T-cell activation mechanisms MCQs With Answer

T-cell activation mechanisms MCQs With Answer

Introduction:
This quiz collection focuses on the molecular and cellular mechanisms that govern T‑cell activation, an essential topic for M.Pharm students studying immunotechnology. The questions emphasize antigen recognition, co‑stimulatory and co‑inhibitory pathways, intracellular signaling cascades (Lck, ZAP‑70, LAT, PLCγ1), cytokine‑driven differentiation, and pharmacologic modulation of T‑cell responses. Each question is designed to test conceptual understanding and practical implications for drug action, vaccine design, and immune modulation. Use these MCQs to strengthen your grasp of how T cells are primed, regulated, and targeted therapeutically, and to prepare for both exams and research applications in immunopharmacology.

Q1. What defines “Signal 1” in T-cell activation?

• Recognition of peptide-MHC by the T-cell receptor (TCR)
• CD28 binding to B7 on the antigen-presenting cell
• Cytokine-driven differentiation such as IL-12
• PD-1 binding to PD-L1

Correct Answer: Recognition of peptide-MHC by the T-cell receptor (TCR)

Q2. Which molecular interaction constitutes the classic “Signal 2” costimulatory signal required for naive T-cell activation?

• CD28 binding to B7 molecules (CD80/CD86) on the antigen-presenting cell
• TCR binding to peptide presented on MHC
• IL-2 binding to its receptor
• CTLA-4 binding to B7

Correct Answer: CD28 binding to B7 molecules (CD80/CD86) on the antigen-presenting cell

Q3. What is commonly referred to as “Signal 3” during T-cell activation?

• Cytokine milieu such as IL-2 that directs T-cell proliferation and differentiation
• Direct TCR recognition of antigenic peptide-MHC
• Adhesion molecule interactions like LFA-1:ICAM-1
• PD-1 mediated inhibition

Correct Answer: Cytokine milieu such as IL-2 that directs T-cell proliferation and differentiation

Q4. Which kinase phosphorylates CD3 ITAMs immediately after TCR engagement?

• Lck (a Src-family tyrosine kinase)
• ZAP-70
• PKCθ
• JAK1

Correct Answer: Lck (a Src-family tyrosine kinase)

Q5. What is the primary role of ZAP-70 in TCR signaling?

• Binds phosphorylated CD3 ITAMs and propagates downstream signaling
• Directly phosphorylates CD28
• Degrades PIP2 into IP3 and DAG
• Acts as a transcription factor in the nucleus

Correct Answer: Binds phosphorylated CD3 ITAMs and propagates downstream signaling

Q6. LAT (Linker for Activation of T cells) functions mainly as:

• An adaptor protein phosphorylated by ZAP-70 to recruit signaling complexes (e.g., PLCγ1, SLP-76)
• A GTPase that activates Ras directly
• An ion channel controlling calcium influx
• A cytokine that promotes Th17 differentiation

Correct Answer: An adaptor protein phosphorylated by ZAP-70 to recruit signaling complexes (e.g., PLCγ1, SLP-76)

Q7. How do calcineurin inhibitors such as cyclosporine and tacrolimus suppress T-cell activation?

• They inhibit calcineurin, preventing NFAT dephosphorylation and IL-2 transcription
• They block CD28:B7 interaction directly
• They increase PD-L1 expression on APCs
• They inhibit proteasomal degradation of IκB

Correct Answer: They inhibit calcineurin, preventing NFAT dephosphorylation and IL-2 transcription

Q8. Which statement best describes the immunological synapse formed between a T cell and an APC?

• Central TCR/MHC-peptide cluster (cSMAC) surrounded by adhesion molecules (pSMAC)
• Random dispersion of receptors across the contact surface
• Exclusive accumulation of cytokines at the contact point without receptor clustering
• Only occurs between B cells and T cells

Correct Answer: Central TCR/MHC-peptide cluster (cSMAC) surrounded by adhesion molecules (pSMAC)

Q9. What is the principal inhibitory mechanism of CTLA-4 in T-cell regulation?

• Inhibitory receptor that outcompetes CD28 for B7 binding and delivers negative signals
• Enhances IL-2 production to cause negative feedback
• Blocks TCR-peptide-MHC interaction directly
• Stimulates PD-L1 expression on T cells

Correct Answer: Inhibitory receptor that outcompetes CD28 for B7 binding and delivers negative signals

Q10. The PD-1/PD-L1 pathway primarily functions to:

• Limit T-cell activity in peripheral tissues, promoting tolerance and preventing tissue damage
• Enhance initial T-cell priming in lymph nodes
• Promote V(D)J recombination during thymic development
• Directly activate NF-κB in T cells

Correct Answer: Limit T-cell activity in peripheral tissues, promoting tolerance and preventing tissue damage

Q11. How do bacterial superantigens activate large numbers of T cells?

