Interferon (IFN)--y was produced with a high yield in cultures of human peripheral mononuclear cells by combined stimulation with OK-432 and staphylococcal enterotoxin B. Human mononuclear cells cultured in serum-free medium produced several times as much IFN as those in RPMI-1640 medium containing 10% fetal bovine serum. A synergistic effect of OK-432 and staphylococcal enterotoxin B on the production of IFN--y was demonstrated. Ultrogel AcA54 column chromatography of crude IFN showed a single peak with an apparent molecular weight of 43,000. Our production system for human IFN--y offers a feasible approach to preparation of large quantities of purified IFN-y for structure studies, antibody production, and clinical applications.Interferons (IFNs) can be divided into three major classes, designated IFN-a, IFN-P, and IFN--y (16). IFN-y is antigenically distinct from IFN-a and IFN-, and is labile at pH 2.

Heterogeneity of human gamma interferon (IFN-gamma) induced by the combined treatment with OK-432 and Staphylococcal enterotoxin B (SEB) was demonstrated by chromatofocusing. Treatment of IFN-gamma with a mixture of neuraminidase, and beta-galactosidase eliminated the charge heterogeneity. Apparent molecular weight of IFN-gamma was decreased by enzyme treatment. These results suggest that the heterogeneity of IFN-gamma induced in our system was the result of the difference in the content of sialic acids.