Characterization and structural analysis of Fcγ receptors of human monocytes, a monoblast cell line (U937) and a myeloblast cell line (HL-60) by a monoclonal antibody

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Abstract
A monoclonal antibody, FR51, raised against the IgG Fc receptor (FcγR) of the human monoblast cell line U937 was used to analyze the distribution of this antigen on various human cells. This antibody inhibited the binding of human IgG to the FcγR on U937 cells, HL-60 cells and human peripheral blood monocytes. In contrast, the FcγR on human granulocytes (neutrophil cells) and on an Epstein-Barr virustransformed human lymphoblastoid cell line (Raji) were not recognized, indicated by the failure of blocking the binding of human IgG ligand to the FcγR on these cells. By affinity chromatography of detergent-containing cell free lysates of surface-iodinated U937 cells, HL-60 cells and monocytes, a protein of 70-kDa was isolated. This protein was identified as the FcγR by rebinding the isolated protein to immobilized human IgG. Removal of the carbohydrate moiety with endo-ß-N-acetylglucosaminidase F demonstrated that the receptors consist of a 40-kDa polypeptide. Analysis of the polypeptide patterns obtained by proteolytic digestion of either mature (70-kDa) or deglycosylated (40-kDa) receptors isolated from monocytes, U937 cells and HL-60 cells strongly suggests that the FcγR are identical. The monoclonal antibody FR51 specifically reacts with FcγR on human monocytes, a myeloblast and a monoblast cell line but not with the receptors on a B cell line and neutrophil cells.