Microbiology 532 Immunology Examination key october 17, 1997 All questions have equal point value. Scenario I



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Microbiology 532

Immunology Examination KEY

October 17, 1997
All questions have equal point value.
SCENARIO I
You are the dental public health official in the new country of Edentia and it is your responsibility to improve the state of dental health in your country. You decide to immunize the entire population with a new caries vaccine that has recently been developed against a carbohydrate antigen of Strep. causealotofcaries, the etiologic agent of caries in your country. After six months of intense immunization (a lot of booster shots), you find that the caries rate has been eliminated in all of the inhabitants, with the exception of those with type A blood. You now have to figure out the reason for this mystery.
Multiple Choice (choose the best answer)

A 1. You develop an agglutination assay using the carbohydrate antigen from Strep. causealotofcaries. The assay indicates that only the blood type B and O subjects are producing antibodies against the carbohydrate antigen. What do you suspect?

a. The carbohydrate antigen may be similar to the A blood group antigen.

b. The carbohydrate antigen may be similar to the B blood group antigen.

c. The carbohydrate antigen may be similar to the O blood group antigen.

d. The carbohydrate antigen may be similar to the AB blood group antigen.

e. None of the above.



D 2. You develop a precipitation assay to detect antibodies to Strep. causealotofcaries and it tells you that none of the subjects are producing antibodies against the carbohydrate antigen. What do you suspect?

a. The antibody providing protection is of the IgG class.

b. The antibody providing protection is of the IgA class.

c. The antibody providing protection is of the IgE class.

d. The antibody providing protection is of the IgM class.

e. None of the above.



D 3. Based on the results in questions 1 and 2, you develop an ELISA assay so that it detects only antibodies of the IgM class. How do you ensure that the assay detects only IgM antibodies?

a. Use a “second antibody” that only detects µ chains.

b. Use a “second antibody” that only detects kappa and lambda chains.

c. Use a “second antibody” that only detects gamma chains.

d. Use a “second antibody” that only detects the entire IgM molecule.

e. None of the above.



A 4. The ELISA assay indicates that all of the subjects make antibodies to the carbohydrate antigen. You are beginning to question whether immunity is a factor at all in protection against this microbe. You are convinced to keep looking and then you think that you need to look at the immunity directed to specific epitopes of the carbohydrate antigen. What made you think of this?

a. A specific epitope important in the microorganism’s adherence to host cells may not be recognized by all subjects’ immune systems.

b. In addition to antigen, other substances called epitopes may be recognized in certain individuals.

c. Antigenic determinants occur in all antigens, but epitopes are present only in carbohydrate antigens.

d. Only substances that cross-react with blood group substances are epitopes.

e. None of the above.



B 5. Your epitope-specific ELISA assay indicates that there is one epitope that is not recognized in the unprotected patients. Since this epitope is not recognized by the type A blood group patients, what do you suspect about the protective antibodies?

a. The protective antibodies are directed against this epitope which is probably part of the type B antigen.

b. The protective antibodies are directed against this epitope which is probably part of the type A antigen.

c. The epitope is probably associated with the H substance.

d. The epitope is probably associated with the RhD antigen.

e. None of the above.



D 6. Why do you think the type A blood group subjects don’t make a protective antibody against the vaccine?

a. There is a response but we can’t detect it.

b. Type A individuals are to hyper to mount a good immune response.

c. The IgM and IgG antibodies that are produced neutralize each other.

d. Because the important component is a “self” epitope, they are unable to recognize it immunologically.

e. None of the above.



B 7. In the protected subjects, there is no evidence of colonization of this microbe. How do you think that protective antibody is working?

a. The antibody activates innate host defense mechanisms.

b. The antibody probably blocks the epitope that is involved in the binding of the microorganism to the host.

c. The antibody neutralizes complement components that interfere with bacterial adherence.

d. All of the above

e. None of the above.



A 8. How would you reformulate the vaccine in order to protect the type A blood group subjects?

a. I would try to identify other epitopes important in microbial virulence that are recognized immunologically by all subjects regardless of blood type.

b. I would heat the vaccine to 56°C for 30 minutes to destroy tissue-fixing ability.

c. I would digest the vaccine with protease to remove all cross-reactive proteins.

d. I would just give up and accept the fact that they won’t be protected (you can’t pick this because you are dedicated to the protection of all).

e. None of the above.



