FAB-M4 and -M5 AML cells produce ROS and express the NADPH oxidase subunit gp91^phox. (A) Nonerythroid BM cells recovered at diagnosis from untreated patients with FAB-M1 AML, FAB-M2 AML, or FAB-M4/M5-AML (patients 11-26) were stimulated with PMA (5 × 10⁻⁸M) and assayed for ROS production. Bars represent extracellular ROS ± SEM. (B) Myeloid cells in BM or peripheral blood cells from newly diagnosed, untreated AML patients were analyzed by FACS for expression of the NADPH oxidase subunit gp91^phox. The data points represent the percentage of CD33⁺ and/or CD34⁺ cells expressing gp91^phox, with medians indicated. Among FAB-M4/M5 cells, M5 indicates FAB-M5 cells. H.D represents gp91^phox expression by peripheral blood monocytes from healthy donors.