• Cross-link TCR Vβ regions with MHC II outside the peptide-binding groove causing polyclonal T-cell activation
• Bind the peptide-binding groove of MHC and are processed into peptides
• Act as cytokines that directly induce T-cell proliferation
• Inhibit apoptosis in thymocytes

Correct Answer: Cross-link TCR Vβ regions with MHC II outside the peptide-binding groove causing polyclonal T-cell activation

Q12. What is “cross-presentation” in the context of antigen presentation?

• Dendritic cells presenting exogenous antigens on MHC class I to prime CD8+ T cells
• Presentation of endogenous antigens on MHC class II
• Transfer of peptide-MHC complexes between B cells
• Loading of peptides onto MHC without APC involvement

Correct Answer: Dendritic cells presenting exogenous antigens on MHC class I to prime CD8+ T cells

Q13. Which chain of the IL-2 receptor is specifically associated with the high-affinity receptor expressed on activated T cells?

• CD25 (IL-2Rα), which forms the high-affinity IL-2 receptor with β and γ chains
• CD3ζ chain
• CD28
• CD45

Correct Answer: CD25 (IL-2Rα), which forms the high-affinity IL-2 receptor with β and γ chains

Q14. Anergy in T cells is best described as:

• Induction of unresponsiveness when TCR engagement occurs without adequate costimulatory signals
• Programmed cell death triggered by Fas-FasL
• Rapid proliferation following strong co-stimulation
• Transformation into a memory T cell

Correct Answer: Induction of unresponsiveness when TCR engagement occurs without adequate costimulatory signals

Q15. Which signaling pathway is primarily responsible for activation of NF-κB following TCR stimulation?

• PKCθ activation leading to the CARMA1–Bcl10–MALT1 complex and NF-κB activation
• Direct phosphorylation of NF-κB by ZAP-70
• PI3K activation producing cAMP
• Calcineurin-mediated dephosphorylation

Correct Answer: PKCθ activation leading to the CARMA1–Bcl10–MALT1 complex and NF-κB activation

Q16. Which metabolic preference differentiates memory T cells from effector T cells?

• Memory T cells preferentially use fatty acid oxidation, while effector T cells rely on glycolysis
• Memory T cells depend solely on anaerobic glycolysis
• Effector T cells use fatty acid oxidation whereas memory T cells use glycolysis
• Both types exclusively use oxidative phosphorylation

Correct Answer: Memory T cells preferentially use fatty acid oxidation, while effector T cells rely on glycolysis

Q17. How does the biologic drug abatacept modulate T-cell activation?

• CTLA-4-Ig fusion that binds B7 and blocks CD28-mediated costimulation
• Anti-PD-1 antibody that enhances T-cell activity
• Calcineurin inhibitor that blocks NFAT
• IL-2 receptor antagonist that depletes CD25+ cells

Correct Answer: CTLA-4-Ig fusion that binds B7 and blocks CD28-mediated costimulation

Q18. Which cytokine and transcription factor pair is most closely linked to Th1 differentiation?

• IL-12 signaling induces T-bet and promotes Th1 differentiation
• IL-4 signaling induces RORγt and promotes Th1 differentiation
• TGF-β induces GATA3 for Th1 differentiation
• IL-6 induces FoxP3 for Th1 differentiation

Correct Answer: IL-12 signaling induces T-bet and promotes Th1 differentiation

Q19. During thymic selection, what distinguishes positive selection from negative selection?

• Positive selection selects thymocytes that recognize self-MHC; negative selection deletes those with high affinity for self-peptides
• Positive selection deletes autoreactive thymocytes; negative selection enhances survival of high-affinity clones
• Both processes occur only after T cells leave the thymus
• Negative selection increases TCR diversity, while positive selection narrows it

Correct Answer: Positive selection selects thymocytes that recognize self-MHC; negative selection deletes those with high affinity for self-peptides

Q20. How does PLCγ1 contribute to sustained calcium signaling and NFAT activation after TCR engagement?

• PLCγ1 hydrolyzes PIP2 to IP3, which increases intracellular Ca2+ and activates calcineurin/NFAT signaling
• PLCγ1 directly phosphorylates NFAT in the nucleus
• PLCγ1 transports calcium into the extracellular space
• PLCγ1 ubiquitinates ZAP-70 to terminate signaling

Correct Answer: PLCγ1 hydrolyzes PIP2 to IP3, which increases intracellular Ca2+ and activates calcineurin/NFAT signaling

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