Microglia

Microglia are the primary immune cells of the central nervous system and act as the brain’s first line of defense against injury, infection, and diseases. Under physiological conditions, these cells maintain normal cellular homeostasis by phagocytosing unwanted neuronal debris. They also help to form neuronal circuits during development, and induce plasticity of activity-dependent synapses in the mature brain. Exposure to pathological stimuli activates microglia, and they transform from their ramified morphology to an amoeboid shape, which allows the cells to be mobile and phagocytic. Depending on the activating stimulus encountered, reactive microglia can acquire diverse and complex phenotypes. The different microglia phenotypes express different cell surface receptors and soluble factors that allow the cells to mediate multiple facets of neuroinflammation including cytotoxicity, repair, regeneration, and immunosuppression. Neuroinflammation induced by microglia is a trait of many neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and multiple sclerosis.