Disease outcomes are influenced by the Yang (M1) or Yin (M2) of macrophage function

Although possibly an oversimplification, macrophages can be divided into 2 major categories based on whether they promote antimicrobial inflammation (M1) or facilitate cleanup and wound healing (M2). These are the fight or fix functions of macrophages. These types are influenced by microbial, cytological, innate, and immune stimuli and reinforced by TH1 and TH2 CD4 helper T-cell responses. The M1/M2 designation provides a useful paradigm for dissecting the influences and outcomes of innate and immune responses to infections, vaccines, wounds, tumors, and obesity as well as designing appropriate immunotherapy.