sFRP-2 immunodepletion restores suppression of mineralization by MM cell CM. MC3T3-E1 cells (A) and human BM-derived osteoblasts (B) were cultured in the osteogenic medium in 24-well culture plates in the presence or absence of rhBMP-2 (50 ng/mL). Control IgG-treated or sFRP-2–depleted CM from RPMI8226 and U266 cell lines as well as primary MM cells from patient no. 4 were added at 20% to the indicated wells. Mineralized nodules were visualized at day 14 and 21 by von Kossa staining in MC3T3-E1 cells and human BM-derived osteoblasts, respectively.