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Fig. 1. Microglia are derived from primitive hematopoiesis in the fetal yolk sac and take up residence in the brain during early fetal development. (B) Two functionally different activation states of microglia. In the presence of LPS and IFN-γ, microglia cells are activated to M1 phenotype and result in production and release of pro-inflammatory cytokines such as TNFα and IL-6, MMP-9, NO, and ROS. In contrast, IL-4 and IL-13 induce alternative activation of microglia to M2 phenotype which downregulates the M1 phenotype and includes tissue repair and extra-cellular matrix composition.
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