ABSTRACT
Historically, the glia were known for their supportive functions of neurons within the central nervous system (CNS). Not as well appreciated by the neuroscience community, however, is the fact that glial cells greatly outnumber neurons (by about eight to one in the cerebral cortex). Astrocytes are the predominant cell type (comprising approximately 80% of the glia within the cortex), whereas microglia (15% of the total glial cells) and oligodendrocytes (5% of the glia) are minority cell populations within the CNS. Because of the predominance of glial cells and their diverse immunological properties, the brain itself has been considered an immune organ (Fabry et al., 1994; Chao et al., 1997a). Due to increasing attention to research on the neuropathogenesis of CNS inflammation, glial cells have become recognized as important immunoregulatory cells.
