Immune-mediated brain atrophy. CD8+ T cells contribute to tissue destruction during borna disease.

Borna disease (BD) is a virus-induced immunopathologic disease of the central nervous system in a variety of species from birds to primates and probably in humans. Severe inflammatory reactions lead to tissue destruction and finally to cortical brain atrophy. After experimental infection of the rat, intraparenchymal CD8+ T cells, MHC class I Ags on Borna disease virus (BDV)-infected neurons, and numerous nerve cell lesions were present. Treatment of BDV-infected rats with the mAb OX-8 directed against CD8+ cells inhibited the immunopathologic reactions and reduced MHC class I Ag expression. Neuronal lesions were minimal and no loss of brain substance could be observed. Because BDV has no acute cytopathic effects, we provide evidence that the presence of CD8+ T cells within the brain parenchyma and the expression of MHC class I Ags on neurons play a major role for immunopathologic brain tissue destruction and virus-infected neurons in vivo can be destroyed by T cell-mediated cytotoxicity.