Case Study Conclusion: Defending Your Defenses<\/h1>\r\n<\/div>\r\nThese people are participating in a bike ride to raise funds for leukemia and lymphoma research (Figure 17.7.1). Leukemia and lymphoma are blood cancers. In 2020,\u00a0 approximately 6,900 Canadians will be diagnosed with leukemia and 3,000 will die from this cancer. Lymphoma is the most common type of blood cancer. As a lymphoma patient, Hakeem, who you learned about in the beginning of this chapter, may eventually benefit from research funded by a bike ride like this one.\r\n\r\nWhat type of blood cell is affected in [pb_glossary id=\"5026\"]lymphoma[\/pb_glossary]? As the name implies, lymphoma is a cancer that affects lymphocytes, which are a type of leukocyte. As you have learned in this chapter, there are different types of lymphocytes, including the B and T cells of the [pb_glossary id=\"4822\"]adaptive immune system[\/pb_glossary]. Different types of lymphoma affect different types of lymphocytes in different ways. It is important to correctly identify the type of lymphoma, so that patients can be treated appropriately.\r\n\r\nYou may recall that one of Hakeem\u2019s symptoms was a swollen [pb_glossary id=\"4831\"]lymph node[\/pb_glossary], and he was diagnosed with lymphoma after a biopsy of that lymph node. Swollen lymph nodes are a common symptom of lymphoma. As you have learned, lymph nodes are distributed throughout the body along lymphatic vessels, as part of the [pb_glossary id=\"2911\"]lymphatic system[\/pb_glossary]. The lymph nodes filter [pb_glossary id=\"4552\"]lymph[\/pb_glossary] and store lymphocytes. Therefore, they play an important role in fighting infections. Because of this, they will often swell in response to an infection. In Hakeem\u2019s case, the swelling and other symptoms did not improve after several weeks and a course of antibiotics, which caused Dr. Hayes to suspect lymphoma instead. The biopsy showed that Hakeem did indeed have cancerous lymphocytes in his lymph nodes.\r\n\r\nBut which type of lymphocytes were affected? Lymphoma most commonly affects B or T lymphocytes. The two major types of lymphoma are called Hodgkin (HL) or non-Hodgkin lymphoma (NHL). NHL is more common than HL. In 2020, the Canadian Cancer Society estimates 10,400 Canadians will be diagnosed with non-Hodgkin lymphoma, whereas 1,000 will be diagnosed with Hodgkin lymphoma. While HL is one distinct type of lymphoma, NHL has about 60 different subtypes, depending on which specific cells are affected and how.\r\n\r\nHakeem was diagnosed with a type of NHL called diffuse large B-cell lymphoma (DLBCL) \u2014 the most common type of NHL. This type of lymphoma affects [pb_glossary id=\"5539\"]B cells<\/span>[\/pb_glossary]<\/span> and causes them to appear large under the microscope. In addition to Hakeem\u2019s symptoms of fatigue, swollen lymph nodes, loss of appetite, and weight loss, common symptoms of this type of lymphoma include fever and night sweats. It is an aggressive and fast-growing type of lymphoma that is fatal if not treated. The good news is that with early detection and proper treatment, about 70% of patients with DLBCL can be cured.<\/span>\r\n\r\n[caption id=\"attachment_5028\" align=\"alignright\" width=\"299\"]![\"17.7.2](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/antigen-stain-2.jpg\")
Figure 17.7.2 A lab technician can apply stains that target specific antigens to help identify which type of lymphoma is present.[\/caption]\r\n\r\nHow do physicians determine the specific type of lymphoma? Tissue obtained from a biopsy can be examined under a microscope to observe physical changes (such as abnormal cell size or shape) that are characteristic of a particular subtype of lymphoma. Additionally, tests can be performed on the tissue to determine which cell-surface antigens are present. Recall that antigens are molecules that bind to specific antibodies. [pb_glossary id=\"5659\"]Antibodies[\/pb_glossary] can be produced in the laboratory and labeled with compounds that can be identified by their colour under a microscope. When these antibodies are applied to a tissue sample, this colour will appear wherever the antigen is present, because it binds to the antibody. This technique was used in the photomicrograph in Figure 17.7.2 to identify the presence of a cell-surface antigen (shown as reddish-brown) in a sample of skin cells. This technique, called immunohistochemistry, is also commonly used to identify antigens in tissue samples from lymphoma patients.\r\n\r\nWhy would identifying cell-surface antigens be important in diagnosing and treating lymphoma? As you have learned, the immune system uses antigens present on the surface of cells or pathogens to distinguish between self and non-self, and to launch adaptive immune responses. Cells that become cancerous often change their cell-surface antigens. This is one way that the immune system can identify and destroy them. Also, different cell types in the body can sometimes be identified by the presence of specific cell-surface antigens. Knowing the types of cell-surface antigens present in a tissue sample can help physicians identify which cells are cancerous, and possibly the specific subtype of cancer. Knowing this information can be helpful in choosing more tailored and effective treatments.\r\n\r\nOne treatment for NHL is, in fact, the use of medications made from antibodies that bind to cell-surface antigens present on cells affected by the specific subtype of NHL. This is called [pb_glossary id=\"5004\"]immunotherapy[\/pb_glossary]. These drugs can directly bind to and kill the cancerous cells. For patients with DLBCL like Hakeem, immunotherapy is often used in conjunction with [pb_glossary id=\"5029\"]chemotherapy[\/pb_glossary] and radiation as a course of treatment. Although Hakeem has a difficult road ahead, he and his medical team are optimistic that \u2014 given the high success rate when DLBCL is caught and treated early \u2014 he may be cured. More research into how the immune system functions may lead to even better treatments for lymphoma \u2014 and other types of cancers \u2014 in the future.\r\n\r\n\r\nChapter 17 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nIn this chapter, you learned about the immune system. Specifically, you learned that:\r\n\r\n \t- Any agent that can cause disease is called a [pb_glossary id=\"5799\"]pathogen[\/pb_glossary]. Most human pathogens are [pb_glossary id=\"5775\"]microorganisms[\/pb_glossary], such as [pb_glossary id=\"2588\"]bacteria[\/pb_glossary] and [pb_glossary id=\"4283\"]viruses[\/pb_glossary]. The immune system is the\u00a0body\u00a0system that defends the human host from pathogens and [pb_glossary id=\"5605\"]cancerous[\/pb_glossary]\u00a0cells.<\/li>\r\n \t
- The [pb_glossary id=\"4820\"]innate immune system[\/pb_glossary] is a subset of the immune system that provides very quick, but non-specific responses to pathogens. It includes multiple types of barriers to pathogens, leukocytes that phagocytize pathogens, and several other general responses.<\/li>\r\n \t
- The [pb_glossary id=\"4822\"]adaptive immune system[\/pb_glossary] is a subset of the immune system that provides specific responses tailored to particular pathogens. It takes longer to put into effect, but it may lead to [pb_glossary id=\"4884\"]immunity[\/pb_glossary] to the pathogens.<\/li>\r\n \t
- Both innate and adaptive immune responses depend on the ability of the immune system to distinguish between self and non-self molecules. Most body cells have [pb_glossary id=\"4825\"]major histocompatibility complex (MHC)[\/pb_glossary] proteins that identify them as self. Pathogens, infected cells, and tumor cells have non-self proteins called antigens that the immune system recognizes as foreign.<\/li>\r\n \t
- [pb_glossary id=\"2704\"]Antigens[\/pb_glossary]\u00a0are proteins that bind to specific receptors on immune system cells and elicit an adaptive immune response. Some immune cells ([pb_glossary id=\"5539\"]B cells[\/pb_glossary]) respond to foreign antigens by producing antibodies that bind with antigens and target pathogens for destruction.<\/li>\r\n \t
- An important role of the immune system is tumor surveillance. [pb_glossary id=\"4893\"]Killer T cells[\/pb_glossary]\u00a0of the adaptive immune system find and destroy tumor cells, which they can identify from their abnormal antigens.<\/li>\r\n \t
- The [pb_glossary id=\"4833\"]neuroimmune system[\/pb_glossary] that protects the [pb_glossary id=\"5933\"]central nervous system[\/pb_glossary] is thought to be distinct from the [pb_glossary id=\"4834\"]peripheral immune system[\/pb_glossary] that protects the rest of the human body. The blood-brain and blood-spinal cord barriers are one type of protection of the neuroimmune system. Neuroglia also play a role in this system, for example, by carrying out [pb_glossary id=\"1680\"]phagocytosis[\/pb_glossary].<\/li>\r\n \t
- The [pb_glossary id=\"2911\"]lymphatic system[\/pb_glossary] is a human organ system that is a vital part of the adaptive immune system. It consists of several organs and a system of vessels that transport or filter the fluid called [pb_glossary id=\"4552\"]lymph[\/pb_glossary]. The main immune function of the lymphatic system is to produce, mature, harbor, and circulate white blood cells called lymphocytes, which are the main cells in the adaptive immune system, and are circulated in lymph.<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- The return of lymph to the bloodstream is one of the functions of the lymphatic system. Lymph flows from tissue spaces, where it leaks out of blood vessels, to major veins in the upper chest. It is then returned to the [pb_glossary id=\"5927\"]cardiovascular system[\/pb_glossary]. Lymph is similar in composition to blood [pb_glossary id=\"4395\"]plasma[\/pb_glossary]. Its main cellular components are lymphocytes.<\/li>\r\n \t
- Lymphatic vessels called [pb_glossary id=\"4607\"]lacteals[\/pb_glossary]\u00a0are found in [pb_glossary id=\"4543\"]villi[\/pb_glossary] that line the [pb_glossary id=\"4559\"]small intestine[\/pb_glossary]. Lacteals absorb fatty acids from the digestion of lipids in the [pb_glossary id=\"5969\"]digestive system[\/pb_glossary]. The fatty acids are then transported through the network of lymphatic vessels to the bloodstream.<\/li>\r\n \t
- Lymphocytes, which include [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0and [pb_glossary id=\"4892\"]T cells[\/pb_glossary], are the subset of leukocytes involved in [pb_glossary id=\"4822\"]adaptive immune responses[\/pb_glossary]. They may create a lasting memory of and [pb_glossary id=\"4884\"]immunity[\/pb_glossary] to specific pathogens.<\/li>\r\n \t
- All lymphocytes are produced in [pb_glossary id=\"4021\"]bone marrow[\/pb_glossary] and then go through a process of maturation, in which they \u201clearn\u201d to distinguish self from non-self. B cells mature in the bone marrow, and T cells mature in the [pb_glossary id=\"4829\"]thymus[\/pb_glossary]. Both the bone marrow and thymus are considered [pb_glossary id=\"4845\"]primary lymphatic organs[\/pb_glossary].<\/li>\r\n \t
- [pb_glossary id=\"4847\"]Secondary lymphatic organs[\/pb_glossary] include the tonsils, spleen, and lymph nodes. There are four pairs of [pb_glossary id=\"4830\"]tonsils[\/pb_glossary]\u00a0that encircle the throat. The [pb_glossary id=\"4497\"]spleen[\/pb_glossary] filters blood, as well as lymph. There are hundreds of [pb_glossary id=\"4831\"]lymph nodes[\/pb_glossary]\u00a0located in clusters along the lymphatic vessels. All of these secondary organs filter lymph and store lymphocytes, so they are sites where pathogens encounter and activate lymphocytes and initiate adaptive immune responses.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- Unlike the adaptive immune system, the [pb_glossary id=\"4820\"]innate immune system[\/pb_glossary] does not confer immunity. The innate immune system includes surface barriers, inflammation, the complement system, and a variety of cellular responses.<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- The body\u2019s first line of defense consists of three different types of barriers that keep most pathogens out of body tissues. The types of barriers are mechanical, chemical, and biological barriers.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- \r\n
\r\n \t- [pb_glossary id=\"4857\"]Mechanical barriers[\/pb_glossary]\u00a0\u2014\u00a0which include the [pb_glossary id=\"3521\"]skin[\/pb_glossary], [pb_glossary id=\"3538\"]mucous membranes[\/pb_glossary], and fluids (such as tears and [pb_glossary id=\"4717\"]urine[\/pb_glossary]) \u2014 physically block pathogens from entering the body.<\/li>\r\n \t
- Chemical barriers\u00a0\u2014\u00a0such as enzymes in [pb_glossary id=\"4711\"]sweat[\/pb_glossary], [pb_glossary id=\"4595\"]saliva[\/pb_glossary], and [pb_glossary id=\"4885\"]semen[\/pb_glossary]\u00a0\u2014\u00a0kill pathogens on body surfaces.<\/li>\r\n \t
- Biological barriers are harmless bacteria that use up food and space so pathogenic bacteria cannot colonize the body.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- If pathogens breach the protective barriers, [pb_glossary id=\"4860\"]inflammation[\/pb_glossary] occurs. This creates a physical barrier against the spread of infection and repairs tissue damage. Inflammation is triggered by chemicals (such as [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]), and it causes swelling, redness, and warmth.<\/li>\r\n \t
