Microglia

Abstract

Microglia are known as the resident immune cells in the central nervous system (CNS), including the retina. Under normal physiological conditions, they are involved in the surveillance of the CNS and are required for the construction of neural circuitry during development. Accumulating evidences have shown that microglia change to a reactive phenotype under pathological conditions. Microglial activation is associated with various CNS diseases such as glaucoma. When microglia are activated, they form an amoeboid shape and release inflammatory cytokines. Excessive microglial activation causes retinal tissue damage and contributes to apoptosis. In contrast, microglia act as phagocytes that remove apoptotic neurons, pathogens, and cellular debris. This may proceed to protect retinal neurons. Thus, microglia show dual functions in neurodegeneration. Although it is under debate whether microglia are good or bad for CNS diseases, both effects appear to occur in glaucoma. This chapter reviews the roles of microglia in the retina, with a particular focus on their protective and destructive roles in glaucoma.