Levels of soluble interleukin-18 receptor α complex were increased in sera of rheumatoid arthritis and adult-onset Still's disease patients. IL = interleukin; sIL-18R = soluble IL-18 receptor; AOSD = adult-onset Still's disease; RF, rheumatoid factor; CCP = anticyclic citrullinated peptide; OA = osteoarthritis; SLE = systemic lupus erythematosus. *P < 0.05 vs. healthy controls. +P < 0.05 vs. OA. †P < 0.05 vs. SLE. ‡P < 0.05 vs. RA. §P < 0.05 vs. AOSD.