Chapter 17 Answers: Immune System

17.2 Introduction to the Immune System: Review Questions and Answers

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2. What is a pathogen? A pathogen is an agent that can cause disease. Most human pathogens are microorganisms such as bacteria and viruses.
3. State the purpose of the immune system. The purpose of the immune system is to defend the human body from pathogens and cancerous cells.
4. Compare and contrast the innate and adaptive immune systems. The innate immune system 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. The adaptive immune system 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 to the pathogens.
5. Explain how the immune system distinguishes self molecules from non-self molecules. Most body cells have major histocompatibility complex (MHC) proteins that identify them as self. Pathogens and tumor cells have non-self antigens that the immune system recognizes as foreign.
6. What are antigens? Antigens are proteins that bind to specific receptors on immune system cells and elicit an adaptive immune response. Generally they are non-self molecules on pathogens or infected cells.
7. Define tumor surveillance. Tumor surveillance is an important role of the immune system in which killer T cells of the adaptive immune system find and destroy tumor cells, which they can identify from their abnormal antigens.
8. Briefly describe the lymphatic system and its role in immune function. The lymphatic system is a human organ system that consists of several organs and a system of vessels that transport lymph. The main immune function of the lymphatic system is to produce, mature, and circulate lymphocytes, which are the main cells in the adaptive immune system.
9. Identify the neuroimmune system. The neuroimmune system is a system that protects the brain and spinal cord from pathogens and other causes of disease. It includes the blood-brain and blood-spinal cord barriers. Glial cells also play role in this system, for example, by carrying out phagocytosis.
10. What does it mean that the immune system is not just composed of organs? Answers may vary. Sample answer: While organs are included in the immune system, a major component of the immune system is individual cells, such as white blood cells, which identify and destroy pathogens or damaged body cells.
11. Why is the immune system considered “layered?” Answers may vary. Sample answer: The immune system is considered to be layered because it has different layers of defenses that are increasingly more specific for pathogens or cancerous cells. For example, the skin and mucous membranes are first layers of defense against pathogens. If pathogens penetrate this layer, immune cells generate a non-specific, innate response against them. If that is not sufficient, the adaptive immune response is activated which is tailored to the particular pathogen.

17.3 Lymphatic System: Review Questions and Answers

1. What is the lymphatic system? The lymphatic system is a collection of organs involved in the production, maturation, and harboring of white blood cells called lymphocytes. It also includes a network of vessels that transport or filter the fluid called lymph in which lymphocytes circulate.
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3. Summarize the immune function of the lymphatic system. The immune function of the lymphatic system is producing mature lymphocytes and circulating them in lymph. Lymphocytes, which include B cells and T cells, are the subset of white blood cells that are involved in adaptive immune responses. They may create a lasting memory of and immunity to specific pathogens.
4. Explain the difference between lymphocyte maturation and lymphocyte activation. Lymphocyte maturation involves gaining the ability to distinguish between self and non-self. Lymphocyte activation occurs after exposure to a pathogen and involves the development pathogen-specific adaptive responses.

