that is usually treated with injections of epinephrine. [pb_glossary id=\"5004\"]Immunotherapy[\/pb_glossary] for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary] occur when the immune system fails to recognize the body\u2019s own molecules as self and attacks them, causing damage to tissues and organs. A family history of autoimmunity and female gender are risk factors for autoimmune diseases.<\/li>\r\n \t
- In some autoimmune diseases, such as [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary], the immune system attacks and damages specific body cells. In other autoimmune diseases, such as [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary], many different tissues and organs may be attacked and injured. Autoimmune diseases generally cannot be cured, but their symptoms can often be managed with drugs or other treatments.<\/li>\r\n \t
- [pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary] occurs when the immune system is not working properly, generally because one or more of its components are inactive. As a result, the immune system is unable to fight off pathogens or cancers that a normal immune system would be able to resist.<\/li>\r\n \t
- [pb_glossary id=\"5012\"]Primary immunodeficiency[\/pb_glossary] is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. [pb_glossary id=\"5013\"]Secondary immunodeficiency[\/pb_glossary] occurs because of some event or exposure experienced after birth. Possible causes include aging, certain medications, infections with pathogens, and other disorders, such as obesity or malnutrition.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]), which infects and destroys helper T cells. HIV is transmitted through mucous membranes or body fluids. The virus may eventually lead to such low levels of helper T cells that opportunistic infections occur. When this happens, the patient is diagnosed with [pb_glossary id=\"5016\"]acquired immunodeficiency syndrome[\/pb_glossary] (AIDS). Medications can control the multiplication of HIV in the human body \u2014 but they don't eliminate the [pb_glossary id=\"4283\"]virus[\/pb_glossary] completely.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"641\"]<\/li>\r\n \t
- How does immunotherapy for allergies work?<\/li>\r\n \t
- What are autoimmune diseases?<\/li>\r\n \t
- Identify two risk factors for autoimmune diseases.<\/li>\r\n \t
- Autoimmune diseases may be specific to particular tissues, or they may be systemic. Give an example of each type of autoimmune disease.<\/li>\r\n \t
- What is immunodeficiency? Compare and contrast primary and secondary immunodeficiency. Give an example of each.<\/li>\r\n \t
- What is the most common cause of immunodeficiency in the world today? How does this affect the immune system?<\/li>\r\n \t
- Distinguish between HIV and AIDS.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/-q7Fz7NIMWM\r\nWhy do people have seasonal allergies? - Eleanor Nelsen, TED-Ed, 2016.<\/p>\r\nhttps:\/\/youtu.be\/0TipTogQT3E\r\n
Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, TED-Ed, 2015.<\/p>\r\nhttps:\/\/youtu.be\/pJa6KVLwl9U\r\n
The Boy in the Bubble | Retro Report | The New York Times, 2015.<\/p>\r\nhttps:\/\/youtu.be\/Mjr9h_QmdeM\r\n
Why Are Peanut Allergies Becoming So Common? Seeker, 2014.<\/p>\r\nhttps:\/\/youtu.be\/RiMSmDBvgto\r\n
What Are Tonsil Stones? | Gross Science, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 17.6.1<\/strong>\r\n\r\nOedema<\/a> by Championswimmer<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.2<\/strong>\r\n\r\n \t- Medical (latex) gloves<\/a> from pngimg.com is used under a CC BY-NC 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/) license.<\/li>\r\n \t
- House dust mites (5247996458)<\/a> by Gilles San Martin<\/a> from Namur, Belgium on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\r\n \t
- \u00a0Honey bee macro<\/a> by Karunakar Rayker<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/li>\r\n \t
- Peanuts<\/a> by Karolina Grabowska<\/a> on Pexels<\/a> is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Photo of dog and grey cat<\/a> by ERC4N51<\/a> on pxhere is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Tags: Pollen Allergy Spring<\/a>\u00a0by Castagnari53<\/a> on Pixabay<\/a>, is used under the Pixabay License<\/a> (https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\nFigure 17.6.3<\/strong>\r\n\r\n512px-Mast_cells<\/a> by National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute<\/a> (p.29) is in\u00a0the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.4<\/strong>\r\n\r\nSigns_and_symptoms_of_anaphylaxis<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\n\r\nFigure 17.6.5<\/strong>\r\n\r\nAllergy Tests<\/a> by Dan Pupius<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 17.6.6<\/strong>\r\n\r\n1024px-Symptoms_of_SLE<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons\u00a0is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\nFigure 17.6.7<\/strong>\r\n\r\nHIV transmission<\/a>\u00a0by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 17.6.8<\/strong>\r\n\r\nHIV life cycle<\/a> by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 17.6.9<\/strong>\r\n\r\nEpipen by Stock Catalog on flickr<\/a> by Stock Catalog<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n
References<\/h2>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 8 HIV may be transmitted in all of the ways shown here [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nBrainard, J\/ CK-12 Foundation. (2016). Figure 9 This diagram shows how HIV infects and destroys helper T cells [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nCBS News. (2016, August 16). Rising cost of potentially life-saving EpiPen puts pinch on families [online article]. CBS Interactive Inc. https:\/\/www.cbsnews.com\/news\/allergy-medication-epipen-epinephrine-rising-costs-impact-on-families\/<\/p>\r\n
Gross Science. (2015, June 29). What are tonsil stones? | Gross Science. YouTube. https:\/\/www.youtube.com\/watch?v=RiMSmDBvgto&feature=youtu.be<\/p>\r\n
H\u00e4ggstr\u00f6m, M. (2014). Medical gallery of Mikael H\u00e4ggstr\u00f6m 2014.\u00a0WikiJournal of Medicine<\/i>\u00a01<\/b>\u00a0(2).\u00a0DOI:10.15347\/wjm\/2014.008.\u00a0ISSN\u00a02002-4436<\/p>\r\n
National Institute of Allergy and Infectious Diseases (NIAID). (n.d.). Severe combined immunodeficiency (SCID) [online article]. National Institute of Health (NIH). https:\/\/www.niaid.nih.gov\/diseases-conditions\/severe-combined-immunodeficiency-scid<\/p>\r\n
National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute (U.S.). (2003, September). Understanding the immune system and how it works [NIH Publication No. 03-5423]. Scholar Works<\/em> - \u00a0Indiana University. https:\/\/scholarworks.iupui.edu\/handle\/1805\/748<\/p>\r\n[The] New York Times. (2015, December 15). The boy in the bubble | Retro Report | The New York Times. YouTube. https:\/\/www.youtube.com\/watch?v=pJa6KVLwl9U&feature=youtu.be<\/p>\r\n
Seeker. (2014, October 3). Why are peanut allergies becoming so common? YouTube. https:\/\/www.youtube.com\/watch?v=Mjr9h_QmdeM&feature=youtu.be<\/p>\r\n
Summary: Estimates of HIV incidence, prevalence, and Canada's progress on meeting the 90-90-90 HIV targets 2016. (2018, July). Public Health Agency of Canada. https:\/\/www.canada.ca\/content\/dam\/phac-aspc\/documents\/services\/publications\/diseases-conditions\/summary-estimates-hiv-incidence-prevalence-canadas-progress-90-90-90\/pub-eng.pdf<\/p>\r\n
Swetlitz, I., Silverman, E. (2016, August 25). Mylan may have violated antitrust law in its EpiPen sales to schools, legal experts say [online article]. STATNews.com. https:\/\/www.statnews.com\/2016\/08\/25\/mylan-antitrust-epipen-schools\/<\/p>\r\n
TED-Ed. (2016, May 26). Why do people have seasonal allergies? - Eleanor Nelsen. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=-q7Fz7NIMWM&feature=youtu.be<\/p>\r\n
TED-Ed. (2015, March 16). Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, https:\/\/www.youtube.com\/watch?v=0TipTogQT3E&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 17.6.1 Oh m-eye!<\/em><\/figcaption><\/figure>\n\nAllergy Eyes<\/h1>\n<\/div>\n
Eyes that are red, watery, and itchy are typical of an allergic reaction known as allergic rhinitis. Commonly called hay fever, allergic rhinitis is an immune system reaction, typically to the pollen of certain plants. Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes, it responds to harmless foreign substances as though they were pathogens. This is the basis of allergies like hay fever.<\/p>\n
\nAllergies<\/h1>\n<\/div>\n
An\u00a0allergy<\/a><\/strong>\u00a0is a disorder in which the immune system makes an inflammatory response<\/a> to a harmless antigen<\/a>. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.<\/p>\nAllergens<\/h2>\n
Any antigen that causes an allergy is called an\u00a0allergen<\/a>.<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.<\/p>\n\n\n<\/div>\n<\/div>\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em><\/p>\n<\/div>\nPrevalence of Allergies<\/h2>\n
There has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.<\/p>\n
One explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.<\/p>\n
How Allergies Occur<\/h2>\n
The diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.<\/p>\nFigure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em><\/figcaption><\/figure>\nTreating Allergies<\/h2>\n
The symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with antihistamines<\/span><\/strong><\/a><\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span><\/p>\nTreating Anaphylaxis<\/h3>\n
The most severe allergic reaction is a systemic reaction called\u00a0anaphylaxis<\/a>.<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.<\/p>\nFigure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em><\/figcaption><\/figure>\nImmunotherapy for Allergies<\/h3>\nFigure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em><\/figcaption><\/figure>\nAnother way to treat allergies is called\u00a0immunotherapy<\/a>,<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.<\/p>\nAutoimmune Diseases<\/span><\/p>\nAutoimmune diseases<\/a><\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, B cells<\/span><\/a><\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to pathogen<\/span>s<\/span><\/a><\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span><\/p>\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.<\/p>\n
At a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.<\/p>\n
Common Autoimmune Diseases<\/h2>\n
An estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are type I diabetes<\/a> and multiple sclerosis<\/a>. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys insulin<\/a>-secreting islet cells in the pancreas<\/a>. In the case of multiple sclerosis, the immune system attacks and destroys the myelin sheaths<\/span><\/a><\/span>\u00a0that normally insulate the axon<\/span>s<\/span><\/a><\/span>\u00a0of <\/span>neuron<\/span>s<\/span><\/a><\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span><\/p>\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include rheumatoid arthritis<\/a> and systemic lupus erythematosus<\/a> (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.<\/p>\nFigure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em><\/figcaption><\/figure>\nTreatment for Autoimmune Diseases<\/h2>\n
None of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.<\/p>\n
\nImmunodeficiency<\/h1>\n<\/div>\n
Immunodeficiency<\/a><\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.<\/p>\nCauses of Immunodeficiency<\/h2>\n
Dozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0primary immunodeficiency<\/a><\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked recessive<\/a> mutation<\/a> that interferes with normal B cell and T cell production.<\/p>\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0secondary immunodeficiency<\/a><\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:<\/p>\n\n- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\n
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\n
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\n
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\n
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\n<\/ul>\n\n
Focus on HIV<\/h1>\n<\/div>\n
Human immunodeficiency virus (
Figure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em>[\/caption]\r\nTreatment for Autoimmune Diseases<\/h2>\r\nNone of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.\r\n\r\nImmunodeficiency<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary]<\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.\r\nCauses of Immunodeficiency<\/h2>\r\nDozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0[pb_glossary id=\"5012\"]primary immunodeficiency[\/pb_glossary]<\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked [pb_glossary id=\"2479\"]recessive[\/pb_glossary] [pb_glossary id=\"2381\"]mutation[\/pb_glossary] that interferes with normal B cell and T cell production.\r\n\r\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0[pb_glossary id=\"5013\"]secondary immunodeficiency[\/pb_glossary]<\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:\r\n\r\n \t- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\r\n \t
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\r\n \t
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\r\n \t
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\r\n \t
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\r\n<\/ul>\r\n\r\n
Focus on HIV<\/h1>\r\n<\/div>\r\nHuman immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary])<\/strong> is the most common cause of immunodeficiency in the world today. HIV infections of human hosts are a relatively recent phenomenon. Scientists think that the virus originally infected monkeys, but then jumped to human populations. most likely from a bite, probably sometime during the early to mid-1900s. This most likely occurred in West Africa, but the virus soon spread around the world. HIV was first identified by medical researchers in 1981. Since then, HIV has killed almost 40 million people worldwide, and its economic toll has also been enormous. The hardest hit countries are in Africa, where the virus has infected human populations the longest, and medications to control the virus are least available.\u00a0 In 2016, over 63,000 Canadians were living with HIV.\r\nHIV Transmission<\/h2>\r\nHIV is transmitted through direct contact of [pb_glossary id=\"3538\"]mucous membranes<\/span>[\/pb_glossary]<\/span> or body fluids such as blood, semen, or breast milk. As shown in Figure 17.6.7, transmission of the virus can occur through sexual contact or the use of contaminated hypodermic needles. It can also be transmitted from an infected mother\u2019s blood during late pregnancy or childbirth, or through breast milk after birth. In the past, HIV was also transmitted occasionally through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way.<\/span>\r\n\r\n[caption id=\"attachment_5014\" align=\"aligncenter\" width=\"500\"] Figure 17.6.7 HIV may be transmitted in all of the ways shown here: through sexual activities, from mother to child (in utero, during childbirth, through breastmilk), and by sharing needles.<\/em>[\/caption]\r\nHIV and the Immune System<\/h2>\r\nHIV infects and destroys [pb_glossary id=\"5537\"]helper T cells<\/span>[\/pb_glossary]<\/span>, the type of [pb_glossary id=\"4832\"]lymphocyte<\/span>s<\/span>[\/pb_glossary]<\/span> that regulate the immune response. This process is illustrated in the diagram in Figure 17.6.8. The virus injects its own DNA into a helper T cell and uses the T cell\u2019s \u201cmachinery\u201d to make copies of itself. In the process, the helper T cell is destroyed, and the virus copies go on to infect other helper T cells. HIV is able to evade the immune system and keep destroying helper T cells by mutating frequently so its surface antigens keep changing, and by using the host cell\u2019s membrane to hide its own antigens.<\/span>\r\n\r\n[caption id=\"attachment_5015\" align=\"aligncenter\" width=\"500\"] Figure 17.6.8 This diagram shows how HIV infects and destroys helper T cells.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"5016\"]Acquired immunodeficiency syndrome[\/pb_glossary] (AIDS)<\/strong> may result from years of damage to the immune system by HIV. It occurs when helper T cells fall to a very low level and opportunistic diseases occur. Opportunistic diseases are infections and tumors that are rare, except in people with a damaged immune system. The diseases take advantage of the \u201copportunity\u201d presented by people whose immune system cannot fight back. Opportunistic diseases are usually the direct cause of death for people with AIDS.\r\nTreating HIV\/AIDS<\/h2>\r\nFor patients who have access to HIV medications, infection with the virus is no longer the death sentence\u00a0that it once was. By 1995, combinations of drugs called \u201chighly active antiretroviral therapy\u201d were developed. For some patients, these drugs can reduce the amount of virus they are carrying to undetectable levels. However, some\u00a0level\u00a0of virus always hides in the body\u2019s immune cells, and it will multiply again if a patient stops taking the medications. Researchers are trying to develop drugs to kill these hidden viruses, as well. If their efforts are successful, it could end AIDS.\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nEpiPens\u00ae and their sole manufacturer (pharmaceutical company Mylan) were featured in headlines in 2016, but not for a good reason. The media\u00a0outburst\u00a0was triggered by a drastic price hike in EpiPens\u00ae \u2014 and Mylan\u2019s apparent greed.\r\n\r\n[caption id=\"attachment_5017\" align=\"alignleft\" width=\"290\"] Figure 17.6.9 An Epipen\u00ae is a hypodermic device that administers a dose of epinephrine, used for the emergency treatment of an acute allergic reaction.<\/em>[\/caption]\r\n\r\nEpiPens\u00ae are auto-injectable syringes preloaded with a measured dose of epinephrine, a drug that can rapidly stop a life-threatening anaphylactic response to an allergen. Using the device is easy and does not require any special training. The injector just needs to be jammed against the thigh, which can be done through clothing or on bare skin. Each year, doctors write millions of prescriptions for EpiPens\u00ae. Many people with severe allergies always carry two of the devices with them, just in case they experience anaphylaxis, although most of them never need to use them. Other people with severe allergies have literally had their lives saved multiple times by EpiPens\u00ae when they had anaphylactic reactions. Even when the devices haven\u2019t been used, they must be replaced each year due to expiration of the epinephrine.\r\n\r\nYou might think that EpiPens\u00ae would be relatively inexpensive, given their life-saving potential. As recently as 2009, a two-pack of EpiPens\u00ae cost about $100. However, in just seven years, the cost of the same two-pack of EpiPens\u00ae skyrocketed by an incredible 400%! By 2016, the cost was $600 or more. Mylan apparently raised the price for the sole purpose of increasing profits. The company also raised prices significantly on many other drugs. The price hike in EpiPens\u00ae alone was certainly profitable. In 2015, the sale of EpiPens\u00ae earned Mylan $1 billion. Mylan\u2019s CEO took home almost $19 million the same year, which was an increase of more than 600% over her prior salary.\r\n\r\nNews coverage of the price hike in EpiPens\u00ae began in the summer of 2016 after a price increase in May of that year. Both private citizens and elected officials expressed outrage over the price increase, especially when coupled with the gluttonous profits of the company and its CEO. By late August, Mylan responded to the backlash by offering discount coupons for EpiPens\u00ae. A few days later, the company promised to introduce a cheaper, generic version of the device. Analysts quickly determined that selling a generic version would allow Mylan to make more money on the product than reducing the price of the name-brand device, which they still declined to do. By September of 2016, Mylan was being investigated for antitrust violations\u00a0related\u00a0to sales of EpiPens\u00ae to public schools in New York City.\r\n\r\nThe Mylan\/EpiPen\u00ae story may still be making the news. But whatever its outcome, the story has already added fuel to public and private debates about important ethical issues\u00a0\u2014\u00a0issues such as the excessive costs of life-saving drugs and the huge profits of big pharma. What is the most recent news on EpiPens\u00ae and Mylan? If you are interested, you can check the headlines online to find out. What are your views on the ethical issues they raise?\r\n\r\n17.6 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless antigen. Any [pb_glossary id=\"2704\"]antigen[\/pb_glossary] that causes allergies is called an [pb_glossary id=\"4999\"]allergen[\/pb_glossary]. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\r\n \t
- The prevalence of allergies has been increasing for decades, especially in developed countries, where they are much more common than in developing countries. The hygiene hypothesis posits that this has occurred because humans evolved to cope with more pathogens than we now typically face in our relatively sterile environments in developed countries. As a result, the immune system \u201ckeeps busy\u201d by attacking harmless antigens.<\/li>\r\n \t
