A biopsy from a pulmonary lesion shows non-necrotising granulomas without caseation composed of epithelioid histiocytes and Langhans-type giant cells. No organisms are found on special stains (ZN, PAS, GMS). Serum ACE is elevated. Which cytokine is most critical for the induction and maintenance of this granuloma type?
- A TNF-alpha — essential for macrophage activation, fusion into giant cells, and granuloma architectural integrity via sustained NF-kB signalling ✓
- B IL-17A — drives Th17-mediated neutrophilic recruitment forming the granuloma core
- C IL-4 and IL-13 — Th2 cytokines drive alternative macrophage activation into epithelioid cells
- D IFN-gamma alone — sufficient for granuloma maintenance independently of TNF-alpha
Explanation
TNF-alpha plays a non-redundant role in granuloma formation and maintenance. It acts via TNFR1-mediated NF-kB activation to sustain macrophage activation, promote fusion into multinucleated giant cells, and maintain the structural integrity of granulomas. This is demonstrated clinically by TNF-alpha antagonist therapy (e.g., infliximab, etanercept) causing reactivation of latent tuberculosis and granulomatous infections due to granuloma disintegration. IFN-gamma (produced by Th1 cells) initiates classical macrophage activation and is the primary signal for macrophage-to-epithelioid transformation but requires ongoing TNF-alpha for granuloma maintenance. IL-17A/Th17 responses mediate neutrophilic/early granulomatous inflammation. IL-4/IL-13 drive Th2/M2 macrophage activation, not classical TB-type granulomas.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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