In vivo significance of NK cell on resistance against virus (HSV-1) infections in mice.

Susceptibility to infection with herpes simplex virus type 1 (HSV-1) was examined in euthymic as well as athymic nude mice which were continuously depleted of natural killer (NK) cell activity by i.v. injection of anti-asialo GM1. In those NK cell activity-depleted mice, the mortality rate of infection with HSV-1 and the virus titers in the brain, liver, and spleen were notably higher than in the control mice. The enhanced susceptibility was demonstrated only in the mice receiving anti-asialo GM1 and HSV-1 simultaneously, but not in the mice in which NK cell deletion was postponed by injecting the antisera 5 days after the virus inoculation. Interferon (IFN) production of peritoneal exudate cells was also reduced in the anti-asialo GM1-injected mice. The decline of resistance against HSV-1 infection proved to be primarily due to deletion of NK cells, but not due to the inability to produce IFN, because repeated injections of IFN increased the NK cell activity and prolonged the life of HSV-1-infected mice with an intact NK cell activity. In the NK cell activity-depleted mice, however, neither the NK cell activity nor the life span was improved by the administration of IFN.