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
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.
