Antibodies reactive with cell surface carbohydrates

Normal and immune sera from various animal species were fractionated on columns of Sepharose covalently coupled with the glycoprotein fetuin. Elution of the material bound to fetuin yielded low but reproducible amounts of protein, ranging from 0.02 to 0.2% of the protein mass of the input sera. This material has been identified by immunoelectrophoresis in agar and by zone electrophoresis on cellulose acetate agglutinated erythrocytes of various species, and also bound to cells from various mouse tissues including heart, kidney, thymus, and spleen. In all cases, the binding was inhibited by glycoproteins such as fetuin and thyroglobulin, by a glycopeptide isolated from fetuin, and by some bacterial lipopolysaccharides. When the binding of these Ig fractions to mouse splenocytes was tested in the presence of 17 saccharides, no inhibition of binding was observed except by sialic acid, D galactose, N acetyl D glucosamine, and D mannose, all of which showed partial inhibition. Inasmuch as these four saccharides are present on the carbohydrate moiety of fetuin, the results that the isolated material is a carbohydrate specific Ig (CS Ig) fraction of serum capable of binding to the carbohydrate portion of cell surface receptors and glycoproteins. When bound to lymphocytes, these CS Ig molecules induced redistribution (patching and capping) of cell surface receptors. Moreover, the CS Ig fractions from chicken and rabbit sera were weakly mitogenic for mouse splenic lymphocytes. CS Ig fractions are useful new reagents for studying glycoproteins and the interactions and activities of cell surface carbohydrates.