A biclonal origin of two monoclonal proteins, IgG3(kappa) and IgA1(lambda), from a single patient.

The cellulose acetate electrophoretic pattern of the serum from patient Sik disclosed two distinct peaks, representing two monoclonal proteins. On immunoelectrophoresis the two M-components were found to differ in heavy chain class as well as in light chain type, IgG3(kappa) and IgA1(lambda). Serum immunoglobulin levels remained relatively constant over a period of 7 years and no clinical symptoms of a malignant deterioration occurred. It was found that the isolated M-components did not share idiotypic antigenicity. Bone marrow cells synthesizing the monoclonal proteins were identified by means of the immunofluorescent technique using isotypic as well as idiotypic antisera. Two distinct monoclonal cell populations were observed, containing either the IgG3(kappa) or the IgA1(lambda) monoclonal protein. The alpha 1-chain belonged to the VHIII subgroup, whereas the gamma 3-chain was found to be blocked. Subsequent sequence determination showed the gamma 3-chain to belong to the VHIII subgroup. It was concluded that the two M-components in the serum of patient Sik resulted from two independent neoplastic transformations.