PCB 3233 Exam 3 V2 | PCB 3233
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 3) | University of Central
Florida
1. Which of the following signaling molecules is essential for the commitment of lymphoid
progenitor cells to the T-cell lineage upon entering the thymus?
A. Pax-5
B. Notch1
C. EBF
D. PU.1
Answer: B
Rationale: The Notch1 receptor on progenitor cells interacts with Notch ligands expressed
by thymic epithelial cells to initiate T-cell specific gene transcription. This interaction is the
definitive signal that diverts progenitors away from the B-cell fate and toward T-cell
development. In the absence of Notch1 signaling, lymphoid progenitors will default to B-
cell development even within the thymic environment.
2. During T-cell development, what is the primary purpose of ‘Positive Selection’ in the
thymic cortex?
A. To eliminate cells that react strongly to self-peptides.
,B. To ensure that T cells can recognize self-MHC molecules.
C. To induce somatic hypermutation in the TCR genes.
D. To promote the development of regulatory T cells.
Answer: B
Rationale: Positive selection is the process by which double-positive thymocytes are
tested for their ability to bind to self-MHC molecules on cortical epithelial cells.
Thymocytes that successfully bind with moderate affinity receive survival signals and
continue their maturation. Those that cannot bind MHC undergo ‘death by neglect,’
ensuring that all circulating T cells are MHC-restricted.
3. Which enzyme is responsible for the expression of tissue-specific antigens (TSAs) in the
thymus to facilitate negative selection?
A. RAG-1/2
B. AIRE
C. AID
D. TdT
Answer: B
Rationale: The Autoimmune Regulator (AIRE) protein is expressed by medullary thymic
epithelial cells (mTECs) and allows for the transcription of genes normally restricted to
specific peripheral tissues, such as insulin or keratin. This enables the thymus to expose
, developing T cells to a wide array of self-antigens. Deficiencies in AIRE lead to the clinical
condition known as APECED, characterized by multi-organ autoimmunity.
4. The ‘Pre-TCR’ consists of a rearranged TCR-beta chain and which of the following
molecules?
A. TCR-alpha
B. CD3 epsilon
C. pT-alpha (Surrogate alpha chain)
D. CD4
Answer: C
Rationale: The pre-TCR serves as a quality control checkpoint during the Double Negative
(DN) stage to ensure a functional beta chain has been rearranged. It consists of the beta
chain paired with an invariant surrogate alpha chain called pT-alpha. Successful signaling
through the pre-TCR induces proliferation, halts further beta-chain rearrangement, and
triggers the transition to the double-positive stage.
5. Which molecule provides the critical ‘Signal 2’ for the activation of naive T cells by binding
to CD28?
A. B7-1 (CD80) or B7-2 (CD86)
B. MHC Class II
C. CD40
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 3) | University of Central
Florida
1. Which of the following signaling molecules is essential for the commitment of lymphoid
progenitor cells to the T-cell lineage upon entering the thymus?
A. Pax-5
B. Notch1
C. EBF
D. PU.1
Answer: B
Rationale: The Notch1 receptor on progenitor cells interacts with Notch ligands expressed
by thymic epithelial cells to initiate T-cell specific gene transcription. This interaction is the
definitive signal that diverts progenitors away from the B-cell fate and toward T-cell
development. In the absence of Notch1 signaling, lymphoid progenitors will default to B-
cell development even within the thymic environment.
2. During T-cell development, what is the primary purpose of ‘Positive Selection’ in the
thymic cortex?
A. To eliminate cells that react strongly to self-peptides.
,B. To ensure that T cells can recognize self-MHC molecules.
C. To induce somatic hypermutation in the TCR genes.
D. To promote the development of regulatory T cells.
Answer: B
Rationale: Positive selection is the process by which double-positive thymocytes are
tested for their ability to bind to self-MHC molecules on cortical epithelial cells.
Thymocytes that successfully bind with moderate affinity receive survival signals and
continue their maturation. Those that cannot bind MHC undergo ‘death by neglect,’
ensuring that all circulating T cells are MHC-restricted.
3. Which enzyme is responsible for the expression of tissue-specific antigens (TSAs) in the
thymus to facilitate negative selection?
A. RAG-1/2
B. AIRE
C. AID
D. TdT
Answer: B
Rationale: The Autoimmune Regulator (AIRE) protein is expressed by medullary thymic
epithelial cells (mTECs) and allows for the transcription of genes normally restricted to
specific peripheral tissues, such as insulin or keratin. This enables the thymus to expose
, developing T cells to a wide array of self-antigens. Deficiencies in AIRE lead to the clinical
condition known as APECED, characterized by multi-organ autoimmunity.
4. The ‘Pre-TCR’ consists of a rearranged TCR-beta chain and which of the following
molecules?
A. TCR-alpha
B. CD3 epsilon
C. pT-alpha (Surrogate alpha chain)
D. CD4
Answer: C
Rationale: The pre-TCR serves as a quality control checkpoint during the Double Negative
(DN) stage to ensure a functional beta chain has been rearranged. It consists of the beta
chain paired with an invariant surrogate alpha chain called pT-alpha. Successful signaling
through the pre-TCR induces proliferation, halts further beta-chain rearrangement, and
triggers the transition to the double-positive stage.
5. Which molecule provides the critical ‘Signal 2’ for the activation of naive T cells by binding
to CD28?
A. B7-1 (CD80) or B7-2 (CD86)
B. MHC Class II
C. CD40
