Humoral immune response and protection from viral infection in mice vaccinated with inactivated MHV-68: effects of type I interferon

Infection of mice by murine gammaherpesvirus 68 (MHV-68) represents a suitable animal model in which to investigate the immune response against gammaherpesviruses and to test the efficacy of vaccination strategies. In this study, we evaluated the efficacy of heat-inactivated MHV-68 as a vaccine as well as the adjuvant activity of type I interferon (IFN-I) administered together with the vaccine. Mice vaccinated with inactivated MHV-68 and subsequently infected with the virus exhibited a significant augmentation of the virus-specific humoral immune response and a considerable inhibition of MHV-68 acute replication in the lungs compared with unvaccinated control mice. The coadministration of IFN-I with inactivated MHV-68 significantly enhanced the humoral immune response elicited by the vaccine by stimulating the production of virus-specific IgG2 antibodies but did not significantly enhance protection from viral challenge. We conclude that IFN-I, recently shown to exhibit a powerful adjuvant activity to a poorly immunogenic subunit vaccine in mice, can also enhance the humoral immune response when used as adjuvant of an inactivated viral vaccine, even though this effect is less marked as a result of the strong immune response elicited by the inactivated virus alone, which may also involve the contribution of endogenous IFN.