PCB 3233 Exam 2 V1 | PCB 3233 Immunology |
Actual Q&A with Rationale (PCB3233 Exam 2) |
University of Central Florida
1. During the processing of exogenous antigens, which molecule prevents the premature
binding of self-peptides to the MHC Class II molecule within the endoplasmic reticulum?
A. HLA-DM
B. TAP1/2
C. Calreticulin
D. Invariant chain (Ii)
Correct Answer: D
Explanation: The invariant chain (Ii) binds to the peptide-binding groove of MHC Class II
molecules in the endoplasmic reticulum to prevent internal peptides from binding. It also
serves to guide the MHC II complex from the ER to the endocytic vesicles where exogenous
antigens are processed. Once in the vesicle, the Ii is cleaved, leaving only the CLIP fragment
to be removed by HLA-DM.
2. Which enzyme is responsible for the somatic hypermutation and isotype switching
processes in activated B cells?
A. Artemis
B. Terminal deoxynucleotidyl transferase (TdT)
,C. RAG-1/RAG-2
D. Activation-induced cytidine deaminase (AID)
Correct Answer: D
Explanation: Activation-induced cytidine deaminase (AID) is the primary enzyme that
converts cytosine to uracil in DNA to initiate somatic hypermutation and class switch
recombination. This process is essential for increasing the affinity of antibodies and
changing their effector functions. Without AID, patients develop Hyper-IgM syndrome
because they cannot undergo class switching or affinity maturation.
3. In the context of T-cell development, what is the primary role of the AIRE (Autoimmune
Regulator) protein in the medulla of the thymus?
A. To induce the expression of tissue-specific antigens for negative selection.
B. To facilitate the rearrangement of the TCR alpha chain.
C. To signal the transition from double-negative to double-positive thymocytes.
D. To act as a co-receptor for MHC Class I molecules.
Correct Answer: A
Explanation: The AIRE protein allows medullary thymic epithelial cells to express proteins
that are normally only found in specific peripheral tissues, such as insulin or keratin. This
expression ensures that developing T cells are screened against a wide array of self-
antigens during negative selection to prevent autoimmunity. A deficiency in AIRE leads to
APECED, a severe multi-organ autoimmune disease.
, 4. Which of the following describes the ‘Signal 2’ required for the full activation of a naive T
cell by a professional antigen-presenting cell?
A. Interaction between B7 (CD80/86) on the APC and CD28 on the T cell.
B. Release of IL-2 by the T cell to act in an autocrine fashion.
C. Interaction between the TCR and the MHC:peptide complex.
D. Binding of CD40 on the B cell to CD40L on the T cell.
Correct Answer: A
Explanation: Signal 2 is a costimulatory signal that is essential for T-cell proliferation and
survival, primarily mediated by the binding of CD28 to B7 molecules. If a T cell receives
Signal 1 (TCR binding) without Signal 2, it typically becomes anergic or undergoes
apoptosis. This mechanism serves as a checkpoint to ensure T cells only activate in
response to pathogens that have triggered innate immune danger signals.
5. MHC Class I molecules primarily present peptides derived from which cellular
compartment?
A. Extracellular fluid via endocytosis.
B. Lysosomes via autophagy.
C. The Golgi apparatus via retrograde transport.
D. The cytosol via proteasomal degradation.
Correct Answer: D
Actual Q&A with Rationale (PCB3233 Exam 2) |
University of Central Florida
1. During the processing of exogenous antigens, which molecule prevents the premature
binding of self-peptides to the MHC Class II molecule within the endoplasmic reticulum?
A. HLA-DM
B. TAP1/2
C. Calreticulin
D. Invariant chain (Ii)
Correct Answer: D
Explanation: The invariant chain (Ii) binds to the peptide-binding groove of MHC Class II
molecules in the endoplasmic reticulum to prevent internal peptides from binding. It also
serves to guide the MHC II complex from the ER to the endocytic vesicles where exogenous
antigens are processed. Once in the vesicle, the Ii is cleaved, leaving only the CLIP fragment
to be removed by HLA-DM.
2. Which enzyme is responsible for the somatic hypermutation and isotype switching
processes in activated B cells?
A. Artemis
B. Terminal deoxynucleotidyl transferase (TdT)
,C. RAG-1/RAG-2
D. Activation-induced cytidine deaminase (AID)
Correct Answer: D
Explanation: Activation-induced cytidine deaminase (AID) is the primary enzyme that
converts cytosine to uracil in DNA to initiate somatic hypermutation and class switch
recombination. This process is essential for increasing the affinity of antibodies and
changing their effector functions. Without AID, patients develop Hyper-IgM syndrome
because they cannot undergo class switching or affinity maturation.
3. In the context of T-cell development, what is the primary role of the AIRE (Autoimmune
Regulator) protein in the medulla of the thymus?
A. To induce the expression of tissue-specific antigens for negative selection.
B. To facilitate the rearrangement of the TCR alpha chain.
C. To signal the transition from double-negative to double-positive thymocytes.
D. To act as a co-receptor for MHC Class I molecules.
Correct Answer: A
Explanation: The AIRE protein allows medullary thymic epithelial cells to express proteins
that are normally only found in specific peripheral tissues, such as insulin or keratin. This
expression ensures that developing T cells are screened against a wide array of self-
antigens during negative selection to prevent autoimmunity. A deficiency in AIRE leads to
APECED, a severe multi-organ autoimmune disease.
, 4. Which of the following describes the ‘Signal 2’ required for the full activation of a naive T
cell by a professional antigen-presenting cell?
A. Interaction between B7 (CD80/86) on the APC and CD28 on the T cell.
B. Release of IL-2 by the T cell to act in an autocrine fashion.
C. Interaction between the TCR and the MHC:peptide complex.
D. Binding of CD40 on the B cell to CD40L on the T cell.
Correct Answer: A
Explanation: Signal 2 is a costimulatory signal that is essential for T-cell proliferation and
survival, primarily mediated by the binding of CD28 to B7 molecules. If a T cell receives
Signal 1 (TCR binding) without Signal 2, it typically becomes anergic or undergoes
apoptosis. This mechanism serves as a checkpoint to ensure T cells only activate in
response to pathogens that have triggered innate immune danger signals.
5. MHC Class I molecules primarily present peptides derived from which cellular
compartment?
A. Extracellular fluid via endocytosis.
B. Lysosomes via autophagy.
C. The Golgi apparatus via retrograde transport.
D. The cytosol via proteasomal degradation.
Correct Answer: D
