Preparation and Characterization of Monoclonal Antibodies Directed at Epitopes of Human IFN-γ

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Abstract
Five monoclonal antibodies (A7, B24, I14, L12, and M2) recognizing different epitopes of the human natural IFN-γ were prepared by immunizing BALB/c mice with a highly purified human natural IFN-γ preparation (107 U/mg). All five antibodies had high IFN-γ-binding activity but exhibited differential IFN-γ-neutralizing activities. Furthermore, none of them neutralized the antiviral activity exhibited by either IFN-α or IFN-β preparations, indicating thus their specificity for IFN-γ. The A7, L12, M2, and I14 monoclonal antibodies, but not the B24, blocked the augmentation of natural killer cytotoxicity, mediated by peripheral blood monocyte-depleted lymphocytes, by Escherichia coli-derived IFN-γ or natural IFN-γ but not by IFN-α2. All five monoclonal antibodies precipitated an identical molecular complex containing two major protein components with molecular weights of 20,000 (20 kD) and 25,000 (25 kD) and two minor components with molecular weights of 17,000 (17 kD) and 45,000 (45 kD). Treatment of the immunoprecipitated IFN-γ molecule with endoglycosylase F led to a stepwise removal of the carbohydrate portions on both the 25 and 20 kD chains, which resulted in the appearance of both 16 kD and 18 kD chains. The hereby reported monoclonal anti-IFN-γ antibodies will prove useful as probes for purification and for rapid assay of human IFN-γ molecule.