Figure 2.

Ex vivo CTL activity of brain lymphocytes from BDV-infected mice is directed mainly against the viral nucleoprotein p40. Brain lymphocytes from severely diseased MRL mice (A) or VV-specific CTLs (B) were used as effectors on VV-infected L929 target cells expressing the indicated recombinant BDV proteins or irrelevant control proteins. (C) CTL assay with lymphocytes from the brain of a severely diseased CBA/J (H-2^k) mouse. (D) Spleen lymphocytes of MRL mice lack BDV-specific CTLs. Effector cells from brains or spleens of either severely diseased BDV-infected or healthy mock-infected MRL mice were incubated with L929 target cells expressing BDV p40. Brain lymphocyte preparations from uninfected MRL mice usually contained less than 10⁵ lymphocytes. They were resuspended in the same volume of medium as lymphocytes from brains of diseased animals, and identical volumes of both cell preparations were used in the CTL assays. (E) MHC restriction of CTL activity. Target cells were either MC57G cells (H-2^b) or L929 cells (H-2^k) infected with the indicated vaccinia viruses. Effector cells were from brains of MRL (H-2^k) mice with severe Borna disease. (F) Specific depletion of CD8⁺ T cells from brain lymphocyte preparations abolishes CTL activity. Brain lymphocyte preparations containing 2 × 10⁶ lymphocytes/ml were incubated for 30 min at 4°C with 10⁷ magnetic beads coated with anti-CD4 or anti-CD8 antibodies (Dynal, Great Neck, NY) to deplete the respective T cell subset. Lymphocytes complexed to magnetic beads were removed, and the remaining cells were used as effectors in standard cytotoxicity assays. Spontaneous lysis of target cells usually was less than 20% except in F, where it was 40%. Specific lysis is plotted against the indicated effector-to-target-cell ratios.