Characterization and purification of a macrophage-triggering factor produced in Mycoplasma arginini-infected L5178Y cell cultures

The supernatant of Mycoplasma arginini-infected murine L5178Y T lymphoma cell cultures (SN-L51) synergizes with small concentrations of IFN-gamma to activate murine peritoneal, thioglycollate-elicited macrophages (M phi) to exhibit cytostatic activity against tumor cells. Treatment of M phi with IFN-gamma and SN-L51 sequentially, but not in the reverse order, activates M phi, which indicates that SN-L51 contains a M phi-triggering factor (MTF). MTF activity could be inhibited by small concentrations of prostaglandin E2, but not by polymyxin B. M phi activated by IFN-gamma plus MTF produce cytostatic effects on tumor cells through a nitric oxide-dependent pathway. MTF activity in SN-L51 is associated with infection of L5178Y cells by M. arginini. Mycoplasma-free L5178Y cells do not produce MTF activity, infection of these L5178Y cells with M. arginini generates the activity, and supernatants of pure M. arginini cultures contain MTF activity. MTF activity is thermostable and resistant to acid, dilute alkali, proteases, and nucleases. MTF was partially purified by ammonium sulfate precipitation, chromatography, electrophoresis, and electroelution. On 12.5% SDS-urea gels, MTF activity migrated with a molecular mass of 2.5 to 4 kDa. MTF activity and the silver staining of this band was resistant to proteinase K; however, Coomassie staining of this band was abolished by proteinase K. The combined data suggest that MTF is either a stable peptide or a peptide linked to lipid or carbohydrate.