Figure 1.

Age-related changes of microglial cell function. In aged brains, there is an increased number, size and activation of microglia. Age-related microglia changes depend both on gained and lost functions. Diverse stimuli or injury processes can further promote an inflammatory environment, promoting cytotoxic microglial cell activation. Aged microglia show increased basal phagocytic activity, although a reduced capacity to induce phagocytosis when stimulated, together with reduced lysosomal activity, resulting in a decreased clearance activity. They also have increased production of inflammatory cytokines and reactive species. Those changes result in a shift of balance towards decreased protective functions and an increased neurotoxicity. PRRs, pattern recognition receptors; SRs, scavenger receptors; TLRs, Toll-like receptors.