Astrocytes provide crucial support for neurons and their impairment by viruses or their interactions with anti-viral or autoimmune responses could contribute to neurological disease. We have developed a transgenic mouse model to assess lymphocyte-astrocyte interactions. The major histocompatibility complex (MHC) class I molecule, Db, was expressed in astrocytes under the transcriptional control of regulatory sequences from the glial fibrillary acidic protein (GFAP) gene. Baseline cerebral MHC class I mRNA levels from transgenic mice were elevated over those of non-transgenic controls, and a prominent increase in cerebral MHC class I expression occurred following focal, injury-induced astroglial activation within transgenic brains but not in non-transgenic controls. FACS analysis of explant astrocyte cultures from established transgenic lines demonstrated astroglial expression of the GFAP-Db fusion gene at the protein level. Functional antigen-presenting capacity was conferred by the Db transgene, as virus-infected primary astrocytes obtained from transgenic BALB/c mice (KdIdDdLd) expressing the Db molecule were lysed by Db-restricted anti-viral CTL.