- Allergies occur when [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]. On subsequent exposures to the allergen, the mast cells immediately release [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]\u00a0that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with [pb_glossary id=\"5469\"]antihistamines[\/pb_glossary]\u00a0that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called [pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary], is a medical emergency that is usually treated with injections of epinephrine. [pb_glossary id=\"5004\"]Immunotherapy[\/pb_glossary] for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary] occur when the immune system fails to recognize the body\u2019s own molecules as self and attacks them, causing damage to tissues and organs. A family history of autoimmunity and female gender are risk factors for autoimmune diseases.<\/li>\r\n \t
- In some autoimmune diseases, such as [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary], the immune system attacks and damages specific body cells. In other autoimmune diseases, such as [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary], many different tissues and organs may be attacked and injured. Autoimmune diseases generally cannot be cured, but their symptoms can often be managed with drugs or other treatments.<\/li>\r\n \t
- [pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary] occurs when the immune system is not working properly, generally because one or more of its components are inactive. As a result, the immune system is unable to fight off pathogens or cancers that a normal immune system would be able to resist.<\/li>\r\n \t
- [pb_glossary id=\"5012\"]Primary immunodeficiency[\/pb_glossary] is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. [pb_glossary id=\"5013\"]Secondary immunodeficiency[\/pb_glossary] occurs because of some event or exposure experienced after birth. Possible causes include aging, certain medications, infections with pathogens, and other disorders, such as obesity or malnutrition.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]), which infects and destroys helper T cells. HIV is transmitted through mucous membranes or body fluids. The virus may eventually lead to such low levels of helper T cells that opportunistic infections occur. When this happens, the patient is diagnosed with [pb_glossary id=\"5016\"]acquired immunodeficiency syndrome[\/pb_glossary] (AIDS). Medications can control the multiplication of HIV in the human body \u2014 but they don't eliminate the [pb_glossary id=\"4283\"]virus[\/pb_glossary] completely.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"641\"]<\/li>\r\n \t
- How does immunotherapy for allergies work?<\/li>\r\n \t
- What are autoimmune diseases?<\/li>\r\n \t
- Identify two risk factors for autoimmune diseases.<\/li>\r\n \t
- Autoimmune diseases may be specific to particular tissues, or they may be systemic. Give an example of each type of autoimmune disease.<\/li>\r\n \t
- What is immunodeficiency? Compare and contrast primary and secondary immunodeficiency. Give an example of each.<\/li>\r\n \t
- What is the most common cause of immunodeficiency in the world today? How does this affect the immune system?<\/li>\r\n \t
- Distinguish between HIV and AIDS.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/-q7Fz7NIMWM\r\nWhy do people have seasonal allergies? - Eleanor Nelsen, TED-Ed, 2016.<\/p>\r\nhttps:\/\/youtu.be\/0TipTogQT3E\r\n
Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, TED-Ed, 2015.<\/p>\r\nhttps:\/\/youtu.be\/pJa6KVLwl9U\r\n
The Boy in the Bubble | Retro Report | The New York Times, 2015.<\/p>\r\nhttps:\/\/youtu.be\/Mjr9h_QmdeM\r\n
Why Are Peanut Allergies Becoming So Common? Seeker, 2014.<\/p>\r\nhttps:\/\/youtu.be\/RiMSmDBvgto\r\n
What Are Tonsil Stones? | Gross Science, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 17.6.1<\/strong>\r\n\r\nOedema<\/a> by Championswimmer<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.2<\/strong>\r\n\r\n \t- Medical (latex) gloves<\/a> from pngimg.com is used under a CC BY-NC 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/) license.<\/li>\r\n \t
- House dust mites (5247996458)<\/a> by Gilles San Martin<\/a> from Namur, Belgium on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\r\n \t
- \u00a0Honey bee macro<\/a> by Karunakar Rayker<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/li>\r\n \t
- Peanuts<\/a> by Karolina Grabowska<\/a> on Pexels<\/a> is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Photo of dog and grey cat<\/a> by ERC4N51<\/a> on pxhere is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Tags: Pollen Allergy Spring<\/a>\u00a0by Castagnari53<\/a> on Pixabay<\/a>, is used under the Pixabay License<\/a> (https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\nFigure 17.6.3<\/strong>\r\n\r\n512px-Mast_cells<\/a> by National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute<\/a> (p.29) is in\u00a0the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.4<\/strong>\r\n\r\nSigns_and_symptoms_of_anaphylaxis<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\n\r\nFigure 17.6.5<\/strong>\r\n\r\nAllergy Tests<\/a> by Dan Pupius<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 17.6.6<\/strong>\r\n\r\n1024px-Symptoms_of_SLE<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons\u00a0is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\nFigure 17.6.7<\/strong>\r\n\r\nHIV transmission<\/a>\u00a0by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 17.6.8<\/strong>\r\n\r\nHIV life cycle<\/a> by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 17.6.9<\/strong>\r\n\r\nEpipen by Stock Catalog on flickr<\/a> by Stock Catalog<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n
References<\/h2>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 8 HIV may be transmitted in all of the ways shown here [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nBrainard, J\/ CK-12 Foundation. (2016). Figure 9 This diagram shows how HIV infects and destroys helper T cells [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nCBS News. (2016, August 16). Rising cost of potentially life-saving EpiPen puts pinch on families [online article]. CBS Interactive Inc. https:\/\/www.cbsnews.com\/news\/allergy-medication-epipen-epinephrine-rising-costs-impact-on-families\/<\/p>\r\n
Gross Science. (2015, June 29). What are tonsil stones? | Gross Science. YouTube. https:\/\/www.youtube.com\/watch?v=RiMSmDBvgto&feature=youtu.be<\/p>\r\n
H\u00e4ggstr\u00f6m, M. (2014). Medical gallery of Mikael H\u00e4ggstr\u00f6m 2014.\u00a0WikiJournal of Medicine<\/i>\u00a01<\/b>\u00a0(2).\u00a0DOI:10.15347\/wjm\/2014.008.\u00a0ISSN\u00a02002-4436<\/p>\r\n
National Institute of Allergy and Infectious Diseases (NIAID). (n.d.). Severe combined immunodeficiency (SCID) [online article]. National Institute of Health (NIH). https:\/\/www.niaid.nih.gov\/diseases-conditions\/severe-combined-immunodeficiency-scid<\/p>\r\n
National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute (U.S.). (2003, September). Understanding the immune system and how it works [NIH Publication No. 03-5423]. Scholar Works<\/em> - \u00a0Indiana University. https:\/\/scholarworks.iupui.edu\/handle\/1805\/748<\/p>\r\n[The] New York Times. (2015, December 15). The boy in the bubble | Retro Report | The New York Times. YouTube. https:\/\/www.youtube.com\/watch?v=pJa6KVLwl9U&feature=youtu.be<\/p>\r\n
Seeker. (2014, October 3). Why are peanut allergies becoming so common? YouTube. https:\/\/www.youtube.com\/watch?v=Mjr9h_QmdeM&feature=youtu.be<\/p>\r\n
Summary: Estimates of HIV incidence, prevalence, and Canada's progress on meeting the 90-90-90 HIV targets 2016. (2018, July). Public Health Agency of Canada. https:\/\/www.canada.ca\/content\/dam\/phac-aspc\/documents\/services\/publications\/diseases-conditions\/summary-estimates-hiv-incidence-prevalence-canadas-progress-90-90-90\/pub-eng.pdf<\/p>\r\n
Swetlitz, I., Silverman, E. (2016, August 25). Mylan may have violated antitrust law in its EpiPen sales to schools, legal experts say [online article]. STATNews.com. https:\/\/www.statnews.com\/2016\/08\/25\/mylan-antitrust-epipen-schools\/<\/p>\r\n
TED-Ed. (2016, May 26). Why do people have seasonal allergies? - Eleanor Nelsen. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=-q7Fz7NIMWM&feature=youtu.be<\/p>\r\n
TED-Ed. (2015, March 16). Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, https:\/\/www.youtube.com\/watch?v=0TipTogQT3E&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 17.6.1 Oh m-eye!<\/em><\/figcaption><\/figure>\n\nAllergy Eyes<\/h1>\n<\/div>\n
Eyes that are red, watery, and itchy are typical of an allergic reaction known as allergic rhinitis. Commonly called hay fever, allergic rhinitis is an immune system reaction, typically to the pollen of certain plants. Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes, it responds to harmless foreign substances as though they were pathogens. This is the basis of allergies like hay fever.<\/p>\n
\nAllergies<\/h1>\n<\/div>\n
An\u00a0allergy<\/a><\/strong>\u00a0is a disorder in which the immune system makes an inflammatory response<\/a> to a harmless antigen<\/a>. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.<\/p>\nAllergens<\/h2>\n
Any antigen that causes an allergy is called an\u00a0allergen<\/a>.<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.<\/p>\n\n\n<\/div>\n<\/div>\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em><\/p>\n<\/div>\nPrevalence of Allergies<\/h2>\n
There has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.<\/p>\n
One explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.<\/p>\n
How Allergies Occur<\/h2>\n
The diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.<\/p>\nFigure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em><\/figcaption><\/figure>\nTreating Allergies<\/h2>\n
The symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with antihistamines<\/span><\/strong><\/a><\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span><\/p>\nTreating Anaphylaxis<\/h3>\n
The most severe allergic reaction is a systemic reaction called\u00a0anaphylaxis<\/a>.<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.<\/p>\nFigure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em><\/figcaption><\/figure>\nImmunotherapy for Allergies<\/h3>\nFigure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em><\/figcaption><\/figure>\nAnother way to treat allergies is called\u00a0immunotherapy<\/a>,<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.<\/p>\nAutoimmune Diseases<\/span><\/p>\nAutoimmune diseases<\/a><\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, B cells<\/span><\/a><\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to pathogen<\/span>s<\/span><\/a><\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span><\/p>\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.<\/p>\n
At a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.<\/p>\n
Common Autoimmune Diseases<\/h2>\n
An estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are type I diabetes<\/a> and multiple sclerosis<\/a>. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys insulin<\/a>-secreting islet cells in the pancreas<\/a>. In the case of multiple sclerosis, the immune system attacks and destroys the myelin sheaths<\/span><\/a><\/span>\u00a0that normally insulate the axon<\/span>s<\/span><\/a><\/span>\u00a0of <\/span>neuron<\/span>s<\/span><\/a><\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span><\/p>\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include rheumatoid arthritis<\/a> and systemic lupus erythematosus<\/a> (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.<\/p>\nFigure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em><\/figcaption><\/figure>\nTreatment for Autoimmune Diseases<\/h2>\n
None of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.<\/p>\n
\nImmunodeficiency<\/h1>\n<\/div>\n
Immunodeficiency<\/a><\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.<\/p>\nCauses of Immunodeficiency<\/h2>\n
Dozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0primary immunodeficiency<\/a><\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked recessive<\/a> mutation<\/a> that interferes with normal B cell and T cell production.<\/p>\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0secondary immunodeficiency<\/a><\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:<\/p>\n\n- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\n
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\n
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\n
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\n
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\n<\/ul>\n\n
Focus on HIV<\/h1>\n<\/div>\n
Human immunodeficiency virus (
Immunodeficiency<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary]<\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.\r\nCauses of Immunodeficiency<\/h2>\r\nDozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0[pb_glossary id=\"5012\"]primary immunodeficiency[\/pb_glossary]<\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked [pb_glossary id=\"2479\"]recessive[\/pb_glossary] [pb_glossary id=\"2381\"]mutation[\/pb_glossary] that interferes with normal B cell and T cell production.\r\n\r\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0[pb_glossary id=\"5013\"]secondary immunodeficiency[\/pb_glossary]<\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:\r\n\r\n \t- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\r\n \t
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\r\n \t
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\r\n \t
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\r\n \t
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\r\n<\/ul>\r\n\r\n
Focus on HIV<\/h1>\r\n<\/div>\r\nHuman immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary])<\/strong> is the most common cause of immunodeficiency in the world today. HIV infections of human hosts are a relatively recent phenomenon. Scientists think that the virus originally infected monkeys, but then jumped to human populations. most likely from a bite, probably sometime during the early to mid-1900s. This most likely occurred in West Africa, but the virus soon spread around the world. HIV was first identified by medical researchers in 1981. Since then, HIV has killed almost 40 million people worldwide, and its economic toll has also been enormous. The hardest hit countries are in Africa, where the virus has infected human populations the longest, and medications to control the virus are least available.\u00a0 In 2016, over 63,000 Canadians were living with HIV.\r\nHIV Transmission<\/h2>\r\nHIV is transmitted through direct contact of [pb_glossary id=\"3538\"]mucous membranes<\/span>[\/pb_glossary]<\/span> or body fluids such as blood, semen, or breast milk. As shown in Figure 17.6.7, transmission of the virus can occur through sexual contact or the use of contaminated hypodermic needles. It can also be transmitted from an infected mother\u2019s blood during late pregnancy or childbirth, or through breast milk after birth. In the past, HIV was also transmitted occasionally through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way.<\/span>\r\n\r\n[caption id=\"attachment_5014\" align=\"aligncenter\" width=\"500\"] Figure 17.6.7 HIV may be transmitted in all of the ways shown here: through sexual activities, from mother to child (in utero, during childbirth, through breastmilk), and by sharing needles.<\/em>[\/caption]\r\nHIV and the Immune System<\/h2>\r\nHIV infects and destroys [pb_glossary id=\"5537\"]helper T cells<\/span>[\/pb_glossary]<\/span>, the type of [pb_glossary id=\"4832\"]lymphocyte<\/span>s<\/span>[\/pb_glossary]<\/span> that regulate the immune response. This process is illustrated in the diagram in Figure 17.6.8. The virus injects its own DNA into a helper T cell and uses the T cell\u2019s \u201cmachinery\u201d to make copies of itself. In the process, the helper T cell is destroyed, and the virus copies go on to infect other helper T cells. HIV is able to evade the immune system and keep destroying helper T cells by mutating frequently so its surface antigens keep changing, and by using the host cell\u2019s membrane to hide its own antigens.<\/span>\r\n\r\n[caption id=\"attachment_5015\" align=\"aligncenter\" width=\"500\"] Figure 17.6.8 This diagram shows how HIV infects and destroys helper T cells.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"5016\"]Acquired immunodeficiency syndrome[\/pb_glossary] (AIDS)<\/strong> may result from years of damage to the immune system by HIV. It occurs when helper T cells fall to a very low level and opportunistic diseases occur. Opportunistic diseases are infections and tumors that are rare, except in people with a damaged immune system. The diseases take advantage of the \u201copportunity\u201d presented by people whose immune system cannot fight back. Opportunistic diseases are usually the direct cause of death for people with AIDS.\r\nTreating HIV\/AIDS<\/h2>\r\nFor patients who have access to HIV medications, infection with the virus is no longer the death sentence\u00a0that it once was. By 1995, combinations of drugs called \u201chighly active antiretroviral therapy\u201d were developed. For some patients, these drugs can reduce the amount of virus they are carrying to undetectable levels. However, some\u00a0level\u00a0of virus always hides in the body\u2019s immune cells, and it will multiply again if a patient stops taking the medications. Researchers are trying to develop drugs to kill these hidden viruses, as well. If their efforts are successful, it could end AIDS.\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nEpiPens\u00ae and their sole manufacturer (pharmaceutical company Mylan) were featured in headlines in 2016, but not for a good reason. The media\u00a0outburst\u00a0was triggered by a drastic price hike in EpiPens\u00ae \u2014 and Mylan\u2019s apparent greed.\r\n\r\n[caption id=\"attachment_5017\" align=\"alignleft\" width=\"290\"] Figure 17.6.9 An Epipen\u00ae is a hypodermic device that administers a dose of epinephrine, used for the emergency treatment of an acute allergic reaction.<\/em>[\/caption]\r\n\r\nEpiPens\u00ae are auto-injectable syringes preloaded with a measured dose of epinephrine, a drug that can rapidly stop a life-threatening anaphylactic response to an allergen. Using the device is easy and does not require any special training. The injector just needs to be jammed against the thigh, which can be done through clothing or on bare skin. Each year, doctors write millions of prescriptions for EpiPens\u00ae. Many people with severe allergies always carry two of the devices with them, just in case they experience anaphylaxis, although most of them never need to use them. Other people with severe allergies have literally had their lives saved multiple times by EpiPens\u00ae when they had anaphylactic reactions. Even when the devices haven\u2019t been used, they must be replaced each year due to expiration of the epinephrine.\r\n\r\nYou might think that EpiPens\u00ae would be relatively inexpensive, given their life-saving potential. As recently as 2009, a two-pack of EpiPens\u00ae cost about $100. However, in just seven years, the cost of the same two-pack of EpiPens\u00ae skyrocketed by an incredible 400%! By 2016, the cost was $600 or more. Mylan apparently raised the price for the sole purpose of increasing profits. The company also raised prices significantly on many other drugs. The price hike in EpiPens\u00ae alone was certainly profitable. In 2015, the sale of EpiPens\u00ae earned Mylan $1 billion. Mylan\u2019s CEO took home almost $19 million the same year, which was an increase of more than 600% over her prior salary.\r\n\r\nNews coverage of the price hike in EpiPens\u00ae began in the summer of 2016 after a price increase in May of that year. Both private citizens and elected officials expressed outrage over the price increase, especially when coupled with the gluttonous profits of the company and its CEO. By late August, Mylan responded to the backlash by offering discount coupons for EpiPens\u00ae. A few days later, the company promised to introduce a cheaper, generic version of the device. Analysts quickly determined that selling a generic version would allow Mylan to make more money on the product than reducing the price of the name-brand device, which they still declined to do. By September of 2016, Mylan was being investigated for antitrust violations\u00a0related\u00a0to sales of EpiPens\u00ae to public schools in New York City.\r\n\r\nThe Mylan\/EpiPen\u00ae story may still be making the news. But whatever its outcome, the story has already added fuel to public and private debates about important ethical issues\u00a0\u2014\u00a0issues such as the excessive costs of life-saving drugs and the huge profits of big pharma. What is the most recent news on EpiPens\u00ae and Mylan? If you are interested, you can check the headlines online to find out. What are your views on the ethical issues they raise?\r\n\r\n17.6 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless antigen. Any [pb_glossary id=\"2704\"]antigen[\/pb_glossary] that causes allergies is called an [pb_glossary id=\"4999\"]allergen[\/pb_glossary]. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\r\n \t
- The prevalence of allergies has been increasing for decades, especially in developed countries, where they are much more common than in developing countries. The hygiene hypothesis posits that this has occurred because humans evolved to cope with more pathogens than we now typically face in our relatively sterile environments in developed countries. As a result, the immune system \u201ckeeps busy\u201d by attacking harmless antigens.<\/li>\r\n \t
