Mechanism of interferon action: inhibition of vesicular stomatitis virus replication in human amnion U cells by cloned human leukocyte interferon. I. Effect on early and late stages of the viral multiplication cycle.

The molecular basis of the inhibition of vesicular stomatitis virus (VSV) replication by pure recombinant gamma-interferon (IFN-gamma) in human amnion U cells was examined. A saturating concentration of IFN-gamma induced, at maximum, about a two log10 reduction in infectious VSV yield. The kinetics of induction of the antiviral activity by IFN-gamma were first order over the period of about 6-18 h, following a lag of about 3 h, after treatment with a saturating concentration of IFN-gamma. The relationship of the inhibition in VSV infectivity to the early and late events of the VSV multiplication cycle was investigated. IFN-gamma treatment had no detectable effect on the adsorption and penetration of VSV virions or on their uncoating to yield viral nucleocapsids. The polypeptides of adsorbed or uncoated VSV particles were neither preferentially degraded nor detectably altered in IFN-gamma-treated U cells, as compared to untreated U cells. Progeny virions isolated from IFN-gamma-treated U cells, although greatly reduced in number, were found to be equally as infectious as those isolated from untreated U cells. Progeny virions from IFN-gamma-treated cells also possessed the same composition of viral proteins as was observed for virions from untreated cells. These results suggest that conditions of IFN-gamma treatment sufficient to reduce the yield of infectious VSV progeny 100-fold do not detectably affect either the early or the late stages of the VSV multiplication cycle.