- The [pb_glossary id=\"4868\"]complement system[\/pb_glossary] is a complex biochemical mechanism that helps [pb_glossary id=\"5659\"]antibodies[\/pb_glossary] kill pathogens. Once activated, the complement system consists of more than two dozen proteins that lead to disruption of the [pb_glossary id=\"5621\"]cell membrane[\/pb_glossary] of pathogens and bursting of the cells.<\/li>\r\n \t
- Cellular responses of the innate immune system involve various types of leukocytes (white blood cells). For example, [pb_glossary id=\"5545\"]neutrophils[\/pb_glossary], [pb_glossary id=\"4340\"]macrophages[\/pb_glossary], and [pb_glossary id=\"4875\"]dendritic cells[\/pb_glossary]\u00a0phagocytize pathogens. [pb_glossary id=\"5573\"]Basophils[\/pb_glossary]\u00a0and [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]\u00a0release chemicals that trigger inflammation. [pb_glossary id=\"5515\"]Natural killer cells[\/pb_glossary]\u00a0destroy cancerous or virus-infected cells, and [pb_glossary id=\"5529\"]eosinophils[\/pb_glossary]\u00a0kill parasites.<\/li>\r\n \t
- Many pathogens have evolved mechanisms that help them evade the innate immune system. For example, some pathogens form a protective capsule around themselves, and some mimic host cells so the immune system does not recognize them as foreign.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- The main cells of the adaptive immune system are [pb_glossary id=\"4832\"]lymphocytes[\/pb_glossary]. There are two major types of lymphocytes: T cells and B cells. Both types must be activated by foreign antigens to become functioning immune cells.<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- Most activated T cells become either [pb_glossary id=\"4893\"]killer T cells[\/pb_glossary]\u00a0or [pb_glossary id=\"5537\"]helper T cells[\/pb_glossary]. Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage immune responses by releasing cytokines that control other types of leukocytes.<\/li>\r\n \t
- Activated B cells form [pb_glossary id=\"4902\"]plasma cell[\/pb_glossary]s that secrete antibodies, which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the complement system.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- After an adaptive immune response occurs, long-lasting [pb_glossary id=\"4904\"]memory B cells and memory T cells[\/pb_glossary] may remain to confer [pb_glossary id=\"4884\"]immunity[\/pb_glossary] to the specific pathogen that caused the adaptive immune response. These memory cells are ready to activate an immediate response if they are exposed to the same antigen again in the future.<\/li>\r\n \t
- Immunity may be active or passive.<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- \u00a0[pb_glossary id=\"4906\"]Active immunity[\/pb_glossary] occurs when the immune system has been presented with antigens that elicit an adaptive immune response. This may occur naturally as the result of an infection, or artificially as the result of immunization. Active immunity may last for years or even for life.<\/li>\r\n \t
- [pb_glossary id=\"4910\"]Passive immunity[\/pb_glossary] occurs without an adaptive immune response by the transfer of antibodies or activated T cells. This may occur naturally between a mother and her fetus or her nursing infant, or it may occur artificially by injection. Passive immunity lasts only as long as the antibodies or activated T cells remain alive in the body, generally just weeks or months.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- Many pathogens have evolved mechanisms to evade the adaptive immune system. For example, human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]) evades the adaptive immune system by frequently changing its antigens and by forming its outer envelope from the host\u2019s cell membrane.<\/li>\r\n \t
- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an inflammatory response to a harmless antigen. Any antigen 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<\/ul>\r\n
\r\n \t- \r\n
\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 B cells are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to mast cells. On subsequent exposures to the allergen, the mast cells immediately release cytokines and histamines that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with antihistamines that 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<\/ul>\r\n<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary]\u00a0occur 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<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- In some autoimmune diseases, such as type I diabetes, the immune system attacks and damages specific body cells. In other autoimmune diseases, such as systemic lupus erythematosus, 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<\/ul>\r\n<\/li>\r\n \t
- Immunodeficiency 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<\/ul>\r\n
\r\n \t- \r\n
\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 substance abuse, obesity, and malnutrition, among others.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus (HIV), 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, but\u00a0it can't\u00a0eliminate the virus completely.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\nUp to this point, this book has covered body systems that carry out processes within individuals, such as the digestive, muscular, and immune systems. Read the next chapter to learn about the body system that allows humans to produce new individuals \u2014 the reproductive system.\r\n\r\n<\/div>\r\n<\/div>\r\n
\r\nChapter 17 Review<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"642\"]<\/li>\r\n \t
- Compare and contrast a pathogen and an allergen.<\/li>\r\n \t
- Describe three ways in which pathogens can enter the body.<\/li>\r\n \t
- The complement system involves the activation of several proteins to kill pathogens. Why do you think this is considered part of the innate immune system, instead of the adaptive immune system?<\/li>\r\n \t
- Why are innate immune responses generally faster than adaptive immune responses?<\/li>\r\n \t
- Explain how an autoimmune disease could be triggered by a pathogen.<\/li>\r\n \t
- What is an opportunistic infection?\u00a0Name two diseases or conditions that could result in opportunistic infections. Explain your answer.<\/li>\r\n \t
- Which cell type in the immune system can be considered an \u201cantibody factory?\"<\/li>\r\n \t
- Besides foreign pathogens, what is one thing that the immune system protects the body against?<\/li>\r\n \t
- What cell type in the immune system is infected and killed by HIV?<\/li>\r\n \t
- Name two types of cells that produce cytokines in the immune system.\u00a0What are two functions of cytokines in the immune system?<\/li>\r\n \t
- Many pathogens evade the immune system by altering their outer surface in some way. Based on what you know about the functioning of the immune system, why is this often a successful approach?<\/li>\r\n \t
- What is \u201cmissing self?\" How does this condition arise?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.7 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/Z3B-AaqjyjE\r\nWhat is leukemia? - Danilo Allegra and Dania Puggioni, TED-Ed, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 17.7.1<\/strong>\r\n\r\nCycling to Beat Blood Cancer<\/a> by Blood Cancer UK<\/a> (Formerly Bloodwise) on Flickr<\/a> is used under a CC BY-NC-ND 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-nd\/2.0\/) license.\r\n\r\nFigure 17.7.2<\/strong>\r\n\r\nantigen stain<\/a> by Ed Uthman<\/a> from Houston, TX, USA on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\nReferences<\/h2>\r\n
Hodgkin lymphoma statistics [online article]. (2020). Canadian Cancer Society. https:\/\/www.cancer.ca:443\/en\/cancer-information\/cancer-type\/hodgkin-lymphoma\/statistics\/?region=on<\/p>\r\n
Non-Hodgkin lymphoma statistics [online article]. (2020). Canadian Cancer Society. https:\/\/www.cancer.ca:443\/en\/cancer-information\/cancer-type\/non-hodgkin-lymphoma\/statistics\/?region=on<\/p>\r\n
TED-Ed. (2015, April 30). What is leukemia? - Danilo Allegra and Dania Puggioni. YouTube. https:\/\/www.youtube.com\/watch?v=Z3B-AaqjyjE&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\n![\"17.7.1](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Cycling-to-Beat-Blood-Cancer-2.jpg\")
Figure 17.7.1 Be Unstoppable for Leukemia and Lymphoma Research.<\/em><\/figcaption><\/figure>\n\nCase Study Conclusion: Defending Your Defenses<\/h1>\n<\/div>\n
These people are participating in a bike ride to raise funds for leukemia and lymphoma research (Figure 17.7.1). Leukemia and lymphoma are blood cancers. In 2020,\u00a0 approximately 6,900 Canadians will be diagnosed with leukemia and 3,000 will die from this cancer. Lymphoma is the most common type of blood cancer. As a lymphoma patient, Hakeem, who you learned about in the beginning of this chapter, may eventually benefit from research funded by a bike ride like this one.<\/p>\n
What type of blood cell is affected in lymphoma<\/a>? As the name implies, lymphoma is a cancer that affects lymphocytes, which are a type of leukocyte. As you have learned in this chapter, there are different types of lymphocytes, including the B and T cells of the adaptive immune system<\/a>. Different types of lymphoma affect different types of lymphocytes in different ways. It is important to correctly identify the type of lymphoma, so that patients can be treated appropriately.<\/p>\nYou may recall that one of Hakeem\u2019s symptoms was a swollen lymph node<\/a>, and he was diagnosed with lymphoma after a biopsy of that lymph node. Swollen lymph nodes are a common symptom of lymphoma. As you have learned, lymph nodes are distributed throughout the body along lymphatic vessels, as part of the lymphatic system<\/a>. The lymph nodes filter lymph<\/a> and store lymphocytes. Therefore, they play an important role in fighting infections. Because of this, they will often swell in response to an infection. In Hakeem\u2019s case, the swelling and other symptoms did not improve after several weeks and a course of antibiotics, which caused Dr. Hayes to suspect lymphoma instead. The biopsy showed that Hakeem did indeed have cancerous lymphocytes in his lymph nodes.<\/p>\nBut which type of lymphocytes were affected? Lymphoma most commonly affects B or T lymphocytes. The two major types of lymphoma are called Hodgkin (HL) or non-Hodgkin lymphoma (NHL). NHL is more common than HL. In 2020, the Canadian Cancer Society estimates 10,400 Canadians will be diagnosed with non-Hodgkin lymphoma, whereas 1,000 will be diagnosed with Hodgkin lymphoma. While HL is one distinct type of lymphoma, NHL has about 60 different subtypes, depending on which specific cells are affected and how.<\/p>\n
Hakeem was diagnosed with a type of NHL called diffuse large B-cell lymphoma (DLBCL) \u2014 the most common type of NHL. This type of lymphoma affects B cells<\/span><\/a><\/span> and causes them to appear large under the microscope. In addition to Hakeem\u2019s symptoms of fatigue, swollen lymph nodes, loss of appetite, and weight loss, common symptoms of this type of lymphoma include fever and night sweats. It is an aggressive and fast-growing type of lymphoma that is fatal if not treated. The good news is that with early detection and proper treatment, about 70% of patients with DLBCL can be cured.<\/span><\/p>\nFigure 17.7.2 A lab technician can apply stains that target specific antigens to help identify which type of lymphoma is present.<\/figcaption><\/figure>\nHow do physicians determine the specific type of lymphoma? Tissue obtained from a biopsy can be examined under a microscope to observe physical changes (such as abnormal cell size or shape) that are characteristic of a particular subtype of lymphoma. Additionally, tests can be performed on the tissue to determine which cell-surface antigens are present. Recall that antigens are molecules that bind to specific antibodies. Antibodies<\/a> can be produced in the laboratory and labeled with compounds that can be identified by their colour under a microscope. When these antibodies are applied to a tissue sample, this colour will appear wherever the antigen is present, because it binds to the antibody. This technique was used in the photomicrograph in Figure 17.7.2 to identify the presence of a cell-surface antigen (shown as reddish-brown) in a sample of skin cells. This technique, called immunohistochemistry, is also commonly used to identify antigens in tissue samples from lymphoma patients.<\/p>\nWhy would identifying cell-surface antigens be important in diagnosing and treating lymphoma? As you have learned, the immune system uses antigens present on the surface of cells or pathogens to distinguish between self and non-self, and to launch adaptive immune responses. Cells that become cancerous often change their cell-surface antigens. This is one way that the immune system can identify and destroy them. Also, different cell types in the body can sometimes be identified by the presence of specific cell-surface antigens. Knowing the types of cell-surface antigens present in a tissue sample can help physicians identify which cells are cancerous, and possibly the specific subtype of cancer. Knowing this information can be helpful in choosing more tailored and effective treatments.<\/p>\n
