Which of the following cells is the primary source of TNF-α in granulomatous inflammation?

Explanation

## Role of TNF-α in Granulomatous Inflammation **Key Point:** Activated macrophages are the principal source of TNF-α, a critical cytokine in granuloma formation and maintenance. ### Mechanism of TNF-α Production 1. **Macrophage activation** occurs via: - IFN-γ from Th1 cells - Direct antigen presentation - Pattern recognition receptor signaling 2. **TNF-α functions in granuloma formation:** - Recruits and activates additional macrophages - Promotes epithelioid cell differentiation - Facilitates multinucleated giant cell formation - Maintains granuloma cohesion and prevents dissemination ### Cellular Hierarchy in Granulomatous Inflammation | Cell Type | Primary Role | TNF-α Production | | --- | --- | --- | | Activated macrophages | Epithelioid cells, TNF-α production | **High** | | Th1 lymphocytes | IFN-γ production, macrophage activation | Minimal | | B lymphocytes | Antibody production | Negligible | | Mast cells | Immediate hypersensitivity | Minimal in granulomas | | Neutrophils | Acute inflammation | Not primary source | **High-Yield:** TNF-α is so critical to granuloma maintenance that TNF-α inhibitors (infliximab, adalimumab) can cause reactivation of latent tuberculosis by disrupting granuloma integrity. **Clinical Pearl:** In tuberculosis, TNF-α deficiency leads to granuloma breakdown and disseminated disease, demonstrating its essential protective role.