During the inflammatory phase of wound healing, which cell type is the primary source of transforming growth factor-beta (TGF-β), a key cytokine that promotes fibroblast recruitment and collagen synthesis?

Explanation

## TGF-β Production in Early Wound Healing **Key Point:** Platelets and macrophages are the primary early sources of TGF-β during the inflammatory phase (0–3 days post-injury). Platelets release TGF-β from their alpha-granules immediately upon activation during hemostasis, and infiltrating macrophages produce TGF-β as part of the inflammatory response. **High-Yield:** TGF-β is a **pleiotropic cytokine** with multiple critical roles: - Chemotactic for fibroblasts and myofibroblasts - Stimulates collagen and ECM synthesis - Promotes angiogenesis (indirect, via VEGF induction) - Inhibits matrix metalloproteinases - Promotes epithelialization - Exists in three isoforms (TGF-β1, -β2, -β3); **TGF-β1 is most abundant in wounds** **Clinical Pearl:** Excessive TGF-β signaling is implicated in **hypertrophic scarring and keloid formation**. Conversely, TGF-β3 has been studied as a potential therapeutic agent to reduce scarring by promoting regeneration over fibrosis. ## Timeline of Key Cytokine Production | Phase | Duration | Primary Cells | Key Cytokines | | --- | --- | --- | --- | | **Hemostasis** | 0–minutes | Platelets | TGF-β, PDGF, fibrinogen | | **Inflammatory** | 0–3 days | Macrophages, neutrophils | TNF-α, IL-1, IL-6, TGF-β | | **Proliferative** | 3–21 days | Fibroblasts, endothelial cells | VEGF, bFGF, TGF-β (continued) | | **Maturation** | 3 weeks–2 years | Fibroblasts, myofibroblasts | TGF-β (remodeling signal) | **Mnemonic:** **PLATELET-MACRO TGF-β** — Platelets and Macrophages are the early TGF-β factories in wound healing.