One treatment for NHL is, in fact, the use of medications made from antibodies that bind to cell-surface antigens present on cells affected by the specific subtype of NHL. This is called immunotherapy<\/a>. These drugs can directly bind to and kill the cancerous cells. For patients with DLBCL like Hakeem, immunotherapy is often used in conjunction with chemotherapy<\/a> and radiation as a course of treatment. Although Hakeem has a difficult road ahead, he and his medical team are optimistic that \u2014 given the high success rate when DLBCL is caught and treated early \u2014 he may be cured. More research into how the immune system functions may lead to even better treatments for lymphoma \u2014 and other types of cancers \u2014 in the future.<\/p>\n\n\n\nChapter 17 Summary<\/span><\/h1>\n<\/header>\n\nIn this chapter, you learned about the immune system. Specifically, you learned that:<\/p>\n
\n- Any agent that can cause disease is called a pathogen<\/a>. Most human pathogens are microorganisms<\/a>, such as bacteria<\/a> and viruses<\/a>. The immune system is the\u00a0body\u00a0system that defends the human host from pathogens and cancerous<\/a>\u00a0cells.<\/li>\n
- The innate immune system<\/a> is a subset of the immune system that provides very quick, but non-specific responses to pathogens. It includes multiple types of barriers to pathogens, leukocytes that phagocytize pathogens, and several other general responses.<\/li>\n
- The adaptive immune system<\/a> is a subset of the immune system that provides specific responses tailored to particular pathogens. It takes longer to put into effect, but it may lead to immunity<\/a> to the pathogens.<\/li>\n
- Both innate and adaptive immune responses depend on the ability of the immune system to distinguish between self and non-self molecules. Most body cells have major histocompatibility complex (MHC)<\/a> proteins that identify them as self. Pathogens, infected cells, and tumor cells have non-self proteins called antigens that the immune system recognizes as foreign.<\/li>\n
- Antigens<\/a>\u00a0are proteins that bind to specific receptors on immune system cells and elicit an adaptive immune response. Some immune cells (B cells<\/a>) respond to foreign antigens by producing antibodies that bind with antigens and target pathogens for destruction.<\/li>\n
- An important role of the immune system is tumor surveillance. Killer T cells<\/a>\u00a0of the adaptive immune system find and destroy tumor cells, which they can identify from their abnormal antigens.<\/li>\n
- The neuroimmune system<\/a> that protects the central nervous system<\/a> is thought to be distinct from the peripheral immune system<\/a> that protects the rest of the human body. The blood-brain and blood-spinal cord barriers are one type of protection of the neuroimmune system. Neuroglia also play a role in this system, for example, by carrying out phagocytosis<\/a>.<\/li>\n
- The lymphatic system<\/a> is a human organ system that is a vital part of the adaptive immune system. It consists of several organs and a system of vessels that transport or filter the fluid called lymph<\/a>. The main immune function of the lymphatic system is to produce, mature, harbor, and circulate white blood cells called lymphocytes, which are the main cells in the adaptive immune system, and are circulated in lymph.<\/li>\n<\/ul>\n
\n- \n
\n- The return of lymph to the bloodstream is one of the functions of the lymphatic system. Lymph flows from tissue spaces, where it leaks out of blood vessels, to major veins in the upper chest. It is then returned to the cardiovascular system<\/a>. Lymph is similar in composition to blood plasma<\/a>. Its main cellular components are lymphocytes.<\/li>\n
- Lymphatic vessels called lacteals<\/a>\u00a0are found in villi<\/a> that line the small intestine<\/a>. Lacteals absorb fatty acids from the digestion of lipids in the digestive system<\/a>. The fatty acids are then transported through the network of lymphatic vessels to the bloodstream.<\/li>\n
- Lymphocytes, which include B cells<\/a>\u00a0and T cells<\/a>, are the subset of leukocytes involved in adaptive immune responses<\/a>. They may create a lasting memory of and immunity<\/a> to specific pathogens.<\/li>\n
- All lymphocytes are produced in bone marrow<\/a> and then go through a process of maturation, in which they \u201clearn\u201d to distinguish self from non-self. B cells mature in the bone marrow, and T cells mature in the thymus<\/a>. Both the bone marrow and thymus are considered primary lymphatic organs<\/a>.<\/li>\n
- Secondary lymphatic organs<\/a> include the tonsils, spleen, and lymph nodes. There are four pairs of tonsils<\/a>\u00a0that encircle the throat. The spleen<\/a> filters blood, as well as lymph. There are hundreds of lymph nodes<\/a>\u00a0located in clusters along the lymphatic vessels. All of these secondary organs filter lymph and store lymphocytes, so they are sites where pathogens encounter and activate lymphocytes and initiate adaptive immune responses.<\/li>\n<\/ul>\n<\/li>\n
- Unlike the adaptive immune system, the innate immune system<\/a> does not confer immunity. The innate immune system includes surface barriers, inflammation, the complement system, and a variety of cellular responses.<\/li>\n<\/ul>\n
\n- \n
\n- The body\u2019s first line of defense consists of three different types of barriers that keep most pathogens out of body tissues. The types of barriers are mechanical, chemical, and biological barriers.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
\n- \n
\n- \n
\n- Mechanical barriers<\/a>\u00a0\u2014\u00a0which include the skin<\/a>, mucous membranes<\/a>, and fluids (such as tears and urine<\/a>) \u2014 physically block pathogens from entering the body.<\/li>\n
- Chemical barriers\u00a0\u2014\u00a0such as enzymes in sweat<\/a>, saliva<\/a>, and semen<\/a>\u00a0\u2014\u00a0kill pathogens on body surfaces.<\/li>\n
- Biological barriers are harmless bacteria that use up food and space so pathogenic bacteria cannot colonize the body.<\/li>\n<\/ul>\n<\/li>\n
- If pathogens breach the protective barriers, inflammation<\/a> occurs. This creates a physical barrier against the spread of infection and repairs tissue damage. Inflammation is triggered by chemicals (such as cytokines<\/a>\u00a0and histamines<\/a>), and it causes swelling, redness, and warmth.<\/li>\n
- The complement system<\/a> is a complex biochemical mechanism that helps antibodies<\/a> kill pathogens. Once activated, the complement system consists of more than two dozen proteins that lead to disruption of the cell membrane<\/a> of pathogens and bursting of the cells.<\/li>\n
- Cellular responses of the innate immune system involve various types of leukocytes (white blood cells). For example, neutrophils<\/a>, macrophages<\/a>, and dendritic cells<\/a>\u00a0phagocytize pathogens. Basophils<\/a>\u00a0and mast cells<\/a>\u00a0release chemicals that trigger inflammation. Natural killer cells<\/a>\u00a0destroy cancerous or virus-infected cells, and eosinophils<\/a>\u00a0kill parasites.<\/li>\n
- Many pathogens have evolved mechanisms that help them evade the innate immune system. For example, some pathogens form a protective capsule around themselves, and some mimic host cells so the immune system does not recognize them as foreign.<\/li>\n<\/ul>\n<\/li>\n
- The main cells of the adaptive immune system are lymphocytes<\/a>. There are two major types of lymphocytes: T cells and B cells. Both types must be activated by foreign antigens to become functioning immune cells.<\/li>\n<\/ul>\n
\n- \n
\n- Most activated T cells become either killer T cells<\/a>\u00a0or helper T cells<\/a>. Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage immune responses by releasing cytokines that control other types of leukocytes.<\/li>\n
- Activated B cells form plasma cell<\/a>s that secrete antibodies, which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the complement system.<\/li>\n<\/ul>\n<\/li>\n
- After an adaptive immune response occurs, long-lasting memory B cells and memory T cells<\/a> may remain to confer immunity<\/a> to the specific pathogen that caused the adaptive immune response. These memory cells are ready to activate an immediate response if they are exposed to the same antigen again in the future.<\/li>\n
- Immunity may be active or passive.<\/li>\n<\/ul>\n
\n- \n
\n- \u00a0Active immunity<\/a> occurs when the immune system has been presented with antigens that elicit an adaptive immune response. This may occur naturally as the result of an infection, or artificially as the result of immunization. Active immunity may last for years or even for life.<\/li>\n
- Passive immunity<\/a> occurs without an adaptive immune response by the transfer of antibodies or activated T cells. This may occur naturally between a mother and her fetus or her nursing infant, or it may occur artificially by injection. Passive immunity lasts only as long as the antibodies or activated T cells remain alive in the body, generally just weeks or months.<\/li>\n<\/ul>\n<\/li>\n
- Many pathogens have evolved mechanisms to evade the adaptive immune system. For example, human immunodeficiency virus (HIV<\/a>) evades the adaptive immune system by frequently changing its antigens and by forming its outer envelope from the host\u2019s cell membrane.<\/li>\n
- An allergy<\/a> is a disorder in which the immune system makes an inflammatory response to a harmless antigen. Any antigen that causes allergies is called an allergen<\/a>. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\n<\/ul>\n
\n- \n
\n- 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>\n
- Allergies occur when B cells are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to mast cells. On subsequent exposures to the allergen, the mast cells immediately release cytokines and histamines that cause inflammation.<\/li>\n
- Mild allergy symptoms are frequently treated with antihistamines that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called anaphylaxis<\/a>, is a medical emergency that is usually treated with injections of epinephrine. Immunotherapy<\/a> for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\n<\/ul>\n<\/li>\n
- Autoimmune diseases<\/a>\u00a0occur 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>\n<\/ul>\n
\n- \n
\n- In some autoimmune diseases, such as type I diabetes, the immune system attacks and damages specific body cells. In other autoimmune diseases, such as systemic lupus erythematosus, 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>\n<\/ul>\n<\/li>\n
- Immunodeficiency 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>\n<\/ul>\n
\n- \n
\n- Primary immunodeficiency<\/a> is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. Secondary immunodeficiency<\/a> occurs because of some event or exposure experienced after birth. Possible causes include substance abuse, obesity, and malnutrition, among others.<\/li>\n
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus (HIV), 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 acquired immunodeficiency syndrome<\/a> (AIDS). Medications can control the multiplication of HIV in the human body, but\u00a0it can’t\u00a0eliminate the virus completely.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
Up to this point, this book has covered body systems that carry out processes within individuals, such as the digestive, muscular, and immune systems. Read the next chapter to learn about the body system that allows humans to produce new individuals \u2014 the reproductive system.<\/p>\n<\/div>\n<\/div>\n
\n\nChapter 17 Review<\/span><\/h1>\n<\/header>\n\n\n- \n\n
Chapter 17 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nIn this chapter, you learned about the immune system. Specifically, you learned that:\r\n\r\n \t- Any agent that can cause disease is called a [pb_glossary id=\"5799\"]pathogen[\/pb_glossary]. Most human pathogens are [pb_glossary id=\"5775\"]microorganisms[\/pb_glossary], such as [pb_glossary id=\"2588\"]bacteria[\/pb_glossary] and [pb_glossary id=\"4283\"]viruses[\/pb_glossary]. The immune system is the\u00a0body\u00a0system that defends the human host from pathogens and [pb_glossary id=\"5605\"]cancerous[\/pb_glossary]\u00a0cells.<\/li>\r\n \t
- The [pb_glossary id=\"4820\"]innate immune system[\/pb_glossary] is a subset of the immune system that provides very quick, but non-specific responses to pathogens. It includes multiple types of barriers to pathogens, leukocytes that phagocytize pathogens, and several other general responses.<\/li>\r\n \t
- The [pb_glossary id=\"4822\"]adaptive immune system[\/pb_glossary] is a subset of the immune system that provides specific responses tailored to particular pathogens. It takes longer to put into effect, but it may lead to [pb_glossary id=\"4884\"]immunity[\/pb_glossary] to the pathogens.<\/li>\r\n \t
- Both innate and adaptive immune responses depend on the ability of the immune system to distinguish between self and non-self molecules. Most body cells have [pb_glossary id=\"4825\"]major histocompatibility complex (MHC)[\/pb_glossary] proteins that identify them as self. Pathogens, infected cells, and tumor cells have non-self proteins called antigens that the immune system recognizes as foreign.<\/li>\r\n \t
- [pb_glossary id=\"2704\"]Antigens[\/pb_glossary]\u00a0are proteins that bind to specific receptors on immune system cells and elicit an adaptive immune response. Some immune cells ([pb_glossary id=\"5539\"]B cells[\/pb_glossary]) respond to foreign antigens by producing antibodies that bind with antigens and target pathogens for destruction.<\/li>\r\n \t