D 9. Ten years following the first series of immunizations, your patients still appear to be resistant to caries. How do you explain this?

a. Someone has been secretly re-immunizing these folks every year (don’t pick this answer).

b. All of their teeth fell out and it is not possible to get any more caries (don’t pick this answer).

c. The initial series of immunizations induced immune paralysis.

d. Immunologic memory is maintaining protection.

e. None of the above.



D 10. Twenty years later you discover that the previously immunized subjects were also protected against several other completely unrelated microorganisms. How do you explain this?

a. The adjuvant induced a heightened innate protective response.

b. The immunizations resulted in autoreactive antibodies causing a protective type V hypersensitivity.

c. The immunizations resulted in passive immunity to these other microorganisms.

d. The unrelated microorganisms apparently share common epitopes and the antibodies are cross-reactive.

e. None of the above.


SCENARIO II
You have been asked to consult in a clinical diagnostic laboratory. The lab is trying to determine why its new antibody assay system is not accurately detecting protective antibodies in the sera of persons recently exposed to Bonga-Bonga fever virus. This is very frustrating to the laboratory since they had no problems until the FDA mandated that they discontinue using an agglutination assay. The new assay is a very sensitive radioimmunoassay. It has been telling them that everyone is making antibodies, regardless of exposure (or lack of exposure) to the Bonga-Bonga fever virus. The radioimmunoassay uses a “second antibody” made by immunizing rabbits with purified human IgM. It is imperative that we identify the truly unprotected individuals because we don’t have enough antiviral compounds to effectively treat all of the Bonga-Bonga fever-exposed subjects.

True/False (Please use “a” for true and “b” for false on your answer sheet)

T 11. Since agglutination assays favor the detection of IgM antibodies, the protective antibodies are probably of the IgM class.

T 12. The radioimmunoassay detects the primary interaction between antibody and antigen and is independent of precipitation or agglutination.

F 13. The “second antibody” in the radioimmunoassay is probably contributing to the problem since it reacts with all immunoglobulin heavy chains.

F 14. The “second antibody” is specific for IgM.

F 15. A precipitation assay might work better than the radioimmunoassay as a substitute for the agglutination assay because precipitation doesn’t require cross-linking of antigen and works better with IgM antibodies.
Non-SCENARIO Questions

T 16. The destructive activity of the complement system is limited to the location of its activation due to the short half-lives of the components and the presence of competitive inhibitors.

F 17. Antigen receptors on B cells have the same specificity as the antibody product that those cells will make once they have matured and differentiated to macrophages.

T 18. The major histocompatability complex-encoded proteins on the surface of antigen-presenting cells ensure proper presentation of antigenic peptides to the T-cell.

T 19. In order for cells to communicate with one another, one cell must have a receptor for the signal/soluble factor that the other cell is sending.

F 20. Innate host defense factors are generally not used unless the adaptive defenses fail.
SCENARIO III
You have been treating a periodontitis patient with high doses of a specific antibiotic for a period of several weeks. The gingival inflammation is considerably better and the suppuration has been eliminated, but now the patient complains of joint and skin pain. Because you suspect that the antibiotic is the villain, you suspend the antibiotic therapy. However, even weeks after, the patient continues to complain of joint and skin pain. You have a complete immunology laboratory at your disposal and you begin the evaluate the patient.

Multiple Choice (choose the best answer)

A 21. You suspect that the patient is experiencing serum sickness. You order a biopsy of the patient’s skin and you discover...

a. that the cellular infiltrate is primarily neutrophil.

b. that the cellular infiltrate is primarily plasma cell.

c. that the cellular infiltrate is primarily T-cell.

d. that the cellular infiltrate is primarily NK cell.

e. None of the above.



C 22. You do a renal function test and discover that the kidneys are not functioning to their full capacity. You believe that this is due to

a. blockage of the kidneys with eosinophils

b. the patient not drinking enough water.

c. damage to the kidney due to complement activation and neutrophil infiltration.

d. urinary tract infection.

e. None of the above.



A 23. After several weeks, the patient reports that his symptoms have disappeared. Out of curiosity you obtain a blood sample and find…

a. anti-antibiotic antibodies in the serum.

b. no anti-antibiotic antibodies in the serum.

c. immune complexes in the serum.

d. an old test question.

e. None of the above.



