DNA histograms of human marrow mononuclear cells. Human marrow cells from untreated cultures (A, control) and cultures treated with sin-1, 1 μg/mL (B); sin-1, 100 μg/mL (C); H81.9, 10 μg/mL (D); sin-1, 1 μg/mL + H81.9 (E); and sin-1, 100 μg/mL + H81.9 (F ) were obtained after a 16-hour incubation, stained with PI and analyzed using flow cytometry. Relative numbers of nuclei are shown on the vertical axis and DNA content on the horizontal axis. Apoptotic nuclei are represented by the sub-G₁ peak marked by the percentage. Apoptotic features were confirmed by electron microscopy.22 Results of one of four similar experiments are shown.