PCB3233 Immunology Exam 3 Quiz 2026 – UCF
1. Which molecule is responsible for transporting peptides from the cytosol into
the lumen of the endoplasmic reticulum for MHC class I loading?
A. TAP (Transporter associated with antigen processing)
B. Invariant chain
C. HLA-DM
D. Calnexin
Answer: A
Rationale: TAP1 and TAP2 form a heterodimer in the ER membrane that pumps degraded
cytosolic peptides into the ER to meet MHC class I molecules.
2. Which of the following cells is considered a professional antigen-presenting
cell (APC) capable of activating naive T cells?
A. Dendritic cell
B. Natural Killer cell
C. Neutrophil
D. Erythrocyte
Answer: A
Rationale: Dendritic cells are the most potent professional APCs and are uniquely capable
of activating naive T cells.
,3. MHC class II molecules primarily present antigens derived from which source?
A. Nuclear proteins
B. Cytosolic proteins
C. Extracellular pathogens via endocytosis
D. Mitochondrial proteins
Answer: C
Rationale: MHC class II molecules present exogenous antigens that have been internalized
via phagocytosis or endocytosis.
4. What is the role of the Invariant Chain (Ii) in MHC class II processing?
A. It loads the peptide into the binding groove.
B. It prevents premature peptide binding in the ER.
C. It degrades the protein into peptides.
D. It acts as a co-receptor for CD8 T cells.
Answer: B
Rationale: The invariant chain blocks the peptide-binding groove of MHC II in the ER to
prevent it from binding endogenous peptides intended for MHC I.
5. Which cytokine is primarily responsible for the proliferation and survival of
activated T cells?
A. IL-1
B. IL-10
C. IL-2
D. IFN-gamma
Answer: C
Rationale: IL-2 acts in an autocrine and paracrine fashion to drive the clonal expansion of
activated T lymphocytes.
, 6. The process by which a T cell that binds too strongly to self-antigen in the
thymus is eliminated is called:
A. Negative selection
B. Positive selection
C. Affinity maturation
D. Somatic hypermutation
Answer: A
Rationale: Negative selection ensures central tolerance by inducing apoptosis in
thymocytes with high affinity for self-MHC/self-peptide complexes.
7. Which T cell subset is characterized by the production of IFN-gamma and is
involved in activating macrophages?
A. Th1
B. Th2
C. Th17
D. Treg
Answer: A
Rationale: Th1 cells produce IFN-gamma to enhance the microbicidal activity of
macrophages against intracellular pathogens.
8. What is the function of the CLIP protein?
A. It transports peptides to the cell surface.
B. It targets proteins for proteasomal degradation.
C. It stabilizes MHC I molecules.
D. It remains in the MHC II groove until HLA-DM facilitates its exchange for an antigen.
Answer: D
Rationale: CLIP (Class II-associated invariant chain peptide) is the remnant of the
invariant chain that stays in the MHC II groove until exchanged for an antigenic peptide.
1. Which molecule is responsible for transporting peptides from the cytosol into
the lumen of the endoplasmic reticulum for MHC class I loading?
A. TAP (Transporter associated with antigen processing)
B. Invariant chain
C. HLA-DM
D. Calnexin
Answer: A
Rationale: TAP1 and TAP2 form a heterodimer in the ER membrane that pumps degraded
cytosolic peptides into the ER to meet MHC class I molecules.
2. Which of the following cells is considered a professional antigen-presenting
cell (APC) capable of activating naive T cells?
A. Dendritic cell
B. Natural Killer cell
C. Neutrophil
D. Erythrocyte
Answer: A
Rationale: Dendritic cells are the most potent professional APCs and are uniquely capable
of activating naive T cells.
,3. MHC class II molecules primarily present antigens derived from which source?
A. Nuclear proteins
B. Cytosolic proteins
C. Extracellular pathogens via endocytosis
D. Mitochondrial proteins
Answer: C
Rationale: MHC class II molecules present exogenous antigens that have been internalized
via phagocytosis or endocytosis.
4. What is the role of the Invariant Chain (Ii) in MHC class II processing?
A. It loads the peptide into the binding groove.
B. It prevents premature peptide binding in the ER.
C. It degrades the protein into peptides.
D. It acts as a co-receptor for CD8 T cells.
Answer: B
Rationale: The invariant chain blocks the peptide-binding groove of MHC II in the ER to
prevent it from binding endogenous peptides intended for MHC I.
5. Which cytokine is primarily responsible for the proliferation and survival of
activated T cells?
A. IL-1
B. IL-10
C. IL-2
D. IFN-gamma
Answer: C
Rationale: IL-2 acts in an autocrine and paracrine fashion to drive the clonal expansion of
activated T lymphocytes.
, 6. The process by which a T cell that binds too strongly to self-antigen in the
thymus is eliminated is called:
A. Negative selection
B. Positive selection
C. Affinity maturation
D. Somatic hypermutation
Answer: A
Rationale: Negative selection ensures central tolerance by inducing apoptosis in
thymocytes with high affinity for self-MHC/self-peptide complexes.
7. Which T cell subset is characterized by the production of IFN-gamma and is
involved in activating macrophages?
A. Th1
B. Th2
C. Th17
D. Treg
Answer: A
Rationale: Th1 cells produce IFN-gamma to enhance the microbicidal activity of
macrophages against intracellular pathogens.
8. What is the function of the CLIP protein?
A. It transports peptides to the cell surface.
B. It targets proteins for proteasomal degradation.
C. It stabilizes MHC I molecules.
D. It remains in the MHC II groove until HLA-DM facilitates its exchange for an antigen.
Answer: D
Rationale: CLIP (Class II-associated invariant chain peptide) is the remnant of the
invariant chain that stays in the MHC II groove until exchanged for an antigenic peptide.
