FIGURE 2.

The immune responses of microglia to viral infection. Microglia express all TLRs to sense viral RNA/DNA in the environment and endosomal compartments. Certain TLRs utilize MyD88 as an adaptive molecule to trigger a downstream signaling cascade. Microglia also express RLRs such as RIG-I and MDA5 to identify viral RNA in the cytoplasm. With the adapter molecule MAVS, RIG-I/MDA5 leads to the transcriptional activation of IFNs and other pro-inflammatory cytokine genes. In addition, microglia exhibit robust expression of cGAS and the downstream adaptor STING at rest and upon activation. cGAS recognizes both exogenous and endogenous DNA to initiate potent type-I IFN and pro-inflammatory responses through STING. The production of cytokines and chemokines may attract lymphocytes to promote an adaptive immune response.