Immunology MCQs: Hypersensitivity, Autoimmunity, Transplantation, and Immunodeficiency (With Answers)

Fifteen multiple choice questions (plus three bonus questions) with answers and explanations on clinical immunology: the four types of hypersensitivity, autoimmune disease, blood transfusion, transplantation and graft types, and immunodeficiency including HIV and AIDS. Write down your answers first, then check them against the key at the end.

1. Pollen would most likely evoke which type of hypersensitivity response?
a. Cytotoxic (type II)
b. Immune complex (type III)
c. Cell-mediated (type IV)
d. Immediate type (type I)
e. Latent (type V)

2. Which hypersensitivity reactions are T cell-mediated?
a. Type I
b. Type II
c. Type III
d. Type IV
e. None of these

3. Which of the following binds to mast cells and cross-links, resulting in degranulation and release of histamine?
a. IgM
b. IgA
c. IgG
d. Interleukins
e. IgE

4. Theoretically, type __ blood can be donated to all persons because it lacks __
a. O / antigens
b. AB / antibodies
c. A / antibodies
d. O / antibodies
e. A / IgE

5. Type II hypersensitivity is due to:
a. IgE
b. Activation of cytotoxic T cells
c. Pollen
d. IgM
e. Mismatched blood types in transfusion

6. Production of autoantibodies may be due to:
a. Emergence of mutant clones of B cells
b. Production of antibodies against sequestered (hidden) tissues
c. Genetic factors
d. All are possible
e. None of these

7. A positive tuberculin test is an example of:
a. Type I hypersensitivity
b. Delayed type hypersensitivity
c. Acute contact dermatitis
d. Eczema
e. Pollen allergic response

8. Rheumatoid arthritis is an __ disease that affects the __
a. Allergic / cartilage
b. Autoimmune / nerves
c. Autoimmune / joints
d. Immunodeficiency / muscles
e. Allergic / muscles

9. Contact with poison ivy would elicit which type of hypersensitivity reaction?
a. Type III
b. Type I
c. Type II
d. Type IV
e. Type V

10. A tissue graft between two people who are not genetically identical is termed a. Isograft
b. Heterograft
c. Xenograft
d. Autograft
e. Allograft

11. An example of type III immune complex disease is:
a. Contact dermatitis
b. Graft rejection
c. Serum sickness
d. Atopy
e. Allergies

12. Graft-versus-host disease results when the recipient lacks or has a poor immune system, and the donor organ and recipient express different:
a. HLA
b. T cells
c. Antibodies
d. Autoantibodies
e. Interleukins

13. Agammaglobulinemia is an immunodeficiency disease due to a deficiency in:
a. T cells
b. MHC
c. IgE
d. Cytokines
e. B cells

14. Which disease would be most similar to AIDS in its pathology?
a. SCID
b. DiGeorge syndrome
c. Agammaglobulinemia
d. ADA deficiency
e. Kuru

15. Human immunodeficiency virus (HIV) binds specifically to which immune cell marker?
a. CD8
b. MHC
c. CDC
d. CD4
e. gp120

Bonus questions

Bonus 1. HIV has a high mutation rate due to the imprecise operation of its:
a. Viral membrane
b. CD4 receptor
c. Reverse transcriptase
d. Protease
e. Dismutase

Bonus 2. Which of the following is considered an autoimmune disease?
a. Rheumatoid arthritis
b. AIDS
c. SCID
d. Agammaglobulinemia
e. CJD

Bonus 3. A transplant between individuals of different animal species is termed a:a. Allograft
b. Isograft
c. Enterograft
d. Endograft
e. Xenograft

Answer key

1. d. Immediate type (type I)
2. d. Type IV
3. e. IgE
4. a. O / antigens
5. e. Mismatched blood types in transfusion
6. d. All are possible
7. b. Delayed type hypersensitivity
8. c. Autoimmune / joints
9. d. Type IV
10. e. Allograft
11. c. Serum sickness
12. a. HLA
13. e. B cells
14. b. DiGeorge syndrome
15. d. CD4

Bonus

1. c. Reverse transcriptase Bonus
2. a. Rheumatoid arthritis Bonus
3. e. Xenograft

Why these are the answers

1. Immediate type (type I). Pollen is a classic environmental allergen, and inhaled allergens trigger type I (immediate) hypersensitivity: the allergen cross-links IgE bound to mast cells, which degranulate within minutes and release histamine, causing the sneezing and runny nose of hay fever. The other types operate by different mechanisms and time courses. See the article on Type I Hypersensitivity.

2. Type IV. Type IV hypersensitivity is the only one that is cell-mediated rather than antibody-mediated. It is driven by T cells (and the macrophages they activate) and is delayed, taking a day or two to appear. Types I, II, and III are all antibody-mediated. Read more about Types of Hypersensitivity in this article.