- Allergies occur when [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]. On subsequent exposures to the allergen, the mast cells immediately release [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]\u00a0that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with [pb_glossary id=\"5469\"]antihistamines[\/pb_glossary]\u00a0that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called [pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary], is a medical emergency that is usually treated with injections of epinephrine. [pb_glossary id=\"5004\"]Immunotherapy[\/pb_glossary] for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary] occur when the immune system fails to recognize the body\u2019s own molecules as self and attacks them, causing damage to tissues and organs. A family history of autoimmunity and female gender are risk factors for autoimmune diseases.<\/li>\r\n \t
- In some autoimmune diseases, such as [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary], the immune system attacks and damages specific body cells. In other autoimmune diseases, such as [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary], many different tissues and organs may be attacked and injured. Autoimmune diseases generally cannot be cured, but their symptoms can often be managed with drugs or other treatments.<\/li>\r\n \t
- [pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary] occurs when the immune system is not working properly, generally because one or more of its components are inactive. As a result, the immune system is unable to fight off pathogens or cancers that a normal immune system would be able to resist.<\/li>\r\n \t
- [pb_glossary id=\"5012\"]Primary immunodeficiency[\/pb_glossary] is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. [pb_glossary id=\"5013\"]Secondary immunodeficiency[\/pb_glossary] occurs because of some event or exposure experienced after birth. Possible causes include aging, certain medications, infections with pathogens, and other disorders, such as obesity or malnutrition.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]), which infects and destroys helper T cells. HIV is transmitted through mucous membranes or body fluids. The virus may eventually lead to such low levels of helper T cells that opportunistic infections occur. When this happens, the patient is diagnosed with [pb_glossary id=\"5016\"]acquired immunodeficiency syndrome[\/pb_glossary] (AIDS). Medications can control the multiplication of HIV in the human body \u2014 but they don't eliminate the [pb_glossary id=\"4283\"]virus[\/pb_glossary] completely.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"641\"]<\/li>\r\n \t
- How does immunotherapy for allergies work?<\/li>\r\n \t
- What are autoimmune diseases?<\/li>\r\n \t
- Identify two risk factors for autoimmune diseases.<\/li>\r\n \t
- Autoimmune diseases may be specific to particular tissues, or they may be systemic. Give an example of each type of autoimmune disease.<\/li>\r\n \t
- What is immunodeficiency? Compare and contrast primary and secondary immunodeficiency. Give an example of each.<\/li>\r\n \t
- What is the most common cause of immunodeficiency in the world today? How does this affect the immune system?<\/li>\r\n \t
- Distinguish between HIV and AIDS.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.6 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/-q7Fz7NIMWM\r\nWhy do people have seasonal allergies? - Eleanor Nelsen, TED-Ed, 2016.<\/p>\r\nhttps:\/\/youtu.be\/0TipTogQT3E\r\n
Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, TED-Ed, 2015.<\/p>\r\nhttps:\/\/youtu.be\/pJa6KVLwl9U\r\n
The Boy in the Bubble | Retro Report | The New York Times, 2015.<\/p>\r\nhttps:\/\/youtu.be\/Mjr9h_QmdeM\r\n
Why Are Peanut Allergies Becoming So Common? Seeker, 2014.<\/p>\r\nhttps:\/\/youtu.be\/RiMSmDBvgto\r\n
What Are Tonsil Stones? | Gross Science, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 17.6.1<\/strong>\r\n\r\nOedema<\/a> by Championswimmer<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.2<\/strong>\r\n\r\n \t- Medical (latex) gloves<\/a> from pngimg.com is used under a CC BY-NC 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/) license.<\/li>\r\n \t
- House dust mites (5247996458)<\/a> by Gilles San Martin<\/a> from Namur, Belgium on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\r\n \t
- \u00a0Honey bee macro<\/a> by Karunakar Rayker<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/li>\r\n \t
- Peanuts<\/a> by Karolina Grabowska<\/a> on Pexels<\/a> is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Photo of dog and grey cat<\/a> by ERC4N51<\/a> on pxhere is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Tags: Pollen Allergy Spring<\/a>\u00a0by Castagnari53<\/a> on Pixabay<\/a>, is used under the Pixabay License<\/a> (https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\nFigure 17.6.3<\/strong>\r\n\r\n512px-Mast_cells<\/a> by National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute<\/a> (p.29) is in\u00a0the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.4<\/strong>\r\n\r\nSigns_and_symptoms_of_anaphylaxis<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\n\r\nFigure 17.6.5<\/strong>\r\n\r\nAllergy Tests<\/a> by Dan Pupius<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 17.6.6<\/strong>\r\n\r\n1024px-Symptoms_of_SLE<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons\u00a0is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\nFigure 17.6.7<\/strong>\r\n\r\nHIV transmission<\/a>\u00a0by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 17.6.8<\/strong>\r\n\r\nHIV life cycle<\/a> by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 17.6.9<\/strong>\r\n\r\nEpipen by Stock Catalog on flickr<\/a> by Stock Catalog<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n
References<\/h2>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 8 HIV may be transmitted in all of the ways shown here [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nBrainard, J\/ CK-12 Foundation. (2016). Figure 9 This diagram shows how HIV infects and destroys helper T cells [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\nCBS News. (2016, August 16). Rising cost of potentially life-saving EpiPen puts pinch on families [online article]. CBS Interactive Inc. https:\/\/www.cbsnews.com\/news\/allergy-medication-epipen-epinephrine-rising-costs-impact-on-families\/<\/p>\r\n
Gross Science. (2015, June 29). What are tonsil stones? | Gross Science. YouTube. https:\/\/www.youtube.com\/watch?v=RiMSmDBvgto&feature=youtu.be<\/p>\r\n
H\u00e4ggstr\u00f6m, M. (2014). Medical gallery of Mikael H\u00e4ggstr\u00f6m 2014.\u00a0WikiJournal of Medicine<\/i>\u00a01<\/b>\u00a0(2).\u00a0DOI:10.15347\/wjm\/2014.008.\u00a0ISSN\u00a02002-4436<\/p>\r\n
National Institute of Allergy and Infectious Diseases (NIAID). (n.d.). Severe combined immunodeficiency (SCID) [online article]. National Institute of Health (NIH). https:\/\/www.niaid.nih.gov\/diseases-conditions\/severe-combined-immunodeficiency-scid<\/p>\r\n
National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute (U.S.). (2003, September). Understanding the immune system and how it works [NIH Publication No. 03-5423]. Scholar Works<\/em> - \u00a0Indiana University. https:\/\/scholarworks.iupui.edu\/handle\/1805\/748<\/p>\r\n[The] New York Times. (2015, December 15). The boy in the bubble | Retro Report | The New York Times. YouTube. https:\/\/www.youtube.com\/watch?v=pJa6KVLwl9U&feature=youtu.be<\/p>\r\n
Seeker. (2014, October 3). Why are peanut allergies becoming so common? YouTube. https:\/\/www.youtube.com\/watch?v=Mjr9h_QmdeM&feature=youtu.be<\/p>\r\n
Summary: Estimates of HIV incidence, prevalence, and Canada's progress on meeting the 90-90-90 HIV targets 2016. (2018, July). Public Health Agency of Canada. https:\/\/www.canada.ca\/content\/dam\/phac-aspc\/documents\/services\/publications\/diseases-conditions\/summary-estimates-hiv-incidence-prevalence-canadas-progress-90-90-90\/pub-eng.pdf<\/p>\r\n
Swetlitz, I., Silverman, E. (2016, August 25). Mylan may have violated antitrust law in its EpiPen sales to schools, legal experts say [online article]. STATNews.com. https:\/\/www.statnews.com\/2016\/08\/25\/mylan-antitrust-epipen-schools\/<\/p>\r\n
TED-Ed. (2016, May 26). Why do people have seasonal allergies? - Eleanor Nelsen. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=-q7Fz7NIMWM&feature=youtu.be<\/p>\r\n
TED-Ed. (2015, March 16). Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, https:\/\/www.youtube.com\/watch?v=0TipTogQT3E&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 17.6.1 Oh m-eye!<\/em><\/figcaption><\/figure>\n\nAllergy Eyes<\/h1>\n<\/div>\n
Eyes that are red, watery, and itchy are typical of an allergic reaction known as allergic rhinitis. Commonly called hay fever, allergic rhinitis is an immune system reaction, typically to the pollen of certain plants. Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes, it responds to harmless foreign substances as though they were pathogens. This is the basis of allergies like hay fever.<\/p>\n
\nAllergies<\/h1>\n<\/div>\n
An\u00a0allergy<\/a><\/strong>\u00a0is a disorder in which the immune system makes an inflammatory response<\/a> to a harmless antigen<\/a>. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.<\/p>\nAllergens<\/h2>\n
Any antigen that causes an allergy is called an\u00a0allergen<\/a>.<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.<\/p>\n\n\n<\/div>\n<\/div>\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em><\/p>\n<\/div>\nPrevalence of Allergies<\/h2>\n
There has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.<\/p>\n
One explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.<\/p>\n
How Allergies Occur<\/h2>\n
The diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.<\/p>\nFigure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em><\/figcaption><\/figure>\nTreating Allergies<\/h2>\n
The symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with antihistamines<\/span><\/strong><\/a><\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span><\/p>\nTreating Anaphylaxis<\/h3>\n
The most severe allergic reaction is a systemic reaction called\u00a0anaphylaxis<\/a>.<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.<\/p>\nFigure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em><\/figcaption><\/figure>\nImmunotherapy for Allergies<\/h3>\nFigure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em><\/figcaption><\/figure>\nAnother way to treat allergies is called\u00a0immunotherapy<\/a>,<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.<\/p>\nAutoimmune Diseases<\/span><\/p>\nAutoimmune diseases<\/a><\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, B cells<\/span><\/a><\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to pathogen<\/span>s<\/span><\/a><\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span><\/p>\nCertain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.<\/p>\n
At a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.<\/p>\n
Common Autoimmune Diseases<\/h2>\n
An estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are type I diabetes<\/a> and multiple sclerosis<\/a>. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys insulin<\/a>-secreting islet cells in the pancreas<\/a>. In the case of multiple sclerosis, the immune system attacks and destroys the myelin sheaths<\/span><\/a><\/span>\u00a0that normally insulate the axon<\/span>s<\/span><\/a><\/span>\u00a0of <\/span>neuron<\/span>s<\/span><\/a><\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span><\/p>\nSome relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include rheumatoid arthritis<\/a> and systemic lupus erythematosus<\/a> (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.<\/p>\nFigure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em><\/figcaption><\/figure>\nTreatment for Autoimmune Diseases<\/h2>\n
None of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.<\/p>\n
\nImmunodeficiency<\/h1>\n<\/div>\n
Immunodeficiency<\/a><\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.<\/p>\nCauses of Immunodeficiency<\/h2>\n
Dozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0primary immunodeficiency<\/a><\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked recessive<\/a> mutation<\/a> that interferes with normal B cell and T cell production.<\/p>\nOther types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0secondary immunodeficiency<\/a><\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:<\/p>\n\n- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\n
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\n
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\n
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\n
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\n<\/ul>\n\n
Focus on HIV<\/h1>\n<\/div>\n
Human immunodeficiency virus (
- \r\n \t
- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\r\n \t
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\r\n \t
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\r\n \t
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\r\n \t
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\r\n<\/ul>\r\n
\r\nFocus on HIV<\/h1>\r\n<\/div>\r\nHuman immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary])<\/strong> is the most common cause of immunodeficiency in the world today. HIV infections of human hosts are a relatively recent phenomenon. Scientists think that the virus originally infected monkeys, but then jumped to human populations. most likely from a bite, probably sometime during the early to mid-1900s. This most likely occurred in West Africa, but the virus soon spread around the world. HIV was first identified by medical researchers in 1981. Since then, HIV has killed almost 40 million people worldwide, and its economic toll has also been enormous. The hardest hit countries are in Africa, where the virus has infected human populations the longest, and medications to control the virus are least available.\u00a0 In 2016, over 63,000 Canadians were living with HIV.\r\n
HIV Transmission<\/h2>\r\nHIV is transmitted through direct contact of [pb_glossary id=\"3538\"]mucous membranes<\/span>[\/pb_glossary]<\/span> or body fluids such as blood, semen, or breast milk. As shown in Figure 17.6.7, transmission of the virus can occur through sexual contact or the use of contaminated hypodermic needles. It can also be transmitted from an infected mother\u2019s blood during late pregnancy or childbirth, or through breast milk after birth. In the past, HIV was also transmitted occasionally through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way.<\/span>\r\n\r\n[caption id=\"attachment_5014\" align=\"aligncenter\" width=\"500\"]
Figure 17.6.7 HIV may be transmitted in all of the ways shown here: through sexual activities, from mother to child (in utero, during childbirth, through breastmilk), and by sharing needles.<\/em>[\/caption]\r\nHIV and the Immune System<\/h2>\r\nHIV infects and destroys [pb_glossary id=\"5537\"]helper T cells<\/span>[\/pb_glossary]<\/span>, the type of [pb_glossary id=\"4832\"]lymphocyte<\/span>s<\/span>[\/pb_glossary]<\/span> that regulate the immune response. This process is illustrated in the diagram in Figure 17.6.8. The virus injects its own DNA into a helper T cell and uses the T cell\u2019s \u201cmachinery\u201d to make copies of itself. In the process, the helper T cell is destroyed, and the virus copies go on to infect other helper T cells. HIV is able to evade the immune system and keep destroying helper T cells by mutating frequently so its surface antigens keep changing, and by using the host cell\u2019s membrane to hide its own antigens.<\/span>\r\n\r\n[caption id=\"attachment_5015\" align=\"aligncenter\" width=\"500\"]
Figure 17.6.8 This diagram shows how HIV infects and destroys helper T cells.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"5016\"]Acquired immunodeficiency syndrome[\/pb_glossary] (AIDS)<\/strong> may result from years of damage to the immune system by HIV. It occurs when helper T cells fall to a very low level and opportunistic diseases occur. Opportunistic diseases are infections and tumors that are rare, except in people with a damaged immune system. The diseases take advantage of the \u201copportunity\u201d presented by people whose immune system cannot fight back. Opportunistic diseases are usually the direct cause of death for people with AIDS.\r\nTreating HIV\/AIDS<\/h2>\r\nFor patients who have access to HIV medications, infection with the virus is no longer the death sentence\u00a0that it once was. By 1995, combinations of drugs called \u201chighly active antiretroviral therapy\u201d were developed. For some patients, these drugs can reduce the amount of virus they are carrying to undetectable levels. However, some\u00a0level\u00a0of virus always hides in the body\u2019s immune cells, and it will multiply again if a patient stops taking the medications. Researchers are trying to develop drugs to kill these hidden viruses, as well. If their efforts are successful, it could end AIDS.\r\n
\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nEpiPens\u00ae and their sole manufacturer (pharmaceutical company Mylan) were featured in headlines in 2016, but not for a good reason. The media\u00a0outburst\u00a0was triggered by a drastic price hike in EpiPens\u00ae \u2014 and Mylan\u2019s apparent greed.\r\n\r\n[caption id=\"attachment_5017\" align=\"alignleft\" width=\"290\"]
Figure 17.6.9 An Epipen\u00ae is a hypodermic device that administers a dose of epinephrine, used for the emergency treatment of an acute allergic reaction.<\/em>[\/caption]\r\n\r\nEpiPens\u00ae are auto-injectable syringes preloaded with a measured dose of epinephrine, a drug that can rapidly stop a life-threatening anaphylactic response to an allergen. Using the device is easy and does not require any special training. The injector just needs to be jammed against the thigh, which can be done through clothing or on bare skin. Each year, doctors write millions of prescriptions for EpiPens\u00ae. Many people with severe allergies always carry two of the devices with them, just in case they experience anaphylaxis, although most of them never need to use them. Other people with severe allergies have literally had their lives saved multiple times by EpiPens\u00ae when they had anaphylactic reactions. Even when the devices haven\u2019t been used, they must be replaced each year due to expiration of the epinephrine.\r\n\r\nYou might think that EpiPens\u00ae would be relatively inexpensive, given their life-saving potential. As recently as 2009, a two-pack of EpiPens\u00ae cost about $100. However, in just seven years, the cost of the same two-pack of EpiPens\u00ae skyrocketed by an incredible 400%! By 2016, the cost was $600 or more. Mylan apparently raised the price for the sole purpose of increasing profits. The company also raised prices significantly on many other drugs. The price hike in EpiPens\u00ae alone was certainly profitable. In 2015, the sale of EpiPens\u00ae earned Mylan $1 billion. Mylan\u2019s CEO took home almost $19 million the same year, which was an increase of more than 600% over her prior salary.\r\n\r\nNews coverage of the price hike in EpiPens\u00ae began in the summer of 2016 after a price increase in May of that year. Both private citizens and elected officials expressed outrage over the price increase, especially when coupled with the gluttonous profits of the company and its CEO. By late August, Mylan responded to the backlash by offering discount coupons for EpiPens\u00ae. A few days later, the company promised to introduce a cheaper, generic version of the device. Analysts quickly determined that selling a generic version would allow Mylan to make more money on the product than reducing the price of the name-brand device, which they still declined to do. By September of 2016, Mylan was being investigated for antitrust violations\u00a0related\u00a0to sales of EpiPens\u00ae to public schools in New York City.\r\n\r\nThe Mylan\/EpiPen\u00ae story may still be making the news. But whatever its outcome, the story has already added fuel to public and private debates about important ethical issues\u00a0\u2014\u00a0issues such as the excessive costs of life-saving drugs and the huge profits of big pharma. What is the most recent news on EpiPens\u00ae and Mylan? If you are interested, you can check the headlines online to find out. What are your views on the ethical issues they raise?\r\n\r\n 17.6 Summary<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an [pb_glossary id=\"4860\"]inflammatory response[\/pb_glossary] to a harmless antigen. Any [pb_glossary id=\"2704\"]antigen[\/pb_glossary] that causes allergies is called an [pb_glossary id=\"4999\"]allergen[\/pb_glossary]. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\r\n \t
- The prevalence of allergies has been increasing for decades, especially in developed countries, where they are much more common than in developing countries. The hygiene hypothesis posits that this has occurred because humans evolved to cope with more pathogens than we now typically face in our relatively sterile environments in developed countries. As a result, the immune system \u201ckeeps busy\u201d by attacking harmless antigens.<\/li>\r\n \t
- Allergies occur when [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]. On subsequent exposures to the allergen, the mast cells immediately release [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]\u00a0that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with [pb_glossary id=\"5469\"]antihistamines[\/pb_glossary]\u00a0that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called [pb_glossary id=\"5002\"]anaphylaxis[\/pb_glossary], is a medical emergency that is usually treated with injections of epinephrine. [pb_glossary id=\"5004\"]Immunotherapy[\/pb_glossary] for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary] occur when the immune system fails to recognize the body\u2019s own molecules as self and attacks them, causing damage to tissues and organs. A family history of autoimmunity and female gender are risk factors for autoimmune diseases.<\/li>\r\n \t
