Immune System Answer Key

The Immune System ANSWER KEY (GENERAL IMMUNOLOGY) The answers below may include more detail than would be provided by most students. They are meant to give additional information that you may want to discuss with students. PART 1: INTRODUCTION TO IMMUNE SYSTEM ANATOMY 1. The body has physical and chemical barriers to prevent pathogens from entering and infecting tissues. a. Having a runny nose (and blowing your nose) protects your body from pathogens. How do you think that works? Cells that line the inside of the nose are covered in sticky mucus, which traps pathogens. When you have a runny nose, these cells are making more mucus. Blowing your nose helps to eliminate the mucus and the pathogens trapped in it. b. Why do cells that line the respiratory tract (including the nose and lungs) have hairs? The hairs sweep mucus and pathogens out of the body. 2. The table below is an example “report” from a blood test. It shows the numbers of five different cell types in a person’s blood. It also shows the expected ranges of numbers if the person is currently healthy. (These values are just examples — other people’s might be different.) Type of cell Number of cells (per microliter of blood) 4,165 Expected number of cells (per microliter of blood) 1,560–6,450 1,050 950–3,070 142 30–480 Monocytes 519 260–810 Basophils 24 10–80 Neutrophils Lymphocytes (T cells, B cells, NK cells) Eosinophils a. Where in the body are these types of cells produced? They are produced in the bone marrow. b. Are this person’s numbers of immune cells within their expected ranges? If not, which cell types are not within their expected ranges? All the numbers of cells (per microliter of blood) are within their expected ranges. 3. Below is a similar report for an adult with leukemia, a cancer of immune cells. Cancer is caused by uncontrolled cell division. Type of cell Expected number of cells Number of cells (per microliter of blood) (per microliter of blood) Neutrophils 2,580 1,560–6,450 Lymphocytes (T cells, B cells, NK cells) Eosinophils Monocytes Basophils 124 950–3,070 30 30–480 2,280 260–810 60 10–80 a. Which parts of this report might show that this person has leukemia? Be specific. The number of monocytes (2,280 cells/microliter) is much higher than expected (260–810 cells/microliter). These results could indicate uncontrolled division of immune cells, which is indicative of leukemia. Students may wonder why the number of lymphocytes is lower than expected. This can happen if the monocytes crowd out other blood cells. Different types of leukemias have different symptoms and numbers of cells. b. One treatment for leukemia is a bone marrow transplant. First, doctors use various methods to kill the cancer cells in the person’s body. They can then replace these cells with stem cells from the bone marrow of a person without leukemia. Why might a bone marrow transplant help a person with leukemia? Immune cells develop from blood stem cells in the bone marrow. When a person has leukemia, it could be because their blood stem cells or the resulting immune cells are dividing uncontrollably. A bone marrow transplant replaces these stem cells with new stem cells, which should divide at more controlled rates and produce the appropriate numbers of immune cells. 4. In very rare cases, a baby may be born without a thymus. How might this affect their immune system? T cells develop in the thymus, so a baby without a thymus might not be able to produce fully developed T cells. Without T cells, the baby could be more likely to get infections. (Students may also suggest that other parts of the baby’s immune system could help compensate for their lack of T cells.) 5. When a person is sick, a doctor may check the lymph nodes under their jaw and on each side of their neck. Swollen lymph nodes can be a sign that the body is responding to an infection. Why do you think this is? Lymph nodes are organs with a variety of immune cells. When you are infected by a pathogen, the lymph nodes may swell due to increased immune cell activity. (Students will learn more about inflammation in the “Immune Response” tab.) 6. An athlete injured their spleen during a game. At the hospital, doctors removed the spleen and then recommended that the athlete get all their vaccines, including the flu vaccine. Vaccines are medicines that help protect the body from infections. Explain why getting vaccines would be particularly important for someone without a spleen. The spleen is an organ that contains many immune cells (such as phagocytes, B cells, and T cells) that are important for destroying pathogens. If a person’s spleen is removed, they might not have as many immune cells to respond to infections. Getting vaccines can help protect the person from some of these infections. (Students will learn more about vaccination in the “Immune Response” tab.) 7. Label two organs of the immune system on the figure below, and explain how they work together. Student answers will vary; an example is shown below. The Immune System The two organs I chose are the bone marrow (1) and lymph nodes (2). The bone marrow produces immune cells, which include phagocytes, B cells, and T cells. Once these cells leave the bone marrow, they can eventually enter the lymph nodes, where they help destroy pathogens. PART 2: IMMUNE RESPONSE 8. Determine whether each statement in the table below is true or false. Write your decision in the “True or False?” column. Statement True or False? Innate immune cells can distinguish between specific types of viruses and bacteria. False Innate immune cells can activate other types of immune cells. True False The innate immune response provides longer-lasting protection than the adaptive response. The innate immune response includes phagocytes and proteins. True 9. Cytokines are often referred to as “messengers.” Provide two examples of “messages” that cytokines can deliver, and describe how cells or the body respond to each message. Student answers will vary. Examples include the following: • Some cytokines signal the brain to raise the body’s temperature, causing a fever. • Some cytokines attract immune cells to the site of an infection. • Some cytokines activate other cells to destroy pathogens, remove dead cells, or repair damaged tissues. 