PCB 3233 Immunology Exam 2 Practice 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. CLIP
Answer: A
Rationale: TAP is a heterodimer in the ER membrane that moves proteasome-derived
peptides into the ER where they can bind to MHC Class I molecules.
2. Which MHC molecule is expressed on nearly all nucleated cells in the body?
A. MHC Class I
B. MHC Class II
C. MHC Class III
D. MHC Class IV
Answer: A
Rationale: MHC Class I is expressed on all nucleated cells to present internal antigens to
CD8+ T cells, whereas MHC Class II is primarily on professional APCs.
,3. What is the primary function of the Invariant Chain (Ii) in MHC Class II
processing?
A. To degrade extracellular proteins
B. To transport MHC II to the cell surface
C. To activate the proteasome
D. To prevent premature binding of self-peptides in the ER
Answer: D
Rationale: The invariant chain occupies the peptide-binding groove of MHC II in the ER to
prevent it from binding peptides destined for MHC I.
4. Which antibody isotype is primarily found in secretions like saliva, tears, and
breast milk?
A. IgG
B. IgA
C. IgE
D. IgM
Answer: B
Rationale: IgA is the predominant immunoglobulin in mucosal secretions, often existing as
a dimer with a secretory component.
5. What is the term for the strength of the total binding between a multivalent
antibody and a multivalent antigen?
A. Affinity
B. Valency
C. Avidity
D. Specificity
Answer: C
Rationale: Avidity refers to the accumulated strength of multiple affinities of individual
binding sites; affinity refers to the strength of a single interaction.
, 6. Which enzyme is essential for somatic hypermutation and isotype switching
in B cells?
A. RAG-1
B. TdT
C. AID (Activation-induced cytidine deaminase)
D. Artemis
Answer: C
Rationale: AID converts cytosine to uracil in DNA, initiating the pathways for both somatic
hypermutation and class switch recombination.
7. CD4+ T cells recognize antigens presented in the context of:
A. MHC Class I
B. CD8 molecules
C. MHC Class II
D. Toll-like receptors
Answer: C
Rationale: CD4 is a co-receptor that specifically binds to the non-polymorphic region of
MHC Class II molecules.
8. Which complement component acts as a potent anaphylatoxin and
chemoattractant for neutrophils?
A. C3b
B. C1q
C. C9
D. C5a
Answer: D
Rationale: C5a (and to a lesser extent C3a) triggers degranulation of mast cells and attracts
phagocytic cells to the site of infection.
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. CLIP
Answer: A
Rationale: TAP is a heterodimer in the ER membrane that moves proteasome-derived
peptides into the ER where they can bind to MHC Class I molecules.
2. Which MHC molecule is expressed on nearly all nucleated cells in the body?
A. MHC Class I
B. MHC Class II
C. MHC Class III
D. MHC Class IV
Answer: A
Rationale: MHC Class I is expressed on all nucleated cells to present internal antigens to
CD8+ T cells, whereas MHC Class II is primarily on professional APCs.
,3. What is the primary function of the Invariant Chain (Ii) in MHC Class II
processing?
A. To degrade extracellular proteins
B. To transport MHC II to the cell surface
C. To activate the proteasome
D. To prevent premature binding of self-peptides in the ER
Answer: D
Rationale: The invariant chain occupies the peptide-binding groove of MHC II in the ER to
prevent it from binding peptides destined for MHC I.
4. Which antibody isotype is primarily found in secretions like saliva, tears, and
breast milk?
A. IgG
B. IgA
C. IgE
D. IgM
Answer: B
Rationale: IgA is the predominant immunoglobulin in mucosal secretions, often existing as
a dimer with a secretory component.
5. What is the term for the strength of the total binding between a multivalent
antibody and a multivalent antigen?
A. Affinity
B. Valency
C. Avidity
D. Specificity
Answer: C
Rationale: Avidity refers to the accumulated strength of multiple affinities of individual
binding sites; affinity refers to the strength of a single interaction.
, 6. Which enzyme is essential for somatic hypermutation and isotype switching
in B cells?
A. RAG-1
B. TdT
C. AID (Activation-induced cytidine deaminase)
D. Artemis
Answer: C
Rationale: AID converts cytosine to uracil in DNA, initiating the pathways for both somatic
hypermutation and class switch recombination.
7. CD4+ T cells recognize antigens presented in the context of:
A. MHC Class I
B. CD8 molecules
C. MHC Class II
D. Toll-like receptors
Answer: C
Rationale: CD4 is a co-receptor that specifically binds to the non-polymorphic region of
MHC Class II molecules.
8. Which complement component acts as a potent anaphylatoxin and
chemoattractant for neutrophils?
A. C3b
B. C1q
C. C9
D. C5a
Answer: D
Rationale: C5a (and to a lesser extent C3a) triggers degranulation of mast cells and attracts
phagocytic cells to the site of infection.
