Involvement of sialic acids in the immunological specificity of plasma membrane glycoproteins

Solubilized membrane antigens (SMA) from a mouse plasma cell tumor were used as immunogens to prepare rabbit antisera. These antisera were tested against native SMA or SMA desialylated with Vibrio cholerae neuraminidase. Radioimmunoprecipitation showed that removal of sialic acids significantly lowered the precipitation curves. When direct measurement of antigen-antibody reaction was performed by a solid-state competitive binding radioimmunoassay, desialylated SMA were only partially able to inhibit the binding of radiolabelled antibodies to native antigens. Indirect immunofluorescence experiments showed that adsorption of the antisera with neuraminidase-treated living plasmacytoma cells did not completely remove antibodies directed against the cell surface. It is suggested that sialic acids are directly or indirectly involved in the formation of a small but definite number of antigenic determinants of membrane glycoproteins.