Idiotypical identity of IgG myeloma protein with monoclonal IgM, Bence Jones protein, and Fv derived from one patient.

Serum from a patient (KK) with IgG2-lambda myeloma was shown to contain multiple paraproteins corresponding to an IgM-lambda monoclonal protein (MMP), a lambda-type Bence Jones protein (BJP), and a 30 kDa component in addition to the IgG2 myeloma protein (GMP). These proteins possessed common idiotypic determinants, as judged by their monoclonal reactivity with rabbit anti-GMP idiotype antibody (aId) in the immunofixation electrophoresis. Analysis with aId absorbed with either H or L chain of GMP revealed that the 30 kDa component shared both VH and VL with GMP and MMP, while BJP carried only the VL idiotype. The 30 kDa component, however, failed to react with antibody to either the mu, gamma, alpha, kappa, or lambda isotype, indicating that it had an Fv-like molecular composition. These results suggest that myeloma cells of KK had diverged from the same precursor B cell clone to produce MPs of different isotypes and altered molecular constructions.