Cellular basis of immune response MCQs With Answer

Introduction: Welcome to this focused MCQ set on the cellular basis of immune responses, designed for M.Pharm students preparing for exams and practical immunotechnology applications. These questions emphasize cellular players—dendritic cells, macrophages, NK cells, T and B lymphocyte subsets—and molecular mechanisms such as antigen processing and presentation, costimulation, cytokine-driven differentiation, cytotoxic effector functions, germinal center reactions, and tolerance. Each question probes mechanistic understanding and clinical or biotechnological relevance, including antigen cross-presentation, AID-driven antibody maturation, and immunological synapse formation. Use this set to test conceptual clarity, identify knowledge gaps, and strengthen reasoning applied to vaccine design, biologics, immune-modulating therapeutics, and translational research.

Q1. Which antigen-presenting cell is considered the most potent activator of naïve T cells due to its high expression of MHC class II and costimulatory molecules?

• B cells
• Macrophages
• Dendritic cells
• Neutrophils

Correct Answer: Dendritic cells

Q2. Peptides presented on MHC class I molecules are primarily derived from which source within the cell?

• Endogenous cytosolic proteins degraded by the proteasome
• Exogenous proteins internalized in endosomes
• Surface-bound immune complexes
• Mitochondrial membrane proteins exclusively

Correct Answer: Endogenous cytosolic proteins degraded by the proteasome

Q3. Which mechanism best describes antigen cross-presentation by dendritic cells to CD8+ T cells?

• Direct transfer of peptides from B cells to CD8+ T cells
• Phagosome-to-cytosol transfer of exogenous antigen followed by proteasomal processing
• Presentation of intact proteins on MHC II to CD8+ T cells
• Secretion of processed peptides into the extracellular space for uptake by CD8+ T cells

Correct Answer: Phagosome-to-cytosol transfer of exogenous antigen followed by proteasomal processing

Q4. The critical second signal required for naïve T cell activation is delivered when CD28 on T cells binds which molecules on antigen-presenting cells?

• ICAM-1 (CD54)
• B7 family (CD80/CD86)
• CD40
• MHC class II

Correct Answer: B7 family (CD80/CD86)

Q5. Which cytokine is the principal driver of Th1 differentiation and promotes cell-mediated immunity against intracellular pathogens?

• IL-4
• IL-12
• IL-10
• TGF-β

Correct Answer: IL-12

Q6. Which transcription factor is the master regulator for differentiation of naïve CD4+ T cells into Th17 cells?

• GATA3
• T-bet
• RORγt
• FOXP3

Correct Answer: RORγt

Q7. Cytotoxic T lymphocytes induce apoptosis of target cells primarily through which pair of effector molecules?

• Perforin and granzyme
• Complement C5b-9 and C3b
• TNF-α and IL-1β
• Reactive oxygen species and nitric oxide

Correct Answer: Perforin and granzyme

Q8. T cell anergy commonly results when TCR engagement occurs in the absence of which signal?

• Antigen-presenting cell migration
• Co-stimulatory signals (e.g., CD28-B7)
• Cytokine release from B cells
• Complement activation

Correct Answer: Co-stimulatory signals (e.g., CD28-B7)

Q9. Somatic hypermutation and class-switch recombination in B cells take place predominantly in which anatomical structure?

• Bone marrow
• Thymus
• Germinal centers of secondary lymphoid organs
• Spleen marginal zone exclusively

Correct Answer: Germinal centers of secondary lymphoid organs

Q10. Activation-induced cytidine deaminase (AID) is required for which processes in B cell maturation?

• V(D)J recombination in pro-B cells
• Somatic hypermutation and class-switch recombination
• Affinity-independent isotype expression
• Complement fixation on antibody Fc regions

Correct Answer: Somatic hypermutation and class-switch recombination

Q11. Natural killer (NK) cells preferentially kill target cells that have downregulated which molecule, a phenomenon termed “missing-self” recognition?

• MHC class I
• MHC class II
• B7 (CD80/CD86)
• CD40

Correct Answer: MHC class I

Q12. Antigen processing for presentation on MHC class II molecules occurs primarily in which intracellular compartments?

• Cytosolic proteasomes
• Endosomal/lysosomal compartments
• Rough endoplasmic reticulum lumen
• Golgi cisternae

Correct Answer: Endosomal/lysosomal compartments

Q13. Which chemokine receptor directs naïve T cells to enter lymph nodes via high endothelial venules (HEVs)?

• CCR7
• CXCR5
• CCR5
• CXCR4

Correct Answer: CCR7

Q14. The T cell receptor recognizes antigen in what form?

• Peptide alone without MHC
• Peptide bound to MHC molecule (peptide-MHC complex)
• Conformational epitopes on native proteins only
• Lipids presented on complement proteins

Correct Answer: Peptide bound to MHC molecule (peptide-MHC complex)

Q15. Regulatory T cell development and suppressive function critically depend on which transcription factor?

• FOXP3
• RORγt
• T-bet
• GATA3

Correct Answer: FOXP3

Q16. Which antigen-presenting cell is a major source of IL-12 and thereby links innate sensing to Th1 polarization and NK cell activation?

• Dendritic cells
• B cells
• Eosinophils
• Neutrophils

Correct Answer: Dendritic cells

Q17. Antibody-dependent cell-mediated cytotoxicity (ADCC) is primarily executed by which effector cell via Fc receptor recognition?

• Natural killer (NK) cells
• Macrophages
• Dendritic cells
• B cells

Correct Answer: Natural killer (NK) cells

Q18. Central tolerance that deletes highly autoreactive T cell clones occurs predominantly in which organ?

• Thymus
• Bone marrow
• Spleen
• Lymph node

Correct Answer: Thymus

Q19. Stabilization of the immunological synapse between a T cell and an antigen-presenting cell is chiefly mediated by which adhesion interaction?

• LFA-1 on T cells binding ICAM-1 on APCs
• CD28 on T cells binding B7 on APCs
• TCR binding peptide-MHC complex
• Fas on T cells binding FasL on APCs

Correct Answer: LFA-1 on T cells binding ICAM-1 on APCs

Q20. Which Toll-like receptor recognizes unmethylated CpG motifs commonly found in bacterial and viral DNA?

• TLR4
• TLR9
• TLR3
• TLR5

Correct Answer: TLR9

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