In the group of patients with suspected viral meningoencephalitis of unknown origin we could identified 2 cases with definite TOSV-infection (anti-TOSV-IgM and IgG TOSV positive), 2 cases with possible TOSV-infection (isolated anti-TOSV-IgM positive) and 2 cases with residual antibody titers (isolated anti-TOSV-IgG positive). This evidence concerns the gene CD40LG and infection.