Detailed in vivo analysis of interferon-gamma induced major histocompatibility complex expression in the central nervous system: Astrocytes fail to express major histocompatibility complex class I and II molecules

To recognize and respond immunologically to foreign antigens, T lymphocytes require the presentation of foreign peptides by MHC molecules. To determin e which cells of the central nervous system (CNS) are capable of expressing MHC molecules, we used confocal microscopy and dual immunofluorescence wit h cell-specific and MHC-specific antibodies to study brain sections of adul t mice. We took advantage of transgenic mice that initiate CNS-specific exp ression of IFN-gamma at 8 weeks of age. This inflammatory cytokine is a str ong inducer of MHC expression both in culture and in vivo. From this analys is, we clearly found MHC class I and II expression on endothelial, microgli al, and oligodendrocyte cell types, but did not find astrocytes or neurons capable of expressing either MHC class I or II molecules under these condit ions. This finding suggests that, although microglia and oligodendrocytes m ay participate in the antigen presentation process in the organism, we foun d no in vivo evidence to support the concept that astrocytes act as antigen -presenting cells.