A 32-year-old woman presents with acute cellulitis of the left leg following a minor laceration. On examination, she has erythema, warmth, edema, and pain at the site. Which of the following mediators of acute inflammation is NOT responsible for the clinical features observed in this patient?

Explanation

## Mediators of Acute Inflammation in Cellulitis **Key Point:** TGF-β is a **pro-fibrotic and anti-inflammatory cytokine** primarily involved in tissue repair and fibrosis during the resolution and chronic phases of inflammation, not in the acute phase. It does NOT cause vasodilation or edema in acute inflammation. ### Acute Phase Mediators: Their Roles | Mediator | Source | Primary Effects | Role in Cellulitis | |----------|--------|-----------------|-------------------| | **Histamine** | Mast cells, basophils | ↑ Vascular permeability, vasodilation | Edema, erythema, warmth | | **Bradykinin** | Kinin cascade (contact system) | Pain, vasodilation, ↑ permeability | Severe pain sensation | | **PGE₂** | Macrophages, endothelial cells | Vasodilation, potentiates pain | Warmth, pain amplification | | **TNF-α** | Macrophages, neutrophils | Vasodilation, ↑ permeability, systemic effects | Fever, systemic inflammation | | **IL-1β** | Macrophages, endothelial cells | Vasodilation, ↑ permeability, fever | Edema, systemic response | | **TGF-β** | Macrophages, platelets, fibroblasts | **Anti-inflammatory, pro-fibrotic** | Resolution & tissue repair (LATE phase) | ### Why TGF-β Is NOT an Acute Mediator 1. **Timing:** TGF-β is upregulated during the **resolution and remodeling phases** (days 3–7 and beyond), not during acute inflammation (0–24 hours). 2. **Function:** TGF-β **suppresses** acute inflammatory responses by inhibiting macrophage activation and neutrophil recruitment. 3. **Mechanism:** TGF-β promotes **fibroblast proliferation and collagen deposition**, leading to scar formation — this is tissue repair, not acute inflammation. 4. **Effect on vasculature:** TGF-β does NOT cause vasodilation or increase vascular permeability; instead, it stabilizes the endothelium. **High-Yield:** In acute cellulitis, the clinical triad of **erythema (rubor), warmth (calor), and edema (tumor)** is driven by histamine, bradykinin, prostaglandins, and cytokines like TNF-α and IL-1β. TGF-β plays no role in these acute features. **Clinical Pearl:** If a patient's cellulitis progresses to chronic inflammation or abscess formation with subsequent healing, TGF-β becomes important for scar formation and fibrosis. But in the acute phase shown here, TGF-β is irrelevant. **Mnemonic:** **HABIT** for acute mediators — **H**istamine, **A**rachidonic acid metabolites (PGE₂, LTC₄), **B**radykinin, **I**nterleukins (IL-1, IL-6, IL-8), **T**NF-α. TGF-β is for **Tissue repair**, not acute inflammation.