M1 and M2 polarization of macrophages: a mini-review

The tissue microenvironment regulates differentiation of precursor monocytes into macrophages. In response to the presence of microbial products, stimulated lymphocytes, or damaged cells in the microenvironment, macrophages differentiate into distinct functional populations. The M1 macrophages are characterized by the generation of high levels of pro-inflammatory cytokines, antimicrobial properties, increased production of reactive nitrogen and oxygen intermediates, and induction of Th1 response. In contrast, M2 macrophages are characterized by their involvement in tissue remodeling, immune regulation, tumor promotion, and efficient phagocytosis. In this minireview, we discuss the stimulation, markers, cytokines, and signaling molecules involved in macrophage polarization.