gp91^phox is expressed by mature malignant FAB-M4 and FAB-M5 AML cells. BM or peripheral blood cells from patients with FAB-M1, FAB-M2, or FAB-M4/M5 AML were stained for gp91^phox. Results show intensity of gp91^phox expression (MFI) of cells with CD33⁺ and/or CD34⁺ phenotype with medians indicated. Immature cells were defined by absence of CD14 and CD15. Mature FAB-M4/M5 cells were defined as cells expressing CD14. H.D represents gp91^phox expression by peripheral blood monocytes from healthy donors. (B) Confocal photomicrographs of FACS-sorted immature M2 cells (left), immature M4 cells (center), and mature M4 cells (right) showing gp91^phox expression. The sorted FAB-M2 (patient 2) cells were NPM1⁺ and FLT3/ITD⁺. Immature and mature cells from the patient with FAB-M4 AML (patient 6) carried t(16;16). The nucleus was made visible by DAPI staining (blue) and gp91 was visualized using a FITC-conjugated primary antibody. Bars represent 2 μm.