Natural and antibody-mediated NK cell cytotoxicity is impaired in patients with XLT and WAS: ability of IL-2 to correct the NK cell functional defect. Cultured NK cells from healthy donors (triangles) or from patients with WAS (circles) or XLT (squares), treated or not with human recombinant IL-2 (250 IU/mL) for 48 hours, were assayed in a 4-hour CRA against K562 (A) or P815 plus anti-CD16 mAb (reverse ADCC) (B). Data are expressed in a log scale as LU/10⁶ cells based on 20% cytotoxicity. (A) Mean LU ± SD was 203.13 ± 80.9 for control NK cells and 41 ± 31.6 for WAS/NK cells (P < .005); mean LU for XLT/NK cells with lytic activity of 100 LU or less was 55.24 ± 38.2 (P < .005). (B) Mean LU ± SD was 89 ± 29.6 for control NK cells and 16 ± 10.4 for WAS/NK cells (P < .005); mean LU for XLT/NK cells with lytic activity of 100 LU or less was 24.4 ± 10.3 (P < .005). P values were calculated by comparing the mean LUs of patients with XLT and WAS with those of control donors using the Student t test. Statistical analysis performed on IL-2-treated XLT or WAS NK cells with respect to IL-2-treated control samples indicates that IL-2 significantly restores natural cytotoxicity and reverse ADCC (P > .01).