Studies on IgA and IgA monoclonal proteins derived from a single patient. Evidence for identical light chains and variable regions of the heavy chain.

Two immunoglobulins, IgA(K) and IgG(K), were isolated from the serum of a single patient with two monoclonal components (biclonal proteins). After chain separation, the light chains from each molecule were found to be identical by the following criteria: electrophoretic mobilities under various pH and dissociating conditions, amino acid compositon, fingerprint analysis of tryptic peptides and of 14C-succinylated chymotryptic peptides, and amino acid sequence of the N-terminal 40 residues. The heavy chains were indistinguishable for the N-terminal 45 amino acid residues. These data are consistent with the hypothesis that a single heavy chain variable (VH) region may be associated with two different heavy chain constant (CH) genes.