Immunology MCQs: Monoclonal Antibodies, MHC, and Antigen Presentation (With Answers)

Ten multiple choice questions with answers and explanations on monoclonal antibodies, opsonization, the major histocompatibility complex (MHC), antigen presentation, and clonal selection. Write down your answers first, then check them against the key at the end.

1. Monoclonal antibodies are produced by:
   a. Hybridomas
   b. Lymphocytes
   c. Myeloma cells
   d. Plasma cells
2. Opsonization refers to:
   a. Adherence to mucosal epithelial cells
   b. Antibody-mediated viral inactivation
   c. Coating of microorganisms or other particles by antibody and/or complement
   d. Parasitic lysosomal degranulation
3. Pregnancy tests detect the presence of which of the following?
   a. Rh
   b. Human chorionic gonadotropin (hCG)
   c. Fetal proteins
   d. Agglutination
   e. Depuration factor
4. An anamnestic response involves a/an:
   a. Effector response
   b. High intensity
   c. Rapid memory
   d. All of the above
5. Cell-associated differentiation antigens (CDs) are functional cell surface proteins or receptors. Which of the following is true?
   a. Detecting these molecules in soluble form may help in the management of disease
   b. In normal individuals the concentration of these molecules in serum is always low
   c. Thousands of CDs have been characterized
   d. All of the above are true
6. The first tenet of clonal selection theory relies specifically on:
   a. Combinatorial joining
   b. Somatic mutations
   c. Variations in the splicing process
   d. B-cell clones
7. B cells do which of the following?
   a. Act as antigen-presenting cells
   b. Respond to antigens by making antibodies
   c. Proliferate and differentiate into plasma cells
   d. All of the above
8. Monoclonal antibodies are routinely used in all of the following except:
   a. The classification of leukemias
   b. The identification and epidemiological study of infectious microorganisms c. The identification of tumor antigens
   d. The manipulation of the immune response
9. Which of the following does not play a role in antigen presentation?
   a. MHC class I molecules
   b. MHC class II molecules
   c. MHC class III molecules
   d. None of the above
10. Which of the following is used for typing when a patient is being prepared for an organ transplant?
    a. MHC class I molecules
    b. MHC class II molecules
    c. MHC class III molecules
    d. All of the above

Answer key

1. a. Hybridomas
2. c. Coating of microorganisms or other particles by antibody and/or complement
3. b. Human chorionic gonadotropin (hCG)
4. d. All of the above
5. a. Detecting these molecules in soluble form may help in the management of disease
6. d. B-cell clones
7. d. All of the above
8. d. The manipulation of the immune response
9. c. MHC class III molecules
10. d. All of the above

Why these are the answers

1. Hybridomas. Monoclonal antibodies are made by hybridoma technology: an antibody-producing plasma B cell is fused with an immortal myeloma (tumor) cell. The fusion combines the B cell's defined antibody specificity with the tumor cell's ability to divide forever, giving a cell line that secretes one identical antibody indefinitely. A plain plasma cell alone is short-lived, and a myeloma cell alone makes no useful specific antibody; it is the fusion that matters. Read more about Monoclonal Antibodies in this article.

2. Coating of microorganisms or other particles by antibody and/or complement. Opsonization is the tagging of a pathogen so that phagocytes engulf it more efficiently. The opsonins are usually the Fc portion of bound IgG and the complement fragment C3b, which coat the microbe; phagocytes carry receptors for both and grab the coated particle far more readily than a bare one. So opsonization is essentially "coating to promote phagocytosis."

3. Human chorionic gonadotropin (hCG). Pregnancy tests are immunoassays that use antibodies to detect hCG, a hormone produced by the placenta (the syncytiotrophoblast) soon after the embryo implants. Rising hCG in urine or blood is the signal these tests are built to catch. The other options are not what the test targets. Read more about pregnancy test in this article.

4. All of the above. An anamnestic response is another name for the secondary immune response, the reaction on re-exposure to an antigen already seen. Because memory cells are already in place, it is fast (rapid memory), strong (high intensity, with high antibody titers), and produces an effective effector response. All three descriptions apply. See more in Primary vs Secondary Immune Response article.

5. Detecting these molecules in soluble form may help in the management of disease. CD (cluster of differentiation) markers are mostly cell-surface proteins, but some are shed into serum as soluble forms during immune activity, and measuring those can serve as clinical biomarkers of disease activity or treatment response. Option b is too absolute (serum levels are not always low), and option c is wrong on the number: more than 400 CD markers have been characterized, not thousands.

6. B-cell clones. The core premise of Burnet's clonal selection theory is that each lymphocyte carries a unique antigen receptor before it ever meets an antigen. When a matching antigen appears, it selects and activates that specific pre-existing cell, driving it to proliferate into a clone of identical, antigen-specific cells. The other options (combinatorial joining, somatic mutation, splicing) are mechanisms that generate receptor diversity, but the defining first tenet is selection of pre-existing specific clones.

7. All of the above. B cells are multifunctional. They act as antigen-presenting cells, taking up antigen and displaying peptide fragments on MHC class II to helper T cells; they respond to antigen through their B-cell receptors by making antibody; and on activation they proliferate and differentiate into antibody-secreting plasma cells. All three are genuine B-cell functions.

8. The manipulation of the immune response. Monoclonal antibodies are workhorse diagnostic tools: they classify leukemias by immunophenotyping, identify and track infectious organisms, and detect tumor antigens. The question asks for the exception, and broad, routine "manipulation of the immune response" is not a standard diagnostic use in this sense. (Therapeutic monoclonals that modulate immunity do exist, but the question is contrasting routine diagnostic applications with general immune manipulation.)

9. MHC class III molecules. MHC class I and class II both present antigen: class I to cytotoxic (CD8) T cells, class II to helper (CD4) T cells. MHC class III is different, it does not present antigen at all. The class III region instead encodes soluble immune proteins, including complement components (C2, C4, factor B) and tumor necrosis factor. So class III is the one with no antigen-presenting role. Read more on MHC I vs MHC II article.

10. All of the above. HLA typing before an organ transplant matches donor and recipient at both MHC class I loci (HLA-A, HLA-B, HLA-C) and MHC class II loci (HLA-DR), because mismatches at either class drive rejection. HLA-A, HLA-B, and HLA-DR matching is the core of organ allocation, so typing covers both classes rather than class I alone. (MHC class III is not used for typing, as it does not carry the transplantation antigens.)