Effect of Cdt on THP-1, monocyte and macrophage DNA fragmentation. THP-1 cells (panels A and B), THP-1-derived macrophages (panels C and D), monocytes (panels E and F) and MDM (panels G and H) were exposed to medium (panels A, C, E, G) or treated with Cdt (panels A, C, F, H) for 48 hr. THP-1 cells were exposed to 10 ng/ml Cdt and THP-1-derived macrophages to 1 µg/ml of toxin; monocytes and MDM were treated with 500 ng/ml Cdt. The cells were then analyzed by flow cytometry for the presence of DNA fragmentation as described in Methods and Materials. Results are plotted as relative cell number versus DNA fragmentation (BrDU-FITC fluorescence). The line represents the analytical gate used to assess cells exhibiting DNA fragmentation and the numbers are the percentage of positive cells. Results are representative of three experiments.