Expression of BLyS in myeloma cells. Expression of BLyS mRNA was analyzed by RT-PCR in 7 CD138⁺ primary MM cell samples or CD19⁺ resting B cells (A) or in a panel of MM cell lines (B). The HL60 monocytic cell line was used as a positive control. (C) Immunohistochemical analysis of BLyS expression in ANBL-6 and KAS-6/1 MM cell lines was performed as described in “Materials and methods.” The antibody used in panels ii and vi was specific for membrane-bound BLyS (Alexis Biotechnology), whereas the antibody used in panels iv and viii was specific for soluble and membranebound BLyS (R&D Systems). Corresponding isotype controls are shown in panels i, iii, v, and vii. Original magnification, ×200.