PCB 3233 Final Exam V3 | PCB 3233 Immunology | Actual Q&A with
Rationale (PCB3233 Final Exam) | University of Central Florida
1. Which of the following molecules is responsible for presenting endogenous antigens to
CD8+ T cells?
A. B7.1
B. MHC Class II
C. CD40
D. MHC Class I
Answer: D
Explanation: MHC Class I molecules are found on almost all nucleated cells and present
peptides derived from the cytoplasm. These molecules interact specifically with the CD8
coreceptor on cytotoxic T cells. This mechanism allows the immune system to monitor and
destroy virally infected or cancerous cells.
2. What is the primary function of the RAG-1 and RAG-2 enzymes during lymphocyte
development?
A. Mediating V(D)J recombination
B. Inducing somatic hypermutation
C. Facilitating isotype switching
D. Promoting T-cell activation
Answer: A
Explanation: Recombination-Activating Genes (RAG) are essential for the assembly of B
and T cell receptor genes. They recognize recombination signal sequences (RSS) to initiate
double-strand breaks in the DNA. Without these enzymes, mature B and T cells cannot
develop, leading to Severe Combined Immunodeficiency (SCID).
3. Which cytokine is primarily responsible for the differentiation of naive T cells into Th1
cells?
A. IL-12
B. IL-10
C. IL-4
D. TGF-beta
Answer: A
,Explanation: IL-12 is produced by macrophages and dendritic cells in response to
intracellular pathogens. It signals through the STAT4 pathway to induce the expression of
the T-bet transcription factor. This process shifts the immune response toward a cell-
mediated defense involving IFN-gamma production.
4. In the classical complement pathway, which molecule acts as the initial recognition
component?
A. C3b
B. Factor B
C. C1q
D. Mannose-binding lectin
Answer: C
Explanation: The classical pathway is typically activated by the binding of C1q to the Fc
portion of antigen-bound IgG or IgM. C1q is part of the C1 complex, which also contains C1r
and C1s proteases. Once bound, C1s cleaves C4 and C2 to form the C3 convertase.
5. Which antibody isotype is predominantly found in mucosal secretions like saliva and breast
milk?
A. IgG
B. IgE
C. IgA
D. IgD
Answer: C
Explanation: Dimeric IgA is transported across epithelial layers via the poly-Ig receptor. It
plays a crucial role in neutralizing pathogens at mucosal surfaces before they can enter the
systemic circulation. This isotype is essential for providing passive immunity to infants
through breastfeeding.
6. What is the process by which B cells increase their surface receptor affinity for an antigen
during a germinal center reaction?
A. Clonal deletion
B. Somatic hypermutation
C. Negative selection
D. V(D)J recombination
Answer: B
, Explanation: Somatic hypermutation involves the introduction of point mutations into the
V regions of immunoglobulin genes. This process occurs in rapidly dividing B cells
(centroblasts) within the germinal center. B cells with higher affinity for the antigen are
then selected to survive and differentiate, a process known as affinity maturation.
7. Which cell type is responsible for the ‘negative selection’ of T cells in the thymus?
A. Thymic epithelial cells and dendritic cells
B. Neutrophils
C. B cells
D. Natural Killer cells
Answer: A
Explanation: Negative selection occurs in the thymic medulla where thymocytes are tested
for reactivity against self-antigens. Medullary thymic epithelial cells (mTECs) express the
AIRE protein to present tissue-specific antigens. Cells that bind too strongly to these self-
antigens are induced to undergo apoptosis to prevent autoimmunity.
8. Which of the following is a characteristic of the innate immune system?
A. Highly specific memory
B. Uses germline-encoded receptors
C. Requires several days to become effective
D. Utilizes T-cell receptors for recognition
Answer: B
Explanation: The innate immune system serves as the first line of defense against
pathogens. It utilizes Pattern Recognition Receptors (PRRs) like Toll-like receptors to
detect conserved microbial structures. Unlike the adaptive system, its receptors do not
undergo gene rearrangement and do not provide long-term immunological memory.
9. Type I hypersensitivity reactions are mediated primarily by which mechanism?
A. Immune complexes
B. IgG-mediated cell lysis
C. T-cell mediated cytotoxicity
D. IgE binding to mast cells
Answer: D
Explanation: Type I hypersensitivity involves the production of IgE antibodies in response
to an allergen. These IgE molecules bind to high-affinity Fc-epsilon receptors on mast cells
Rationale (PCB3233 Final Exam) | University of Central Florida
1. Which of the following molecules is responsible for presenting endogenous antigens to
CD8+ T cells?
