To investigate natural killer (NK) cell proportions, NK cell cytotoxicity, and interleukin 18 (IL-18) expression, in patients with adult-onset Still's disease (AOSD).
Forty-five patients with AOSD (active = 22, inactive = 23) and 32 healthy controls were included. The proportions of NK cells among peripheral blood mononuclear cells were assessed by flow cytometry. IL-18 and IL-18-binding protein (IL-18BP) concentrations were measured by ELISA. Twenty-four patients with AOSD and 18 controls were examined for cytotoxic activity of NK cells by co-incubating NK cells with NK-sensitive K562 cells. The association of NK cell function with clinical and laboratory measures was investigated.
The proportions of NK cells were significantly lower in patients with active AOSD than in patients with inactive disease and controls. NK cell cytotoxic function was significantly lower in patients with AOSD than in controls. NK cell proportions and cytotoxic functions were reexamined in 11 and 6 patients, respectively, after treatment. Low NK cell proportion and cytotoxic dysfunction were improved with clinical improvements of the patients. IL-18 and IL-18BP levels were much higher in patients with active AOSD than in controls. NK cell cytotoxic functions were consistently low and IL-18 and IL-18BP levels were constantly high in patients with AOSD, regardless of disease activity.
Low NK cell proportion, defective cytotoxic function, and elevated IL-18 levels may be significant features of AOSD. After resolution of the acute phase, low NK cell proportion was recovered and NK cell cytolytic function was restored along with clinical improvement. These findings possibly contribute to immunologic abnormalities in AOSD.