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Isolation of a Murine Leukemia Fc Receptor by Selective Release Induced by Surface Redistribution¹

Clinical Immunology and Rheumatic Disease Section, Department of Medicine, University of Southern California School of Medicine, Los Angeles, California, 90033

Abstract

A protein which binds to the Fc region of IgG has been isolated from the murine leukemia L1210. The isolation technique involves surface cross-linking of the cell's Fc receptors with the use of aggregated human IgG and anti-human IgG. This results in the redistribution (patch formation and capping) of the cell's Fc receptors. Lactoperoxidase-catalyzed radioiodination of the cells before complex binding indicates that Fc receptor redistribution results in the selective release of surface proteins. SDS-PAGE analyses of the supernatants from cells thus treated reveals a major peak corresponding to a molecular weight of 45,000 daltons. This protein has been purified from the cell supernatants by immunoprecipitation and chromatography of the percipitates on Sephadex G-200 under dissociating conditions. After separation from the immune complex this protein can be bound to heat-aggregated IgG, but not aggregated F(ab')₂ fragments. The 45,000 dalton protein appears to be the Fc receptor which has been released from the cell surface in association with the complex.

Footnotes

¹ This work was supported by Grant AM 18445 from the National Institutes of Health and from Cancer Center Grant CA 14089 from the National Cancer Institute.