The implication of interferon-γ-producing immunocompetent cells for evaluating disease activity and severity in adult-onset Still's disease.

Objective: To investigate the relationship between interferon-γ (IFN-γ), IFN-γ-producing immunocompetent cells, their related cytokines, and the clinical features in adult-onset Still's disease (AOSD).

Methods: Twenty-five patients with AOSD before initiating treatment (acute AOSD), 9 patients after remission (remission AOSD), and 12 healthy controls (HC) were included. Circulating IFN-γ-producing CD4+ and CD8+ cells, natural killer (NK) cells, and IFN-γ production in NK cells were evaluated by flow cytometry. Serum levels of IFN-γ, interleukin (IL)-6, IL-12, IL-15, and IL-18 were also measured. The obtained results were statistically analyzed with clinical findings.

Results: Serum levels of IFN-γ, IL-6, IL-12, IL-18, intracellular expression of IFN-γ in CD4+, CD8+, and NK cells were significantly higher in acute AOSD than in HC. The proportion of NK cells was significantly lower in acute AOSD than in HC. Serum levels of IFN-γ and IFN-γ expression in CD4+ cells were significantly correlated with serum ferritin levels. The proportion of NK cells had a significant inverse correlation with serum IFN-γ levels. A lower proportion of NK cells was significantly noted in patients refractory to initial immunosuppressive treatment. In remission AOSD, serum levels of IL-6, IL-12, and IL-18 were significantly higher than in HC.

Conclusion: Increased serum levels of IFN-γ, increased expression of IFN-γ in CD4+ cells, and decreased NK cell proportion correlate with disease activity in AOSD. Moreover, a lower proportion of NK cells may be useful for predicting a refractory clinical course. Meanwhile, increased serum levels of IL-6, IL-12, and IL-18 may persist after clinical remission.