Figure 3.

Macrophage plasticity in tissue repair. After injury, the macrophage (Mϕ) arrives at the site of injury from the systemic circulation via diapedesis. In the early phase, the inflammatory milieu drives macrophage toward M1 polarization. M1 macrophages possess potent microbicidal properties and support IL-12–mediated type 1 helper T-cell responses, which are essential in the early stages of wound healing. In the late inflammatory phase, the change in wound microenvironment and the process of efferocytosis (clearance of apoptotic cells) drive the M1 macrophages toward M2 polarization. M2 supports type 2 helper T-cell–related effector functions and plays a more reparative role in the later stages of wound healing. Macrophages play a major role in the transition of the wounds from the inflammatory to the resolution or proliferative phase, driving angiogenesis and matrix production. PDGF, platelet-derived growth factor; TGF, transforming growth factor; TNF, tumor necrosis factor; VEGF, vascular endothelial growth factor.