Immunology Exam 3 - PCB 3233 2026 – UCF
1. Which molecule is responsible for the transport of processed peptides into
the endoplasmic reticulum for MHC Class I loading?
A. Invariant chain
B. HLA-DM
C. TAP1/TAP2 complex
D. Tapasin
Answer: C
Rationale: The Transporter associated with Antigen Processing (TAP) complex pumps
peptides from the cytosol into the ER lumen.
2. Which cell type is primarily responsible for secreting antibodies during an
immune response?
A. Plasma cells
B. Helper T cells
C. Cytotoxic T cells
D. Dendritic cells
Answer: A
Rationale: Plasma cells are terminally differentiated B cells that specialize in large-scale
antibody production.
,3. The primary function of the MHC Class II molecule is to present peptides to:
A. CD4+ T cells
B. Natural Killer cells
C. CD8+ T cells
D. B cells
Answer: A
Rationale: MHC Class II molecules present exogenous antigens to CD4+ helper T cells.
4. Which antibody isotype is primarily found as a dimer in mucosal secretions
like saliva and breast milk?
A. IgG
B. IgM
C. IgE
D. IgA
Answer: D
Rationale: Secretory IgA exists as a dimer and is the predominant antibody in mucosal
surfaces.
5. What is the role of the Invariant Chain (Ii) in MHC Class II processing?
A. It transports peptides to the ER
B. It helps in the folding of MHC Class I
C. It cleaves antigens into peptides
D. It blocks the peptide-binding groove in the ER
Answer: D
Rationale: The invariant chain prevents endogenous peptides from binding to MHC Class II
in the ER.
, 6. Which enzyme is essential for initiating Somatic Hypermutation and Isotype
Switching?
A. Activation-Induced Deaminase (AID)
B. RAG-2
C. RAG-1
D. Terminal Deoxynucleotidyl Transferase (TdT)
Answer: A
Rationale: AID converts cytosine to uracil in DNA, triggering mutations and class switch
recombination.
7. T-cell receptors (TCRs) recognize antigens only when they are:
A. In their native, three-dimensional form
B. Soluble in the plasma
C. Opsonized by complement
D. Bound to an MHC molecule
Answer: D
Rationale: T cells require MHC-restricted antigen presentation to recognize peptides.
8. Which cytokine is most critical for the differentiation of naive T cells into Th1
cells?
A. IL-4
B. IL-10
C. IL-17
D. IL-12
Answer: D
Rationale: IL-12, often produced by DCs and macrophages, promotes Th1 differentiation
for intracellular pathogen defense.
1. Which molecule is responsible for the transport of processed peptides into
the endoplasmic reticulum for MHC Class I loading?
A. Invariant chain
B. HLA-DM
C. TAP1/TAP2 complex
D. Tapasin
Answer: C
Rationale: The Transporter associated with Antigen Processing (TAP) complex pumps
peptides from the cytosol into the ER lumen.
2. Which cell type is primarily responsible for secreting antibodies during an
immune response?
A. Plasma cells
B. Helper T cells
C. Cytotoxic T cells
D. Dendritic cells
Answer: A
Rationale: Plasma cells are terminally differentiated B cells that specialize in large-scale
antibody production.
,3. The primary function of the MHC Class II molecule is to present peptides to:
A. CD4+ T cells
B. Natural Killer cells
C. CD8+ T cells
D. B cells
Answer: A
Rationale: MHC Class II molecules present exogenous antigens to CD4+ helper T cells.
4. Which antibody isotype is primarily found as a dimer in mucosal secretions
like saliva and breast milk?
A. IgG
B. IgM
C. IgE
D. IgA
Answer: D
Rationale: Secretory IgA exists as a dimer and is the predominant antibody in mucosal
surfaces.
5. What is the role of the Invariant Chain (Ii) in MHC Class II processing?
A. It transports peptides to the ER
B. It helps in the folding of MHC Class I
C. It cleaves antigens into peptides
D. It blocks the peptide-binding groove in the ER
Answer: D
Rationale: The invariant chain prevents endogenous peptides from binding to MHC Class II
in the ER.
, 6. Which enzyme is essential for initiating Somatic Hypermutation and Isotype
Switching?
A. Activation-Induced Deaminase (AID)
B. RAG-2
C. RAG-1
D. Terminal Deoxynucleotidyl Transferase (TdT)
Answer: A
Rationale: AID converts cytosine to uracil in DNA, triggering mutations and class switch
recombination.
7. T-cell receptors (TCRs) recognize antigens only when they are:
A. In their native, three-dimensional form
B. Soluble in the plasma
C. Opsonized by complement
D. Bound to an MHC molecule
Answer: D
Rationale: T cells require MHC-restricted antigen presentation to recognize peptides.
8. Which cytokine is most critical for the differentiation of naive T cells into Th1
cells?
A. IL-4
B. IL-10
C. IL-17
D. IL-12
Answer: D
Rationale: IL-12, often produced by DCs and macrophages, promotes Th1 differentiation
for intracellular pathogen defense.
