B cell compartments in multiple myeloma: flow cytometric analysis of their labelling indices and Bcl-2 protein expression.

Because recent reports have suggested that non plasmacytic tumor B cells are very rare in Multiple Myeloma (MM), we tried to characterize the B lineage in this disease by comparing by flow cytometry in the PB and BM of MM patients and of controls the proliferative activity (BrdU incorporation) and the Bcl-2 expression of different B cell subsets defined by cytoplasmic light chain, CD19 or CD10 antigen expression. The labelling indices (LI) of CD19+ and CD10+ BM cells in treated patients were higher than in controls and untreated patients. Plasma cell LI (PCLI) were close to previously published values of PCLI flow assays and did not correlate with the LI of BM B cells. Bcl-2 expression by BM CD19+ and CD10+ cells in patients was inferior to controls. These results agree with previously published data about the likely polyclonal nature of most pre PC B cells in MM.