Macrophage and microglial plasticity in the injured spinal cord.

Macrophages in the injured spinal cord arise from resident microglia and from infiltrating peripheral myeloid cells. Microglia respond within minutes after central nervous system (CNS) injury and along with other CNS cells signal the influx of their peripheral counterpart. Although some of the functions they carry out are similar, they appear to be specialized to perform particular roles after CNS injury. Microglia and macrophages are very plastic cells that can change their phenotype drastically in response to in vitro and in vivo conditions. They can change from pro-inflammatory, cytotoxic cells to anti-inflammatory, pro-repair phenotypes. The microenvironment of the injured CNS importantly influences macrophage plasticity. This review discusses the phagocytosis and cytokine-mediated effects on macrophage plasticity in the context of spinal cord injury.