- An important role of the immune system is tumor surveillance. [pb_glossary id=\"4893\"]Killer T cells[\/pb_glossary]\u00a0of the adaptive immune system find and destroy tumor cells, which they can identify from their abnormal antigens.<\/li>\r\n \t
- The [pb_glossary id=\"4833\"]neuroimmune system[\/pb_glossary] that protects the [pb_glossary id=\"5933\"]central nervous system[\/pb_glossary] is thought to be distinct from the [pb_glossary id=\"4834\"]peripheral immune system[\/pb_glossary] that protects the rest of the human body. The blood-brain and blood-spinal cord barriers are one type of protection of the neuroimmune system. Neuroglia also play a role in this system, for example, by carrying out [pb_glossary id=\"1680\"]phagocytosis[\/pb_glossary].<\/li>\r\n \t
- The [pb_glossary id=\"2911\"]lymphatic system[\/pb_glossary] is a human organ system that is a vital part of the adaptive immune system. It consists of several organs and a system of vessels that transport or filter the fluid called [pb_glossary id=\"4552\"]lymph[\/pb_glossary]. The main immune function of the lymphatic system is to produce, mature, harbor, and circulate white blood cells called lymphocytes, which are the main cells in the adaptive immune system, and are circulated in lymph.<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- The return of lymph to the bloodstream is one of the functions of the lymphatic system. Lymph flows from tissue spaces, where it leaks out of blood vessels, to major veins in the upper chest. It is then returned to the [pb_glossary id=\"5927\"]cardiovascular system[\/pb_glossary]. Lymph is similar in composition to blood [pb_glossary id=\"4395\"]plasma[\/pb_glossary]. Its main cellular components are lymphocytes.<\/li>\r\n \t
- Lymphatic vessels called [pb_glossary id=\"4607\"]lacteals[\/pb_glossary]\u00a0are found in [pb_glossary id=\"4543\"]villi[\/pb_glossary] that line the [pb_glossary id=\"4559\"]small intestine[\/pb_glossary]. Lacteals absorb fatty acids from the digestion of lipids in the [pb_glossary id=\"5969\"]digestive system[\/pb_glossary]. The fatty acids are then transported through the network of lymphatic vessels to the bloodstream.<\/li>\r\n \t
- Lymphocytes, which include [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0and [pb_glossary id=\"4892\"]T cells[\/pb_glossary], are the subset of leukocytes involved in [pb_glossary id=\"4822\"]adaptive immune responses[\/pb_glossary]. They may create a lasting memory of and [pb_glossary id=\"4884\"]immunity[\/pb_glossary] to specific pathogens.<\/li>\r\n \t
- All lymphocytes are produced in [pb_glossary id=\"4021\"]bone marrow[\/pb_glossary] and then go through a process of maturation, in which they \u201clearn\u201d to distinguish self from non-self. B cells mature in the bone marrow, and T cells mature in the [pb_glossary id=\"4829\"]thymus[\/pb_glossary]. Both the bone marrow and thymus are considered [pb_glossary id=\"4845\"]primary lymphatic organs[\/pb_glossary].<\/li>\r\n \t
- [pb_glossary id=\"4847\"]Secondary lymphatic organs[\/pb_glossary] include the tonsils, spleen, and lymph nodes. There are four pairs of [pb_glossary id=\"4830\"]tonsils[\/pb_glossary]\u00a0that encircle the throat. The [pb_glossary id=\"4497\"]spleen[\/pb_glossary] filters blood, as well as lymph. There are hundreds of [pb_glossary id=\"4831\"]lymph nodes[\/pb_glossary]\u00a0located in clusters along the lymphatic vessels. All of these secondary organs filter lymph and store lymphocytes, so they are sites where pathogens encounter and activate lymphocytes and initiate adaptive immune responses.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- Unlike the adaptive immune system, the [pb_glossary id=\"4820\"]innate immune system[\/pb_glossary] does not confer immunity. The innate immune system includes surface barriers, inflammation, the complement system, and a variety of cellular responses.<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- The body\u2019s first line of defense consists of three different types of barriers that keep most pathogens out of body tissues. The types of barriers are mechanical, chemical, and biological barriers.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- \r\n
\r\n \t- [pb_glossary id=\"4857\"]Mechanical barriers[\/pb_glossary]\u00a0\u2014\u00a0which include the [pb_glossary id=\"3521\"]skin[\/pb_glossary], [pb_glossary id=\"3538\"]mucous membranes[\/pb_glossary], and fluids (such as tears and [pb_glossary id=\"4717\"]urine[\/pb_glossary]) \u2014 physically block pathogens from entering the body.<\/li>\r\n \t
- Chemical barriers\u00a0\u2014\u00a0such as enzymes in [pb_glossary id=\"4711\"]sweat[\/pb_glossary], [pb_glossary id=\"4595\"]saliva[\/pb_glossary], and [pb_glossary id=\"4885\"]semen[\/pb_glossary]\u00a0\u2014\u00a0kill pathogens on body surfaces.<\/li>\r\n \t
- Biological barriers are harmless bacteria that use up food and space so pathogenic bacteria cannot colonize the body.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- If pathogens breach the protective barriers, [pb_glossary id=\"4860\"]inflammation[\/pb_glossary] occurs. This creates a physical barrier against the spread of infection and repairs tissue damage. Inflammation is triggered by chemicals (such as [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]), and it causes swelling, redness, and warmth.<\/li>\r\n \t
- The [pb_glossary id=\"4868\"]complement system[\/pb_glossary] is a complex biochemical mechanism that helps [pb_glossary id=\"5659\"]antibodies[\/pb_glossary] kill pathogens. Once activated, the complement system consists of more than two dozen proteins that lead to disruption of the [pb_glossary id=\"5621\"]cell membrane[\/pb_glossary] of pathogens and bursting of the cells.<\/li>\r\n \t
- Cellular responses of the innate immune system involve various types of leukocytes (white blood cells). For example, [pb_glossary id=\"5545\"]neutrophils[\/pb_glossary], [pb_glossary id=\"4340\"]macrophages[\/pb_glossary], and [pb_glossary id=\"4875\"]dendritic cells[\/pb_glossary]\u00a0phagocytize pathogens. [pb_glossary id=\"5573\"]Basophils[\/pb_glossary]\u00a0and [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]\u00a0release chemicals that trigger inflammation. [pb_glossary id=\"5515\"]Natural killer cells[\/pb_glossary]\u00a0destroy cancerous or virus-infected cells, and [pb_glossary id=\"5529\"]eosinophils[\/pb_glossary]\u00a0kill parasites.<\/li>\r\n \t
- Many pathogens have evolved mechanisms that help them evade the innate immune system. For example, some pathogens form a protective capsule around themselves, and some mimic host cells so the immune system does not recognize them as foreign.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- The main cells of the adaptive immune system are [pb_glossary id=\"4832\"]lymphocytes[\/pb_glossary]. There are two major types of lymphocytes: T cells and B cells. Both types must be activated by foreign antigens to become functioning immune cells.<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- Most activated T cells become either [pb_glossary id=\"4893\"]killer T cells[\/pb_glossary]\u00a0or [pb_glossary id=\"5537\"]helper T cells[\/pb_glossary]. Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage immune responses by releasing cytokines that control other types of leukocytes.<\/li>\r\n \t
- Activated B cells form [pb_glossary id=\"4902\"]plasma cell[\/pb_glossary]s that secrete antibodies, which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the complement system.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- After an adaptive immune response occurs, long-lasting [pb_glossary id=\"4904\"]memory B cells and memory T cells[\/pb_glossary] may remain to confer [pb_glossary id=\"4884\"]immunity[\/pb_glossary] to the specific pathogen that caused the adaptive immune response. These memory cells are ready to activate an immediate response if they are exposed to the same antigen again in the future.<\/li>\r\n \t
- Immunity may be active or passive.<\/li>\r\n<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- \u00a0[pb_glossary id=\"4906\"]Active immunity[\/pb_glossary] occurs when the immune system has been presented with antigens that elicit an adaptive immune response. This may occur naturally as the result of an infection, or artificially as the result of immunization. Active immunity may last for years or even for life.<\/li>\r\n \t
- [pb_glossary id=\"4910\"]Passive immunity[\/pb_glossary] occurs without an adaptive immune response by the transfer of antibodies or activated T cells. This may occur naturally between a mother and her fetus or her nursing infant, or it may occur artificially by injection. Passive immunity lasts only as long as the antibodies or activated T cells remain alive in the body, generally just weeks or months.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- Many pathogens have evolved mechanisms to evade the adaptive immune system. For example, human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]) evades the adaptive immune system by frequently changing its antigens and by forming its outer envelope from the host\u2019s cell membrane.<\/li>\r\n \t
- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an inflammatory response to a harmless antigen. Any antigen 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<\/ul>\r\n
\r\n \t- \r\n
\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 B cells are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to mast cells. On subsequent exposures to the allergen, the mast cells immediately release cytokines and histamines that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with antihistamines that 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<\/ul>\r\n<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary]\u00a0occur 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<\/ul>\r\n
\r\n \t- \r\n
\r\n \t- In some autoimmune diseases, such as type I diabetes, the immune system attacks and damages specific body cells. In other autoimmune diseases, such as systemic lupus erythematosus, 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<\/ul>\r\n<\/li>\r\n \t
- Immunodeficiency 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<\/ul>\r\n
\r\n \t- \r\n
\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 substance abuse, obesity, and malnutrition, among others.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus (HIV), 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, but\u00a0it can't\u00a0eliminate the virus completely.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\nUp to this point, this book has covered body systems that carry out processes within individuals, such as the digestive, muscular, and immune systems. Read the next chapter to learn about the body system that allows humans to produce new individuals \u2014 the reproductive system.\r\n\r\n<\/div>\r\n<\/div>\r\n
\r\nChapter 17 Review<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"642\"]<\/li>\r\n \t
- Compare and contrast a pathogen and an allergen.<\/li>\r\n \t
- Describe three ways in which pathogens can enter the body.<\/li>\r\n \t
- The complement system involves the activation of several proteins to kill pathogens. Why do you think this is considered part of the innate immune system, instead of the adaptive immune system?<\/li>\r\n \t
- Why are innate immune responses generally faster than adaptive immune responses?<\/li>\r\n \t
- Explain how an autoimmune disease could be triggered by a pathogen.<\/li>\r\n \t
- What is an opportunistic infection?\u00a0Name two diseases or conditions that could result in opportunistic infections. Explain your answer.<\/li>\r\n \t
- Which cell type in the immune system can be considered an \u201cantibody factory?\"<\/li>\r\n \t
- Besides foreign pathogens, what is one thing that the immune system protects the body against?<\/li>\r\n \t
- What cell type in the immune system is infected and killed by HIV?<\/li>\r\n \t
- Name two types of cells that produce cytokines in the immune system.\u00a0What are two functions of cytokines in the immune system?<\/li>\r\n \t
- Many pathogens evade the immune system by altering their outer surface in some way. Based on what you know about the functioning of the immune system, why is this often a successful approach?<\/li>\r\n \t
- What is \u201cmissing self?\" How does this condition arise?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n17.7 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/Z3B-AaqjyjE\r\nWhat is leukemia? - Danilo Allegra and Dania Puggioni, TED-Ed, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 17.7.1<\/strong>\r\n\r\nCycling to Beat Blood Cancer<\/a> by Blood Cancer UK<\/a> (Formerly Bloodwise) on Flickr<\/a> is used under a CC BY-NC-ND 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-nd\/2.0\/) license.\r\n\r\nFigure 17.7.2<\/strong>\r\n\r\nantigen stain<\/a> by Ed Uthman<\/a> from Houston, TX, USA on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\nReferences<\/h2>\r\n
Hodgkin lymphoma statistics [online article]. (2020). Canadian Cancer Society. https:\/\/www.cancer.ca:443\/en\/cancer-information\/cancer-type\/hodgkin-lymphoma\/statistics\/?region=on<\/p>\r\n
Non-Hodgkin lymphoma statistics [online article]. (2020). Canadian Cancer Society. https:\/\/www.cancer.ca:443\/en\/cancer-information\/cancer-type\/non-hodgkin-lymphoma\/statistics\/?region=on<\/p>\r\n
