PCB3233 Immunology Exam 2 Practice 2026 – UCF
1. Which molecule is responsible for transporting peptides from the cytosol into
the endoplasmic reticulum for loading onto MHC Class I?
A. Calnexin
B. Invariant chain
C. TAP (Transporter associated with antigen processing)
D. HLA-DM
Answer: C
Rationale: TAP1 and TAP2 form a heterodimer in the ER membrane that actively
transports cytosolic peptides into the ER lumen to meet MHC Class I molecules.
2. Which of the following MHC Class II genes are found in humans?
A. HLA-A, B, and C
B. HLA-DP, DQ, and DR
C. H2-K, D, and L
D. HLA-DM and DO only
Answer: B
Rationale: The human MHC Class II region contains the DP, DQ, and DR loci, which encode
the alpha and beta chains of the functional molecules.
,3. The process by which B cells produce antibodies with higher affinity for an
antigen during an immune response is known as:
A. Allelic exclusion
B. V(D)J recombination
C. Class switch recombination
D. Somatic hypermutation
Answer: D
Rationale: Somatic hypermutation occurs in germinal centers and involves point
mutations in the V regions, followed by selection for higher affinity.
4. Which chaperone molecule stabilizes the MHC Class I heavy chain until beta-2
microglobulin binds?
A. Calreticulin
B. Erp57
C. Calnexin
D. Tapasin
Answer: C
Rationale: Calnexin is the initial chaperone that binds the nascent MHC Class I heavy chain
until it associates with beta-2 microglobulin.
5. What is the primary function of the Invariant Chain (Ii) in the MHC Class II
pathway?
A. To block the peptide-binding groove from binding ER-resident peptides
B. To facilitate peptide loading in the ER
C. To degrade misfolded proteins
D. To act as a co-receptor for CD8 T cells
Answer: A
Rationale: The Invariant Chain occupies the MHC Class II groove in the ER to prevent it
from binding peptides destined for MHC Class I.
, 6. Which enzyme is essential for both Somatic Hypermutation and Class Switch
Recombination?
A. AID (Activation-induced cytidine deaminase)
B. Artemis
C. RAG-1/RAG-2
D. TdT (Terminal deoxynucleotidyl transferase)
Answer: A
Rationale: AID deaminates cytosine to uracil in DNA, initiating the pathways for both
affinity maturation and isotype switching.
7. T-cell positive selection occurs in which part of the thymus?
A. Medulla
B. Cortex
C. Subcapsular zone
D. Cortico-medullary junction
Answer: B
Rationale: Positive selection, where thymocytes are tested for their ability to bind self-
MHC, occurs in the thymic cortex.
8. Which protein is responsible for expressing tissue-specific antigens in the
thymus to promote negative selection?
A. AIRE (Autoimmune Regulator)
B. Pax-5
C. Notch-1
D. FoxP3
Answer: A
Rationale: AIRE allows medullary thymic epithelial cells to express proteins normally
found only in peripheral tissues to eliminate self-reactive T cells.
1. Which molecule is responsible for transporting peptides from the cytosol into
the endoplasmic reticulum for loading onto MHC Class I?
A. Calnexin
B. Invariant chain
C. TAP (Transporter associated with antigen processing)
D. HLA-DM
Answer: C
Rationale: TAP1 and TAP2 form a heterodimer in the ER membrane that actively
transports cytosolic peptides into the ER lumen to meet MHC Class I molecules.
2. Which of the following MHC Class II genes are found in humans?
A. HLA-A, B, and C
B. HLA-DP, DQ, and DR
C. H2-K, D, and L
D. HLA-DM and DO only
Answer: B
Rationale: The human MHC Class II region contains the DP, DQ, and DR loci, which encode
the alpha and beta chains of the functional molecules.
,3. The process by which B cells produce antibodies with higher affinity for an
antigen during an immune response is known as:
A. Allelic exclusion
B. V(D)J recombination
C. Class switch recombination
D. Somatic hypermutation
Answer: D
Rationale: Somatic hypermutation occurs in germinal centers and involves point
mutations in the V regions, followed by selection for higher affinity.
4. Which chaperone molecule stabilizes the MHC Class I heavy chain until beta-2
microglobulin binds?
A. Calreticulin
B. Erp57
C. Calnexin
D. Tapasin
Answer: C
Rationale: Calnexin is the initial chaperone that binds the nascent MHC Class I heavy chain
until it associates with beta-2 microglobulin.
5. What is the primary function of the Invariant Chain (Ii) in the MHC Class II
pathway?
A. To block the peptide-binding groove from binding ER-resident peptides
B. To facilitate peptide loading in the ER
C. To degrade misfolded proteins
D. To act as a co-receptor for CD8 T cells
Answer: A
Rationale: The Invariant Chain occupies the MHC Class II groove in the ER to prevent it
from binding peptides destined for MHC Class I.
, 6. Which enzyme is essential for both Somatic Hypermutation and Class Switch
Recombination?
A. AID (Activation-induced cytidine deaminase)
B. Artemis
C. RAG-1/RAG-2
D. TdT (Terminal deoxynucleotidyl transferase)
Answer: A
Rationale: AID deaminates cytosine to uracil in DNA, initiating the pathways for both
affinity maturation and isotype switching.
7. T-cell positive selection occurs in which part of the thymus?
A. Medulla
B. Cortex
C. Subcapsular zone
D. Cortico-medullary junction
Answer: B
Rationale: Positive selection, where thymocytes are tested for their ability to bind self-
MHC, occurs in the thymic cortex.
8. Which protein is responsible for expressing tissue-specific antigens in the
thymus to promote negative selection?
A. AIRE (Autoimmune Regulator)
B. Pax-5
C. Notch-1
D. FoxP3
Answer: A
Rationale: AIRE allows medullary thymic epithelial cells to express proteins normally
found only in peripheral tissues to eliminate self-reactive T cells.
