Immune System

Answers

1. The answer is b. (Murray, 5/e, p 93.) IgG makes up about 85% of the immunoglobulin in adult serum.

2. The answer is c. (Murray, 5/e, p 93.) Most of the antibody produced in a primary immune response is IgM. As time passes or at a second encounter with the same antigen, isotype (class) switching can occur.

3. The answer is d. (Murray, 5/e, p 93.) IgE is found on the surface of mast cells and basophils. When antigen binds to the IgE, the mast cell releases various mediators involved in allergic reactions and antiparasitic defense.

4. The answer is a. (Murray, 5/e, p 93.) IgA is the predominant immunoglobulin class in mucosal secretions such as saliva, colostrum, bronchial, and genitourinary tract secretions. It is often called secretory immunoglobulin.

5. The answer is b. (Murray, 5/e, p 93.) IgG can cross the placenta and confer passive immunity to the fetus and newborn.

6. The answer is c. (Murray, 5/e, p 110-111.) Innate immunity involves antigen-nonspecific immune defense. Neutrophils circulate in the blood and can migrate into tissue to ingest and kill bacteria. Although T and B cells can augment the innate immune response, they become inactivated in an antigen-specific manner. Eosinophils, also part of the innate immune response, are important in parasitic, rather than bacterial, infections.

7. The answer is e. (Fauci, 14/e, p 1767.) Dendritic/Langerhans cells are the most potent and effective antigen-presenting cells (APC). The other cells do not possess as effective an antigen-presenting capability.

8. The answer is a. (Murray, 5/e, p 86.) The major cell type within follicles is the B cell; a germinal center is a follicle where cells are undergoing active proliferation. A deficiency in B cells would result in decreased size and number of follicles. The paracortex is predominately a T cell area. Heinz bodies (red cell inclusion body of denatured hemoglobin) and Howell-Jolly bodies (red cell inclusion body of parasites) are found in the spleen.

9. The answer is a. (Roitt, 5/e, p 168.) A normal newborn can make IgM antibody in response to challenge with antigen. If IgG is detected in the newborn, it is most likely the result of placental transfer from the mother.

10. The answer is d. (Fauci, 14/e, p 358.) Eosinophils are associated with invasive parasitic infections. They localize near the parasite, degranulate, and release antiparasitic molecules. Eosinophils do not exhibit any effective function against intracellular bacteria or virus, which reside within host cells, or mycoplasma. Neutrophils are usually associated with extracellular bacterial infections.

11. The answer is b. (Roitt, 5/e, p 168.) The fetus and newborn infant can only produce measurable IgM antibody in response to infection. If IgG is detected, it is the result of an immune response by the mother and the antibody has crossed the placenta.

12. The answer is d. (Murray, 5/e, p 88, 121.) Usually an immunogen contains more than one molecule that can elicit an antibody response. These different molecules are called epitopes (or antigenic determinants) and are the structures with which antibodies react. Isotypes refer to the different classes of immunoglobulins (e.g., IgM, IgG, and IgA). Allotypes refer to isotypes that differ among individuals within a species. Adjuvants are substances that can enhance an immune response to antigen. Alleles are variations of a gene.

13. The answer is c. (Murray, 5/e, pp 98-99.) The cleavage component of C3, C3b, when bound to the surface of a cell, promotes the phagocytosis of that cell by a process referred to as opsonization.

14. The answer is e. (Murray, 5/e, pp 98-99.) Complement components C5b, 6, 7, 8, and 9 associate to generate the membrane attack complex (MAC) that disrupts the integrity of the cell membrane on which it is formed.

15. The answer is d. (Murray, 5/e, pp 98-99.) Several complement cleavage products promote inflammatory responses: C3a, C4a, and C5a. They can also induce the degranulation of mast cells and so are also referred to as anaphylatoxins. C5a has the additional property whereby it is a neutrophil-chemoattracting substance.

16. The answer is a. (Murray, 5/e, pp 98-99.) The classical pathway is initiated by antigen-antibody complexes. Binding of C1 to the complex activates the complement cascade.

17. The answer is a. (Fauci, 14/e, pp 911-912.) Patients with a familial deficiency in the terminal complement components fail to assemble the membrane attack complex (C5-C9), and they are at risk for disseminated Neisseria infections, including attacks of recurrent meningococcal disease. The other components of the complement system do not play a role in this unique susceptibility.

