Biclonal gammopathy of kappa light chain type in a case of multiple myeloma

This immunoglobulin abnormality was found in the serum of a 33 years old man presenting with anemia, weight loss, bone pain and a single bone lesion. The cellulose acetate electrophoresis of his serum showed 2 homogeneous bands migrating in the gamma and alpha-2 regions. Agar gel immunoelectrophoresis using anti-whole normal serum revealed 2 abnormal precipitin arcs of gamma-2 and alpha-2 respective mobility. These 2 M-components precipitated with anti-human kappa light chain antiserum but failed to react with lambda-light chain specific and H-chains specific anti-sera. Furthermore, the 2 monoclonal kappa chains were still demonstrated in the supernatant of the se-rum treated with 50% saturated ammonium sulphate. The 2 kappa chains were isolated from the supernatant using goat anti-kappa antibodies bound to Sepharose-4B. Their SDS-polyacrylamide gel electrophoresis pattern showed a single protein band of 25 Kd molecular weight. This suggest the presence of 2 monomeric kappa chains of different clonal origin. Subsequently, the difference in their electrophoretic mobility was probably due to different V-kappa sequences. However, it is also possible that the unusual alpha-2 mobility is a consequence of a moderate glycosylation without increase in molecular weight.