D 24. The antibiotic caused this problem in your patient because…

a. it had adjuvant properties.

b. it stimulated macrophages.

c. it shared a common epitope with a serum protein.

d. it bound to serum proteins and induced the formation of anti-drug antibodies the patient.

e. None of the above.



A 25. You administer the same drug with the same regimen to the patient several years later. What do you expect will happen?

a. Same thing, maybe faster due to the booster response.

b. Nothing, ‘cause lightning don’t strike twice in the same place.

c. Nothing, ‘cause the drug wasn’t the problem the first time.

d. I can’t make predictions, ‘cause there’s not enough information given.

e. None of the above.


Non-SCENARIO Questions

D 26. You have developed a compound that blocks the ability of a virus to adhere to the mucosal lining of the respiratory tract. It is effective in protecting you against a large number of viruses, but not all. What do you suspect?

a. It may induce antibodies to specific virus receptors.

b. It probably blocks the receptors of specific viruses, but some viruses use different receptors.

c. I don’t suspect anything.

d. A and B

e. None of the above.



D 27. You wish to prepare antibodies to an antigen which appears to be a very poor immunogen. You have repeatedly attempted to immunize a rabbit with this antigen and have had no success in raising any antibody. What do you try next to get this antibody?

a. I would try feeding the rabbit so he doesn’t die this time (don’t pick this).

b. I would try to activate the rabbit’s complement system.

c. I would try to find an atopic rabbit with abnormal immunity.

d. I would try using an adjuvant.

e. None of the above.



D 28. You have obtained a bottle of antibody from a colleague and find that the affinity of the antibody is too low to work in your assay. Having just learned about affinity maturation, you believe that like good wine, antibody gets better with time. You put the antibody in your wine cellar and retest the affinity a year later. What do you learn about the affinity of this antibody?

a. It has gotten better.

b. It has gotten worse.

c. It has turned blue.

d. It has not changed.

e. None of the above.



D 29. You suffer from atopic hypersensitivity and are told to use an antihistamine for your allergies. Why were you told to use antihistamines?

a. Histamine is a major component of the complement cascade.

b. Histamine is a product of the MHC.

c. Mast cells won’t degranulate in the absence of histamine.

d. Histamine is a substance released by mast cells casing many of the symptoms associated with allergies.

e. None of the above.



D 30. The long lag phase in the primary immune response is caused by…

a. earth, wind and fire.

b. hook, line and sinker.

c. Breakfast, lunch and dinner.

d. clonal selection, expansion and maturation.

e. None of the above


SCENARIO IV
The patient who just sat down in your chair tells you that she has no family history of atopy, but she thinks that she might be allergic to milk because she gets sick to her stomach whenever she drinks it. She has normal levels of IgE in her serum. You notice that there is an inflamed image of a watch on her wrist and when asked, she tells you that always happens when she wears cheap jewelry.
True/False (Please use “a” for true and “b” for false on your answer sheet)

F 31. It is likely that this patient has a predisposition to be atopic based on your knowledge of the family history.

F 32. It is likely that this patient has a predisposition to be atopic based on your knowledge of the serum IgE levels.

T 33. The inflammation associated with the watch is probably caused by contact hypersensitivity and mediated by sensitized T-cells.

T 34. Based on the information provided, there is no way to tell if the reaction that she has to milk is due to atopy.

T 35. It is likely that the reaction to the watch was a result of a hapten-carrier phenomenon.
Non-SCENARIO Questions

F 36. ABO blood group differences between mother and fetus do not cause problems because the naturally-occurring hemagglutinins are of the IgG class, which do not pass through the placental barrier.

T 37. The Arthus reaction occurs when specific antibody is present at high levels and a small amount of antigen precipitates at the site of local injection

T 38. The specificity of the natural killer cell for tumor cells and virally-infected cells is determined by its cell surface receptors.

F 39. Antibody-dependent cellular cytotoxicity is mediated by NK cells and is a result of complement receptors on their surface.

T 40. Programmed cell death is thought to be triggered by cytotoxic T-cells and results in the death of target cells.
SCENARIO V

It is your responsibility to manage a patient who has just received total body irradiation and chemotherapy to eliminate his leukemia. The treatment has destroyed all of his white cells and all precursor cells in his bone marrow. He has no immunity at all. This treatment was then followed by a bone marrow transplant from an unrelated, matched donor to reconstitute his bone marrow and immunity. The transplant appears to be successful (the white cell counts are returning to normal levels), but you notice that your patient is capable of mounting immune responses to viruses but not bacteria. You are asked to figure out what is going on.