TED-Ed. (2015, April 30). What is leukemia? - Danilo Allegra and Dania Puggioni. YouTube. https:\/\/www.youtube.com\/watch?v=Z3B-AaqjyjE&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 17.7.1 Be Unstoppable for Leukemia and Lymphoma Research.<\/em><\/figcaption><\/figure>\n\nCase Study Conclusion: Defending Your Defenses<\/h1>\n<\/div>\n
These people are participating in a bike ride to raise funds for leukemia and lymphoma research (Figure 17.7.1). Leukemia and lymphoma are blood cancers. In 2020,\u00a0 approximately 6,900 Canadians will be diagnosed with leukemia and 3,000 will die from this cancer. Lymphoma is the most common type of blood cancer. As a lymphoma patient, Hakeem, who you learned about in the beginning of this chapter, may eventually benefit from research funded by a bike ride like this one.<\/p>\n
What type of blood cell is affected in lymphoma<\/a>? As the name implies, lymphoma is a cancer that affects lymphocytes, which are a type of leukocyte. As you have learned in this chapter, there are different types of lymphocytes, including the B and T cells of the adaptive immune system<\/a>. Different types of lymphoma affect different types of lymphocytes in different ways. It is important to correctly identify the type of lymphoma, so that patients can be treated appropriately.<\/p>\nYou may recall that one of Hakeem\u2019s symptoms was a swollen lymph node<\/a>, and he was diagnosed with lymphoma after a biopsy of that lymph node. Swollen lymph nodes are a common symptom of lymphoma. As you have learned, lymph nodes are distributed throughout the body along lymphatic vessels, as part of the lymphatic system<\/a>. The lymph nodes filter lymph<\/a> and store lymphocytes. Therefore, they play an important role in fighting infections. Because of this, they will often swell in response to an infection. In Hakeem\u2019s case, the swelling and other symptoms did not improve after several weeks and a course of antibiotics, which caused Dr. Hayes to suspect lymphoma instead. The biopsy showed that Hakeem did indeed have cancerous lymphocytes in his lymph nodes.<\/p>\nBut which type of lymphocytes were affected? Lymphoma most commonly affects B or T lymphocytes. The two major types of lymphoma are called Hodgkin (HL) or non-Hodgkin lymphoma (NHL). NHL is more common than HL. In 2020, the Canadian Cancer Society estimates 10,400 Canadians will be diagnosed with non-Hodgkin lymphoma, whereas 1,000 will be diagnosed with Hodgkin lymphoma. While HL is one distinct type of lymphoma, NHL has about 60 different subtypes, depending on which specific cells are affected and how.<\/p>\n
Hakeem was diagnosed with a type of NHL called diffuse large B-cell lymphoma (DLBCL) \u2014 the most common type of NHL. This type of lymphoma affects B cells<\/span><\/a><\/span> and causes them to appear large under the microscope. In addition to Hakeem\u2019s symptoms of fatigue, swollen lymph nodes, loss of appetite, and weight loss, common symptoms of this type of lymphoma include fever and night sweats. It is an aggressive and fast-growing type of lymphoma that is fatal if not treated. The good news is that with early detection and proper treatment, about 70% of patients with DLBCL can be cured.<\/span><\/p>\nFigure 17.7.2 A lab technician can apply stains that target specific antigens to help identify which type of lymphoma is present.<\/figcaption><\/figure>\nHow do physicians determine the specific type of lymphoma? Tissue obtained from a biopsy can be examined under a microscope to observe physical changes (such as abnormal cell size or shape) that are characteristic of a particular subtype of lymphoma. Additionally, tests can be performed on the tissue to determine which cell-surface antigens are present. Recall that antigens are molecules that bind to specific antibodies. Antibodies<\/a> can be produced in the laboratory and labeled with compounds that can be identified by their colour under a microscope. When these antibodies are applied to a tissue sample, this colour will appear wherever the antigen is present, because it binds to the antibody. This technique was used in the photomicrograph in Figure 17.7.2 to identify the presence of a cell-surface antigen (shown as reddish-brown) in a sample of skin cells. This technique, called immunohistochemistry, is also commonly used to identify antigens in tissue samples from lymphoma patients.<\/p>\nWhy would identifying cell-surface antigens be important in diagnosing and treating lymphoma? As you have learned, the immune system uses antigens present on the surface of cells or pathogens to distinguish between self and non-self, and to launch adaptive immune responses. Cells that become cancerous often change their cell-surface antigens. This is one way that the immune system can identify and destroy them. Also, different cell types in the body can sometimes be identified by the presence of specific cell-surface antigens. Knowing the types of cell-surface antigens present in a tissue sample can help physicians identify which cells are cancerous, and possibly the specific subtype of cancer. Knowing this information can be helpful in choosing more tailored and effective treatments.<\/p>\n
One treatment for NHL is, in fact, the use of medications made from antibodies that bind to cell-surface antigens present on cells affected by the specific subtype of NHL. This is called immunotherapy<\/a>. These drugs can directly bind to and kill the cancerous cells. For patients with DLBCL like Hakeem, immunotherapy is often used in conjunction with chemotherapy<\/a> and radiation as a course of treatment. Although Hakeem has a difficult road ahead, he and his medical team are optimistic that \u2014 given the high success rate when DLBCL is caught and treated early \u2014 he may be cured. More research into how the immune system functions may lead to even better treatments for lymphoma \u2014 and other types of cancers \u2014 in the future.<\/p>\n\n\n\nChapter 17 Summary<\/span><\/h1>\n<\/header>\n\nIn this chapter, you learned about the immune system. Specifically, you learned that:<\/p>\n
\n- Any agent that can cause disease is called a pathogen<\/a>. Most human pathogens are microorganisms<\/a>, such as bacteria<\/a> and viruses<\/a>. The immune system is the\u00a0body\u00a0system that defends the human host from pathogens and cancerous<\/a>\u00a0cells.<\/li>\n
- The innate immune system<\/a> is a subset of the immune system that provides very quick, but non-specific responses to pathogens. It includes multiple types of barriers to pathogens, leukocytes that phagocytize pathogens, and several other general responses.<\/li>\n
- The adaptive immune system<\/a> is a subset of the immune system that provides specific responses tailored to particular pathogens. It takes longer to put into effect, but it may lead to immunity<\/a> to the pathogens.<\/li>\n
- Both innate and adaptive immune responses depend on the ability of the immune system to distinguish between self and non-self molecules. Most body cells have major histocompatibility complex (MHC)<\/a> proteins that identify them as self. Pathogens, infected cells, and tumor cells have non-self proteins called antigens that the immune system recognizes as foreign.<\/li>\n
- Antigens<\/a>\u00a0are proteins that bind to specific receptors on immune system cells and elicit an adaptive immune response. Some immune cells (B cells<\/a>) respond to foreign antigens by producing antibodies that bind with antigens and target pathogens for destruction.<\/li>\n
- An important role of the immune system is tumor surveillance. Killer T cells<\/a>\u00a0of the adaptive immune system find and destroy tumor cells, which they can identify from their abnormal antigens.<\/li>\n
- The neuroimmune system<\/a> that protects the central nervous system<\/a> is thought to be distinct from the peripheral immune system<\/a> that protects the rest of the human body. The blood-brain and blood-spinal cord barriers are one type of protection of the neuroimmune system. Neuroglia also play a role in this system, for example, by carrying out phagocytosis<\/a>.<\/li>\n
- The lymphatic system<\/a> is a human organ system that is a vital part of the adaptive immune system. It consists of several organs and a system of vessels that transport or filter the fluid called lymph<\/a>. The main immune function of the lymphatic system is to produce, mature, harbor, and circulate white blood cells called lymphocytes, which are the main cells in the adaptive immune system, and are circulated in lymph.<\/li>\n<\/ul>\n
\n- \n
\n- The return of lymph to the bloodstream is one of the functions of the lymphatic system. Lymph flows from tissue spaces, where it leaks out of blood vessels, to major veins in the upper chest. It is then returned to the cardiovascular system<\/a>. Lymph is similar in composition to blood plasma<\/a>. Its main cellular components are lymphocytes.<\/li>\n
- Lymphatic vessels called lacteals<\/a>\u00a0are found in villi<\/a> that line the small intestine<\/a>. Lacteals absorb fatty acids from the digestion of lipids in the digestive system<\/a>. The fatty acids are then transported through the network of lymphatic vessels to the bloodstream.<\/li>\n
- Lymphocytes, which include B cells<\/a>\u00a0and T cells<\/a>, are the subset of leukocytes involved in adaptive immune responses<\/a>. They may create a lasting memory of and immunity<\/a> to specific pathogens.<\/li>\n
- All lymphocytes are produced in bone marrow<\/a> and then go through a process of maturation, in which they \u201clearn\u201d to distinguish self from non-self. B cells mature in the bone marrow, and T cells mature in the thymus<\/a>. Both the bone marrow and thymus are considered primary lymphatic organs<\/a>.<\/li>\n
- Secondary lymphatic organs<\/a> include the tonsils, spleen, and lymph nodes. There are four pairs of tonsils<\/a>\u00a0that encircle the throat. The spleen<\/a> filters blood, as well as lymph. There are hundreds of lymph nodes<\/a>\u00a0located in clusters along the lymphatic vessels. All of these secondary organs filter lymph and store lymphocytes, so they are sites where pathogens encounter and activate lymphocytes and initiate adaptive immune responses.<\/li>\n<\/ul>\n<\/li>\n
- Unlike the adaptive immune system, the innate immune system<\/a> does not confer immunity. The innate immune system includes surface barriers, inflammation, the complement system, and a variety of cellular responses.<\/li>\n<\/ul>\n
\n- \n
\n- The body\u2019s first line of defense consists of three different types of barriers that keep most pathogens out of body tissues. The types of barriers are mechanical, chemical, and biological barriers.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
\n- \n
\n- \n
\n- Mechanical barriers<\/a>\u00a0\u2014\u00a0which include the skin<\/a>, mucous membranes<\/a>, and fluids (such as tears and urine<\/a>) \u2014 physically block pathogens from entering the body.<\/li>\n
- Chemical barriers\u00a0\u2014\u00a0such as enzymes in sweat<\/a>, saliva<\/a>, and semen<\/a>\u00a0\u2014\u00a0kill pathogens on body surfaces.<\/li>\n
- Biological barriers are harmless bacteria that use up food and space so pathogenic bacteria cannot colonize the body.<\/li>\n<\/ul>\n<\/li>\n
- If pathogens breach the protective barriers, inflammation<\/a> occurs. This creates a physical barrier against the spread of infection and repairs tissue damage. Inflammation is triggered by chemicals (such as cytokines<\/a>\u00a0and histamines<\/a>), and it causes swelling, redness, and warmth.<\/li>\n
- The complement system<\/a> is a complex biochemical mechanism that helps antibodies<\/a> kill pathogens. Once activated, the complement system consists of more than two dozen proteins that lead to disruption of the cell membrane<\/a> of pathogens and bursting of the cells.<\/li>\n
- Cellular responses of the innate immune system involve various types of leukocytes (white blood cells). For example, neutrophils<\/a>, macrophages<\/a>, and dendritic cells<\/a>\u00a0phagocytize pathogens. Basophils<\/a>\u00a0and mast cells<\/a>\u00a0release chemicals that trigger inflammation. Natural killer cells<\/a>\u00a0destroy cancerous or virus-infected cells, and eosinophils<\/a>\u00a0kill parasites.<\/li>\n
- Many pathogens have evolved mechanisms that help them evade the innate immune system. For example, some pathogens form a protective capsule around themselves, and some mimic host cells so the immune system does not recognize them as foreign.<\/li>\n<\/ul>\n<\/li>\n
- The main cells of the adaptive immune system are lymphocytes<\/a>. There are two major types of lymphocytes: T cells and B cells. Both types must be activated by foreign antigens to become functioning immune cells.<\/li>\n<\/ul>\n
\n- \n
\n- Most activated T cells become either killer T cells<\/a>\u00a0or helper T cells<\/a>. Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage immune responses by releasing cytokines that control other types of leukocytes.<\/li>\n
- Activated B cells form plasma cell<\/a>s that secrete antibodies, which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the complement system.<\/li>\n<\/ul>\n<\/li>\n
- After an adaptive immune response occurs, long-lasting memory B cells and memory T cells<\/a> may remain to confer immunity<\/a> to the specific pathogen that caused the adaptive immune response. These memory cells are ready to activate an immediate response if they are exposed to the same antigen again in the future.<\/li>\n
