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

Abstract

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.