Immunology Exam 3 Practice 2026 – UCF
1. Which molecule is responsible for transporting peptides from the cytosol into
the endoplasmic reticulum for MHC Class I loading?
A. HLA-DM
B. TAP1/TAP2
C. Invariant chain
D. Calnexin
Answer: B
Rationale: The Transporter associated with Antigen Processing (TAP) complex moves
degraded cytosolic peptides into the ER lumen.
2. Which of the following cells is considered a ‘professional’ antigen-presenting
cell (APC)?
A. Neutrophil
B. Natural Killer cell
C. Dendritic cell
D. Erythrocyte
Answer: C
Rationale: Dendritic cells, macrophages, and B cells are professional APCs because they
express MHC Class II and costimulatory molecules.
,3. MHC Class II molecules typically bind peptides of what length?
A. 8-10 amino acids
B. Over 30 amino acids
C. 13-18 amino acids
D. 5-7 amino acids
Answer: C
Rationale: MHC Class II molecules have an open binding groove allowing longer peptides,
typically 13-18 residues, unlike the closed groove of MHC I.
4. Which cytokine is primary for the differentiation of naive T cells into Th1
cells?
A. IL-4
B. IL-12
C. IL-10
D. TGF-beta
Answer: B
Rationale: IL-12 produced by macrophages and dendritic cells promotes Th1
differentiation, which is crucial for intracellular pathogen defense.
5. The process of negative selection in the thymus ensures that:
A. T cells can recognize self-MHC
B. T cells with high affinity for self-antigens are deleted
C. B cells produce high-affinity antibodies
D. T cells undergo isotype switching
Answer: B
Rationale: Negative selection eliminates self-reactive thymocytes to prevent
autoimmunity, establishing central tolerance.
, 6. Which surface marker is found on all mature T cells?
A. CD3
B. CD8
C. CD4
D. CD19
Answer: A
Rationale: CD3 is a multi-protein complex required for TCR signaling and is present on all
T lymphocytes.
7. What is the function of the Invariant Chain (Ii)?
A. To stabilize MHC Class I
B. To block the MHC Class II binding groove in the ER
C. To facilitate peptide loading onto MHC Class I
D. To degrade viral proteins
Answer: B
Rationale: The invariant chain prevents endogenous peptides from binding to MHC II
while it is in the ER.
8. Where does the ‘signal 2’ for T cell activation usually come from?
A. TCR binding to MHC
B. Cytokine receptors
C. CD4 binding to MHC II
D. CD28 binding to B7-1/B7-2
Answer: D
Rationale: Signal 2 is costimulation, primarily provided by the interaction between CD28
on the T cell and B7 (CD80/86) on the APC.
1. Which molecule is responsible for transporting peptides from the cytosol into
the endoplasmic reticulum for MHC Class I loading?
A. HLA-DM
B. TAP1/TAP2
C. Invariant chain
D. Calnexin
Answer: B
Rationale: The Transporter associated with Antigen Processing (TAP) complex moves
degraded cytosolic peptides into the ER lumen.
2. Which of the following cells is considered a ‘professional’ antigen-presenting
cell (APC)?
A. Neutrophil
B. Natural Killer cell
C. Dendritic cell
D. Erythrocyte
Answer: C
Rationale: Dendritic cells, macrophages, and B cells are professional APCs because they
express MHC Class II and costimulatory molecules.
,3. MHC Class II molecules typically bind peptides of what length?
A. 8-10 amino acids
B. Over 30 amino acids
C. 13-18 amino acids
D. 5-7 amino acids
Answer: C
Rationale: MHC Class II molecules have an open binding groove allowing longer peptides,
typically 13-18 residues, unlike the closed groove of MHC I.
4. Which cytokine is primary for the differentiation of naive T cells into Th1
cells?
A. IL-4
B. IL-12
C. IL-10
D. TGF-beta
Answer: B
Rationale: IL-12 produced by macrophages and dendritic cells promotes Th1
differentiation, which is crucial for intracellular pathogen defense.
5. The process of negative selection in the thymus ensures that:
A. T cells can recognize self-MHC
B. T cells with high affinity for self-antigens are deleted
C. B cells produce high-affinity antibodies
D. T cells undergo isotype switching
Answer: B
Rationale: Negative selection eliminates self-reactive thymocytes to prevent
autoimmunity, establishing central tolerance.
, 6. Which surface marker is found on all mature T cells?
A. CD3
B. CD8
C. CD4
D. CD19
Answer: A
Rationale: CD3 is a multi-protein complex required for TCR signaling and is present on all
T lymphocytes.
7. What is the function of the Invariant Chain (Ii)?
A. To stabilize MHC Class I
B. To block the MHC Class II binding groove in the ER
C. To facilitate peptide loading onto MHC Class I
D. To degrade viral proteins
Answer: B
Rationale: The invariant chain prevents endogenous peptides from binding to MHC II
while it is in the ER.
8. Where does the ‘signal 2’ for T cell activation usually come from?
A. TCR binding to MHC
B. Cytokine receptors
C. CD4 binding to MHC II
D. CD28 binding to B7-1/B7-2
Answer: D
Rationale: Signal 2 is costimulation, primarily provided by the interaction between CD28
on the T cell and B7 (CD80/86) on the APC.
