Ia expression and antigen presentation by glia: strain and cell type-specific differences among rat astrocytes and microglia.

Astrocytes from experimental allergic encephalomyelitis (EAE)-susceptible Lewis rats expressed higher levels of Interferon-gamma-inducible Ia than astrocytes from EAE-resistant Brown Norway (BN) rats, whereas BN microglia expressed higher Ia than Lewis at both mRNA and protein levels. Lewis astrocytes induced proliferation of MBP-specific T cells selected on Lewis background as efficiently as Lewis thymocytes, whereas BN astrocytes were much less efficient in stimulating T cells selected in the presence of BN thymocytes. Microglia, irrespective of strain, induced only weak proliferative responses of these T cells despite the high expression of Ia. Antigen-stimulated T cells underwent apoptosis in the presence of microglia but not astrocytes. Thus, astrocyte-mediated proliferation of MBP-specific T cells may contribute to the development of EAE, while microglia-induced T cell apoptosis may downregulate immunopathological processes in the brain.