Colony stimulating factors and macrophage heterogeneity

Abstract

Macrophages or mononuclear phagocytes are heterogeneous populations present throughout the body which can adapt quite dramatically to the surrounding milieu, both in the steady state and during immune/inflammatory responses. To assist in our understanding of this diversity, they have been classified into polarization or “activation” states, termed M1 and M2, respectively. This in vitro classification commonly incorporates interferon γ (± lipopolysaccharide) as the stimulus for M1 macrophages and IL-4 or IL-13 for M2 macrophages. Attempts are underway to place tissue macrophages, isolated from ongoing immune/inflammatory reactions, into these categories. However, more flexible classifications..