10. Examine the diagram below. It represents some of the steps (A to F) that can occur when a person is infected. A B C D E F Assign each letter in the diagram to a step in the table below. Some of the letters have already been filled in as examples. Steps Phagocytes with antigens on their surface activate T cells to start the adaptive immune response. Letter E Pathogens get through the body’s physical and chemical barriers. A Innate immune cells, which include phagocytes, respond to the pathogens. B Pieces of pathogens (antigens) attach to proteins on the surface of phagocytes. D The adaptive immune response destroys the pathogens, and the infection ends. F The innate immune response destroys the pathogens, and the infection ends. C 11. In two or three sentences, describe how the innate and adaptive immune responses interact. Student answers will vary. An example response is as follows: Some cells from the innate immune response — such as dendritic cells and macrophages — engulf and destroy pathogens, then “display” antigens from these pathogens on their surfaces using MHC proteins. These antigen-MHC complexes bind to and activate T cells, which activate other cells in the adaptive immune response. The adaptive immune response can also strengthen the innate response by producing cytokines and antibodies, which promote inflammation, phagocytosis, etc. The Immune System 12. Fill in the table below… Immune response Innate immune response skin and mucous membranes inflammation fever Adaptive immune response cell-mediated immune response humoral immune response 13. Hypogammaglobulinemia is a medical condition in which you have low levels of antibodies. People with hypogammaglobulinemia tend to get a lot of infections. Why do you think this is? Antibodies can neutralize pathogens and mark them for destruction. If your body does not produce enough antibodies, the body might not be able to neutralize or destroy pathogens as effectively, resulting in more infections. 14. Explain the difference between an antibody and an antigen. An antigen is a piece of biological material (protein, nucleic acid, carbohydrate, or lipid) that can trigger an immune response. An antibody is a specific protein produced by immune cells in response to a specific antigen. Antibodies bind to antigens. 15. What does it mean to say that the adaptive immune response has “memory”? Some of the T and B cells that responded to a pathogen stay in the body. These cells, called memory cells, can respond quickly to a new infection with the same type of pathogen. The presence of these cells represents a “memory” of that specific pathogen. PART 3: VACCINES 16. The figure below shows the antibody levels of an individual who was injected with a specific antigen. The individual was injected with this antigen twice: once in Week 1 and again in Week 5. a. Which cells produce antibodies? Either B cells or plasma cells are acceptable answers. B cells develop (differentiate) into plasma cells, which produce antibodies. b. Between the first and second antigen injections, when are antibody levels the highest? Around Week 3 The Immune System c. Describe two differences between the antibody levels after the first and second injections. Student answers will vary. They may indicate that the antibody levels were higher, and rose more rapidly, after the second injection compared to the first. d. What might explain the differences you described? It takes longer to activate B cells and produce antibodies after the first injection. After the second injection, memory B cells can start producing antibodies right away. As a result, we see more antibodies being produced more quickly after the second injection. 17. The table below lists the four main types of vaccines. a. Complete the table with a short description of what the vaccine consists of. Type of vaccine Description Live-attenuated weakened, harmless form of a pathogen Inactivated killed or inactive version of a pathogen Subunit/recombinant specific pieces of a pathogen, like part of a protein Toxoid an inactivated toxic substance produced by a pathogen b. Explain why vaccines do not cause disease. Vaccines do not contain a form of the pathogen that can cause disease. They either use a part of the pathogen that is harmless on its own or a form of the pathogen that is harmless (because it has been killed or weakened). 18. The graph below shows how many cases of measles were reported in the United States from 1921 to 2015. Measles is an infectious disease caused by a virus. The measles vaccine has been available in the United States since 1963. What happened to the number of reported measles cases at that time? The number of reported measles cases significantly decreased after 1963. After around 1990, the number of reported cases each year appears negligible. The Immune System ANSWER KEY (IMMUNOTHERAPY) PART 1: ORGANS OF THE IMMUNE SYSTEM 1. The thymus is essential for preventing the immune system from attacking self-antigens. a. Define “antigen” and “self-antigen.” Antigens are small pieces of biological material (protein, carbohydrate, lipid, or nucleic acid) that can be recognized by the immune system. Self-antigens are antigens that are part of a person’s body. b. What happens to T cells that bind to self-antigens? They are destroyed (through apoptosis). c. What type of condition may be caused by T cells that bind to self-antigens? An autoimmune disease (such as rheumatoid arthritis) 2. How does the body replace immune cells and red blood cells that have died? Where does this process occur? Blood stem cells develop (differentiate) into