3. IgE. IgE is the antibody of allergy. Its Fc region binds high-affinity receptors on mast cells and basophils; when allergen cross-links two adjacent IgE molecules, the cell degranulates and releases histamine and other mediators. The other immunoglobulins do not perform this mast-cell-triggering role.

4. O / antigens. Type O red cells lack the A and B surface antigens, so they do not provoke anti-A or anti-B antibodies in the recipient, which is why type O is the theoretical universal red-cell donor. The key idea is that it is the absence of antigens on the donor cells (not antibodies) that makes them broadly compatible.

5. Mismatched blood types in transfusion. Type II hypersensitivity is antibody-mediated cytotoxicity, where antibody binds antigens on a cell surface and marks the cell for destruction. A mismatched blood transfusion is the classic example: recipient antibodies attack the donor red cells. IgE-driven allergy is type I, and cytotoxic-T-cell action is type IV.

6. All are possible. Autoantibodies can arise in several ways: mutant B-cell clones that escape tolerance, exposure of normally hidden (sequestered) self-antigens after injury, and inherited genetic susceptibility. Because each of these can contribute, the inclusive answer is correct; autoimmunity usually has more than one route.

7. Delayed type hypersensitivity. A positive tuberculin (Mantoux) skin test is the textbook example of delayed (type IV) hypersensitivity: sensitized T cells react to the injected tuberculin, and the firm red swelling develops over 48 to 72 hours, not immediately. It is not an immediate (type I) reaction or an allergic response in the type I sense.

8. Autoimmune / joints. Rheumatoid arthritis is a chronic autoimmune disease in which the immune system attacks the synovial joints, causing inflammation, pain, and progressive joint damage. It is not an allergic or immunodeficiency disorder, and its main target is the joints.

9. Type IV. Poison ivy causes allergic contact dermatitis, which is a delayed, T cell-mediated (type IV) reaction. The plant oil (urushiol) modifies skin proteins, sensitized T cells recognize them, and the itchy rash appears a day or two after contact. Despite involving the skin, it is not an immediate (IgE) reaction.

10. Allograft. An allograft is a graft between two genetically different members of the same species, the usual human-to-human transplant. An isograft is between genetically identical individuals (identical twins), an autograft is from one site to another in the same person, and a xenograft is between different species. "Heterograft" is not standard transplantation terminology.

11. Serum sickness. Type III hypersensitivity is caused by antigen-antibody (immune) complexes that deposit in tissues and trigger inflammation. Serum sickness, the reaction to foreign serum proteins, is the classic example. Contact dermatitis and graft rejection are type IV, and atopy and allergy are type I.

12. HLA. Graft-versus-host disease occurs when immunocompetent donor cells (for example in a bone marrow transplant) attack a recipient who cannot reject them, and the trigger is a difference in HLA (the human major histocompatibility antigens) between donor and recipient. The greater the HLA mismatch, the greater the risk. The other options are not the antigens that drive this mismatch.

13. B cells. Agammaglobulinemia (as in X-linked/Bruton agammaglobulinemia) is the near-absence of antibodies, and it results from failure of B cells to develop, since B cells and their plasma-cell descendants are the source of all antibody. It is not a T-cell, MHC, or cytokine deficiency.

14. DiGeorge syndrome. AIDS is fundamentally a T-cell disease: HIV depletes CD4 helper T cells, crippling cell-mediated immunity. DiGeorge syndrome, caused by failure of thymic development, is also fundamentally a T-cell deficiency, so it most closely mirrors the pathology of AIDS among these options. SCID is a broader combined T-and-B-cell defect, agammaglobulinemia is a B-cell defect, and Kuru is a prion disease, so none matches the selective T-cell loss of AIDS as closely as DiGeorge does.

15. CD4. HIV enters cells by binding the CD4 molecule (with a coreceptor such as CCR5 or CXCR4), which is why it targets CD4 helper T cells and gradually destroys them. CD8 marks cytotoxic T cells, and gp120 is the viral protein that does the binding, not the host marker it binds to.

Bonus 1. Reverse transcriptase. HIV mutates rapidly because its reverse transcriptase, which copies the viral RNA into DNA, has no proofreading ability and makes frequent errors. This high mutation rate is a major reason HIV evades the immune response and develops drug resistance. The viral membrane, CD4 receptor, and protease do not generate this variability.

Bonus 2. Rheumatoid arthritis. Of the options, only rheumatoid arthritis is an autoimmune disease (immune attack on the joints). AIDS, SCID, and agammaglobulinemia are immunodeficiencies (too little immune function, not misdirected function), and CJD is a prion disease.

Bonus 3. Xenograft. A transplant between different species is a xenograft (for example, a pig heart valve into a human). An allograft is within a species, an isograft is between identical twins, and "enterograft" and "endograft" are not species-based transplant terms.