PCB 3233 Exam 3 V3 | PCB 3233
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 3) | University of Central
Florida
1. During T-cell development in the thymus, which process ensures that maturing T cells are
restricted to recognizing self-MHC molecules?
A. Negative selection
B. Somatic hypermutation
C. Positive selection
D. Isotype switching
Answer: C
Rationale: Positive selection occurs in the thymic cortex and involves the interaction of
double-positive thymocytes with cortical epithelial cells expressing MHC. This process
selects for T cells that have a TCR capable of binding to self-MHC with moderate affinity. T
cells that fail to recognize self-MHC undergo apoptosis by neglect, ensuring the peripheral
T cell pool is MHC-restricted.
2. The enzyme Activation-Induced Cytidine Deaminase (AID) is essential for which of the
following B-cell processes?
A. V(D)J recombination
,B. Somatic hypermutation and class-switch recombination
C. Allelic exclusion
D. Light chain editing
Answer: B
Rationale: AID is specifically expressed in activated B cells within the germinal center of
secondary lymphoid organs. It functions by deaminating cytosine residues to uracil in the
DNA of immunoglobulin genes, leading to mutations or double-strand breaks. This
biochemical activity is the fundamental requirement for both affinity maturation and the
switching of antibody isotypes.
3. Which transcription factor is considered the ‘master regulator’ for the differentiation of
Th1 cells?
A. GATA-3
B. T-bet
C. RORgammat
D. FoxP3
Answer: B
Rationale: T-bet is induced by IL-12 and IFN-gamma signaling during the initial activation
of a naive CD4 T cell. It drives the expression of effector cytokines like IFN-gamma and
, enhances the cell’s ability to respond to intracellular pathogens. Without T-bet, T cells
cannot effectively polarize into the Th1 lineage, impairing macrophage activation.
4. A naive T cell requires ‘Signal 2’ to become fully activated. Which of the following
molecules provides this costimulatory signal?
A. MHC Class II
B. CD40
C. CD28
D. ICAM-1
Answer: C
Rationale: Signal 2 is provided by the interaction between CD28 on the T cell and B7
molecules (CD80/86) on the professional antigen-presenting cell. This interaction is
necessary to prevent anergy and promote the production of IL-2 for clonal expansion. In
the absence of this costimulation, TCR engagement alone leads to a state of long-term non-
responsiveness.
5. In the context of the B-cell coreceptor complex, which molecule is responsible for
recognizing C3d tagged antigens?
A. CD19
B. CD81
C. CD21 (CR2)
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 3) | University of Central
Florida
1. During T-cell development in the thymus, which process ensures that maturing T cells are
restricted to recognizing self-MHC molecules?
A. Negative selection
B. Somatic hypermutation
C. Positive selection
D. Isotype switching
Answer: C
Rationale: Positive selection occurs in the thymic cortex and involves the interaction of
double-positive thymocytes with cortical epithelial cells expressing MHC. This process
selects for T cells that have a TCR capable of binding to self-MHC with moderate affinity. T
cells that fail to recognize self-MHC undergo apoptosis by neglect, ensuring the peripheral
T cell pool is MHC-restricted.
2. The enzyme Activation-Induced Cytidine Deaminase (AID) is essential for which of the
following B-cell processes?
A. V(D)J recombination
,B. Somatic hypermutation and class-switch recombination
C. Allelic exclusion
D. Light chain editing
Answer: B
Rationale: AID is specifically expressed in activated B cells within the germinal center of
secondary lymphoid organs. It functions by deaminating cytosine residues to uracil in the
DNA of immunoglobulin genes, leading to mutations or double-strand breaks. This
biochemical activity is the fundamental requirement for both affinity maturation and the
switching of antibody isotypes.
3. Which transcription factor is considered the ‘master regulator’ for the differentiation of
Th1 cells?
A. GATA-3
B. T-bet
C. RORgammat
D. FoxP3
Answer: B
Rationale: T-bet is induced by IL-12 and IFN-gamma signaling during the initial activation
of a naive CD4 T cell. It drives the expression of effector cytokines like IFN-gamma and
, enhances the cell’s ability to respond to intracellular pathogens. Without T-bet, T cells
cannot effectively polarize into the Th1 lineage, impairing macrophage activation.
4. A naive T cell requires ‘Signal 2’ to become fully activated. Which of the following
molecules provides this costimulatory signal?
A. MHC Class II
B. CD40
C. CD28
D. ICAM-1
Answer: C
Rationale: Signal 2 is provided by the interaction between CD28 on the T cell and B7
molecules (CD80/86) on the professional antigen-presenting cell. This interaction is
necessary to prevent anergy and promote the production of IL-2 for clonal expansion. In
the absence of this costimulation, TCR engagement alone leads to a state of long-term non-
responsiveness.
5. In the context of the B-cell coreceptor complex, which molecule is responsible for
recognizing C3d tagged antigens?
A. CD19
B. CD81
C. CD21 (CR2)
