A 35-year-old is found to have granulomatous inflammation on lymph node biopsy. Caseous necrosis is present in the center of the granulomas. Ziehl-Neelsen staining reveals acid-fast bacilli. The key cytokine produced by CD4 T helper cells that drives macrophage activation and granuloma formation is:

• A IL-4
• B IL-17
• C IL-10
• D IFN-γ (interferon-gamma) ✓

Explanation

IFN-γ produced by Th1 CD4+ T cells and NK cells is the critical activating signal for macrophages, transforming them into epithelioid cells and multinucleated giant cells that form granulomas. Activated macrophages kill mycobacteria via reactive oxygen and nitrogen intermediates. IL-4 drives Th2 responses and alternative macrophage activation; IL-17 is produced by Th17 cells and recruits neutrophils; IL-10 is anti-inflammatory and inhibits granuloma formation.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.