Microglia in normal condition and pathology

Microglia, one of three types of glial cells in the central nervous system (CNS), plays an important role as resident immunocompetent and phagocytic cells in CNS in the event of injury and disease. It was del Rio Hortego who in 1927 determined that microglia belong a distinct glial cell type apart from astrocytes and oligodendrocytes. Since 1970s there has been wide recognition that microglial cells are immune effectors in the CNS that respond to pathological conditions and participate in initiation and progression of neurological disorders including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and acquired immune deficiency syndrome dementia complex by releasing potentially cytotoxic molecules such as proinflammatory cytokine, reactive oxygen intermediates, proteinases and complement proteins. There is also evidence to suggest that microglia is capable of secreting neurotrophic or neuron survival factors upon activation during inflammation or injury. It is thus timely to review the current status of knowledge on origin, morphology and functional features of microglial cells.