Abstract
The capacity of herpes simplex virus type 1 (HSV-1) to replicate in vitro decreases tremendously when animal cell cultures are exposed to ligands of both the alpha/beta interferon (IFN-alpha/beta) receptor and IFN-gamma receptor prior to inoculation with low m.o.i.s of HSV-1. However, the available evidence provides no insight into the possible mechanisms by which co-activation of the IFN-alpha/beta- and IFN-gamma-signalling pathways produces this effect. Therefore, it has not been possible to differentiate between whether these observations represent an important in vitro model of host immunological suppression of HSV-1 infection or an irrelevant laboratory phenomenon. Therefore, the current study was initiated to determine whether co-activation of the host cell's IFN-alpha/beta and IFN-gamma pathways either (i) induced death of HSV-1-infected cells such that virus replication was unable to occur; or (ii) disrupted one or more steps in the process of HSV-1 replication. To this end, multiple steps in HSV-1 infection were compared in populations of Vero cells infected with HSV-1 strain KOS (m.o.i. of 2.5) and exposed to ligands of the IFN-alpha/beta receptor, the IFN-gamma receptor or both. The results demonstrated that IFN-beta and IFN-gamma interact in a synergistic manner to block the efficient synthesis of viral DNA and nucleocapsid formation in HSV-1-infected cells and do so without compromising host-cell viability. It was inferred that IFN-mediated suppression of HSV-1 replication may be a central mechanism by which the host immune system limits the spread of HSV-1 infection in vivo.