Multiple Choice (choose the best answer)

A 41. You suspect that the immune system has not been fully reconstituted because…

a. immunity to bacteria, generally mediated by humoral immunity, is compromised, leading me to think that there is a problem with B cells.

b. antigen-presenting cell function appears to be absent.

c. immunity to viruses does not require T cell participation, thus you suspect a T-cell defect.

d. All of the above.

e. None of the above.



C 42. You decide to perform a FACS analysis on his blood cells to identify the cell populations that are actually present in his circulation. The fluorescent labeled antibodies that you use in the analysis are…

a. prepared against cell surface FM antigens allowing you to identify different white cell subpopulations.

b. prepared against cell surface complement antigens allowing you to identify different white cell subpopulation.

c. prepared against cell surface CD antigens allowing you to identify different white cell subpopulation.

d. All of the above.

e. None of the above.



D 43. The FACS analysis indicates that all of the expected T cell populations are present, but B cells are absent. To confirm this, you measure the level of which proteins in his serum?

a. Albumin

b. Cytokines

c. Transferrin

d. Immunoglobulin

e. None of the above.



D 44. Your suspicions regarding B cells are confirmed and you decide to provide passive immunity (from a horse) to protect this person from tetanus toxin. What do you expect will happen?

a. You will protect the patient from tetanus, but will induce serum sickness.

b. You will protect the patient from tetanus, but will induce Hashimoto’s thyroiditis.

c. You will not protect the patient from tetanus, but will induce serum sickness .

d. You will protect the patient from tetanus, but not induce serum sickness.

e. None of the above.



D 45. Several months later the patient begins to make B cells, but he can only make humoral immune responses to antigens against which the donor was exposed before the transplant. How do you interpret this observation?

a. The donor’s antigen presenting cells were transplanted, but they could only present antigens that were seen by the donor in the past.

b. The donor’s T cells were transplanted, but no antigen-presenting cells were present to permit immune responses to new antigens.

c. The donor’s megakaryocytes were transplanted, but no granulocytic cells to permit immune responses to new antigens.

d. The donor’s memory cells were transplanted, but no other precursor B cells were present to permit immune responses to new antigens.

e. None of the above.


NON-Scenario Questions

A 46. You administered a tuberculin test to a patient and the test was positive. You indicate to the patient that she must now get a chest x-ray to confirm the finding. Why can’t you tell that the patient has tuberculosis from the tuberculin test alone?

a. The tuberculin test indicates only that the person has sensitized T cells.

b. The tuberculin test indicates only that the person has sensitized B cells.

c. The tuberculin test indicates only that the person has sensitized NK cells.

d. The tuberculin test indicates only that the person has sensitized plasma cells.

e. None of the above.


B 47. How does the body define “self”?

a. All antigens encoded by the host’s genome.

b. Those antigens accessible and recognized by the developing immune system during the “inventory” process.

c. Only antigens encoded by the host’s genome

d. A and C

e. None of the above.



B 48. Why doesn’t the first exposure to an allergen induce an anaphylactic reaction in an atopic subject?

a. Histamine has not yet been put into the granules of the mast cells.

b. The mast cells have not yet been sensitized with IgE antibody.

c. The Fc receptors on the neutrophils have not yet bound sufficient antigen.

d. The Fc receptors on the neutrophils have not yet bound sufficient IgE.

e. None of the above.



B 49. What is the advantage of artificial active immunity over immunity derived from natural infection?

a. There is no advantage.

b. Immunity can be induced artificially prior to the infection, eliminating the lag phase which follows natural infection.

c. Artificial immunity is longer lasting.

d. Artificial immunity does not require adjuvants and occurs with lower antigen doses.

e. None of the above.



A 50. Stress has been demonstrated to have a negative influence on the immune system. This influence is probably mediated through the production of cytokines and other soluble factors. How can a relatively non-specific signal such as a cytokine influence specific types of cells?

a. Cells that are influenced by the so-called non-specific signal must have a receptor for that signal.

b. Cytokines are not non-specific and actually possess the same specificity as antibodies.

c. Non-specific signals such as hormones will only affect specific cells of a single system because there is no sharing of receptors between different cell types.

d. Communication between cell systems is mediated by antibodies and the presence of Fc receptors.

e. None of the above.






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