Correlations between CD3–CD56⁺CD16⁺-cell numbers corresponding to NK cells and free IL-18 calculated concentrations in HPS patients during the acute phase of the disease. Correlations were studied between NK-cell numbers and free IL-18 concentrations (A), NK natural cytotoxicity (B), and antibody-dependent cell cytotoxicity (ADCC; C) in HPS and control patients. In vitro NK cytotoxicity and ADCC were studied in HPS patients (n = 7) and compared with 2 control groups (healthy controls, n = 30; and disease controls, n = 21). Box plot representation, horizontal line within boxes represents median (*P < .01, **P = .001 compared with healthy controls). ○ indicates outside values.