Macrophage-activating factor produced by a T cell hybridoma: physiochemical and biosynthetic resemblance to gamma-interferon.

Biochemical and biosynthetic evidence has been obtained which indicates that the macrophage activating factor (MAF) produced by the murine T cell hybridoma clone 24/G1, which primes macrophages for nonspecific tumoricidal activity, is a form of gamma-interferon (IFN gamma). MAF and antiviral activities were generated by the clone in proportional amounts under a variety of culture conditions. Production of both activities showed identical dependence on cell density even when production precipitously ceased at cell concentrations greater than 1.2 X 10(6) cells/ml. MAF and antiviral activities displayed identical sensitivities to pH and temperature and were indistinguishable on the basis of binding to insolubilized polynucleotides. Dye-ligand chromatography of a stimulated hybridoma supernatant on a column of Matrex Gel Red A resulted in the 1500-fold purification and 100% recovery of the MAF activity. A qualitatively identical elution profile was also obtained for the antiviral activity; however, only 32% of the original activity was recovered. When subjected to gel filtration on a high performance liquid chromatography system (HPLC), the MAF and antiviral activities present in the Matrex Red pool displayed identical elution profiles and exhibited an apparent m.w. of 50,000. This technique resulted in another 10-fold purification and 50% recovery of the two activities. On HPLC chromatofocusing the MAF activity in the Matrex Red pool could be resolved into seven chromatographically distinct species yet could not be resolved from the antiviral activity on either a qualitative or quantitative basis. These results thus provide quantitative molecular evidence to support the concept that IFN gamma can act as a MAF.