MCQ – 10817

Correct Answer » A Explanation

Interferon-gamma (IFN-γ) is the most important macrophage-activating cytokine.

Its major functions include:

• Activation of macrophages
• Enhancement of intracellular killing of microbes
• Promotion of antigen presentation (↑ MHC expression)
• Stimulation of cell-mediated immunity
• Promotion of Th1 immune responses

The principal source of IFN-γ is CD4⁺ T helper 1 (Th1) cells

Other cells that can produce IFN-γ include:

• Natural Killer (NK) cells
• CD8⁺ T cells

However, among the given options, CD4⁺ Th1 cells are the best answer.

Option Analysis

A. CD4⁺ T cell

More specifically:

• Th1 subset of CD4⁺ T cells
• Secretes:
  • IFN-γ
  • IL-2
  • TNF-β

Functions:

• Macrophage activation
• Defense against intracellular organisms (e.g., Mycobacterium tuberculosis)

B. CD8⁺ T cells

CD8⁺ cytotoxic T cells can produce IFN-γ, but they are primarily involved in:

• Killing virus-infected cells
• Tumor cell destruction

The principal source tested in immunology MCQs is Th1 CD4⁺ cells.

C. RBC

Red blood cells:

• Transport oxygen and carbon dioxide
• Do not participate in cytokine secretion

D. Neutrophils

Neutrophils are important phagocytes but are not a major source of IFN-γ.

They mainly:

• Phagocytose bacteria
• Release reactive oxygen species
• Form NETs (Neutrophil Extracellular Traps)