Heterogeneity of human gamma interferon preparations: evidence for presence of alpha interferon

Human gamma interferon (HulFN-gamma) preparations induced with several mitogens (Staphylococcal enterotoxin A, Phytohemagglutinin, or Pokeweed mitogen) had low levels of cross-species antiviral activity on bovine cells (approximately 1-5%) and were not neutralized by antisera to either human interferon alpha (HulFN-alpha) or beta (HulFN-beta). After purification on controlled pore glass beads (CPG) these preparations could be fractionated into a minor component which was highly active on bovine cells and a major component that was virtually inactive on bovine cells. The highly cross-active component was pH2 stable and was neutralized by an anti-HulFN-alpha antiserum, while the major, lowly cross-active component was pH2 labile and was not neutralized by either anti-HulFN-alpha or HulFN-beta antisera. Chromatography of a CPG-purified mitogen-induced IFN preparation on anti-HulFN-alpha Sepharose showed that, while the large majority of HulFN-gamma preparations passed through the column, a minor component was retained and eluted at pH2. Thus, human leukocyte suspensions stimulated by mitogens produced predominantly HulFN-gamma, but also produce some HulFN-alpha.