PCB3233 Immunology Exam 3 Comprehensive Quiz 2026 – UCF
1. Which molecule is responsible for presenting endogenous antigens to CD8+ T
cells?
A. Toll-like receptor
B. MHC Class II
C. B-cell receptor
D. MHC Class I
Answer: D
Rationale: MHC Class I molecules present peptides derived from the cytosol (endogenous)
to CD8+ cytotoxic T cells.
2. Which of the following is the primary cytokine that drives the differentiation
of naive T cells into Th1 cells?
A. IL-4
B. IL-10
C. IL-12
D. TGF-beta
Answer: C
Rationale: IL-12, produced by dendritic cells and macrophages, is the major inducer of Th1
differentiation.
,3. The process of ‘negative selection’ in the thymus ensures that:
A. T cells can recognize MHC molecules
B. T cells that react too strongly to self-antigens are eliminated
C. T cells differentiate into CD4 or CD8 lineages
D. B cells produce high-affinity antibodies
Answer: B
Rationale: Negative selection eliminates self-reactive thymocytes to maintain central
tolerance.
4. Which enzyme is essential for both Somatic Hypermutation (SHM) and Class
Switch Recombination (CSR)?
A. RAG-1
B. RAG-2
C. Activation-Induced Deaminase (AID)
D. Artemis
Answer: C
Rationale: AID is the critical enzyme that initiates DNA lesions required for both SHM and
CSR in B cells.
5. What is the role of the Invariant Chain (Ii) in MHC Class II processing?
A. It transports MHC II to the cell surface
B. It degrades extracellular proteins
C. It prevents premature peptide binding in the ER
D. It activates the proteasome
Answer: C
Rationale: The invariant chain blocks the peptide-binding groove of MHC II in the ER,
preventing it from binding endogenous peptides.
, 6. Which of the following cells are the main source of IL-4, IL-5, and IL-13?
A. Th1 cells
B. Th17 cells
C. Th2 cells
D. Cytotoxic T cells
Answer: C
Rationale: Th2 cells specialize in producing cytokines that promote humoral immunity
and anti-parasitic responses.
7. The ‘Signal 2’ required for T-cell activation is provided by the interaction
between:
A. CD28 and B7 (CD80/86)
B. CD4 and MHC II
C. TCR and MHC
D. CD40 and CD40L
Answer: A
Rationale: Costimulation (Signal 2) occurs when CD28 on the T cell binds to B7 molecules
on the Antigen Presenting Cell.
8. Which complement component is known as the ‘potent opsonin’?
A. C3a
B. C3b
C. C5a
D. C9
Answer: B
Rationale: C3b binds covalently to pathogen surfaces, tagging them for phagocytosis by
cells with complement receptors.
1. Which molecule is responsible for presenting endogenous antigens to CD8+ T
cells?
A. Toll-like receptor
B. MHC Class II
C. B-cell receptor
D. MHC Class I
Answer: D
Rationale: MHC Class I molecules present peptides derived from the cytosol (endogenous)
to CD8+ cytotoxic T cells.
2. Which of the following is the primary cytokine that drives the differentiation
of naive T cells into Th1 cells?
A. IL-4
B. IL-10
C. IL-12
D. TGF-beta
Answer: C
Rationale: IL-12, produced by dendritic cells and macrophages, is the major inducer of Th1
differentiation.
,3. The process of ‘negative selection’ in the thymus ensures that:
A. T cells can recognize MHC molecules
B. T cells that react too strongly to self-antigens are eliminated
C. T cells differentiate into CD4 or CD8 lineages
D. B cells produce high-affinity antibodies
Answer: B
Rationale: Negative selection eliminates self-reactive thymocytes to maintain central
tolerance.
4. Which enzyme is essential for both Somatic Hypermutation (SHM) and Class
Switch Recombination (CSR)?
A. RAG-1
B. RAG-2
C. Activation-Induced Deaminase (AID)
D. Artemis
Answer: C
Rationale: AID is the critical enzyme that initiates DNA lesions required for both SHM and
CSR in B cells.
5. What is the role of the Invariant Chain (Ii) in MHC Class II processing?
A. It transports MHC II to the cell surface
B. It degrades extracellular proteins
C. It prevents premature peptide binding in the ER
D. It activates the proteasome
Answer: C
Rationale: The invariant chain blocks the peptide-binding groove of MHC II in the ER,
preventing it from binding endogenous peptides.
, 6. Which of the following cells are the main source of IL-4, IL-5, and IL-13?
A. Th1 cells
B. Th17 cells
C. Th2 cells
D. Cytotoxic T cells
Answer: C
Rationale: Th2 cells specialize in producing cytokines that promote humoral immunity
and anti-parasitic responses.
7. The ‘Signal 2’ required for T-cell activation is provided by the interaction
between:
A. CD28 and B7 (CD80/86)
B. CD4 and MHC II
C. TCR and MHC
D. CD40 and CD40L
Answer: A
Rationale: Costimulation (Signal 2) occurs when CD28 on the T cell binds to B7 molecules
on the Antigen Presenting Cell.
8. Which complement component is known as the ‘potent opsonin’?
A. C3a
B. C3b
C. C5a
D. C9
Answer: B
Rationale: C3b binds covalently to pathogen surfaces, tagging them for phagocytosis by
cells with complement receptors.
