Glia
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Microglia are key players of the immune response in the central nervous system (CNS) and, being the resident innate immune cells, they are responsible for the early control of infections and for the recruitment of cells of the adaptive immune system required for pathogen clearance. The innate and adaptive immune responses triggered by microglia include the release of proinflammatory mediators. Although an efficient immune response is required for the defense against invading pathogens, an inflammatory response in the CNS may also lead to tissue injury and neurodegeneration. ⋯ Although there is an increasing body of evidence that TLR signaling mediates beneficial effects in the CNS, it has become clear that TLR-induced activation of microglia and the release of proinflammatory molecules are responsible for neurotoxic processes in the course of various CNS diseases. Thus, the functional outcome of TLR-induced activation of microglia in the CNS depends on a subtle balance between protective and harmful effects. This review focuses on the neurodegenerative effects of TLR signaling in the CNS.