Immunology MCQs (11-20): Answers with Explanations

11. Monoclonal antibodies are produced by:

a. Hybridomas

b. Lymphocytes

c. Myeloma cells

d. Plasma cells

12. 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

13. 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

14. An anamnestic response involves a/an:

a. Effector response

b. High intensity

c. Rapid memory

d. All of the above

15. Cell-associated differentiation antigens (CDs) are functional cell surface proteins or receptors that can be measured in situ.

a. Detecting these soluble molecules 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.

16. The first tenet of clonal selection theory relies SPECIFICALLY on:

a. Combinatorial joinings

b. Somatic mutations

c. Variations in the splicing process

d. B-cell clones

17. B-cells do which of the following?

a. Act as antigen-processing cells

b. Respond to antigens by making antibodies

c. Proliferate and differentiate into plasma cells

d. All of the above

18. 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

19. 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

20. 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 & Explanations

**11. Correct Answer: a (Hybridomas)**

• Explanation: Monoclonal antibodies are produced using hybridoma technology. A hybridoma is an immortal, engineered cell line created by fusing a specific, antibody-producing splenocyte (plasma B cell) with an un-programmed cancerous B cell (myeloma cell). This combined cell line yields identical antibodies with uniform antigen specificity indefinitely.

**12. Correct Answer: c (Coating of microorganisms or other particles by antibody and/or complement)**

• Explanation: Opsonization is an enhancement mechanism for phagocytosis. Receptors on professional phagocytes (like neutrophils and macrophages) recognize specific tag molecules—such as the Fc portion of IgG antibodies or the complement fragment C3b—bound to the surface of an invading pathogen, vastly accelerating engulfment and destruction.

**13. Correct Answer: b (Human Chorionic Gonadotropin (HCG))**

• Explanation: Rapid immunochromatographic pregnancy tests utilize targeted antibodies to identify the presence of Human Chorionic Gonadotropin (HCG) in a urine or blood sample. HCG is a hormone synthesized by the developing syncytiotrophoblast cells of the placenta shortly after embryonic implantation.

**14. Correct Answer: d (All of the above)**

• Explanation: An anamnestic response is another term for a secondary immune response. Because the immune system relies on pre-established memory cells generated during primary contact, the response to a repeat antigen exposure is characterized by a rapid memory phase, significantly higher intensity (elevated IgG tiers), and a rapid, highly effective effector response.

**15. Correct Answer: a (Detecting these soluble molecules may help in the management of disease)**

• Explanation: While "Cluster of Differentiation" (CD) markers are typically surface-bound proteins (like CD4 or CD8), some can be shed or secreted as soluble molecules into serum during intense immune activity. Tracking these soluble markers can serve as vital clinical biomarkers to monitor disease progression or therapy responses. Statement b is not absolute across all clinical statuses, and statement c is incorrect because roughly 400 CD markers have been formally characterized, not thousands.

**16. Correct Answer: d (B-cell clones)**

• Explanation: The definitive core premise of Frank Macfarlane Burnet's clonal selection theory is that individual lymphocytes express unique antigen receptors before encountering any foreign agent. Once a matching antigen enters the system, it selectively activates that pre-existing, distinct cell line, driving the proliferation of highly specific B-cell clones to combat that exact pathogen.

**17. Correct Answer: d (All of the above)**

• Explanation: B lymphocytes are multifunctional components of adaptive immunity. They act as professional antigen-presenting cells (APCs) by internalizing and presenting peptide fragments via MHC-II to T helper cells. Concurrently, they respond directly to foreign antigens through their B-cell receptors (BCRs), driving clonal expansion and final differentiation into antibody-secreting plasma cells.

**18. Correct Answer: d (The manipulation of the immune response)**

• Explanation: While monoclonal antibodies are widely used as specialized diagnostic tools—such as immunophenotyping for leukemia classification, locating tumor markers, or diagnosing microbial pathogens via ELISA—they are not routinely used for general manipulation or redirection of the host's broad native immune response.

**19. Correct Answer: c (MHC class III molecules)**

• Explanation: Unlike Major Histocompatibility Complex (MHC) classes I and II, MHC class III molecules do not express structure capable of binding and presenting antigen fragments to T-cell receptors. Instead, the MHC class III locus encodes various soluble inflammatory proteins, including specific complement components (such as C2, C4, and Factor B) and tumor necrosis factors (TNF).

**20. Correct Answer: a (MHC class I molecules)**

• Explanation: Human Leukocyte Antigen (HLA) typing before a solid organ transplant focuses heavily on matching polymorphic MHC Class I (specifically HLA-A, HLA-B, and HLA-C) and MHC Class II (HLA-DR) alleles between the donor and recipient to reduce the risk of T-cell mediated acute allograft rejection. While your traditional key notes option "a" as the primary answer focus due to cross-matching assays checking for pre-formed anti-HLA antibodies against Class I targets, modern clinical tissue typing platforms generally assess both Class I and Class II loci carefully.