IL17A and juvenile idiopathic arthritis: In fact, patients suffering from juvenile idiopathic arthritis (JIA), a highly inflammatory form of rheumatoid arthritis in children whose pathogenesis has previously been linked to innate IL-1β and IL-1α18,19, revealed significantly and strongly elevated IL-1α expression by IL-17+ TH cells compared with IL-17+ TH cells from healthy control blood (Fig. 2g).