In Crohn's disease, non-caseating granulomas are found in 30–60% of biopsies. The macrophage differentiation pathway required for granuloma maintenance involves which transcription factor and cytokine axis?
- A IL-4 activating STAT6 and PPARgamma to differentiate macrophages into M2 (alternatively activated) cells forming the granuloma
- B TGF-beta activating SMAD2/3 to differentiate macrophages into regulatory macrophages suppressing granuloma formation
- C IL-10 activating STAT3 and SOCS3 to recruit DC-SIGN+ dendritic cells as the primary granuloma-organizing cell
- D IFN-gamma activating STAT1 and IRF1 to drive macrophage differentiation into M1 (classically activated) epithelioid macrophages forming the granuloma core ✓
Explanation
Granuloma formation in Crohn's disease requires sustained Th1-driven IFN-gamma signaling that activates STAT1 and IRF1 in macrophages, driving classical (M1) activation into epithelioid macrophages — the primary cellular component of non-caseating granulomas. TNF-alpha (also produced by Th1 cells) cooperates with IFN-gamma to maintain granuloma integrity by promoting macrophage clustering and survival. This explains why anti-TNF biologics (infliximab, adalimumab) can dissolve granulomas in Crohn's disease. IL-4/STAT6-driven M2 macrophages are involved in type 2 immune responses (allergies, helminth infection), not granuloma formation. TGF-beta and IL-10 are anti-inflammatory and suppress granuloma formation.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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