The human B cell-associated antigen CD24 is a single chain sialoglycoprotein.
The CD24 human B cell-associated antigen was originally characterized in this laboratory with the use of monoclonal antibody BA-1 combined with a standard radioimmuneprecipitation technique, and was reported to be a three chain glycoprotein complex of 45, 55, and 65 kilodaltons. We have compared our standard radioimmuneprecipitation technique (BA-1 ascites followed by rabbit anti-mouse IgM-coated protein A-Sepharose) to BA-1 conjugated directly to CNBr-Sepharose (BA-1-Sepharose) and report striking differences in the electrophoretic profile of CD24 immuneprecipitates. The CD24 immuneprecipitate obtained with BA-1-Sepharose showed a single broad band with a relative mobility of 42 kilodaltons. A series of experiments performed with the two immuneprecipitation techniques, reducing or nonreducing electrophoretic conditions, and addition of preformed mock BA-1 immuneprecipitate to BA-1-Sepharose immuneprecipitates convincingly demonstrated that the previously described 55 and 65 kilodalton components were artifacts caused by co-migration of CD24 with IgG and IgM heavy chains, respectively. Because of the consistent association and co-migration of CD24 with IgG heavy chains, we investigated the possibility that CD24 might be related to the 45 kilodalton Fc-gamma receptor expressed on B cells and eosinophils. We found, however, no evidence for such a relationship by cross adsorption analysis with BA-1-Sepharose and IgG-Sepharose.
D000944:Antigens, Differentiation, B-Lymphocyte; D000954:Antigens, Surface / Q000276:immunology* / Q000302:isolation & purification; D001402:B-Lymphocytes / Q000276:immunology*; D006801:Humans; D007526:Isoelectric Point; D046911:Macromolecular Substances; D008970:Molecular Weight; D011961:Receptors, Fc / Q000276:immunology*; D017452:Receptors, IgG; D012795:Sialoglycoproteins / Q000096:biosynthesis / Q000276:immunology* / Q000302:isolation & purification
D000944:Antigens, Differentiation, B-Lymphocyte; D000954:Antigens, Surface; D046911:Macromolecular Substances; D011961:Receptors, Fc; D017452:Receptors, IgG; D012795:Sialoglycoproteins