- Immunity may be active or passive.<\/li>\n<\/ul>\n
\n- \n
\n- \u00a0Active immunity<\/a> occurs when the immune system has been presented with antigens that elicit an adaptive immune response. This may occur naturally as the result of an infection, or artificially as the result of immunization. Active immunity may last for years or even for life.<\/li>\n
- Passive immunity<\/a> occurs without an adaptive immune response by the transfer of antibodies or activated T cells. This may occur naturally between a mother and her fetus or her nursing infant, or it may occur artificially by injection. Passive immunity lasts only as long as the antibodies or activated T cells remain alive in the body, generally just weeks or months.<\/li>\n<\/ul>\n<\/li>\n
- Many pathogens have evolved mechanisms to evade the adaptive immune system. For example, human immunodeficiency virus (HIV<\/a>) evades the adaptive immune system by frequently changing its antigens and by forming its outer envelope from the host\u2019s cell membrane.<\/li>\n
- An allergy<\/a> is a disorder in which the immune system makes an inflammatory response to a harmless antigen. Any antigen that causes allergies is called an allergen<\/a>. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\n<\/ul>\n
\n- \n
\n- 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>\n
- Allergies occur when B cells are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to mast cells. On subsequent exposures to the allergen, the mast cells immediately release cytokines and histamines that cause inflammation.<\/li>\n
- Mild allergy symptoms are frequently treated with antihistamines that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called anaphylaxis<\/a>, is a medical emergency that is usually treated with injections of epinephrine. Immunotherapy<\/a> for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\n<\/ul>\n<\/li>\n
- Autoimmune diseases<\/a>\u00a0occur 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>\n<\/ul>\n
\n- \n
\n- In some autoimmune diseases, such as type I diabetes, the immune system attacks and damages specific body cells. In other autoimmune diseases, such as systemic lupus erythematosus, 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>\n<\/ul>\n<\/li>\n
- Immunodeficiency 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>\n<\/ul>\n
\n- \n
\n- Primary immunodeficiency<\/a> is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. Secondary immunodeficiency<\/a> occurs because of some event or exposure experienced after birth. Possible causes include substance abuse, obesity, and malnutrition, among others.<\/li>\n
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus (HIV), 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 acquired immunodeficiency syndrome<\/a> (AIDS). Medications can control the multiplication of HIV in the human body, but\u00a0it can’t\u00a0eliminate the virus completely.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
Up to this point, this book has covered body systems that carry out processes within individuals, such as the digestive, muscular, and immune systems. Read the next chapter to learn about the body system that allows humans to produce new individuals \u2014 the reproductive system.<\/p>\n<\/div>\n<\/div>\n
\n\nChapter 17 Review<\/span><\/h1>\n<\/header>\n\n\n- \n\n
- \r\n \t
- Any agent that can cause disease is called a [pb_glossary id=\"5799\"]pathogen[\/pb_glossary]. Most human pathogens are [pb_glossary id=\"5775\"]microorganisms[\/pb_glossary], such as [pb_glossary id=\"2588\"]bacteria[\/pb_glossary] and [pb_glossary id=\"4283\"]viruses[\/pb_glossary]. The immune system is the\u00a0body\u00a0system that defends the human host from pathogens and [pb_glossary id=\"5605\"]cancerous[\/pb_glossary]\u00a0cells.<\/li>\r\n \t
- The [pb_glossary id=\"4820\"]innate immune system[\/pb_glossary] is a subset of the immune system that provides very quick, but non-specific responses to pathogens. It includes multiple types of barriers to pathogens, leukocytes that phagocytize pathogens, and several other general responses.<\/li>\r\n \t
- The [pb_glossary id=\"4822\"]adaptive immune system[\/pb_glossary] is a subset of the immune system that provides specific responses tailored to particular pathogens. It takes longer to put into effect, but it may lead to [pb_glossary id=\"4884\"]immunity[\/pb_glossary] to the pathogens.<\/li>\r\n \t
- Both innate and adaptive immune responses depend on the ability of the immune system to distinguish between self and non-self molecules. Most body cells have [pb_glossary id=\"4825\"]major histocompatibility complex (MHC)[\/pb_glossary] proteins that identify them as self. Pathogens, infected cells, and tumor cells have non-self proteins called antigens that the immune system recognizes as foreign.<\/li>\r\n \t
- [pb_glossary id=\"2704\"]Antigens[\/pb_glossary]\u00a0are proteins that bind to specific receptors on immune system cells and elicit an adaptive immune response. Some immune cells ([pb_glossary id=\"5539\"]B cells[\/pb_glossary]) respond to foreign antigens by producing antibodies that bind with antigens and target pathogens for destruction.<\/li>\r\n \t
- An important role of the immune system is tumor surveillance. [pb_glossary id=\"4893\"]Killer T cells[\/pb_glossary]\u00a0of the adaptive immune system find and destroy tumor cells, which they can identify from their abnormal antigens.<\/li>\r\n \t
- The [pb_glossary id=\"4833\"]neuroimmune system[\/pb_glossary] that protects the [pb_glossary id=\"5933\"]central nervous system[\/pb_glossary] is thought to be distinct from the [pb_glossary id=\"4834\"]peripheral immune system[\/pb_glossary] that protects the rest of the human body. The blood-brain and blood-spinal cord barriers are one type of protection of the neuroimmune system. Neuroglia also play a role in this system, for example, by carrying out [pb_glossary id=\"1680\"]phagocytosis[\/pb_glossary].<\/li>\r\n \t
- The [pb_glossary id=\"2911\"]lymphatic system[\/pb_glossary] is a human organ system that is a vital part of the adaptive immune system. It consists of several organs and a system of vessels that transport or filter the fluid called [pb_glossary id=\"4552\"]lymph[\/pb_glossary]. The main immune function of the lymphatic system is to produce, mature, harbor, and circulate white blood cells called lymphocytes, which are the main cells in the adaptive immune system, and are circulated in lymph.<\/li>\r\n<\/ul>\r\n
- \r\n \t
- \r\n
- \r\n \t
- The return of lymph to the bloodstream is one of the functions of the lymphatic system. Lymph flows from tissue spaces, where it leaks out of blood vessels, to major veins in the upper chest. It is then returned to the [pb_glossary id=\"5927\"]cardiovascular system[\/pb_glossary]. Lymph is similar in composition to blood [pb_glossary id=\"4395\"]plasma[\/pb_glossary]. Its main cellular components are lymphocytes.<\/li>\r\n \t
- Lymphatic vessels called [pb_glossary id=\"4607\"]lacteals[\/pb_glossary]\u00a0are found in [pb_glossary id=\"4543\"]villi[\/pb_glossary] that line the [pb_glossary id=\"4559\"]small intestine[\/pb_glossary]. Lacteals absorb fatty acids from the digestion of lipids in the [pb_glossary id=\"5969\"]digestive system[\/pb_glossary]. The fatty acids are then transported through the network of lymphatic vessels to the bloodstream.<\/li>\r\n \t
- Lymphocytes, which include [pb_glossary id=\"5539\"]B cells[\/pb_glossary]\u00a0and [pb_glossary id=\"4892\"]T cells[\/pb_glossary], are the subset of leukocytes involved in [pb_glossary id=\"4822\"]adaptive immune responses[\/pb_glossary]. They may create a lasting memory of and [pb_glossary id=\"4884\"]immunity[\/pb_glossary] to specific pathogens.<\/li>\r\n \t
- All lymphocytes are produced in [pb_glossary id=\"4021\"]bone marrow[\/pb_glossary] and then go through a process of maturation, in which they \u201clearn\u201d to distinguish self from non-self. B cells mature in the bone marrow, and T cells mature in the [pb_glossary id=\"4829\"]thymus[\/pb_glossary]. Both the bone marrow and thymus are considered [pb_glossary id=\"4845\"]primary lymphatic organs[\/pb_glossary].<\/li>\r\n \t
- [pb_glossary id=\"4847\"]Secondary lymphatic organs[\/pb_glossary] include the tonsils, spleen, and lymph nodes. There are four pairs of [pb_glossary id=\"4830\"]tonsils[\/pb_glossary]\u00a0that encircle the throat. The [pb_glossary id=\"4497\"]spleen[\/pb_glossary] filters blood, as well as lymph. There are hundreds of [pb_glossary id=\"4831\"]lymph nodes[\/pb_glossary]\u00a0located in clusters along the lymphatic vessels. All of these secondary organs filter lymph and store lymphocytes, so they are sites where pathogens encounter and activate lymphocytes and initiate adaptive immune responses.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- Unlike the adaptive immune system, the [pb_glossary id=\"4820\"]innate immune system[\/pb_glossary] does not confer immunity. The innate immune system includes surface barriers, inflammation, the complement system, and a variety of cellular responses.<\/li>\r\n<\/ul>\r\n
- \r\n \t
- \r\n
- \r\n \t
- The body\u2019s first line of defense consists of three different types of barriers that keep most pathogens out of body tissues. The types of barriers are mechanical, chemical, and biological barriers.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n
- \r\n \t
- \r\n
- \r\n \t
- \r\n
- \r\n \t
- [pb_glossary id=\"4857\"]Mechanical barriers[\/pb_glossary]\u00a0\u2014\u00a0which include the [pb_glossary id=\"3521\"]skin[\/pb_glossary], [pb_glossary id=\"3538\"]mucous membranes[\/pb_glossary], and fluids (such as tears and [pb_glossary id=\"4717\"]urine[\/pb_glossary]) \u2014 physically block pathogens from entering the body.<\/li>\r\n \t
- Chemical barriers\u00a0\u2014\u00a0such as enzymes in [pb_glossary id=\"4711\"]sweat[\/pb_glossary], [pb_glossary id=\"4595\"]saliva[\/pb_glossary], and [pb_glossary id=\"4885\"]semen[\/pb_glossary]\u00a0\u2014\u00a0kill pathogens on body surfaces.<\/li>\r\n \t
- Biological barriers are harmless bacteria that use up food and space so pathogenic bacteria cannot colonize the body.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- If pathogens breach the protective barriers, [pb_glossary id=\"4860\"]inflammation[\/pb_glossary] occurs. This creates a physical barrier against the spread of infection and repairs tissue damage. Inflammation is triggered by chemicals (such as [pb_glossary id=\"4865\"]cytokines[\/pb_glossary]\u00a0and [pb_glossary id=\"4879\"]histamines[\/pb_glossary]), and it causes swelling, redness, and warmth.<\/li>\r\n \t
- The [pb_glossary id=\"4868\"]complement system[\/pb_glossary] is a complex biochemical mechanism that helps [pb_glossary id=\"5659\"]antibodies[\/pb_glossary] kill pathogens. Once activated, the complement system consists of more than two dozen proteins that lead to disruption of the [pb_glossary id=\"5621\"]cell membrane[\/pb_glossary] of pathogens and bursting of the cells.<\/li>\r\n \t
- Cellular responses of the innate immune system involve various types of leukocytes (white blood cells). For example, [pb_glossary id=\"5545\"]neutrophils[\/pb_glossary], [pb_glossary id=\"4340\"]macrophages[\/pb_glossary], and [pb_glossary id=\"4875\"]dendritic cells[\/pb_glossary]\u00a0phagocytize pathogens. [pb_glossary id=\"5573\"]Basophils[\/pb_glossary]\u00a0and [pb_glossary id=\"4881\"]mast cells[\/pb_glossary]\u00a0release chemicals that trigger inflammation. [pb_glossary id=\"5515\"]Natural killer cells[\/pb_glossary]\u00a0destroy cancerous or virus-infected cells, and [pb_glossary id=\"5529\"]eosinophils[\/pb_glossary]\u00a0kill parasites.<\/li>\r\n \t
- Many pathogens have evolved mechanisms that help them evade the innate immune system. For example, some pathogens form a protective capsule around themselves, and some mimic host cells so the immune system does not recognize them as foreign.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- The main cells of the adaptive immune system are [pb_glossary id=\"4832\"]lymphocytes[\/pb_glossary]. There are two major types of lymphocytes: T cells and B cells. Both types must be activated by foreign antigens to become functioning immune cells.<\/li>\r\n<\/ul>\r\n
- \r\n \t
- \r\n
- \r\n \t
- Most activated T cells become either [pb_glossary id=\"4893\"]killer T cells[\/pb_glossary]\u00a0or [pb_glossary id=\"5537\"]helper T cells[\/pb_glossary]. Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage immune responses by releasing cytokines that control other types of leukocytes.<\/li>\r\n \t
- Activated B cells form [pb_glossary id=\"4902\"]plasma cell[\/pb_glossary]s that secrete antibodies, which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the complement system.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- After an adaptive immune response occurs, long-lasting [pb_glossary id=\"4904\"]memory B cells and memory T cells[\/pb_glossary] may remain to confer [pb_glossary id=\"4884\"]immunity[\/pb_glossary] to the specific pathogen that caused the adaptive immune response. These memory cells are ready to activate an immediate response if they are exposed to the same antigen again in the future.<\/li>\r\n \t
- Immunity may be active or passive.<\/li>\r\n<\/ul>\r\n
- \r\n \t
- \r\n
- \r\n \t
