Leukocytes: The Double-Edged Sword in Fibrosis

Figure 2

The divergent macrophage activation pathway. Macrophage activation and differentiation from monocyte in the wounded tissue depends on chemokine and growth factors availability. Two macrophage activation pathways might be distinguished, classical activation (M1) depending on interferon gamma (IFN-γ) and tumor necrosis factor-α (TNF-α) and alternative activation pathway (M2). Alternative activation is divided into two separate macrophage populations, IL-4 and IL-13 derived wound-healing macrophage population and TGF-β derived regulatory macrophage population. Despite monocyte origin, different activation pathway results in production and secretion of different chemokines and proteins into wounded tissue.