18. The answer is d. (Fauci, 14/e, p 1771.) Individuals with C3 deficiency have recurrent serious pyogenic bacterial infections that can be fatal. The absence of C3 leads to the inability to generate the opsonin, C3b, which, when deposited on the surface of the bacteria, promotes phagocytosis. Membrane attack complex deficiencies can lead to disseminated Neisseria infections. A deficiency in C1 inhibitor is associated with hereditary angioneurotic edema (HANE). Individuals with C2 deficiency have a predisposition for immune complex disease such as systemic lupus erythe-matosus.

19. The answer is c. (Murray, 5/e, p 98.) C3 plays a central role in both the classical and alternate pathways. An abnormality in this component would disrupt both pathways. C1 and C2 are used only by the classical pathway; therefore, an abnormality in either one or both of these components would leave the alternate pathway intact. Likewise, a defect in factor B (a component of the alternate pathway) would still permit the activation of the classical pathway.

20. The answer is e. (Murray, 5/e, pp 128-129.) Because the boy received his booster within the last 2 years, his level of immunity should be adequate. If an individual has no history of immunization, both antitoxin (passive immunization with tetanus immune globulin) for temporary and fast protection and toxoid (toxin detoxified with formaldehyde) for future and long-lasting protection should be given at different sites.

21. The answer is a. (Fauci, 14/e, p 877.) A superantigen can activate T cells without binding to the T cell receptor in an antigen-specific manner. Therefore, the superantigen can stimulate a large number of T cells, which can result in massive cytokine release, causing shock and tissue damage. An antigen that can activate B cells without T cell help is called a T-independent antigen. Haptens, usually small molecules, can become antigenic when attached to carrier proteins. Adjuvants can help in maintaining antigen at a tissue site. It does not evoke IgE, which is found in allergic reactions.

22. The answer is b. (Fauci, 14/e, p 1070.) During infection by enveloped viruses, antibody is produced, which reacts with the surface gly-coproteins to neutralize the virus. Neutralizing antibody does not react with the other components of the virus. Usually, neutralizing (or protective) antibody is formed to surface components of the virus and not internal components.

23. The answer is a. (Murray, 5/e, p 119.) CD8-positive T cells are cytolytic T cells that can respond to viral peptides/MHC class I complexes on infected cells. CD4-positive T helper 1 cells usually function by releasing cytokines that promote an inflammatory response. CD4-positive T helper 2 cells produce cytokines important in generating antibody production. Plasma cells secrete antibody CD19-positive B cells regulate B cell activation.

24. The answer is c. (Murray, 5/e, p 114.) Delayed type hypersensitivity (DTH) responses are important in protection against intracellular bacteria. In this type of response, macrophages and other inflammatory processes are activated to kill the infected cell. NK cells, cytotoxic T cells, and complement do not seem to provide adequate protection against intracellular bacteria. Eosinophilia occurs in allergy reactions.

25. The answer is c. (Fauci, 2/e, pp 1090-1091, 1754-1755.) Burkitt's lymphoma is a B cell neoplasm associated with Epstein-Barr virus (EBV) infection in about 15% of the disease in the United States and about 90%

of the disease in Africa. Hodgkin's disease and histiocytosis X are monocyte neoplasms, and non-Hodgkin's lymphoma and acute lymphoblastic leukemia are T cell neoplasms.

26. The answer is a. (Murray, 5/e, p 87.) M cells deliver antigen to Peyer's patches, but they do not act as antigen-presenting cells to lymphocytes. Antibody is made by B cells within the Peyer's patch. T helper 2 cells are the main source of cytokines functioning in helping B cells make and secrete antibody.

27. The answer is b. (Murray, 5/e, pp 147, 149.) ELISA can be used to determine the relative antibody concentration to a specific antigen (titer); the assay can also be used to quantitate antibody.

28. The answer is d. (Roitt, 5/e, pp 322-324.) An indirect Coombs' test is used to detect circulating anti-Rh antibody: anti-Rh antibody reacts with Rh+ erythrocytes causing agglutination of the erythrocytes. The direct Coombs' tests for cell-bound anti-Rh antibody.

29. The answer is a. (Murray, 5/e, pp 146, 147.) In flow cytometry, cells in suspension tagged with fluorescent-labeled antibody can be identified and quantitated.

30. The answer is e. (Roitt, 5/e, pp 361-362.) A mixed lymphocyte reaction assays the histocompatibility between two individuals. Donor cells are treated to prevent DNA synthesis and proliferation. The recipient's cells are mixed with the donor's cells. If the donor's cells express foreign MHC antigens, the recipient's lymphocytes will proliferate. Proliferation can be measured by the uptake of radioactive thymidine.

