## Source of TNF-α in Chronic Inflammation **Key Point:** Activated macrophages are the principal source of TNF-α, a central pro-inflammatory cytokine in chronic inflammatory responses. ### Role of TNF-α in Chronic Inflammation TNF-α (tumor necrosis factor-alpha) is produced predominantly by: - **Activated macrophages** — the hallmark cell of chronic inflammation - Also produced by: T lymphocytes, NK cells, and endothelial cells (to a lesser extent) ### Functions of TNF-α 1. **Endothelial activation** — increases vascular permeability and adhesion molecule expression 2. **Recruitment of inflammatory cells** — acts as a chemoattractant 3. **Systemic effects** — fever, cachexia, shock (in high concentrations) 4. **Fibroblast activation** — promotes collagen deposition and fibrosis 5. **Apoptosis** — can induce programmed cell death in target cells ### Macrophage Activation States | Feature | M1 (Classical) | M2 (Alternative) | |---------|---|---| | **Stimulus** | IFN-γ, LPS | IL-4, IL-13 | | **TNF-α production** | High | Low | | **IL-10 production** | Low | High | | **Role** | Pro-inflammatory | Anti-inflammatory, tissue remodeling | **High-Yield:** In chronic inflammation, macrophages remain activated and continuously secrete TNF-α, IL-1, IL-6, and other cytokines, perpetuating the inflammatory response. **Clinical Pearl:** Excessive TNF-α production in chronic inflammatory diseases (rheumatoid arthritis, inflammatory bowel disease) is the rationale for TNF-α inhibitor therapy (infliximab, etanercept, adalimumab).
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