Induction of apoptosis of myeloma cells by syndecan-1. Myeloma cell lines ([A] and [B] ARH-77 cells; [C] and [D], arp cells) were incubated with media alone (A and C) or purified syndecan-1 (4 nmol/L) for 48 hours (B and D). Apoptosis was examined using flow cytometry-based TUNEL (TdT-mediated dUTP nick end labeling) assay (Boehringer Mannheim) using the manufacturer's protocol. For negative control (thin line), cells were stained with label solution in the absence of TdT. For test sample (thick line), cells were stained with TUNEL reaction mixture according to manufacturer's protocol. The apoptotic population is marked by an arrow. Figures represent one of three representative experiments.