Rescue of SV40 from interferon-treated heterokaryons.

Simian virus 40 (SV40)-transformed nonpermissive cells express only the early products of SV40. Heterokaryons formed by fusion of these transformed cells with uninfected permissive cells support the activation of the resident viral genome leading to subsequent viral DNA replication, late protein synthesis and release of progeny virus. Pretreatment of heterokaryon cultures with either mouse or monkey interferon (IFN) before fusion with polyethylene glycol (PEG) produced a dose-dependent inhibition in the appearance of free viral DNA as well as production of infectious virus. The decreased yield of SV40 in these cultures was similar to the inhibition which was observed in mouse or monkey cells incubated with homologous IFN prior to exogenous infection with SV40. When IFN was added to the cultures at progressively later times after fusion with PEG, there was less inhibition of virus production. Although there was a comparable decrease in the production of virus by pretreatment with either mouse or monkey IFN, monkey IFN exerted the inhibition for a longer period of time when added after heterokaryon formation. These results demonstrate that IFN treatment applied even after initiation of SV40 replication can still inhibit virus multiplication.