IL18BP and systemic-onset juvenile idiopathic arthritis: Serum or plasma samples from Still’s disease patients (AOSD, n = 23; sJIA, n = 40) and autoimmune and/or inflammatory disease controls (n = 478) were analyzed for autoantibodies against progranulin (PGRN), IL-1Ra, IL-18 binding protein (IL-18BP), and IL-36Ra, as well as circulating IL-1Ra and IL-36Ra levels by ELISA.