Sorted mature FAB-M4/M5 AML cells trigger apoptosis in NK cells. Each row shows data obtained from individual patients with FAB-M4 or FAB-M5 AML as indicated. Histograms show the expression of gp91^phox in myeloid cells. Center panels show fMLF-induced ROS production by the corresponding sorted gp91^phox-positive population. Right panels show NK-cell apoptosis after overnight incubation with mature leukemic cells at indicated ratios of AML cells to NK cells.