Prevention of H81.9 induced apoptosis by NMMA. Human marrow mononuclear cells were analyzed for apoptotic nuclei (DNA histograms) as described for Fig 3. The relative number of nuclei is shown on the vertical axis, the DNA content on the horizontal axis. In the presence of NMMA the apoptotic (sub-G₁ ) peak was reduced from 12.5% (A; H81.9 alone) to 1.2% (B; H81.9 + NMMA).