Expression of the receptors for BAFF and APRIL in MMCs. (Top) Expression of BCMA, BAFF-R, TACI, and GAPDH mRNA were determined by RT-PCR in CD138⁺ purified primary MMCs from 10 patients with intramedullary MM. (Bottom) The ability of MMCs to bind BAFF was determined by flow cytometry using a biotinylated human BAFF-murine CD8 fusion protein and phycoerythrin-conjugated streptavidin. Dotted lines indicate Ig control; solid lines, Baff-mu CD8.