Macrophage activation factor from EL-4, a murine T-cell line: antigenic characterization by hamster monoclonal antibodies to murine interferon-gamma.
A cloned variant of the EL-4 murine T-cell line treated with phorbol myristate acetate (PMA) releases a factor that activates macrophages for nonspecific tumor cytotoxicity. This macrophage activation factor (MAF) is both physicochemically (Mr 25,000; pH 2 stable) and biologically different from interferon-gamma (IFN-gamma). However, EL-4 MAF may represent a breakdown product or otherwise altered fragment of IFN-gamma. We examined this possibility with a unique pair of hamster monoclonal antibodies against different epitopes of murine IFN-gamma. Both antibodies inhibited IFN-gamma-induced fibroblast antiviral activity; H21 but not H1 antibody also inhibited lymphokine (LK)-induced macrophage-mediated tumor cytotoxicity. Neither antibody, however, had any effect on the EL-4 MAF throughout a broad dose response. Moreover, passage through a H21 immunoaffinity chromatography column or addition of staphylococcal protein A and antibody completely inhibited LK-induced macrophage tumoricidal activity but did not affect the activity in EL-4 MAF. Identical effects in both fluid and solid phase were observed with polyclonal rabbit antisera to murine IFN-gamma. Results with all of these antibodies strongly suggest that the EL-4 MAF and murine IFN-gamma are antigenically distinct.
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002460:Cell Line; D007158:Immunologic Techniques; D007371:Interferon-gamma / Q000276:immunology*; D008222:Lymphokines / Q000276:immunology*; D008262:Macrophage Activation; D016215:Macrophage-Activating Factors; D051379:Mice; D013154:Spleen / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
D000911:Antibodies, Monoclonal; D008222:Lymphokines; D016215:Macrophage-Activating Factors; D007371:Interferon-gamma