Immune and inflammatory responses in the CNS: modulation by astrocytes

Because the skull bones, the cerebrospinal fluid, the blood-brain barrier ( BBB), and the meninges effectively shield the central nervous system from o ther tissues, it was proposed that the brain is an 'immunologically privile ged' organ. However, with recent evidence that in response to invasion by m icroorganisms, resident cells, such as astrocytes and microglia can fully m ount an immune response, this long-standing view has been rethought and rev ised. Over the last two decades, both astrocytes and microglia have been sh own to secrete numerous cytokines, and, therefore, it is presently widely a ccepted that these cells actively participate in an integrative communicati ve pathway between resident immune cells of the CNS and those of the periph ery. While clearly implicated in the initiation, maintenance, and suppressi on of immune responses, cytokines produced by these cells (e.g. astrocytes and microglia), as well as the responses of these cells to cytokines produc ed elsewhere, has also been shown to propagate CNS damage. Therefore the po tential involvement of these cells in neurodegenerative disorders has been raised and subjected to intense experimentation. The objective of this syno psis is to review the role played by astrocytes in the initiation and modul ation of immune responses. (C) 1998 Elsevier Science Ireland Ltd. All right s reserved.