Blocking of SDF-1/CXCR-4 interactions induces apoptosis in 32D cells. On day 0, cultures were initiated with 2 × 10⁵ 32D/G-CSF-R cells/mL. Cells were counted and cultures were readjusted to 2 × 10⁵ cells/mL on a daily basis. Cultures were either performed in the presence of G-CSF, G-CSF + a CXCR4-blocking antibody, or G-CSF + an SDF-1 neutralizing antibody. The percentage of cells in apoptosis (y-axis) was determined by a flow cytometric analysis of the number of annexin-V⁺ 7-AAD^- cells. Error bars indicate ± 1 SD.