2 M-COMPONENTS IN A SINGLE-CELL LINEAGE IN A PATIENT WITH A DUAL ISOTYPE SECRETORY B-CELL TUMOR

We describe a case of Waldenstrom's macroglobulinaemia with two M-comp onents (IgM and IgG) with the same lambda light chain, Southern blot a nalysis of bone marrow cells showed rearrangements of immunoglobulin h eavy and lambda light chain genes. Sequencing of the complementarity d etermining region 3 of the two gamma and mu transcripts showed 100% ho mology. Immunofluorescence study showed that most cells stained for bo th IgG and IgM. These findings indicated that a single population of c ells was expressing two isotypic variants of IgG and IgM, as the genes responsible for production of both components had the same origin.