A novel interaction involving a polypeptide chain (P33) in covalent linkage with IgM on the surface of a Burkitt lymphoma cell line (Daudi).

The surface IgM of Daudi Burkitt lymphoma cells has been shown to consist of mu chains and kappa chains covalently linked, by disulfide bonding, to a novel polypeptide chain of approximate molecular weight 33,000. This novel polypeptide chain (P33) is similar in several properties to the heavy chain of the Ia antigen: glycoprotein nature; apparent molecular weight; isoelectric behavior and cysteine content. The linkage of P33 to surface immunoglobulin has not been observed with any other human lymphoma or lymphoblastoid cell lines.