Dose-dependent inhibition of myeloma cell growth by syndecan-1 ectodomain. (A) ARH-77 cells; (B) mer cells; (C) ark cells; (D) arp cells. Effect of addition of purified syndecan-1 ectodomain on the growth of myeloma cell lines (ARH-77, mer, arp, and ark) in culture. Cells (3 × 10⁴) were incubated with various concentrations of syndecan-1 or in media alone for 72 hours, and cell growth was analyzed by ³H-thymidine proliferation assays. Cell growth is expressed as a percentage of control (media only).