A. B7.1
B. MHC Class II
C. CD40
D. MHC Class I
Answer: D
Explanation: MHC Class I molecules are found on almost all nucleated cells and present
peptides derived from the cytoplasm. These molecules interact specifically with the CD8
coreceptor on cytotoxic T cells. This mechanism allows the immune system to monitor and
destroy virally infected or cancerous cells.
2. What is the primary function of the RAG-1 and RAG-2 enzymes during lymphocyte
development?
A. Mediating V(D)J recombination
B. Inducing somatic hypermutation
C. Facilitating isotype switching
D. Promoting T-cell activation
Answer: A
Explanation: Recombination-Activating Genes (RAG) are essential for the assembly of B
and T cell receptor genes. They recognize recombination signal sequences (RSS) to initiate
double-strand breaks in the DNA. Without these enzymes, mature B and T cells cannot
develop, leading to Severe Combined Immunodeficiency (SCID).
3. Which cytokine is primarily responsible for the differentiation of naive T cells into Th1
cells?
A. IL-12
B. IL-10
C. IL-4
D. TGF-beta
Answer: A
,Explanation: IL-12 is produced by macrophages and dendritic cells in response to
intracellular pathogens. It signals through the STAT4 pathway to induce the expression of
the T-bet transcription factor. This process shifts the immune response toward a cell-
mediated defense involving IFN-gamma production.
4. In the classical complement pathway, which molecule acts as the initial recognition
component?
A. C3b
B. Factor B
C. C1q
D. Mannose-binding lectin
Answer: C
Explanation: The classical pathway is typically activated by the binding of C1q to the Fc
portion of antigen-bound IgG or IgM. C1q is part of the C1 complex, which also contains C1r
and C1s proteases. Once bound, C1s cleaves C4 and C2 to form the C3 convertase.
5. Which antibody isotype is predominantly found in mucosal secretions like saliva and breast
milk?
A. IgG
B. IgE
C. IgA
D. IgD
Answer: C
Explanation: Dimeric IgA is transported across epithelial layers via the poly-Ig receptor. It
plays a crucial role in neutralizing pathogens at mucosal surfaces before they can enter the
systemic circulation. This isotype is essential for providing passive immunity to infants
through breastfeeding.
6. What is the process by which B cells increase their surface receptor affinity for an antigen
during a germinal center reaction?
A. Clonal deletion
B. Somatic hypermutation
C. Negative selection
D. V(D)J recombination
Answer: B
, Explanation: Somatic hypermutation involves the introduction of point mutations into the
V regions of immunoglobulin genes. This process occurs in rapidly dividing B cells
(centroblasts) within the germinal center. B cells with higher affinity for the antigen are
then selected to survive and differentiate, a process known as affinity maturation.
7. Which cell type is responsible for the ‘negative selection’ of T cells in the thymus?
A. Thymic epithelial cells and dendritic cells
B. Neutrophils
C. B cells
D. Natural Killer cells
Answer: A
Explanation: Negative selection occurs in the thymic medulla where thymocytes are tested
for reactivity against self-antigens. Medullary thymic epithelial cells (mTECs) express the
AIRE protein to present tissue-specific antigens. Cells that bind too strongly to these self-
antigens are induced to undergo apoptosis to prevent autoimmunity.
8. Which of the following is a characteristic of the innate immune system?
A. Highly specific memory
B. Uses germline-encoded receptors
C. Requires several days to become effective
D. Utilizes T-cell receptors for recognition
Answer: B
Explanation: The innate immune system serves as the first line of defense against
pathogens. It utilizes Pattern Recognition Receptors (PRRs) like Toll-like receptors to
detect conserved microbial structures. Unlike the adaptive system, its receptors do not
undergo gene rearrangement and do not provide long-term immunological memory.
9. Type I hypersensitivity reactions are mediated primarily by which mechanism?
A. Immune complexes
B. IgG-mediated cell lysis
C. T-cell mediated cytotoxicity
D. IgE binding to mast cells
Answer: D
Explanation: Type I hypersensitivity involves the production of IgE antibodies in response
to an allergen. These IgE molecules bind to high-affinity Fc-epsilon receptors on mast cells
