Figure 1.

Microglial priming and altering. In the absence of disease, microglia are in a resting state with a small cell body and morphological branches extending to all directions so as to survey and maintain the normal function of CNS actively. With long-term stimuli from different kinds of inducement, the homeostasis of CNS is bankrupt and through different signaling pathways the microglia are changing their morphology and profile, altering their phenotypes that have different kinds and density of receptors. M1 and M2 are not separated complete though M1 is regarded as bad cell and M2 as good cell. Both the primed cells have a change in their phagocytosis and the release of NFs and pro-inflammatory mediators (IL-1β, TNF-α). Under chronic and sustained stimulation M2 can turn into M1. NFs, neurotrophic factors; CNS, central nervous system; TGF, transforming growth factor; IL-1β, interleukin-1β; TNF, tumor necrosis factor.