PCB 3233 Immunology Exam 2 Practice Quiz 2026 – UCF
1. Which molecule is responsible for transporting peptides from the cytosol into
the lumen of the endoplasmic reticulum for loading onto MHC Class I?
A. HLA-DM
B. TAP (Transporter associated with antigen processing)
C. Invariant chain (Ii)
D. Calnexin
Answer: B
Rationale: TAP proteins (TAP1 and TAP2) form a channel in the ER membrane to move
degraded cytosolic peptides into the ER where MHC Class I molecules are waiting.
2. What is the primary function of the Invariant Chain (Ii) in the MHC Class II
pathway?
A. To facilitate peptide loading in the ER
B. To prevent premature peptide binding in the ER and guide MHC II to endosomes
C. To degrade misfolded proteins
D. To act as a co-receptor for CD8 T cells
Answer: B
Rationale: The Invariant chain blocks the peptide-binding groove of MHC Class II in the ER,
preventing it from binding ER-resident peptides intended for MHC I.
,3. During T cell development, what occurs during ‘Positive Selection’?
A. T cells that react too strongly to self-antigens are killed
B. T cells that can recognize self-MHC molecules are signaled to survive
C. B cells are converted into T cells
D. T cells migrate from the bone marrow to the lymph nodes
Answer: B
Rationale: Positive selection ensures that mature T cells are MHC-restricted, meaning they
can recognize peptides only when presented by the body’s own MHC molecules.
4. Which enzyme is responsible for Somatic Hypermutation and Isotype
Switching in B cells?
A. RAG-1/RAG-2
B. TdT (Terminal deoxynucleotidyl transferase)
C. Artemis
D. AID (Activation-induced cytidine deaminase)
Answer: D
Rationale: AID is crucial for diversification of the B cell response after activation,
facilitating both affinity maturation and class switching.
5. Which of the following describes ‘MHC Restriction’?
A. The binding of antibodies to MHC molecules
B. The ability of MHC molecules to bind many different peptides
C. The suppression of MHC expression by viral infections
D. A T cell receptor recognizes a specific peptide only when bound to a specific MHC molecule
Answer: D
Rationale: T cells are ‘restricted’ to recognizing antigen only in the context of the specific
MHC isoform they encountered during thymic selection.
, 6. What is the role of the HLA-DM molecule in the endocytic pathway?
A. It stabilizes MHC Class I molecules
B. It functions as a proteasome subunit
C. It catalyzes the release of the CLIP peptide from MHC Class II
D. It transports antibodies across the placenta
Answer: C
Rationale: HLA-DM acts as a catalyst to swap the CLIP fragment for a high-affinity foreign
peptide within the MIIC (MHC class II compartment).
7. Which transcription factor is characteristic of Regulatory T cells (Tregs)?
A. T-bet
B. GATA3
C. FoxP3
D. ROR-gamma-t
Answer: C
Rationale: FoxP3 is the master regulator for the development and function of Tregs, which
help maintain peripheral tolerance.
8. Endogenous antigens (from the cytosol) are primarily presented on which
molecule?
A. CD1
B. MHC Class II
C. MHC Class I
D. B cell receptor
Answer: C
Rationale: Proteins synthesized within the cell (endogenous) are degraded by the
proteasome and presented on MHC Class I to CD8+ T cells.
1. Which molecule is responsible for transporting peptides from the cytosol into
the lumen of the endoplasmic reticulum for loading onto MHC Class I?
A. HLA-DM
B. TAP (Transporter associated with antigen processing)
C. Invariant chain (Ii)
D. Calnexin
Answer: B
Rationale: TAP proteins (TAP1 and TAP2) form a channel in the ER membrane to move
degraded cytosolic peptides into the ER where MHC Class I molecules are waiting.
2. What is the primary function of the Invariant Chain (Ii) in the MHC Class II
pathway?
A. To facilitate peptide loading in the ER
B. To prevent premature peptide binding in the ER and guide MHC II to endosomes
C. To degrade misfolded proteins
D. To act as a co-receptor for CD8 T cells
Answer: B
Rationale: The Invariant chain blocks the peptide-binding groove of MHC Class II in the ER,
preventing it from binding ER-resident peptides intended for MHC I.
,3. During T cell development, what occurs during ‘Positive Selection’?
A. T cells that react too strongly to self-antigens are killed
B. T cells that can recognize self-MHC molecules are signaled to survive
C. B cells are converted into T cells
D. T cells migrate from the bone marrow to the lymph nodes
Answer: B
Rationale: Positive selection ensures that mature T cells are MHC-restricted, meaning they
can recognize peptides only when presented by the body’s own MHC molecules.
4. Which enzyme is responsible for Somatic Hypermutation and Isotype
Switching in B cells?
A. RAG-1/RAG-2
B. TdT (Terminal deoxynucleotidyl transferase)
C. Artemis
D. AID (Activation-induced cytidine deaminase)
Answer: D
Rationale: AID is crucial for diversification of the B cell response after activation,
facilitating both affinity maturation and class switching.
5. Which of the following describes ‘MHC Restriction’?
A. The binding of antibodies to MHC molecules
B. The ability of MHC molecules to bind many different peptides
C. The suppression of MHC expression by viral infections
D. A T cell receptor recognizes a specific peptide only when bound to a specific MHC molecule
Answer: D
Rationale: T cells are ‘restricted’ to recognizing antigen only in the context of the specific
MHC isoform they encountered during thymic selection.
, 6. What is the role of the HLA-DM molecule in the endocytic pathway?
A. It stabilizes MHC Class I molecules
B. It functions as a proteasome subunit
C. It catalyzes the release of the CLIP peptide from MHC Class II
D. It transports antibodies across the placenta
Answer: C
Rationale: HLA-DM acts as a catalyst to swap the CLIP fragment for a high-affinity foreign
peptide within the MIIC (MHC class II compartment).
7. Which transcription factor is characteristic of Regulatory T cells (Tregs)?
A. T-bet
B. GATA3
C. FoxP3
D. ROR-gamma-t
Answer: C
Rationale: FoxP3 is the master regulator for the development and function of Tregs, which
help maintain peripheral tolerance.
8. Endogenous antigens (from the cytosol) are primarily presented on which
molecule?
A. CD1
B. MHC Class II
C. MHC Class I
D. B cell receptor
Answer: C
Rationale: Proteins synthesized within the cell (endogenous) are degraded by the
proteasome and presented on MHC Class I to CD8+ T cells.
