Identification and characterization of a human T cell line-derived lymphokine with MAF-like activity distinct from interferon-γ

Culture supernatants of several human T cell leukemia cell lines were screened for macrophage-activating activity (MAF) as defined by induction of tumoricidal activity against human melanoma cells in a 72-hr assay. Two cell lines, MT-2 and C10/MJ2, were found to produce high levels of MAF activity constitutively, but the MT-2 cell line, unlike C10/MJ2, produced little IFN-γ. This observation was confirmed by Northern blot analysis performed with specific IFN-γ cDNA probe. The MT-2 cell line thus provides a useful system to evaluate the existence of lymphokines with MAF activity that are distinct from IFN-γ. The MAF activity produced by MT-2 cells was distinguished from IFN-γ by the following criteria. MAF activity was not removed by immunoaffinity chromatography with the use of immobilized specific polyclonal antibodies to IFN-γ and was not neutralized by a monoclonal antibody to IFN-γ. Heat or acid treatments of IFN-γ resulted in loss of its antiviral activity, but these treatments had no effect on MAF activity. MAF activity was not abolished by polymyxin B sulfate, suggesting that this activity is not mediated by or dependent on LPS. Initial characterization studies performed by using membrane filtration, gel filtration chromatography, and isoelectric focusing indicate that the non-IFN-γ MAF activity produced by MT-2 cells has an apparent m.w. of 55,000 and an isoelectric point of 5.5. Collectively, these data suggest that the MT-2 human T cell line constitutively produces high levels of MAF and low levels of IFN-γ and offers a useful source for the further purification of a unique human lymphokine with macrophage-activating activity that is distinct from IFN-γ.