IL2RA and adult-onset Still disease: Regarding the cytokines, we found that AST had the strongest correlation with sIL-2R, a truncated protein cleaved from the IL-2Rα protein when T cells are activated, acting as a surrogate indicator of T cell activation as well as an important diagnostic marker of HLH, followed by IL-18, IL-10, and TNF-α, cytokines reflecting the diseases activity of AOSD (22–24).