Ectopic expression of gamma interferon in the eye protects transgenic mice from intraocular herpes simplex virus type 1 infections

Transgenic (rhoγ) mice provide a model for studying the influence of gamma interferon (IFN-γ) produced in the eye on ocular and cerebral viral infection. To establish this model, we injected BALB/c- and C57BL/6-derived transgenic and nontransgenic mice of different ages intravitreally with herpes simplex virus type 1 (HSV-1) strain F. Eye and brain tissues of these mice were assessed for pathological and immunocytochemical changes. HSV-1 infection induced severe retinitis of the injected eyes and infection of the brain in all mice. In transgenic mice inoculated with HSV-1, the left, nontreated eyes were protected from retinitis, whereas nontransgenic mice developed bilateral retinitis. Additional intravitreal injection of IFN-γ with the virus protected the noninoculated eyes of nontransgenic mice. Three- week-old nontransgenic mice died from HSV-1 infection, whereas transgenic mice of the same age and nontransgenic mice intravitreally treated with IFN- γ survived. Ocular IFN-γ production increased the extent of inflammation in transgenic mice but did not have a significant influence on the growth of HSV-1 until day 3 after inoculation and did not influence the neuroinvasion of this virus. Thus, the effects of IFN-γ were not caused by an early block of viral replication. Possible mechanisms of IFN-γ action include activation of the immune response, alteration of the properties of the virus, and direct protection of neurons.