| Abstract: | A receptor, specific for the Fc portion of IgG, was purified from several lymphoblastoid cell lines using immunoadsorbents prepared from either immobilized antigen-antibody or heat aggregated immunoglobulin columns. Biochemical analysis revealed that the receptor is a multimeric glycoprotein with a subunit polypeptide mass of 46,000 daltons, held together by disulfide bonds. Integrity of these disulfide bonds is essential for successful binding of the receptor complexes to the Fc portion of complexed Ig. The association of receptor with immunoglobulin, once formed, was found to be highly stable even in the presence of low pH or high concentrations of chaotropic agents. The receptor, present on the surface of several human lymphoblastoid cell lines, was found to represent as much as 4–5% of the total cytoplasmic membrane proteins. The receptor showed no affinity to staphylococcal Protein A, but did bind to Protein A-immunoglobulin complexes, indicating separate binding sites for these proteins on the Fc portion of IgG. The purified receptor was found to be insoluble in aqueous buffers after detergent removal. Nevertheless, in functional assays, the precipitated receptor was able to agglutinate sheep erythrocytes sensitized with rabbit anti-SRBC IgG, but not unsensitized SRBC or SRBC sensitized with IgM. Antiserum against the receptor was found to react with a specific subclass of normal human or mouse peripheral blood lymphocyte, and with all Fc receptor positive but not with Fc receptor negative cell lines tested. |
