PCB 3233 Exam 3 V1 | PCB 3233
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 3) | University of Central
Florida
1. During T-cell development, which process ensures that maturing T cells are capable of
recognizing self-MHC molecules?
A. Negative Selection
B. Somatic Hypermutation
C. Positive Selection
D. Allelic Exclusion
Answer: C
Rationale: Positive selection occurs in the thymic cortex where double-positive
thymocytes interact with cortical epithelial cells. This process tests the ability of the TCR to
bind to self-MHC complexes with moderate affinity. If the T cell fails to recognize self-MHC,
it undergoes apoptosis by neglect.
2. What is the primary role of the AIRE (Autoimmune Regulator) protein in the thymus?
A. To allow expression of tissue-specific antigens for negative selection.
B. To facilitate the migration of progenitor cells from the bone marrow.
C. To induce the differentiation of Th17 cells.
,D. To promote the expression of RAG-1 and RAG-2 enzymes.
Answer: A
Rationale: AIRE is expressed in the medullary thymic epithelial cells (mTECs) and drives
the transcription of genes normally found only in peripheral tissues. This exposure allows
developing T cells to be screened against self-antigens not normally present in the thymus.
Defects in the AIRE gene lead to the autoimmune polyendocrinopathy-candidiasis-
ectodermal dystrophy (APECED) syndrome.
3. Which cytokine is primarily responsible for the differentiation of naive CD4 T cells into the
Th1 effector subset?
A. IL-4
B. IL-10
C. IL-5
D. IL-12
Answer: D
Rationale: IL-12, often produced by dendritic cells and macrophages, acts on naive T cells
to activate the STAT4 signaling pathway. This leads to the expression of the master
transcription factor T-bet, which defines the Th1 lineage. Th1 cells are characterized by
their production of IFN-gamma to activate macrophages.
, 4. Which enzyme is essential for both somatic hypermutation and class-switch recombination
in B cells?
A. Terminal deoxynucleotidyl transferase (TdT)
B. Artemis
C. DNA Ligase IV
D. Activation-induced cytidine deaminase (AID)
Answer: D
Rationale: AID functions by deaminating cytosine residues in DNA to uracil within the
variable and switch regions. This creates mutations or double-strand breaks that are
processed by DNA repair machinery. Without AID, patients develop Hyper-IgM syndrome
because they cannot diversify their antibody responses.
5. In the context of B cell activation, what is the role of Follicular Dendritic Cells (FDCs)?
A. To process and present antigens via MHC class II to T cells.
B. To phagocytose apoptotic B cells in the germinal center.
C. To secrete IL-2 for T cell proliferation.
D. To display intact antigens on their surface for B cell recognition.
Answer: D
Rationale: Unlike myeloid dendritic cells, FDCs are not hematopoietic in origin and do not
express MHC class II for antigen presentation. They use Fc receptors and complement
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 3) | University of Central
Florida
1. During T-cell development, which process ensures that maturing T cells are capable of
recognizing self-MHC molecules?
A. Negative Selection
B. Somatic Hypermutation
C. Positive Selection
D. Allelic Exclusion
Answer: C
Rationale: Positive selection occurs in the thymic cortex where double-positive
thymocytes interact with cortical epithelial cells. This process tests the ability of the TCR to
bind to self-MHC complexes with moderate affinity. If the T cell fails to recognize self-MHC,
it undergoes apoptosis by neglect.
2. What is the primary role of the AIRE (Autoimmune Regulator) protein in the thymus?
A. To allow expression of tissue-specific antigens for negative selection.
B. To facilitate the migration of progenitor cells from the bone marrow.
C. To induce the differentiation of Th17 cells.
,D. To promote the expression of RAG-1 and RAG-2 enzymes.
Answer: A
Rationale: AIRE is expressed in the medullary thymic epithelial cells (mTECs) and drives
the transcription of genes normally found only in peripheral tissues. This exposure allows
developing T cells to be screened against self-antigens not normally present in the thymus.
Defects in the AIRE gene lead to the autoimmune polyendocrinopathy-candidiasis-
ectodermal dystrophy (APECED) syndrome.
3. Which cytokine is primarily responsible for the differentiation of naive CD4 T cells into the
Th1 effector subset?
A. IL-4
B. IL-10
C. IL-5
D. IL-12
Answer: D
Rationale: IL-12, often produced by dendritic cells and macrophages, acts on naive T cells
to activate the STAT4 signaling pathway. This leads to the expression of the master
transcription factor T-bet, which defines the Th1 lineage. Th1 cells are characterized by
their production of IFN-gamma to activate macrophages.
, 4. Which enzyme is essential for both somatic hypermutation and class-switch recombination
in B cells?
A. Terminal deoxynucleotidyl transferase (TdT)
B. Artemis
C. DNA Ligase IV
D. Activation-induced cytidine deaminase (AID)
Answer: D
Rationale: AID functions by deaminating cytosine residues in DNA to uracil within the
variable and switch regions. This creates mutations or double-strand breaks that are
processed by DNA repair machinery. Without AID, patients develop Hyper-IgM syndrome
because they cannot diversify their antibody responses.
5. In the context of B cell activation, what is the role of Follicular Dendritic Cells (FDCs)?
A. To process and present antigens via MHC class II to T cells.
B. To phagocytose apoptotic B cells in the germinal center.
C. To secrete IL-2 for T cell proliferation.
D. To display intact antigens on their surface for B cell recognition.
Answer: D
Rationale: Unlike myeloid dendritic cells, FDCs are not hematopoietic in origin and do not
express MHC class II for antigen presentation. They use Fc receptors and complement
