Structural studies on a human IgA1 myeloma protein with a carboxy terminal deletion.

Abstract

Low molecular weight variants of complete immuno-globulin molecules have frequently been described in multiple myeloma. The first such variant to be characterized was Bence-Jones protein, which has been shown to be free intact light chains. More recently, variants involving deletions of polypeptide chains have also been described. The deletions found, result in either a polypeptide chain being secreted singly or in association with another polypeptide chain. Those deletions which involve significant portions of the Fd fragment of heavy chains have been defined as heavy chain disease proteins since the deletion results in the lack of any association with light chains (1, 2). These proteins appear to have normal Fc fragments and have been described for all the major immunoglobulin classes. Proteins with deletions in the Fc fragment have also been described in both man and mouse (3, 4). These proteins, because they possess intact Fd fragments, are found in association with light chains. In the mouse in situations when significant portions of the Fc fragment are deleted, these molecules may exist as L-H half molecules rather than a 4 polypeptide chain molecule due to the lack of significant interaction between the foreshortened Fc fragments. Deletions involving small areas of the hinge region have also been described (5, 6).