PCB 3233 Exam 3: Immunology Chapters 5 & 6 2026 – UCF
1. Which pathway is primarily responsible for processing endogenous antigens
for presentation on MHC Class I molecules?
A. Exocytic pathway
B. Cytosolic pathway
C. Endocytic pathway
D. Retrograde pathway
Answer: B
Rationale: Endogenous antigens are found in the cytosol and are processed via the
cytosolic pathway for MHC Class I presentation.
2. Which chaperone protein initially binds to the MHC Class I heavy chain in the
ER to aid its folding?
A. Calnexin
B. Tapasin
C. Calreticulin
D. ERp57
Answer: A
Rationale: Calnexin is the first chaperone that binds the MHC Class I heavy chain until
beta-2 microglobulin binds.
,3. The proteasome is modified into an ‘immunoproteasome’ during an infection
by the presence of which cytokine?
A. IL-4
B. IFN-gamma
C. TNF-alpha
D. IL-10
Answer: B
Rationale: Interferon-gamma (IFN-gamma) induces the expression of alternative subunits
that convert the constitutive proteasome into the immunoproteasome.
4. What is the function of the TAP1/TAP2 heterodimer?
A. Binding MHC Class II to the invariant chain
B. Degrading extracellular proteins
C. Stabilizing the T-cell receptor
D. Transporting peptides from the cytosol into the ER
Answer: D
Rationale: TAP (Transporter associated with Antigen Processing) moves peptides
generated in the cytosol across the ER membrane.
5. MHC Class II molecules primarily present peptides derived from which
source?
A. Cytosolic proteins
B. Nuclear proteins
C. Mitochondrial proteins
D. Extracellular pathogens
Answer: D
Rationale: MHC Class II molecules present antigens taken up from the extracellular
environment via endocytosis or phagocytosis.
, 6. What protein prevents peptides from binding to MHC Class II molecules while
they are still in the ER?
A. CLIP
B. Calreticulin
C. HLA-DM
D. Invariant chain (Ii)
Answer: D
Rationale: The invariant chain binds the MHC Class II groove in the ER, blocking peptide
binding and directing the molecule to endosomes.
7. Which molecule facilitates the dissociation of CLIP from MHC Class II to allow
peptide binding?
A. Cathepsin S
B. HLA-DO
C. TAP
D. HLA-DM
Answer: D
Rationale: HLA-DM binds to MHC Class II/CLIP complexes, catalyzing the release of CLIP
and the loading of high-affinity peptides.
8. Which of the following describes ‘cross-presentation’?
A. MHC Class I presenting exogenous antigens
B. TCRs recognizing MHC Class I and II simultaneously
C. MHC Class II presenting cytosolic antigens
D. B cells presenting antigens to other B cells
Answer: A
Rationale: Cross-presentation is the unique ability of certain dendritic cells to present
exogenous antigens on MHC Class I molecules to activate CD8+ T cells.
1. Which pathway is primarily responsible for processing endogenous antigens
for presentation on MHC Class I molecules?
A. Exocytic pathway
B. Cytosolic pathway
C. Endocytic pathway
D. Retrograde pathway
Answer: B
Rationale: Endogenous antigens are found in the cytosol and are processed via the
cytosolic pathway for MHC Class I presentation.
2. Which chaperone protein initially binds to the MHC Class I heavy chain in the
ER to aid its folding?
A. Calnexin
B. Tapasin
C. Calreticulin
D. ERp57
Answer: A
Rationale: Calnexin is the first chaperone that binds the MHC Class I heavy chain until
beta-2 microglobulin binds.
,3. The proteasome is modified into an ‘immunoproteasome’ during an infection
by the presence of which cytokine?
A. IL-4
B. IFN-gamma
C. TNF-alpha
D. IL-10
Answer: B
Rationale: Interferon-gamma (IFN-gamma) induces the expression of alternative subunits
that convert the constitutive proteasome into the immunoproteasome.
4. What is the function of the TAP1/TAP2 heterodimer?
A. Binding MHC Class II to the invariant chain
B. Degrading extracellular proteins
C. Stabilizing the T-cell receptor
D. Transporting peptides from the cytosol into the ER
Answer: D
Rationale: TAP (Transporter associated with Antigen Processing) moves peptides
generated in the cytosol across the ER membrane.
5. MHC Class II molecules primarily present peptides derived from which
source?
A. Cytosolic proteins
B. Nuclear proteins
C. Mitochondrial proteins
D. Extracellular pathogens
Answer: D
Rationale: MHC Class II molecules present antigens taken up from the extracellular
environment via endocytosis or phagocytosis.
, 6. What protein prevents peptides from binding to MHC Class II molecules while
they are still in the ER?
A. CLIP
B. Calreticulin
C. HLA-DM
D. Invariant chain (Ii)
Answer: D
Rationale: The invariant chain binds the MHC Class II groove in the ER, blocking peptide
binding and directing the molecule to endosomes.
7. Which molecule facilitates the dissociation of CLIP from MHC Class II to allow
peptide binding?
A. Cathepsin S
B. HLA-DO
C. TAP
D. HLA-DM
Answer: D
Rationale: HLA-DM binds to MHC Class II/CLIP complexes, catalyzing the release of CLIP
and the loading of high-affinity peptides.
8. Which of the following describes ‘cross-presentation’?
A. MHC Class I presenting exogenous antigens
B. TCRs recognizing MHC Class I and II simultaneously
C. MHC Class II presenting cytosolic antigens
D. B cells presenting antigens to other B cells
Answer: A
Rationale: Cross-presentation is the unique ability of certain dendritic cells to present
exogenous antigens on MHC Class I molecules to activate CD8+ T cells.
