PCB 3233 Exam 2 V1 | PCB 3233
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 2) | University of Central
Florida
1. Which chaperone protein is responsible for stabilizing the MHC Class I heavy chain before it
binds to beta-2 microglobulin?
A. Calreticulin
B. Tapasin
C. Calnexin
D. ERp57
Answer: C
Rationale: Calnexin is a membrane-bound chaperone that stabilizes the MHC Class I alpha
chain until beta-2 microglobulin binds. Once the light chain binds, calnexin is released and
replaced by other members of the peptide-loading complex. This step is critical for proper
protein folding in the endoplasmic reticulum.
2. Which molecule is responsible for removing the CLIP peptide from MHC Class II molecules
to allow for high-affinity peptide binding?
A. HLA-DM
B. Invariant chain
,C. TAP1/2
D. HLA-DO
Answer: A
Rationale: HLA-DM acts as a catalyst in the endosomal compartment to release the CLIP
fragment from the MHC II groove. This facilitates the loading of peptides derived from
internalized pathogens. Without HLA-DM, MHC II molecules would remain occupied by
CLIP and fail to present relevant antigens to CD4+ T cells.
3. During T cell development, which protein acts as a signal to commit a lymphoid progenitor
to the T cell lineage?
A. Pax5
B. Notch1
C. EBF
D. Ikaros
Answer: B
Rationale: Notch1 signaling is the essential driver for T cell commitment in the thymus.
When the Notch1 receptor on a progenitor cell interacts with its ligand on thymic stroma, it
is cleaved and the intracellular domain travels to the nucleus to act as a transcription
factor. In the absence of Notch1, progenitors would default to a B cell lineage.
, 4. What is the correct sequence of gene rearrangement for the T-cell receptor beta chain?
A. V to J, then VJ to D
B. V to D, then VD to J
C. D to J, then V to DJ
D. L to V, then V to J
Answer: C
Rationale: The TCR beta chain follows the same rearrangement sequence as the
immunoglobulin heavy chain. First, a Diversity (D) segment joins a Joining (J) segment. This
is followed by a Variable (V) segment joining the DJ complex to form a functional VDJ unit.
5. Which transcription factor is responsible for the expression of tissue-specific antigens in
the thymus for negative selection?
A. T-bet
B. AIRE
C. GATA3
D. FoxP3
Answer: B
Rationale: AIRE (Autoimmune Regulator) allows medullary thymic epithelial cells to
express proteins normally found only in specific peripheral tissues, such as insulin. This
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 2) | University of Central
Florida
1. Which chaperone protein is responsible for stabilizing the MHC Class I heavy chain before it
binds to beta-2 microglobulin?
A. Calreticulin
B. Tapasin
C. Calnexin
D. ERp57
Answer: C
Rationale: Calnexin is a membrane-bound chaperone that stabilizes the MHC Class I alpha
chain until beta-2 microglobulin binds. Once the light chain binds, calnexin is released and
replaced by other members of the peptide-loading complex. This step is critical for proper
protein folding in the endoplasmic reticulum.
2. Which molecule is responsible for removing the CLIP peptide from MHC Class II molecules
to allow for high-affinity peptide binding?
A. HLA-DM
B. Invariant chain
,C. TAP1/2
D. HLA-DO
Answer: A
Rationale: HLA-DM acts as a catalyst in the endosomal compartment to release the CLIP
fragment from the MHC II groove. This facilitates the loading of peptides derived from
internalized pathogens. Without HLA-DM, MHC II molecules would remain occupied by
CLIP and fail to present relevant antigens to CD4+ T cells.
3. During T cell development, which protein acts as a signal to commit a lymphoid progenitor
to the T cell lineage?
A. Pax5
B. Notch1
C. EBF
D. Ikaros
Answer: B
Rationale: Notch1 signaling is the essential driver for T cell commitment in the thymus.
When the Notch1 receptor on a progenitor cell interacts with its ligand on thymic stroma, it
is cleaved and the intracellular domain travels to the nucleus to act as a transcription
factor. In the absence of Notch1, progenitors would default to a B cell lineage.
, 4. What is the correct sequence of gene rearrangement for the T-cell receptor beta chain?
A. V to J, then VJ to D
B. V to D, then VD to J
C. D to J, then V to DJ
D. L to V, then V to J
Answer: C
Rationale: The TCR beta chain follows the same rearrangement sequence as the
immunoglobulin heavy chain. First, a Diversity (D) segment joins a Joining (J) segment. This
is followed by a Variable (V) segment joining the DJ complex to form a functional VDJ unit.
5. Which transcription factor is responsible for the expression of tissue-specific antigens in
the thymus for negative selection?
A. T-bet
B. AIRE
C. GATA3
D. FoxP3
Answer: B
Rationale: AIRE (Autoimmune Regulator) allows medullary thymic epithelial cells to
express proteins normally found only in specific peripheral tissues, such as insulin. This
