Simultaneous production of IgG lambda and IgA lambda in a clone of myeloma cells.

We describe a patient (KY) with multiple myeloma and double paraproteinemia. The patient's serum contained IgG lambda and IgA lambda myeloma proteins. An anti-idiotypic antiserum to purified KY IgA was prepared in rabbits, and it was found that KY IgA and KY IgG shared common antigenic determinants, which appeared to be located in variable regions of both the heavy and light chains. Double staining experiments using an anti-alpha chain antibody conjugated with fluorescein isothiocyanate and anti-gamma chain antibody conjugated with rhodamine showed that virtually all plasma cells were stained for both antibodies simultaneously.