Enhancement of retrovirus production by anti-interferon serum

In order to investigate the role of endogenous interferon in retrovirus production by infected or induced cells, the effect of two sera raised against mouse interferon has been tested on various C-type murine viruses. Addition of a highly potent anti-interferon serum to 3T3/IC cells chronically infected by the Moloney strain of MLV results in a considerable increase of virus production, as tested by reverse transcriptase assay. This effect is neutralized by an excess of exogenous interferon. The greatest effect of anti-interferon sera was obtained in the derepression of endogenous retroviruses: in K. BALB/c cells treated by IUDR, anti-interferon serum increases up to 50-fold the expression of the endogenous virus. The extinction of virus production which secondarily occurs after its induction by IUdR is likely to be caused by cellular endogenous interferon. The biological parameters of the viral agent produced in the presence of anti-interferon serum are those of the xenotropic endogenous virus.