Macrophage polarization and its mechanism

Macrophages are a heterogeneous population of immune cells that are essential for the initiation and resolution of pathogen- or tissue damage-induced inflammation. The plasticity of macrophages allows them to respond efficiently and alter their phenotype and physiology in response to environmental cues. Based on T helper type 1 (Th1) and Th2 polarization, macrophages have been classified according to their functional polarization, to either M1 (classic) macrophages, which produce proinflammatory cytokines, boost resistance to pathogens and contribute to tissue destruction, or M2 (alternative) macrophages, which secrete anti-inflammatory cytokines, promote tissue repair and remodeling as well as tumor progression. In this review, we summarize the current knowledge of macrophage activation and the ideas that are under development in the study of macrophage polarization.