Figure 3: Neurons express a wide range of “selfdefence” proteins and receptors that reduce inappropriate bystander attack from activated microglia. Semaphorin 3a and CD22, CD45 all reduce proinflammatory cytokine expression and inhibit microglial activity. The neuro immunoregulatory (NI Regs) CD200 and CD47 that interact with the their counter receptors CD200R and CD172 on microglia and myeloid cells, reducing microglial activation (Black arrows). Regulators of complement activation RCAs) such as CD46 also act as “don’t eat me” signals preventing attack from host microglia. Neurons also express “Death signals” to initiate apoptosis in damaged cells or infiltrating T cells making them targets for phagocytosis.