Theiler's virus is eliminated by a gamma-interferon-independent mechanism in the brain

The intravenous infection of Theiler's virus GD VII strain causes acute encephalomyelitis in infected mice. To determine the cellular mechanism of resistance and interferon (IFN)-γ-producing cell populations, mononuclear cells isolated from tissues of the brain were analyzed by the flow cytometry method. Antibodies specific for CD3, CD4, CD8, T cell receptor (TCR)-αβ, and Asialo GM1 were used to deplete the corresponding cell populations in Theiler's virus-infected mice. CD4(+) lymphocytes and CD8(+) lymphocytes infiltrated in the brains of infected mice from 5 days postinfection (p.i.). The number of CD3(+)/TCR-γδ(+) lymphocytes increased in the brains on Day 6 p.i. The elimination of CD3(+) lymphocytes or CD4(+) lymphocytes augmented viral replication and suppressed the production of IFN-γ. The suppression of IFN-γ production by anti-CD3 monoclonal antibody (mAb) persisted, although the suppression by anti-CD4 mAb was observed only on Day 6 p.i. The depletion of CD8(+) lymphocytes as well as TCR-αβ(+) lymphocytes also augmented the viral replication; however, it did not alter the production of IFN-γ. Anti-Asialo GM1 antibody had no effect on viral replication and IFN-γ production. These results indicate that T lymphocytes are important for eliminating Theiler's virus from the brain, CD3(+)/CD4(+)/CD8(−) lymphocytes and CD3(+)/TCRαβ(−)/CD4(−)/CD8(−) lymphocytes would produce IFN-γ in brain. However, from the result on the experiment of the depletion of TCR-αβ(+) lymphocytes, the defence mechanisms by T lymphocytes against Theiler's virus would be independent of endogenous IFN-γ production.