- In some autoimmune diseases, such as [pb_glossary id=\"3507\"]type I diabetes[\/pb_glossary], the immune system attacks and damages specific body cells. In other autoimmune diseases, such as [pb_glossary id=\"5009\"]systemic lupus erythematosus[\/pb_glossary], many different tissues and organs may be attacked and injured. Autoimmune diseases generally cannot be cured, but their symptoms can often be managed with drugs or other treatments.<\/li>\r\n \t
- [pb_glossary id=\"5011\"]Immunodeficiency[\/pb_glossary] occurs when the immune system is not working properly, generally because one or more of its components are inactive. As a result, the immune system is unable to fight off pathogens or cancers that a normal immune system would be able to resist.<\/li>\r\n \t
- [pb_glossary id=\"5012\"]Primary immunodeficiency[\/pb_glossary] is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. [pb_glossary id=\"5013\"]Secondary immunodeficiency[\/pb_glossary] occurs because of some event or exposure experienced after birth. Possible causes include aging, certain medications, infections with pathogens, and other disorders, such as obesity or malnutrition.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]), which infects and destroys helper T cells. HIV is transmitted through mucous membranes or body fluids. The virus may eventually lead to such low levels of helper T cells that opportunistic infections occur. When this happens, the patient is diagnosed with [pb_glossary id=\"5016\"]acquired immunodeficiency syndrome[\/pb_glossary] (AIDS). Medications can control the multiplication of HIV in the human body \u2014 but they don't eliminate the [pb_glossary id=\"4283\"]virus[\/pb_glossary] completely.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n 17.6 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- [h5p id=\"641\"]<\/li>\r\n \t
- How does immunotherapy for allergies work?<\/li>\r\n \t
- What are autoimmune diseases?<\/li>\r\n \t
- Identify two risk factors for autoimmune diseases.<\/li>\r\n \t
- Autoimmune diseases may be specific to particular tissues, or they may be systemic. Give an example of each type of autoimmune disease.<\/li>\r\n \t
- What is immunodeficiency? Compare and contrast primary and secondary immunodeficiency. Give an example of each.<\/li>\r\n \t
- What is the most common cause of immunodeficiency in the world today? How does this affect the immune system?<\/li>\r\n \t
- Distinguish between HIV and AIDS.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n 17.6 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/youtu.be\/-q7Fz7NIMWM\r\nWhy do people have seasonal allergies? - Eleanor Nelsen, TED-Ed, 2016.<\/p>\r\nhttps:\/\/youtu.be\/0TipTogQT3E\r\n
Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, TED-Ed, 2015.<\/p>\r\nhttps:\/\/youtu.be\/pJa6KVLwl9U\r\n
The Boy in the Bubble | Retro Report | The New York Times, 2015.<\/p>\r\nhttps:\/\/youtu.be\/Mjr9h_QmdeM\r\n
Why Are Peanut Allergies Becoming So Common? Seeker, 2014.<\/p>\r\nhttps:\/\/youtu.be\/RiMSmDBvgto\r\n
What Are Tonsil Stones? | Gross Science, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 17.6.1<\/strong>\r\n\r\nOedema<\/a> by Championswimmer<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.2<\/strong>\r\n
- \r\n \t
- Medical (latex) gloves<\/a> from pngimg.com is used under a CC BY-NC 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/) license.<\/li>\r\n \t
- House dust mites (5247996458)<\/a> by Gilles San Martin<\/a> from Namur, Belgium on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\r\n \t
- \u00a0Honey bee macro<\/a> by Karunakar Rayker<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/li>\r\n \t
- Peanuts<\/a> by Karolina Grabowska<\/a> on Pexels<\/a> is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Photo of dog and grey cat<\/a> by ERC4N51<\/a> on pxhere is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/li>\r\n \t
- Tags: Pollen Allergy Spring<\/a>\u00a0by Castagnari53<\/a> on Pixabay<\/a>, is used under the Pixabay License<\/a> (https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\nFigure 17.6.3<\/strong>\r\n\r\n512px-Mast_cells<\/a> by National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute<\/a> (p.29) is in\u00a0the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/en:public_domain).\r\n\r\nFigure 17.6.4<\/strong>\r\n\r\nSigns_and_symptoms_of_anaphylaxis<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\n\r\nFigure 17.6.5<\/strong>\r\n\r\nAllergy Tests<\/a> by Dan Pupius<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 17.6.6<\/strong>\r\n\r\n1024px-Symptoms_of_SLE<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons\u00a0is used under a CC0 1.0<\/a> Universal Public Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).\r\n\r\nFigure 17.6.7<\/strong>\r\n\r\nHIV transmission<\/a>\u00a0by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n
\u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a><\/div>\r\nFigure 17.6.8<\/strong>\r\n\r\nHIV life cycle<\/a> by CK-12 Foundation<\/a> is used under a CC BY NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 17.6.9<\/strong>\r\n\r\nEpipen by Stock Catalog on flickr<\/a> by Stock Catalog<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\nReferences<\/h2>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 8 HIV may be transmitted in all of the ways shown here [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 9 This diagram shows how HIV infects and destroys helper T cells [digital image]. In CK-12 College Human Biology<\/em> (Section 19.6) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/19.6\/<\/p>\r\n
CBS News. (2016, August 16). Rising cost of potentially life-saving EpiPen puts pinch on families [online article]. CBS Interactive Inc. https:\/\/www.cbsnews.com\/news\/allergy-medication-epipen-epinephrine-rising-costs-impact-on-families\/<\/p>\r\n
Gross Science. (2015, June 29). What are tonsil stones? | Gross Science. YouTube. https:\/\/www.youtube.com\/watch?v=RiMSmDBvgto&feature=youtu.be<\/p>\r\n
H\u00e4ggstr\u00f6m, M. (2014). Medical gallery of Mikael H\u00e4ggstr\u00f6m 2014.\u00a0WikiJournal of Medicine<\/i>\u00a01<\/b>\u00a0(2).\u00a0DOI:10.15347\/wjm\/2014.008.\u00a0ISSN\u00a02002-4436<\/p>\r\n
National Institute of Allergy and Infectious Diseases (NIAID). (n.d.). Severe combined immunodeficiency (SCID) [online article]. National Institute of Health (NIH). https:\/\/www.niaid.nih.gov\/diseases-conditions\/severe-combined-immunodeficiency-scid<\/p>\r\n
National Institute of Allergy and Infectious Diseases (U.S.) & National Cancer Institute (U.S.). (2003, September). Understanding the immune system and how it works [NIH Publication No. 03-5423]. Scholar Works<\/em> - \u00a0Indiana University. https:\/\/scholarworks.iupui.edu\/handle\/1805\/748<\/p>\r\n
[The] New York Times. (2015, December 15). The boy in the bubble | Retro Report | The New York Times. YouTube. https:\/\/www.youtube.com\/watch?v=pJa6KVLwl9U&feature=youtu.be<\/p>\r\n
Seeker. (2014, October 3). Why are peanut allergies becoming so common? YouTube. https:\/\/www.youtube.com\/watch?v=Mjr9h_QmdeM&feature=youtu.be<\/p>\r\n
Summary: Estimates of HIV incidence, prevalence, and Canada's progress on meeting the 90-90-90 HIV targets 2016. (2018, July). Public Health Agency of Canada. https:\/\/www.canada.ca\/content\/dam\/phac-aspc\/documents\/services\/publications\/diseases-conditions\/summary-estimates-hiv-incidence-prevalence-canadas-progress-90-90-90\/pub-eng.pdf<\/p>\r\n
Swetlitz, I., Silverman, E. (2016, August 25). Mylan may have violated antitrust law in its EpiPen sales to schools, legal experts say [online article]. STATNews.com. https:\/\/www.statnews.com\/2016\/08\/25\/mylan-antitrust-epipen-schools\/<\/p>\r\n
TED-Ed. (2016, May 26). Why do people have seasonal allergies? - Eleanor Nelsen. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=-q7Fz7NIMWM&feature=youtu.be<\/p>\r\n
TED-Ed. (2015, March 16). Why it\u2019s so hard to cure HIV\/AIDS - Janet Iwasa, https:\/\/www.youtube.com\/watch?v=0TipTogQT3E&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\n
Figure 17.6.1 Oh m-eye!<\/em><\/figcaption><\/figure>\n \nAllergy Eyes<\/h1>\n<\/div>\n
Eyes that are red, watery, and itchy are typical of an allergic reaction known as allergic rhinitis. Commonly called hay fever, allergic rhinitis is an immune system reaction, typically to the pollen of certain plants. Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes, it responds to harmless foreign substances as though they were pathogens. This is the basis of allergies like hay fever.<\/p>\n
\nAllergies<\/h1>\n<\/div>\n
An\u00a0allergy<\/a><\/strong>\u00a0is a disorder in which the immune system makes an inflammatory response<\/a> to a harmless antigen<\/a>. It occurs when the immune system is hypersensitive to an antigen in the environment that causes little or no response in most people. Allergies are strongly familial. Allergic parents are more likely to have allergic children, and those children\u2019s allergies are likely to be more severe, which is evidence that there is a heritable tendency to develop allergies. Allergies are more common in children than adults, because many children outgrow their allergies by adulthood.<\/p>\n
Allergens<\/h2>\n
Any antigen that causes an allergy is called an\u00a0allergen<\/a>.<\/strong> Common allergens are plant pollens, dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain common medications (such as aspirin and penicillin). Allergens may be inhaled or ingested, or they may come into contact with the skin or eyes. Symptoms vary depending on the type of exposure, and the severity of the immune system response. Some of the most common causes of allergies are shown in Figure 17.6.2: latex, pollen, dust mites, pet dander, insect stings and various foods. Inhaling pollen may cause symptoms of allergic rhinitis, such as sneezing and red itchy eyes. Insect stings may cause an itchy rash. This type of allergy is called contact dermatitis.<\/p>\n
\n\n<\/div>\n<\/div>\nFigure 17.6.2 Common allergens include latex, pollen, dust mites, pet dander, insect stings, and foods.<\/em><\/p>\n<\/div>\n
Prevalence of Allergies<\/h2>\n
There has been a significant increase in the prevalence of allergies over the past several decades, especially in the rich nations of the world, where allergies are now very common disorders. In the developed countries, about 20% of people have or have had hay fever, another 20% have had contact dermatitis, and about 6% have food allergies. In the poorer nations of the world, on the other hand, allergies of all types are much less common.<\/p>\n
