Three monoclonal immunoglobulins, an IgG2(kappa), an IgM(kappa) and an IgM/A hybrid, in one patient. II. Sharing of common variable regions.

Amino acid sequencing and haemagglutination inhibition studies were performed on three monoclonal immunoglobulins (an IgG2, an IgM and an IgM/A hybrid) isolated from a patient afflicted with a multiple gammopathy. The results demonstrated that all three proteins have shared idiotypic determinant(s). Furthermore, the light chains of all three paraproteins have identical NH2-terminal amino-acid sequences at all positions determined thus far. Similarly, the NH2-terminal amino-acid sequence of the gamma 2 chains is identical to that of the mu chain. The evidence strongly suggests a common ancestral clonal origin for cells which produce these paraproteins and that identical variable region (VH and VL) genes were used by the ESM lymphocyte subclones in the biosynthesis of the respective IgM, IgG, and IgM/A hybrid molecules. The occurrence of a mu/alpha hybrid chain, which shares identical V regions with a mu and a gamma chain, is consistent with the concept that IgM-producing cells can develop directly into cells producing other classes of immunoglobulins via separate pathways during B-cell maturation.