Receptor Is Associated with Alternative Macrophage Activation

Macrophages are versatile players in the immune sys-tem. They effectively neutralize pathogens and harmful endogenous products via phagocytosis but also contrib-ute to efficient immunity by production and secretion of multiple cytokines and chemokines. Next to effector functions, macrophages possess important activities dur-ing the resolution phase of an immune response and at sites where antigenic material needs to be ignored (lung and colon) or tolerated (eye, brain, ovary, and testis). The different macrophage activities result from the initiation of distinct gene expression programs [1–5]. IFN and TNF induce classical activation of macrophages. These macrophages, also known as M1 cells, produce high amounts of pro-inflammatory cytokines, nitric oxide, and reactive oxygen species and efficiently clear patho-gens either directly or by facilitating T H 1 immune re-sponses. In contrast, stimulation with IL-4 or IL-13 trig-gers pathways that program macrophages to exert anti-inflammatory functions. These alternatively activated macrophages, also known as M2a cells, are considered to be involved in T H 2 immune responses and wound heal-ing. Finally, IL-10 and glucocorticoids give rise to regula-tory macrophages that can inhibit immune responses