Impaired NK cell maturation and function in patients with AIN. Total NK cell (CD3⁻CD56⁺; A) and percentages of CD56^bright NK cells (B) in peripheral blood of healthy control individuals (black squares) and AIN patients (open circles). (C–F) PBMCs from healthy controls (black squares) or AIN patients (open circles) were stimulated for 4 h with K562 target cells (C–E) or ADCC (D–F) at an effector/target ratio of 5:2 and 50:1, respectively. (C and D) Frequencies of IFN-γ–producing NK cells and (E and F) NK cell cytotoxic activity were measured by FACS. Statistical significance was determined in a Mann-Whitney test. *, P < 0.05; **, P < 0.01; ***, P < 0.005. (G) Representation of the neutrophil count (cells/microliter) in peripheral blood of AIN patient #25 during neutropenia and after remission. Dashed line indicates the neutropenia threshold of 1,500 neutrophils/µl. (H) PBMCs from AIN patient #25 during neutropenia (top) or after remission (bottom) were stimulated for 4 h with K562 target cells, ADCC, or medium. FACS profiles show IFN-γ⁺ NK cells among (CD3⁻ CD56⁺) NK cells. Percentages of IFN-γ⁺ NK cells are indicated.