- \u00a0[pb_glossary id=\"4906\"]Active immunity[\/pb_glossary] occurs when the immune system has been presented with antigens that elicit an adaptive immune response. This may occur naturally as the result of an infection, or artificially as the result of immunization. Active immunity may last for years or even for life.<\/li>\r\n \t
- [pb_glossary id=\"4910\"]Passive immunity[\/pb_glossary] occurs without an adaptive immune response by the transfer of antibodies or activated T cells. This may occur naturally between a mother and her fetus or her nursing infant, or it may occur artificially by injection. Passive immunity lasts only as long as the antibodies or activated T cells remain alive in the body, generally just weeks or months.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
- Many pathogens have evolved mechanisms to evade the adaptive immune system. For example, human immunodeficiency virus ([pb_glossary id=\"4501\"]HIV[\/pb_glossary]) evades the adaptive immune system by frequently changing its antigens and by forming its outer envelope from the host\u2019s cell membrane.<\/li>\r\n \t
- An [pb_glossary id=\"4877\"]allergy[\/pb_glossary] is a disorder in which the immune system makes an inflammatory response to a harmless antigen. Any antigen 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<\/ul>\r\n
- \r\n \t
- \r\n
- \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 B cells are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to mast cells. On subsequent exposures to the allergen, the mast cells immediately release cytokines and histamines that cause inflammation.<\/li>\r\n \t
- Mild allergy symptoms are frequently treated with antihistamines that 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<\/ul>\r\n<\/li>\r\n \t
- [pb_glossary id=\"5006\"]Autoimmune diseases[\/pb_glossary]\u00a0occur 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<\/ul>\r\n
- \r\n \t
- \r\n
- \r\n \t
- In some autoimmune diseases, such as type I diabetes, the immune system attacks and damages specific body cells. In other autoimmune diseases, such as systemic lupus erythematosus, 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<\/ul>\r\n<\/li>\r\n \t
- Immunodeficiency 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<\/ul>\r\n
- \r\n \t
- \r\n
- \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 substance abuse, obesity, and malnutrition, among others.<\/li>\r\n \t
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus (HIV), 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, but\u00a0it can't\u00a0eliminate the virus completely.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\nUp to this point, this book has covered body systems that carry out processes within individuals, such as the digestive, muscular, and immune systems. Read the next chapter to learn about the body system that allows humans to produce new individuals \u2014 the reproductive system.\r\n\r\n<\/div>\r\n<\/div>\r\n
\r\n Chapter 17 Review<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- [h5p id=\"642\"]<\/li>\r\n \t
- Compare and contrast a pathogen and an allergen.<\/li>\r\n \t
- Describe three ways in which pathogens can enter the body.<\/li>\r\n \t
- The complement system involves the activation of several proteins to kill pathogens. Why do you think this is considered part of the innate immune system, instead of the adaptive immune system?<\/li>\r\n \t
- Why are innate immune responses generally faster than adaptive immune responses?<\/li>\r\n \t
- Explain how an autoimmune disease could be triggered by a pathogen.<\/li>\r\n \t
- What is an opportunistic infection?\u00a0Name two diseases or conditions that could result in opportunistic infections. Explain your answer.<\/li>\r\n \t
- Which cell type in the immune system can be considered an \u201cantibody factory?\"<\/li>\r\n \t
- Besides foreign pathogens, what is one thing that the immune system protects the body against?<\/li>\r\n \t
- What cell type in the immune system is infected and killed by HIV?<\/li>\r\n \t
- Name two types of cells that produce cytokines in the immune system.\u00a0What are two functions of cytokines in the immune system?<\/li>\r\n \t
- Many pathogens evade the immune system by altering their outer surface in some way. Based on what you know about the functioning of the immune system, why is this often a successful approach?<\/li>\r\n \t
- What is \u201cmissing self?\" How does this condition arise?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n 17.7 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/youtu.be\/Z3B-AaqjyjE\r\nWhat is leukemia? - Danilo Allegra and Dania Puggioni, TED-Ed, 2015.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 17.7.1<\/strong>\r\n\r\nCycling to Beat Blood Cancer<\/a> by Blood Cancer UK<\/a> (Formerly Bloodwise) on Flickr<\/a> is used under a CC BY-NC-ND 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-nd\/2.0\/) license.\r\n\r\nFigure 17.7.2<\/strong>\r\n\r\nantigen stain<\/a> by Ed Uthman<\/a> from Houston, TX, USA on Wikimedia Commons is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0) license.\r\n
References<\/h2>\r\n
Hodgkin lymphoma statistics [online article]. (2020). Canadian Cancer Society. https:\/\/www.cancer.ca:443\/en\/cancer-information\/cancer-type\/hodgkin-lymphoma\/statistics\/?region=on<\/p>\r\n
Non-Hodgkin lymphoma statistics [online article]. (2020). Canadian Cancer Society. https:\/\/www.cancer.ca:443\/en\/cancer-information\/cancer-type\/non-hodgkin-lymphoma\/statistics\/?region=on<\/p>\r\n
TED-Ed. (2015, April 30). What is leukemia? - Danilo Allegra and Dania Puggioni. YouTube. https:\/\/www.youtube.com\/watch?v=Z3B-AaqjyjE&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\n
Figure 17.7.1 Be Unstoppable for Leukemia and Lymphoma Research.<\/em><\/figcaption><\/figure>\n \nCase Study Conclusion: Defending Your Defenses<\/h1>\n<\/div>\n
These people are participating in a bike ride to raise funds for leukemia and lymphoma research (Figure 17.7.1). Leukemia and lymphoma are blood cancers. In 2020,\u00a0 approximately 6,900 Canadians will be diagnosed with leukemia and 3,000 will die from this cancer. Lymphoma is the most common type of blood cancer. As a lymphoma patient, Hakeem, who you learned about in the beginning of this chapter, may eventually benefit from research funded by a bike ride like this one.<\/p>\n
What type of blood cell is affected in lymphoma<\/a>? As the name implies, lymphoma is a cancer that affects lymphocytes, which are a type of leukocyte. As you have learned in this chapter, there are different types of lymphocytes, including the B and T cells of the adaptive immune system<\/a>. Different types of lymphoma affect different types of lymphocytes in different ways. It is important to correctly identify the type of lymphoma, so that patients can be treated appropriately.<\/p>\n
You may recall that one of Hakeem\u2019s symptoms was a swollen lymph node<\/a>, and he was diagnosed with lymphoma after a biopsy of that lymph node. Swollen lymph nodes are a common symptom of lymphoma. As you have learned, lymph nodes are distributed throughout the body along lymphatic vessels, as part of the lymphatic system<\/a>. The lymph nodes filter lymph<\/a> and store lymphocytes. Therefore, they play an important role in fighting infections. Because of this, they will often swell in response to an infection. In Hakeem\u2019s case, the swelling and other symptoms did not improve after several weeks and a course of antibiotics, which caused Dr. Hayes to suspect lymphoma instead. The biopsy showed that Hakeem did indeed have cancerous lymphocytes in his lymph nodes.<\/p>\n
But which type of lymphocytes were affected? Lymphoma most commonly affects B or T lymphocytes. The two major types of lymphoma are called Hodgkin (HL) or non-Hodgkin lymphoma (NHL). NHL is more common than HL. In 2020, the Canadian Cancer Society estimates 10,400 Canadians will be diagnosed with non-Hodgkin lymphoma, whereas 1,000 will be diagnosed with Hodgkin lymphoma. While HL is one distinct type of lymphoma, NHL has about 60 different subtypes, depending on which specific cells are affected and how.<\/p>\n
Hakeem was diagnosed with a type of NHL called diffuse large B-cell lymphoma (DLBCL) \u2014 the most common type of NHL. This type of lymphoma affects B cells<\/span><\/a><\/span> and causes them to appear large under the microscope. In addition to Hakeem\u2019s symptoms of fatigue, swollen lymph nodes, loss of appetite, and weight loss, common symptoms of this type of lymphoma include fever and night sweats. It is an aggressive and fast-growing type of lymphoma that is fatal if not treated. The good news is that with early detection and proper treatment, about 70% of patients with DLBCL can be cured.<\/span><\/p>\n
Figure 17.7.2 A lab technician can apply stains that target specific antigens to help identify which type of lymphoma is present.<\/figcaption><\/figure>\n How do physicians determine the specific type of lymphoma? Tissue obtained from a biopsy can be examined under a microscope to observe physical changes (such as abnormal cell size or shape) that are characteristic of a particular subtype of lymphoma. Additionally, tests can be performed on the tissue to determine which cell-surface antigens are present. Recall that antigens are molecules that bind to specific antibodies. Antibodies<\/a> can be produced in the laboratory and labeled with compounds that can be identified by their colour under a microscope. When these antibodies are applied to a tissue sample, this colour will appear wherever the antigen is present, because it binds to the antibody. This technique was used in the photomicrograph in Figure 17.7.2 to identify the presence of a cell-surface antigen (shown as reddish-brown) in a sample of skin cells. This technique, called immunohistochemistry, is also commonly used to identify antigens in tissue samples from lymphoma patients.<\/p>\n
Why would identifying cell-surface antigens be important in diagnosing and treating lymphoma? As you have learned, the immune system uses antigens present on the surface of cells or pathogens to distinguish between self and non-self, and to launch adaptive immune responses. Cells that become cancerous often change their cell-surface antigens. This is one way that the immune system can identify and destroy them. Also, different cell types in the body can sometimes be identified by the presence of specific cell-surface antigens. Knowing the types of cell-surface antigens present in a tissue sample can help physicians identify which cells are cancerous, and possibly the specific subtype of cancer. Knowing this information can be helpful in choosing more tailored and effective treatments.<\/p>\n
One treatment for NHL is, in fact, the use of medications made from antibodies that bind to cell-surface antigens present on cells affected by the specific subtype of NHL. This is called immunotherapy<\/a>. These drugs can directly bind to and kill the cancerous cells. For patients with DLBCL like Hakeem, immunotherapy is often used in conjunction with chemotherapy<\/a> and radiation as a course of treatment. Although Hakeem has a difficult road ahead, he and his medical team are optimistic that \u2014 given the high success rate when DLBCL is caught and treated early \u2014 he may be cured. More research into how the immune system functions may lead to even better treatments for lymphoma \u2014 and other types of cancers \u2014 in the future.<\/p>\n
\n\n\n Chapter 17 Summary<\/span><\/h1>\n<\/header>\n
\nIn this chapter, you learned about the immune system. Specifically, you learned that:<\/p>\n
- \n
- Any agent that can cause disease is called a pathogen<\/a>. Most human pathogens are microorganisms<\/a>, such as bacteria<\/a> and viruses<\/a>. The immune system is the\u00a0body\u00a0system that defends the human host from pathogens and cancerous<\/a>\u00a0cells.<\/li>\n
- The innate immune system<\/a> is a subset of the immune system that provides very quick, but non-specific responses to pathogens. It includes multiple types of barriers to pathogens, leukocytes that phagocytize pathogens, and several other general responses.<\/li>\n
- The adaptive immune system<\/a> is a subset of the immune system that provides specific responses tailored to particular pathogens. It takes longer to put into effect, but it may lead to immunity<\/a> to the pathogens.<\/li>\n
- Both innate and adaptive immune responses depend on the ability of the immune system to distinguish between self and non-self molecules. Most body cells have major histocompatibility complex (MHC)<\/a> proteins that identify them as self. Pathogens, infected cells, and tumor cells have non-self proteins called antigens that the immune system recognizes as foreign.<\/li>\n
- Antigens<\/a>\u00a0are proteins that bind to specific receptors on immune system cells and elicit an adaptive immune response. Some immune cells (B cells<\/a>) respond to foreign antigens by producing antibodies that bind with antigens and target pathogens for destruction.<\/li>\n
- An important role of the immune system is tumor surveillance. Killer T cells<\/a>\u00a0of the adaptive immune system find and destroy tumor cells, which they can identify from their abnormal antigens.<\/li>\n
- The neuroimmune system<\/a> that protects the central nervous system<\/a> is thought to be distinct from the peripheral immune system<\/a> that protects the rest of the human body. The blood-brain and blood-spinal cord barriers are one type of protection of the neuroimmune system. Neuroglia also play a role in this system, for example, by carrying out phagocytosis<\/a>.<\/li>\n
