[Interferon production-stimulating factor].

A factor stimulating interferon production (FSIP) has been isolated from cells treated once or twice (at an interval of 6-8 hours) with poly(rI).poly(rC) followed by actinomycin D (2 microgram/ml) or dehydrorifampicin (50 microgram/ml). In a dilution 1:512 the preparation stimulated interferon production 4-fold. In higher concentrations, the preparation induced interferon yields of 1280-2560 IE50/ml, i.e. exceeded the control values 16-fold. The factor does not affect the antiviral activity of interferon and has the tissue specificity. Its stimulating effect was not manifested with inducers of other nature. All the properties of FSIP studied show it to be similar with homologous interferon and repressor of its production but, unlike the latter, it was thermolabile and sensitive to acid pH.