new immune cells and red blood cells. This process occurs in the bone marrow. PART 2: THE IMMUNE RESPONSE 3. The innate immune response includes both cells and proteins. a. Give one example of a cell in the innate immune system, and briefly describe its function. Answers will vary. Options include: o dendritic cell: engulfs and destroys pathogens, displays antigens to activate other cells o macrophage: engulfs and destroys pathogens, can release cytokines o neutrophil: usually the first cell type to respond to pathogens o mast cell: releases histamine to cause inflammation, which helps get rid of infections o natural killer (NK) cell: kills infected and abnormal cells o monocyte: engulfs and destroys pathogens, differentiates into macrophages b. Give one example of a protein in the innate immune system, and briefly describe its function. Answers will vary. Options include: o cytokines: help cells communicate with each other o complement proteins: help destroy pathogens and infected cells, can be activated by antibodies Some students may also mention antigens. If so, clarify that antigens are not part of the immune system but rather something that the immune system responds to. 4. Any cell in the body that accumulates DNA mutations can become a cancer cell. Cancer cells divide uncontrollably and cause disease. Which type of innate immune cell can destroy cancer cells by making them undergo apoptosis (cell death)? Natural killer (NK) cells 5. Both the innate immune response and the adaptive immune response involve dendritic cells. a. Briefly describe the function of dendritic cells in the innate immune response. Dendritic cells bind to and engulf pathogens, destroying them. b. Briefly describe their function in the adaptive immune response. Dendritic cells activate T cells to start the adaptive immune response. Students may mention that dendritic cells do this by displaying antigens on their surface (becoming antigen-presenting cells). The Immune System 6. List three ways in which the innate immune response differs from the adaptive immune response. Answers should include some of the following points (summarized in the “Immune Response” section of the Click & Learn under the “Summary” tab): • The innate immune response involves phagocytes, NK cells, and inflammatory cells. The adaptive immune response involves T cells and B cells. • The innate immune response is less specific than the adaptive immune response. • The innate immune response generally acts more quickly than the adaptive response. • The adaptive immune response is more powerful than the innate immune response. • The innate immune response does not have memory cells like the adaptive immune response. 7. What are antigen-presenting cells (APCs)? What do they do? APCs are cells (often dendritic cells or macrophages) displaying antigens on their surface using MHC proteins. APCs can activate T cells that bind to the antigen-MHC complex. 8. How does the function of helper T cells differ from the function of cytotoxic T cells? Helper T cells activate other immune cells, such as B cells. Cytotoxic T cells destroy infected cells. 9. What do B cells do? B cells help produce antibodies, which help the body fight a specific pathogen. (Specifically, activated B cells differentiate into plasma cells that produce antibodies.) 10. Do antibodies affect the function of the innate immune response in any way? If so, how? Students may indicate that phagocytes (which are part of the innate immune response) engulf pathogens bound to antibodies. Antibodies also activate complement proteins. PART 3: VACCINES 11. Draw a graph showing what the primary immune response would look like if this person had been vaccinated against the pathogen. Include the relative amounts of pathogen, innate immune cells, adaptive immune cells, and antibodies. In general, students’ graphs should resemble the graph of the secondary immune response in Figure 1. An example is shown below. PART 4: USING THE IMMUNE SYSTEM IN A CANCER TREATMENT 12. Which type of T cell would you expect to attack the cancer cells after being activated by sipuleucel-T? Cytotoxic T cells The Immune System 13. Which other types of immune cells would you expect to be activated and recognize the PAP antigen? Helper T cells and B cells 14. For each type of cell you listed in Questions 12 and 13, briefly explain how it might help destroy the prostate cancer cells. Cytotoxic T cells could recognize the PAP antigen and then kill the cancer cells producing it. Helper T cells could recognize the PAP antigen and activate B cells, which could help generate antibodies to the PAP antigen. 15. Some news articles refer to sipuleucel-T as a “cancer vaccine.” Students’ answers will vary and may include some of the points below. a. How is sipuleucel-T similar to a typical vaccine against a pathogen? Both sipuleucel-T and a typical vaccine cause an immune response to a specific antigen. Both responses involve antigen-presenting cells, the activation of T cells and B cells, and the creation of memory cells. b. How does sipuleucel-T differ from a typical vaccine? Typical vaccines include only an antigen, not antigen-presenting cells like in sipuleucel-T. For typical vaccines, the antigen is also from a different organism (the pathogen) rather than from cells in the body like in sipuleucel-T. 16. The thymus removes all immune cells that recognize self-antigens. So why would a prostate cancer patient have immune cells that recognize the PAP antigen? The PAP antigen is an abnormal protein produced only by prostate cancer cells. Since it is not produced by “normal” noncancer cells, it is not treated as a self-antigen. You may want students to know that T cell development and selection in the thymus occurs early in an individual’s life, most likely before they have any prostate cancer cells. So, the PAP antigen would not be present among the antigens for which T cells are selected against in the thymus.