Figure 1.

Overview of microglial subtypes and their pro- and anti-inflammatory cellular environment. Proinflammatory interactions and factors are depicted in red, anti-inflammatory interactions and factors are depicted in green. Asterisks (*) indicate a higher complexity of signaling and, in the case of T lymphocytes, a higher diversity of subtypes. Generally, the complexity of interactions is even higher and also concerns differences between various diseases, but the figure had to be kept within an intelligible frame. Damaging factors caused by dying cells at sites of injury have been omitted; this would especially play a role in the focal activation that causes the transformation of ramified microglial cells into amoeboid phagocytes. Additional signaling via microRNAs and other constituents of exosomes has been also omitted. Abbreviations: BDNF, brain-derived neurotrophic factor; CCL, CXCL, and CX3CL refer to the respective chemokine families; CD, cluster of differentiation; CSF1, colony-stimulating factor-1; FGF, fibroblast growth factor; GDNF, glia-derived neurotrophic factor; IFNγ, interferon-γ; IL, interleukin; NG2 glia, neural-glial-2 expressing cells; NGF, nerve growth factor; NO, nitric oxide; NT, neurotrophin (several subforms); PGRN, progranulin; ROS, reactive oxygen species; TNFα, tumor necrosis factor-α; TGFβ, transforming growth factor-β.