A biopsy from a patient with Crohn disease shows non-caseating granulomas. In granuloma formation, the key cytokine that drives macrophage fusion into multinucleated giant cells and maintains granuloma integrity is:

• A IL-4 and IL-13
• B IL-17 from TH17 cells, recruiting neutrophils
• C IFN-γ produced by CD4+ TH1 cells, stimulating macrophage activation and fusion ✓
• D TNF-α from mast cells activating eosinophils

Explanation

Granuloma formation requires persistent antigen stimulation of CD4+ T helper cells, which polarize toward TH1 phenotype and produce IFN-γ. IFN-γ activates macrophages (M1 polarization), inducing production of IL-12 and TNF, and drives macrophage fusion into epithelioid cells and multinucleated giant cells (Langhans or foreign body type). TNF is critically important for granuloma maintenance — anti-TNF therapies (infliximab) can cause reactivation of latent tuberculosis by disrupting granulomas. IL-4/IL-13 promote M2 (alternatively activated) macrophages; IL-17 recruits neutrophils.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.