Suppression of in vitro growth of virulent and avirulent herpes simplex viruses by cell-mediated immune mechanisms, antibody, and interferon

A rounding cell-forming--GC strain, which is a variant of a syncytial giant cell-forming herpes simplex virus (+GC Miyama strain), was highly attenuated for Swiss, BALB/c nu/nu, and nu/+ mice, whereas +GC was highly virulent to all the mice tested. +GC and -GC were antigenically indistinguishable from each other by cross-neutralization and cross-immunization. Immunosuppression induced by cyclophosphamide converted the nonlethal -GC infection of mice into a fatal infection. -GC replication in tissue culture was more effectively suppressed by spleen cells immunized with either +GC or -GC than was the +GC replication. -GC replication was also inhibited more effectively by antibody or the antibody-dependent cell-mediated system than was the +GC replication. -GC is highly sensitive to mouse interferon, but +GC was relatively resistant. These findings indicate that attenuation of this avirulent -GC strain may be due to a high susceptibility of its replication to humoral and cell-mediated defense factors. The probable roles of each defense factor in recovery from the infection with virulent and attenuated herpes simplex virus are also discussed.