31. The answer is c. (Murray, 5/e, pp 145, 195.) In a latex agglutination test, antigen-specific antibody is attached to latex beads. When the beads are mixed with a specimen containing antigen, the beads agglutinate, which can be detected visually.

32. The answer is b. (Murray, 5/e, pp 123-124.) The hypersensitivity reaction in Goodpasture's syndrome is type II in which antibody mediates cell lysis. Antiglomerular basement membrane antibody is cytotoxic. In

Goodpasture's syndrome, antibody forms to lung and kidney basement membranes causing damage to the tissue.

33. The answer is c. (Murray, 5/e, pp 123-125.) Serum sickness results from the injection of serum made in non-human species into humans. Antibody to the soluble nonhuman proteins are generated and immune complexes form. The complexes are trapped in capillaries and initiate an inflammatory response that causes damage to tissue.

34. The answer is d. (Murray, 5/e, p 125.) Antigen injected intrader-mally into a previously sensitized individual elicits a delayed type hyper-sensitivity response. This involves the recruitment of CD4+ T lymphocytes and macrophages to the site.

35. The answer is d. (Murray, 5/e, p 125.) Poison ivy, an allergic contact dermatitis, is a delayed hypersensitivity reaction mediated by CD4+ T lymphocytes in the skin.

36. The answer is a. (Murray, 5/e, p 123.) Anaphylaxis is a severe immediate hypersensitivity response. IgE, produced at the time of initial exposure to antigen (bee venom), binds to mast cells. On subsequent exposure, the antigen (bee venom) reacts with the mast cell-bound IgE, leading to the release of mediators from the mast cells. The mediators produce the symptoms associated with the anaphylactic reaction.

37. The answer is b. (Murray, 5/e, pp 123-124.) This is a cytotoxic hypersensitivity reaction in which IgG anti-Rh antibody, produced in a previous pregnancy, crosses the placenta and binds to Rh+ fetal red blood cells. This triggers the classical complement pathway leading to the lysis of the fetal red cells.

38. The answer is c. (Murray, 5/e, pp 123-124,195.) Complexes of bacterial antigen and antibody form and become trapped in the renal vasculature. Complement is activated and neutrophils are recruited to the site. During the process of removal of the immune complexes, tissue damage may occur.

39. The answer is a. (Murray, 5/e, pp 126-127.) Individuals with T cell deficiencies are susceptible to infections with microbes that reside within host cells (virus, Mycobacterium species, and fungi). Humoral immune deficiency or complement deficiency usually results in recurrent bacterial, rather than viral, infections. Granulocyte deficiency may also result in bacterial and yeast infections. Because the statement indicates that the patient has problems with viral infections, the best answer is a deficiency in T cell immunity.

40. The answer is b. (Murray, 5/e, p 123.) Graft versus host (GVH) disease can develop in an immunosuppressed individual who receives immu-nocompetent donor cells. The donor cells respond to histocompatibility antigens present on the recipient's cells, which are NOT found on the donor cells. Bone marrow contains immunocompetent T cells; liver, kidney, and skin do not have a sufficient number of immunocompetent T cells to elicit GVH reactions. Corneal transplants do not evoke GVH.

41. The answer is b. (Murray, 5/e, p 81.) IL-2 acts on T cells to induce their progression through the cell cycle; it also acts as a growth factor for B cells.

42. The answer is d. (Murray, 5/e, p 81.) TNF-a activities depend partly on the quantity of cytokine produced. TNF-a is also associated with the production of IL-1 and IL-6. At low levels, it induces a local inflammatory effect by stimulating leukocyte recruitment. At moderate levels, it can have systemic effects, inducing fever and acute-phase protein synthesis within the liver. At high quantities, TNF-a (in conjunction with IL-1 and IL-6) can produce septic shock syndrome.

43. The answer is e. (Murray, 5/e, p 81.) TGF-0 seems to be a signal that "turns off" inflammatory or immune responses.

44. The answer is c. (Murray, 5/e, p 81.) IL-4 promotes the development of the T helper 2 subset of CD4+ T lymphocytes. It also is important for class switching to IgE.

45. The answer is a. (Murray, 5/e, p 81.) IFN-y acts on macrophages to enhance killing of ingested microbes. It also stimulates the cytolytic activity of NK cells.

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