PCB 3233 Exam 2 V2 | PCB 3233 Immunology |
Actual Q&A with Rationale (PCB3233 Exam 2) |
University of Central Florida
1. Which molecule is responsible for the removal of the CLIP peptide from the MHC class II
binding groove?
A. Invariant chain
B. HLA-DO
C. Calnexin
D. HLA-DM
Correct Answer: D
Explanation: HLA-DM acts as a catalyst in the endosomal compartment to facilitate the
release of the Class II-associated invariant chain peptide (CLIP). This allows high-affinity
antigenic peptides to bind to the MHC class II molecule before it is transported to the cell
surface. Without HLA-DM, MHC class II molecules would remain occupied by CLIP and fail
to present exogenous antigens to CD4+ T cells.
2. Which of the following enzymes is responsible for adding N-nucleotides to the junctions
between gene segments during TCR rearrangement?
A. RAG-1/2
B. Terminal deoxynucleotidyl transferase (TdT)
,C. DNA-PK
D. Artemis
Correct Answer: B
Explanation: Terminal deoxynucleotidyl transferase (TdT) is a specialized DNA
polymerase that adds non-templated nucleotides (N-nucleotides) to the V, D, and J
junctions. This process significantly increases the junctional diversity of the T-cell receptor
repertoire. TdT activity is primarily observed during the rearrangement of the TCR beta
chain and immunoglobulin heavy chains.
3. In the endogenous pathway of antigen processing, which protein complex is responsible for
degrading cytosolic proteins into peptides?
A. Lysosome
B. Endosome
C. TAP transporter
D. Proteasome
Correct Answer: D
Explanation: The proteasome is a large multi-subunit protease complex that degrades
ubiquitinated or misfolded proteins in the cytosol. During an immune response, interferon-
gamma can induce the formation of the immunoproteasome, which optimizes peptide
cleavage for MHC class I binding. These resulting peptides are then transported into the
endoplasmic reticulum for loading.
, 4. What is the primary function of the AIRE (Autoimmune Regulator) protein in the thymus?
A. To promote the proliferation of double-negative thymocytes.
B. To facilitate the rearrangement of the TCR alpha chain.
C. To induce the expression of tissue-specific antigens for negative selection.
D. To signal the commitment of progenitor cells to the T-cell lineage.
Correct Answer: C
Explanation: AIRE is expressed by medullary thymic epithelial cells (mTECs) and allows
for the transcription of genes that are normally only expressed in peripheral tissues, such
as insulin or keratin. This process ensures that developing T cells are exposed to a wide
range of self-antigens during negative selection. Mutations in the AIRE gene lead to
APECED, a severe multi-organ autoimmune disease.
5. During B-cell development, which of the following characterizes the ‘Pre-B cell’ stage?
A. Successful rearrangement of the light chain gene segments.
B. Expression of the pre-B cell receptor consisting of a heavy chain and surrogate light
chain.
C. Expression of both IgM and IgD on the cell surface.
D. Interaction with follicular dendritic cells in the lymph node.
Correct Answer: B
Actual Q&A with Rationale (PCB3233 Exam 2) |
University of Central Florida
1. Which molecule is responsible for the removal of the CLIP peptide from the MHC class II
binding groove?
A. Invariant chain
B. HLA-DO
C. Calnexin
D. HLA-DM
Correct Answer: D
Explanation: HLA-DM acts as a catalyst in the endosomal compartment to facilitate the
release of the Class II-associated invariant chain peptide (CLIP). This allows high-affinity
antigenic peptides to bind to the MHC class II molecule before it is transported to the cell
surface. Without HLA-DM, MHC class II molecules would remain occupied by CLIP and fail
to present exogenous antigens to CD4+ T cells.
2. Which of the following enzymes is responsible for adding N-nucleotides to the junctions
between gene segments during TCR rearrangement?
A. RAG-1/2
B. Terminal deoxynucleotidyl transferase (TdT)
,C. DNA-PK
D. Artemis
Correct Answer: B
Explanation: Terminal deoxynucleotidyl transferase (TdT) is a specialized DNA
polymerase that adds non-templated nucleotides (N-nucleotides) to the V, D, and J
junctions. This process significantly increases the junctional diversity of the T-cell receptor
repertoire. TdT activity is primarily observed during the rearrangement of the TCR beta
chain and immunoglobulin heavy chains.
3. In the endogenous pathway of antigen processing, which protein complex is responsible for
degrading cytosolic proteins into peptides?
A. Lysosome
B. Endosome
C. TAP transporter
D. Proteasome
Correct Answer: D
Explanation: The proteasome is a large multi-subunit protease complex that degrades
ubiquitinated or misfolded proteins in the cytosol. During an immune response, interferon-
gamma can induce the formation of the immunoproteasome, which optimizes peptide
cleavage for MHC class I binding. These resulting peptides are then transported into the
endoplasmic reticulum for loading.
, 4. What is the primary function of the AIRE (Autoimmune Regulator) protein in the thymus?
A. To promote the proliferation of double-negative thymocytes.
B. To facilitate the rearrangement of the TCR alpha chain.
C. To induce the expression of tissue-specific antigens for negative selection.
D. To signal the commitment of progenitor cells to the T-cell lineage.
Correct Answer: C
Explanation: AIRE is expressed by medullary thymic epithelial cells (mTECs) and allows
for the transcription of genes that are normally only expressed in peripheral tissues, such
as insulin or keratin. This process ensures that developing T cells are exposed to a wide
range of self-antigens during negative selection. Mutations in the AIRE gene lead to
APECED, a severe multi-organ autoimmune disease.
5. During B-cell development, which of the following characterizes the ‘Pre-B cell’ stage?
A. Successful rearrangement of the light chain gene segments.
B. Expression of the pre-B cell receptor consisting of a heavy chain and surrogate light
chain.
C. Expression of both IgM and IgD on the cell surface.
D. Interaction with follicular dendritic cells in the lymph node.
Correct Answer: B
