Natural Killer T Cell Deficiency in Active Adult-Onset Still's Disease Correlation of Deficiency of Natural Killer T Cells With Dysfunction of Natural Killer Cells

Objective. To examine the levels and functions of natural killer (NK) and natural killer T (NKT) cells, investigate relationships between NK and NKT cells, and determine the clinical relevance of NKT cell levels in patients with adult-onset Still's disease (AOSD). Methods. Patients with active untreated AOSD (n = 20) and age- and sex-matched healthy controls (n = 20) were studied. NK and NKT cell levels were measured by flow cytometry. Peripheral blood mononuclear cells were cultured in vitro with alpha-galactosylceramide (alpha GalCer). NK cytotoxicity against K562 cells and proliferation indices of NKT cells were estimated by flow cytometry. Results. Percentages and absolute numbers of NKT cells were significantly lower in the peripheral blood of AOSD patients than in that of healthy controls. Proliferative responses of NKT cells to alpha GalCer were also lower in patients, and this was found to be due to proinflammatory cytokines and NKT cell apoptosis. In addition, NK cytotoxicity was found to be significantly lower in patients than in healthy controls, but NK cell levels were comparable in the 2 groups. Notably, this NKT cell deficiency was found to be correlated with NK cell dysfunction and to reflect active disease status. Furthermore, alpha GalCer-mediated NK cytotoxicity, showing the interaction between NK and NKT cells, was significantly lower in AOSD patients than in healthy controls. Conclusion. These findings demonstrate that NK and NKT cell functions are defective in AOSD patients and suggest that these abnormalities contribute to innate immune dysfunction in AOSD.