17.4 Innate Immune System: Review Questions and Answers

1. What is the innate immune system? The innate immune system is a subset of the human immune system that produces rapid but non-specific responses to pathogens and does not confer long-lasting immunity. The innate immune system includes surface barriers, inflammation, the complement system, and a variety of cellular responses by leukocytes.
2. Identify the body’s first line of defense. The body’s 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.
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4. What are biological barriers? How do they protect the body? Biological barriers are the trillions of harmless bacteria that normally live in or on the human body. These harmless bacteria protect the body by using up food and space so pathogenic bacteria cannot colonize the body.
5. State the purposes of inflammation. What triggers inflammation, and what signs and symptoms does it cause? The purposes of inflammation include creating a physical barrier against the spread of infection, killing pathogens, removing debris, and repairing tissue damage. Inflammation is triggered by chemicals such as cytokines and histamines that are released by infected or damaged cells or by certain types of leukocytes. Signs and symptoms caused by inflammation include swelling, redness, warmth, and pain.
6. Define the complement system. How does it help destroy pathogens?The complement system is a complex biochemical mechanism that helps antibodies kill pathogens. Once activated, the complement system consists of a cascade of more than two dozen proteins that lead eventually to disruption of the cell membrane of pathogens and bursting of the cells.
7. Describe two ways that pathogens can evade the innate immune system. Answers may vary. Sample answer: Two ways that pathogens may evade the innate immune system include forming a protective capsule around themselves so leukocytes cannot kill them and mimicking host cells so the immune system does not recognize them as foreign.
8. What are the ways in which phagocytes can encounter pathogens in the body? Phagocytes usually circulate through the body in order to encounter pathogens, but they may also be called to a specific location by cytokines when inflammation occurs, or may permanently reside in certain tissues and wait for pathogens to appear there.
9. Describe two different ways in which enzymes play a role in the innate immune response. Answers may vary. Sample answer: Enzymes play roles as both chemical barriers and in cellular responses such as phagocytosis. For example, protease enzymes in the stomach act as a chemical barrier by killing pathogens that enter the gastrointestinal tract. Digestive enzymes in lysosomes in phagocytes kill and digest pathogens that were enveloped by the phagocyte.

17.5 Adaptive Immune Responses: Review Questions and Answers

1. What is the adaptive immune system? The adaptive immune system is a subsystem of the overall immune system that recognizes and makes a tailored attack against specific pathogens or tumor cells. It is a slower but more effective response than the innate immune response and also usually leads to immunity to particular pathogens.
2. Define immunity. Immunity is the ability to identify and quickly respond to specific pathogens, generally because the immune system has an immunological memory of the pathogens through the formation of memory B and T cells.
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4. How are lymphocytes activated? Lymphocytes are activated by exposure to foreign antigens, either by being presented with antigens by other immune cells (called antigen-presenting cells) or by engulfing pathogens and their antigens.
5. Identify two common types of T cells and their functions. Two common types of T cells are killer T cells and helper T cells. Killer T cells destroy cells that are infected with pathogens or are cancerous. Helper T cells manage the immune response by releasing cytokines that control other types of leukocytes.
6. How do activated B cells help defend against pathogens? Activated B cells form plasma cells that secrete antibodies, which bind to specific antigens on pathogens or infected cells. The antibody-antigen complexes that form generally lead to the destruction of the cells, for example, by attracting phagocytes or triggering the complement system.
7. How does passive immunity differ from active immunity? How may passive immunity occur? Passive immunity, unlike adaptive immunity, does not result from an adaptive immune response. Instead, it occurs by the transfer of antibodies or activated T cells to an individual who has no prior exposure to a specific pathogen. Passive immunity is short term, lasting only as long as the transferred antigens or T cells are alive, whereas activity immunity is long term and may even last for life. Passive immunity may occur naturally when a mother passes antibodies from her blood directly to the blood of her fetus or to her infant through breast milk. Passive immunity may occur artificially in older children and adults by the injection of antibodies or activated T cells.
8. What are two ways that active immunity may come about? Active immunity may come about naturally as the result of an infection or artificially as the result of immunization.
9. What ways of evading the human adaptive immune system evolved in human immunodeficiency virus (HIV)? Human immunodeficiency virus (HIV) evolved two ways of evading the human adaptive immune system. It frequently changes its antigens so the adaptive immune system cannot form immunological memory to the virus, and it forms its outer envelope from the host’s cell membrane so its antigens cannot be detected by the host’s immune system.
10. Why do vaccinations expose a person to a version of a pathogen? Answers may vary. Sample answer: Vaccinations work by triggering the body’s own adaptive immune response to generate long-term immunity to that pathogen through the creation of specific memory cells. A modified version of the pathogen is used in the vaccine so that the immune system can launch a specific response to that pathogen if the person later becomes naturally exposed to it, but the vaccination itself does not make the person sick.

