Which cells act as the first and main form of active immune defense in the central nervous system?

The primary active immune defenders in the central nervous system (CNS) are microglia. These specialized glial cells play a crucial role in maintaining the health of the CNS by acting as the resident immune cells. Microglia are capable of identifying and responding to pathogens, cellular debris, and other injury signals within the brain and spinal cord. They constantly monitor the environment and can become activated in response to inflammation or infection, at which point they can engage in phagocytosis, clearing away dead cells and pathogens.

Unlike neurons, which primarily are responsible for transmitting signals, or astrocytes, which support neuronal function and maintain homeostasis, microglia are equipped with receptors that allow them to detect perturbations and activate immune responses. Schwann cells are involved in myelination in the peripheral nervous system and do not play the same immune role as microglia do in the CNS.

Thus, microglia are essential for the CNS’s immune responses, making them the first and main form of active immune defense in this region.