The Local Inflammatory Responses to Infection of the Peritoneal Cavity in Humans: Their Regulation by Cytokines, Macrophages, and Other Leukocytes
Figure 1
Simplified model of the paradigm of polarized macrophage activation. Monocytes are either classically (M1) or alternatively (M2) activated. Substances such as IFN-γ and LPS induce classical activation while IL-4, IL-13, and TGFβ cause alternative activation. M1 macrophages typically produce high levels of proinflammatory proteins including TNFα, IL-1β, IL-12, and IL-23 as well as reactive oxygen and nitrogen intermediates. M2 produce high levels of the anti-inflammatory cytokines IL-10 and IL-1ra and show a high expression of scavenger and mannose receptors. Under the influence of IL-4, M2 can accumulate in tissues by local proliferation rather than by recruitment. Either functional phenotype can shift to another depending on microenvironmental influences, speaking against rigid interpretation of the dichotomy between the macrophage phenotypes.
