Macrophage activation factor from EL-4, a murine T-cell line: Antigenic characterization by hamster monoclonal antibodies to murine interferon-γ

Monte S. Meltzer, Michael J. Gilbreath, Robert M. Crawford, Robert D. Schreiber, Carol A. Nacy

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Abstract

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-γ (IFN-γ). However, EL-4 MAF may represent a breakdown product or otherwise altered fragment of IFN-γ. We examined this possibility with a unique pair of hamster monoclonal antibodies against different epitopes of murine IFN-γ. Both antibodies inhibited IFN-γ-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-γ. Results with all of these antibodies strongly suggest that the EL-4 MAF and murine IFN-γ are antigenically distinct.

Original languageEnglish
Pages (from-to)340-347
Number of pages8
JournalCellular Immunology
Volume107
Issue number2
DOIs
StatePublished - Jul 1987

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