17.6 Disorders of the Immune System: Review Questions and Answers

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2. How does immunotherapy for allergies work? Immunotherapy for allergies involves injecting increasing amounts of allergens to desensitize the immune system to them. After the immune system has been desensitized to the allergens, it no longer reacts to them.
3. What are autoimmune diseases? Autoimmune diseases are diseases that occur when the immune system fails to recognize the body’s own molecules as self and attacks them, causing damage to tissues and organs.
4. Identify two risk factors for autoimmune diseases. Risk factors for autoimmune diseases include a family history of autoimmunity and female gender.
5. Autoimmune diseases may be specific to particular tissues, or they may be systemic. Give an example of each type of autoimmune disease. Answers may vary. Sample answer: Type I diabetes is an example of an autoimmune disease that is specific to particular tissues. Rheumatoid arthritis is an example of an autoimmune disease that is systemic.
6. What is immunodeficiency? Compare and contrast primary and secondary immunodeficiency. Give an example of each. Immunodeficiency is a condition in which 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.
7. What is the most common cause of immunodeficiency in the world today? How does this affect the immune system? The most common cause of immunodeficiency in the world today is human immunodeficiency virus (HIV). It causes immunodeficiency by infecting and destroying helper T cells.
8. Distinguish between HIV and AIDS. HIV is a virus that may infect the human immune system. In some people, HIV infection progresses to AIDS, or acquired immunodeficiency syndrome. AIDS is diagnosed when HIV causes such low levels of helper T cells that opportunistic infections occur.

17.7 Case Study Conclusion and Chapter Summary: Review Questions and Answers

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2. Compare and contrast a pathogen and an allergen. A pathogen and an allergen are both usually small particles that trigger an immune response when they enter the body. However, a pathogen is actually harmful to the body whereas an allergen is a substance that is normally harmless, but the body mistakenly perceives it as harmful.
3. Describe three ways in which pathogens can enter the body. Answers will vary. Sample answer: Three ways in which pathogens can enter the body are: through a cut in the skin; inhalation through the nose; or through food and drink via the gastrointestinal tract.
4. 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? Answers will vary. Sample answer: I think that the complement system is considered part of the innate immune system because these molecules have a non-specific effect against pathogens, which is a characteristic of the innate immune system. Although they work alongside specific antibodies, they themselves are more generalized molecules that are not precisely matched to particular pathogens.
5. Why are innate immune responses generally faster than adaptive immune responses? Answers may vary. Sample answer: Innate immune responses are generally faster than adaptive immune responses because they do not require exposure to a pathogen and subsequent cell activation to launch a response, unlike adaptive immune responses. For instance, the skin is part of the innate immune system and it simply protects the body against pathogens at all times, while B and T cells (adaptive immune response) require a more time-consuming process involving exposure to a pathogen and subsequent cellular responses in order to defend against the pathogen.
6. Explain how an autoimmune disease could be triggered by a pathogen. Some autoimmune diseases are thought to be caused by exposure to pathogens that have antigens similar to the body’s own molecules. After this exposure, the immune system responds to body cells as though they were pathogens.
7. What is an opportunistic infection? Name two diseases or conditions that could result in opportunistic infections. Explain your answer. An opportunistic infection is an infection that occurs because a person’s immune system is abnormally suppressed. Answers will vary. Sample answer: HIV and disease of the thymus both could result in opportunistic infections because they suppress the immune response by damaging the immune system.
8. Which cell type in the immune system can be considered an “antibody factory?” Plasma cells.
9. Besides foreign pathogens, what is one thing that the immune system protects the body against? Answers may vary. Sample answer: Cancerous cells.
10. What cell type in the immune system is infected and killed by HIV? Helper T cells.
11. Name two types of cells that produce cytokines in the immune system. What are two functions of cytokines in the immune system? Answers will vary. Sample answer: Helper T cells and macrophages both produce cytokines.
12. 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? Answers may vary. Sample answer: Pathogens are usually recognized by the immune system because of antigens on their surface. If pathogens are able to change or hide these antigens, they can often evade detection by the immune system.
13. What is “missing self?” How does this condition arise? “Missing self” refers to cells that have abnormally low levels of MHC cell-surface proteins that identify the cell as self. This condition can arise when a cell becomes damaged due to being cancerous or being infected with a pathogen.