Apoptosis in the MM cell line INA-6. Cells were cultured without or with IL-6 for the times indicated, and aliquots were subjected to annexin V and PI staining. Apoptosis ratio was calculated as the percentage of annexin V–positive cells of all viable (PI-negative) cells. The dotted line represents a culture restimulated with IL-6 after 12 hours of IL-6 starvation. Data are mean values ± SD of 3 independent experiments.