Multiple myeloma protein with three light chains.

A case of immunoglobulin G (kappa) myeloma showed, in addition to the monoclonal IgG(kappa) arc, two kappa chains in the serum. The urine specimen contained 7.75 g of kappa chains per liter. The electrophoretically fast-moving kappa chain in serum was shown by immunoelectrophoresis and Ouchterlony immunodiffusion to be a complex of kappa chains and alpha 1-antitrypsin. This complex, which was detected only transiently in the patient's blood, was composed of a monomeric kappa chain bound to the antitrypsin by a disulfide bond. The predisposing factor for the formation of this complex is unclear, but patients showing this complex usually have kappa type myeloma protein and excrete kappa chain in urine at more than 1 g/L. The relationship between chemotherapy and formation of the kappa chain-antitrypsin complex needs further investigation.