## Hallmark of Chronic Inflammation **Key Point:** The defining histological feature of chronic inflammation is the presence of mononuclear cell infiltration, primarily lymphocytes, macrophages (activated), and plasma cells. ### Cellular Composition | Cell Type | Role in Chronic Inflammation | |-----------|------------------------------| | Lymphocytes (T & B) | Adaptive immune response, antigen presentation | | Macrophages | Phagocytosis, cytokine production, antigen presentation | | Plasma cells | Antibody production | | Fibroblasts | Tissue repair and fibrosis | **High-Yield:** Chronic inflammation is characterized by: - **Duration:** Weeks to months to years (vs. acute: minutes to hours) - **Cellular infiltrate:** Mononuclear cells predominate (vs. acute: neutrophils) - **Tissue damage:** Often accompanied by tissue destruction and fibrosis - **Angiogenesis:** New blood vessel formation ### Why Mononuclear Cells? Mononuclear cells are recruited via chemokines (CCL2, CXCL10) and are capable of: 1. Prolonged survival in tissue 2. Sustained cytokine production 3. Antigen presentation and adaptive immunity 4. Tissue remodeling and fibrosis **Clinical Pearl:** Granulomas (organized collections of epithelioid macrophages and lymphocytes) are a *special form* of chronic inflammation seen in TB, sarcoidosis, and fungal infections—not the hallmark of all chronic inflammation. **Mnemonic:** **MAC** = **M**ononuclear cells, **A**ctivated macrophages, **C**hronic inflammation.
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