T cell-dependent IFN-gamma exerts an antiviral effect in the central nervous system but not in peripheral solid organs

The antiviral relevance of soluble mediators that may operate in the vicinity of virus specific effector T cells was investigated. Mice were immunized with vesicular stomatitis virus (VSV) wild type (wt) and subsequently challenged with a mixture of two vaccinia recombinant viruses, one expressing the nucleoprotein of VSV (vacc-VSV-NP) the other expressing the glycoprotein of lymphocytic choriomeningitis virus (vacc-LCMV-GP). It was determined whether or not the VSV wt-induced memory T cell response that is protective against vacc-VSV-NP would inhibit growth of the nonrecognized vacc-LCMV-GP. In ovaries and testes replication of vacc-LCMV-GP was not inhibited. In contrast, the T cell response against vacc-VSV-NP nonspecifically inhibited growth of the non-recognized vacc-LCMV-GP in the central nervous system. This inhibiting effect was partly abrogated by treatment with anti-IFN-gamma antiserum but not by an anti-TNF-alpha antiserum. Similar results were obtained in VSV wt-immune H-2b mice, which eliminate vacc-VSV-NP by CD8+ T cells and in H-2k mice, which eliminate vacc-VSV-NP by a CD4+ T cell-dependent mechanism. These data suggest that a protective bystander effect mediated by soluble CD8+ and CD4+ T cell-dependent factors may be demonstrated against vaccinia virus only in an organ such as the central nervous system in which the blood-brain barrier inhibits diffusion and draining of the soluble antiviral factors released by specific effector T cells.