Borna disease virus (BDV) infection represents an excellent model system to study immunopathological mechanisms based on a T cell-mediated immune reaction in the central nervous system. The single-stranded RNA Borna disease virus, a member of Bornaviridae in the order of Mononegavirale, lacks cytopathogenicity both in vitro and in vivo. After experimental infection BDV causes a persistent infection of the central nervous system and induces Borna disease, an immune-mediated encephalomyelitis. The infiltrating immune cells have been characterized as CD4-positive, CD8-positive T-cells, macrophages and B cells. CD8-positive T cells represent the effector cell population exhibiting antigen specificity for the nucleoprotein.