Granuloma formation - cell types and mechanism
Core concept
- A granuloma is an organised collection of activated macrophages formed when an antigen cannot be eliminated or degraded
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Persistent antigen (mycobacterium, fungus, beryllium, suture, unknown)
- macrophage phagocytoses but cannot destroy
- -> IL-12 -> CD4+ Th1 -> IFN-gamma
- -> macrophage activation
- -> epithelioid cells (abundant pink cytoplasm, secretory not phagocytic)
- -> fusion -> multinucleated giant cells (Langhans - peripheral horseshoe nuclei)
- -> TNF-alpha maintains the structure
- -> CD4+ T-cell cuff, fibroblast rim, collagen
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- The core cell is the macrophage; the CD4+ T cell is the orchestrator; TNF is the glue
- Blocking TNF dissolves existing granulomas -> reactivation TB is the mechanism, not an idiosyncrasy
3 more sections, plus exam facts
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