One explanation for the rise in allergies in the developed world is the hygiene hypothesis. According to this hypothesis, people in developed countries live in relatively sterile environments because of hygienic practices and sanitation systems. As a result, people in these countries are exposed to fewer pathogens than their immune system evolved to cope with. To compensate, their immune system \u201ckeeps busy\u201d by attacking harmless antigens in allergic responses.<\/p>\n
How Allergies Occur<\/h2>\n
The diagram in Figure 17.6.3 shows how an allergic reaction occurs. At the first exposure to an allergen, B cells are activated to form plasma cells that produce large amounts of antibodies to the allergen. These antibodies attach to leukocytes called mast cells. Subsequently, every time the person encounters the allergen again, the mast cells are already primed and ready to deal with it. The primed mast cells immediately release cytokines and histamines, which in turn cause inflammation and recruitment of leukocytes, among other responses. These responses are responsible for the signs and symptoms of allergies.<\/p>\n
Figure 17.6.3 This diagram shows how the adaptive immune system is activated by an otherwise harmless antigen on ragweed pollen, responding to the allergen as though it was a pathogen.<\/em><\/figcaption><\/figure>\n Treating Allergies<\/h2>\n
The symptoms of allergies can range from mild to life-threatening. Mild allergy symptoms are often treated with antihistamines<\/span><\/strong><\/a><\/span>. These are drugs that reduce or eliminate the effects of the histamines that produce allergy symptoms.<\/span><\/p>\n
Treating Anaphylaxis<\/h3>\n
The most severe allergic reaction is a systemic reaction called\u00a0anaphylaxis<\/a>.<\/strong> This is a life-threatening response caused by a massive release of histamines. Many of the signs and symptoms of anaphylaxis are shown in Figure 17.6.4. Some of them include a drop in blood pressure, changes in heart rate, shortness of breath, and swelling of the tongue and throat, which may threaten the patient with suffocation unless emergency treatment is given. People who have had anaphylactic reactions may carry an epinephrine autoinjector (widely known by its brand name EpiPen\u00ae) so they can inject themselves with epinephrine if they start to experience an anaphylactic response. The epinephrine helps control the immune reaction until medical care can be provided. Epinephrine constricts blood vessels to increase blood pressure, relaxes smooth muscles in the lungs to reduce wheezing and improve breathing, modulates heart rate, and works to reduce swelling that may otherwise block the airways.<\/p>\n
Figure 17.6.4 Anaphylaxis is a rapid, systemic reaction to allergens that may lead to life-threatening symptoms.<\/em><\/figcaption><\/figure>\n Immunotherapy for Allergies<\/h3>\n
Figure 17.6.5 Skin testing for common allergens is one way to identify the cause(s) of a patient\u2019s allergic symptoms.<\/em><\/figcaption><\/figure>\n Another way to treat allergies is called\u00a0immunotherapy<\/a>,<\/strong>\u00a0commonly called \u201callergy shots.\u201d This approach may actually\u00a0cure<\/em> specific allergies, at least for several years if not permanently. It may be particularly beneficial for allergens that are difficult or impossible to avoid (such as pollen). First, however, patients must be tested to identify the specific allergens that are causing their allergies. As shown in Figure 17.6.5, this may involve scratching tiny amounts of common allergens into the skin, and then observing whether there is a localized reaction to any of them. Each allergen is applied in a different numbered location on the skin, so if there is a reaction \u2014 such as redness or swelling \u2014 the responsible allergens can be identified. Then, through periodic injections (usually weekly or monthly), patients are gradually exposed to larger and larger amounts of the allergens. Over time, generally from months to years, the immune system becomes desensitized to the allergens. This method of treating allergies is often effective for allergies to pollen or insect stings, but its usefulness for allergies to food is unclear.<\/p>\n
Autoimmune Diseases<\/span><\/p>\n
Autoimmune diseases<\/a><\/strong>\u00a0occur when the immune system fails to recognize the body\u2019s own molecules as self. As a result, instead of ignoring the body\u2019s healthy cells, it attacks them, causing damage to tissues and\u00a0altering\u00a0organ growth and function. Most often, B cells<\/span><\/a><\/span>\u00a0are at fault for autoimmune responses. They are generally the cells that lose tolerance for self. Why does this occur? Some autoimmune diseases are thought to be caused by exposure to pathogen<\/span>s<\/span><\/a><\/span>\u00a0that have antigens similar to the body\u2019s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens, as well.<\/span><\/p>\n
Certain individuals are genetically susceptible to developing autoimmune diseases. These individuals are also more likely to develop more than one such disease. Gender is a risk factor for autoimmunity \u2014 females are much more likely than males to develop autoimmune diseases. This is likely due, in part, to gender differences in sex hormones.<\/p>\n
At a population level, autoimmune diseases are less common where infectious diseases are more common. The hygiene hypothesis has been proposed to explain the inverse relationship between infectious and autoimmune diseases, as well as the prevalence of allergies. According to the hypothesis, without infectious diseases to \u201ckeep it busy,\u201d the immune system may attack the body\u2019s own cells instead.<\/p>\n
Common Autoimmune Diseases<\/h2>\n
An estimated 15 million or more people worldwide have one or more autoimmune diseases. Two of the most common autoimmune diseases are type I diabetes<\/a> and multiple sclerosis<\/a>. In terms of the specific body cells that are attacked by the immune system, both are localized diseases. In the case of type I diabetes, the immune system attacks and destroys insulin<\/a>-secreting islet cells in the pancreas<\/a>. In the case of multiple sclerosis, the immune system attacks and destroys the myelin sheaths<\/span><\/a><\/span>\u00a0that normally insulate the axon<\/span>s<\/span><\/a><\/span>\u00a0of <\/span>neuron<\/span>s<\/span><\/a><\/span>\u00a0and allow rapid transmission of nerve impulses.<\/span><\/p>\n
Some relatively common autoimmune diseases are systemic \u2014 or body-wide \u2014 diseases. They include rheumatoid arthritis<\/a> and systemic lupus erythematosus<\/a> (SLE). In these diseases, the immune system may attack and injure many tissues and organs. For example, as you can see in Figure 17.6.6, symptoms of SLE may involve the muscular, skeletal, integumentary, respiratory, and cardiovascular systems.<\/p>\n
Figure 17.6.6 Systemic lupus erythematosus is an autoimmune disease that may cause symptoms of body-wide tissue damage.<\/em><\/figcaption><\/figure>\n Treatment for Autoimmune Diseases<\/h2>\n
None of these common autoimmune diseases can be cured, although all of them have treatments that may help relieve symptoms and prevent some of the long-term damage they may cause. Traditional treatments for autoimmune diseases include immunosuppressive drugs to block the immune response, as well as anti-inflammatory drugs to quell inflammation. Hormone replacement may be another option.\u00a0Type I diabetes, for example, is treated with injections of the hormone insulin, because islet cells in the pancreas can no longer secrete it.<\/p>\n
\nImmunodeficiency<\/h1>\n<\/div>\n
Immunodeficiency<\/a><\/strong>\u00a0occurs when the immune system is not working properly, generally because one or more components of the immune system are inactive. As a result, the immune system may be unable to fight off pathogens or cancers that a normal immune system would be able to resist. Immunodeficiency may occur for a variety of reasons.<\/p>\n
Causes of Immunodeficiency<\/h2>\n
Dozens of rare genetic diseases can result in a defective immune system. This type of immunodeficiency is called\u00a0primary immunodeficiency<\/a><\/strong>. One is born with one of these diseases, rather than acquiring it after birth. Probably the best known of these primary immunodeficiency diseases is severe combined immunodeficiency<\/a> (SCID). It is also known as \u201cbubble boy disease,\u201d because people with this disorder are extremely vulnerable to infectious diseases, and some of them have become well known for living inside a bubble that provides a sterile environment. SCID is most often caused by an X-linked recessive<\/a> mutation<\/a> that interferes with normal B cell and T cell production.<\/p>\n
Other types of immunodeficiency are not present at birth, but are acquired due to experiences or exposures that occur after birth. Acquired immunodeficiency is called\u00a0secondary immunodeficiency<\/a><\/strong>\u00a0because it is secondary to some other event or exposure. Secondary immunodeficiency may occur for a number of different reasons:<\/p>\n
- \n
- Some pathogens attack and destroy immune system cells.<\/strong>\u00a0An example is the virus known as HIV, which attacks and destroys T cells.<\/li>\n
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\n
- The immune system may be damaged by another disorder, such as obesity, alcoholism, or the abuse of other drugs.<\/strong><\/li>\n
- In developing countries, malnutrition is the most common cause of immune system damage and immunodeficiency.<\/strong>\u00a0Inadequate protein intake is especially damaging to the immune system. It can lead to impaired complement system activity, phagocyte malfunction, and lower-than-normal production of antibodies and cytokines.<\/li>\n
- Certain medications can suppress the immune system.<\/strong>\u00a0This is the intended effect of immunosuppressant drugs given to people with transplanted organs so they do not reject them. In many cases, however, immunosuppression is an unwanted side effect of drugs used to treat other disorders.<\/li>\n<\/ul>\n
\nFocus on HIV<\/h1>\n<\/div>\n
Human immunodeficiency virus (
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\n
- House dust mites (5247996458)<\/a> by Gilles San Martin<\/a> from Namur, Belgium on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\r\n \t
- Medical (latex) gloves<\/a> from pngimg.com is used under a CC BY-NC 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/) license.<\/li>\r\n \t
- The immune system naturally becomes less effective as people get older.<\/strong>\u00a0This age-related decline \u2014 called immunosenescence \u2014 generally begins around the age of 50 and worsens with increasing age. Immunosenescence is\u00a0the reason\u00a0older people are generally more susceptible to disease than younger people.<\/li>\r\n \t
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