NCR^dull phenotype is common and not dependent of AML subclass. NK cells from 71 patients were analyzed by flow cytometry at diagnosis. (A) AML-NK cells were gated on the CD45^high CD3⁻CD56⁺ fraction of fresh PBMCs. Filled histograms represent isotype-matched mAb staining; open histograms represent staining with specific PE-conjugated mAbs. Represented are 1 healthy donor with NCR^bright NK cells (top), 1 of 13 AML patients with NCR^bright NK cells (middle), and 1 of 47 AML patients with NCR^dull NK cells (bottom). (B) Mean fluorescence intensity (MFI) of surface staining with anti-NKp46 and anti-NKp30 PE-conjugated mAbs of NK cells from healthy donors (Healthy), from AML regardless the FAB subclass (All), and from distinct subclasses (FAB classifications M0-M6). Others are particular forms of AML (Table 1). *P<.001; **P ≤ .01; ***P < .05. n represents number of patients. M0 indicates AML minimally differentiated; M1, AML without maturation; M2, AML with maturation; M3, acute promyelocytic leukemia; M4, acute myelomonocytic leukemia; M5, acute monocytic leukemia; M6, acute erythroid leukemia.