Suppression of an arenavirus by a togavirus in experimental acute double infection

Lymphocytic choriomeningitis virus (LCMV) and tick-borne encephalitis virus (TEV) were inoculated in young and old chick embryo cell (CEC) and in L-cell cultures at various multiplicities per cell, simultaneously or 17 hr apart. The yield of infective LCMV was inhibited in double infection, most in old CEC with elevated interferon mechanisms, and least in L cells producing no interferon. In young CEC, TEV-induced interferon was stimulated by coinfecting LCMV; LCMV alone never has induced interferon. The reproduction of TEV was little affected. In doubly infected L cells the fluorescent antibody techniques revealed more cells positive for each viral antigen than in single infections, but the yield of LCMV per one antigen-positive cell was decreased. The course of TEV infection in cerebrally infected mice was not changed by co-infection with LCMV. The titre of LCMV in the brains of doubly infected mice was markedly suppressed when compared with LCMV monoinfection. High interferon levels in brains of all mice infected with TEV were not affected by LCMV co-infection.