- The lymphatic system<\/a> is a human organ system that is a vital part of the adaptive immune system. It consists of several organs and a system of vessels that transport or filter the fluid called lymph<\/a>. The main immune function of the lymphatic system is to produce, mature, harbor, and circulate white blood cells called lymphocytes, which are the main cells in the adaptive immune system, and are circulated in lymph.<\/li>\n<\/ul>\n
- \n
- \n
- \n
- The return of lymph to the bloodstream is one of the functions of the lymphatic system. Lymph flows from tissue spaces, where it leaks out of blood vessels, to major veins in the upper chest. It is then returned to the cardiovascular system<\/a>. Lymph is similar in composition to blood plasma<\/a>. Its main cellular components are lymphocytes.<\/li>\n
- Lymphatic vessels called lacteals<\/a>\u00a0are found in villi<\/a> that line the small intestine<\/a>. Lacteals absorb fatty acids from the digestion of lipids in the digestive system<\/a>. The fatty acids are then transported through the network of lymphatic vessels to the bloodstream.<\/li>\n
- Lymphocytes, which include B cells<\/a>\u00a0and T cells<\/a>, are the subset of leukocytes involved in adaptive immune responses<\/a>. They may create a lasting memory of and immunity<\/a> to specific pathogens.<\/li>\n
- All lymphocytes are produced in bone marrow<\/a> and then go through a process of maturation, in which they \u201clearn\u201d to distinguish self from non-self. B cells mature in the bone marrow, and T cells mature in the thymus<\/a>. Both the bone marrow and thymus are considered primary lymphatic organs<\/a>.<\/li>\n
- Secondary lymphatic organs<\/a> include the tonsils, spleen, and lymph nodes. There are four pairs of tonsils<\/a>\u00a0that encircle the throat. The spleen<\/a> filters blood, as well as lymph. There are hundreds of lymph nodes<\/a>\u00a0located in clusters along the lymphatic vessels. All of these secondary organs filter lymph and store lymphocytes, so they are sites where pathogens encounter and activate lymphocytes and initiate adaptive immune responses.<\/li>\n<\/ul>\n<\/li>\n
- Unlike the adaptive immune system, the innate immune system<\/a> does not confer immunity. The innate immune system includes surface barriers, inflammation, the complement system, and a variety of cellular responses.<\/li>\n<\/ul>\n
- \n
- \n
- \n
- The body\u2019s first line of defense consists of three different types of barriers that keep most pathogens out of body tissues. The types of barriers are mechanical, chemical, and biological barriers.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
- \n
- \n
- \n
- \n
- \n
- Mechanical barriers<\/a>\u00a0\u2014\u00a0which include the skin<\/a>, mucous membranes<\/a>, and fluids (such as tears and urine<\/a>) \u2014 physically block pathogens from entering the body.<\/li>\n
- Chemical barriers\u00a0\u2014\u00a0such as enzymes in sweat<\/a>, saliva<\/a>, and semen<\/a>\u00a0\u2014\u00a0kill pathogens on body surfaces.<\/li>\n
- Biological barriers are harmless bacteria that use up food and space so pathogenic bacteria cannot colonize the body.<\/li>\n<\/ul>\n<\/li>\n
- If pathogens breach the protective barriers, inflammation<\/a> occurs. This creates a physical barrier against the spread of infection and repairs tissue damage. Inflammation is triggered by chemicals (such as cytokines<\/a>\u00a0and histamines<\/a>), and it causes swelling, redness, and warmth.<\/li>\n
- The complement system<\/a> is a complex biochemical mechanism that helps antibodies<\/a> kill pathogens. Once activated, the complement system consists of more than two dozen proteins that lead to disruption of the cell membrane<\/a> of pathogens and bursting of the cells.<\/li>\n
- Cellular responses of the innate immune system involve various types of leukocytes (white blood cells). For example, neutrophils<\/a>, macrophages<\/a>, and dendritic cells<\/a>\u00a0phagocytize pathogens. Basophils<\/a>\u00a0and mast cells<\/a>\u00a0release chemicals that trigger inflammation. Natural killer cells<\/a>\u00a0destroy cancerous or virus-infected cells, and eosinophils<\/a>\u00a0kill parasites.<\/li>\n
- Many pathogens have evolved mechanisms that help them evade the innate immune system. For example, some pathogens form a protective capsule around themselves, and some mimic host cells so the immune system does not recognize them as foreign.<\/li>\n<\/ul>\n<\/li>\n
- The main cells of the adaptive immune system are lymphocytes<\/a>. There are two major types of lymphocytes: T cells and B cells. Both types must be activated by foreign antigens to become functioning immune cells.<\/li>\n<\/ul>\n
- \n
- \n
- \n
- Most activated T cells become either killer T cells<\/a>\u00a0or helper T cells<\/a>. Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage immune responses by releasing cytokines that control other types of leukocytes.<\/li>\n
- Activated B cells form plasma cell<\/a>s that secrete antibodies, which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the complement system.<\/li>\n<\/ul>\n<\/li>\n
- After an adaptive immune response occurs, long-lasting memory B cells and memory T cells<\/a> may remain to confer immunity<\/a> to the specific pathogen that caused the adaptive immune response. These memory cells are ready to activate an immediate response if they are exposed to the same antigen again in the future.<\/li>\n
- Immunity may be active or passive.<\/li>\n<\/ul>\n
- \n
- \n
- \n
- \u00a0Active immunity<\/a> occurs when the immune system has been presented with antigens that elicit an adaptive immune response. This may occur naturally as the result of an infection, or artificially as the result of immunization. Active immunity may last for years or even for life.<\/li>\n
- Passive immunity<\/a> occurs without an adaptive immune response by the transfer of antibodies or activated T cells. This may occur naturally between a mother and her fetus or her nursing infant, or it may occur artificially by injection. Passive immunity lasts only as long as the antibodies or activated T cells remain alive in the body, generally just weeks or months.<\/li>\n<\/ul>\n<\/li>\n
- Many pathogens have evolved mechanisms to evade the adaptive immune system. For example, human immunodeficiency virus (HIV<\/a>) evades the adaptive immune system by frequently changing its antigens and by forming its outer envelope from the host\u2019s cell membrane.<\/li>\n
- An allergy<\/a> is a disorder in which the immune system makes an inflammatory response to a harmless antigen. Any antigen that causes allergies is called an allergen<\/a>. Common allergens include pollen, dust mites, mold, specific foods (such as peanuts), insect stings, and certain medications (such as aspirin).<\/li>\n<\/ul>\n
- \n
- \n
- \n
- 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>\n
- Allergies occur when B cells are first activated to produce large amounts of antibodies to an otherwise harmless allergen, and the antibodies attach to mast cells. On subsequent exposures to the allergen, the mast cells immediately release cytokines and histamines that cause inflammation.<\/li>\n
- Mild allergy symptoms are frequently treated with antihistamines that counter histamines and reduce allergy symptoms. A severe systemic allergic reaction, called anaphylaxis<\/a>, is a medical emergency that is usually treated with injections of epinephrine. Immunotherapy<\/a> for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them.<\/li>\n<\/ul>\n<\/li>\n
- Autoimmune diseases<\/a>\u00a0occur 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>\n<\/ul>\n
- \n
- \n
- \n
- In some autoimmune diseases, such as type I diabetes, the immune system attacks and damages specific body cells. In other autoimmune diseases, such as systemic lupus erythematosus, 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>\n<\/ul>\n<\/li>\n
- Immunodeficiency 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>\n<\/ul>\n
- \n
- \n
- \n
- Primary immunodeficiency<\/a> is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. Secondary immunodeficiency<\/a> occurs because of some event or exposure experienced after birth. Possible causes include substance abuse, obesity, and malnutrition, among others.<\/li>\n
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus (HIV), 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 acquired immunodeficiency syndrome<\/a> (AIDS). Medications can control the multiplication of HIV in the human body, but\u00a0it can’t\u00a0eliminate the virus completely.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
Up to this point, this book has covered body systems that carry out processes within individuals, such as the digestive, muscular, and immune systems. Read the next chapter to learn about the body system that allows humans to produce new individuals \u2014 the reproductive system.<\/p>\n<\/div>\n<\/div>\n
\n\n Chapter 17 Review<\/span><\/h1>\n<\/header>\n
\n- \n
- \n\n
- The most common cause of immunodeficiency in the world today is human immunodeficiency virus (HIV), 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 acquired immunodeficiency syndrome<\/a> (AIDS). Medications can control the multiplication of HIV in the human body, but\u00a0it can’t\u00a0eliminate the virus completely.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
- Primary immunodeficiency<\/a> is present at birth and caused by rare genetic diseases. An example is severe combined immunodeficiency. Secondary immunodeficiency<\/a> occurs because of some event or exposure experienced after birth. Possible causes include substance abuse, obesity, and malnutrition, among others.<\/li>\n
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- Autoimmune diseases<\/a>\u00a0occur 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>\n<\/ul>\n
- Passive immunity<\/a> occurs without an adaptive immune response by the transfer of antibodies or activated T cells. This may occur naturally between a mother and her fetus or her nursing infant, or it may occur artificially by injection. Passive immunity lasts only as long as the antibodies or activated T cells remain alive in the body, generally just weeks or months.<\/li>\n<\/ul>\n<\/li>\n
- \u00a0Active immunity<\/a> occurs when the immune system has been presented with antigens that elicit an adaptive immune response. This may occur naturally as the result of an infection, or artificially as the result of immunization. Active immunity may last for years or even for life.<\/li>\n
- Activated B cells form plasma cell<\/a>s that secrete antibodies, which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the complement system.<\/li>\n<\/ul>\n<\/li>\n
- Most activated T cells become either killer T cells<\/a>\u00a0or helper T cells<\/a>. Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage immune responses by releasing cytokines that control other types of leukocytes.<\/li>\n
- Chemical barriers\u00a0\u2014\u00a0such as enzymes in sweat<\/a>, saliva<\/a>, and semen<\/a>\u00a0\u2014\u00a0kill pathogens on body surfaces.<\/li>\n
- Mechanical barriers<\/a>\u00a0\u2014\u00a0which include the skin<\/a>, mucous membranes<\/a>, and fluids (such as tears and urine<\/a>) \u2014 physically block pathogens from entering the body.<\/li>\n
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- The body\u2019s first line of defense consists of three different types of barriers that keep most pathogens out of body tissues. The types of barriers are mechanical, chemical, and biological barriers.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
- Lymphatic vessels called lacteals<\/a>\u00a0are found in villi<\/a> that line the small intestine<\/a>. Lacteals absorb fatty acids from the digestion of lipids in the digestive system<\/a>. The fatty acids are then transported through the network of lymphatic vessels to the bloodstream.<\/li>\n
- The return of lymph to the bloodstream is one of the functions of the lymphatic system. Lymph flows from tissue spaces, where it leaks out of blood vessels, to major veins in the upper chest. It is then returned to the cardiovascular system<\/a>. Lymph is similar in composition to blood plasma<\/a>. Its main cellular components are lymphocytes.<\/li>\n
- The innate immune system<\/a> is a subset of the immune system that provides very quick, but non-specific responses to pathogens. It includes multiple types of barriers to pathogens, leukocytes that phagocytize pathogens, and several other general responses.<\/li>\n
- Any agent that can cause disease is called a pathogen<\/a>. Most human pathogens are microorganisms<\/a>, such as bacteria<\/a> and viruses<\/a>. The immune system is the\u00a0body\u00a0system that defends the human host from pathogens and cancerous<\/a>\u00a0cells.<\/li>\n
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- The body\u2019s first line of defense consists of three different types of barriers that keep most pathogens out of body tissues. The types of barriers are mechanical, chemical, and biological barriers.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n
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![antigen stain<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Langerhans_Cells_in_Normal_Epidermis,_CD1a_Immunostain_(4435883030).jpg\"){kind=link}