IL17A and juvenile idiopathic arthritis: Thus, we demonstrated that the proinflammatory T cell subset that produces interleukin-17 (IL-17), IL-21, and IL-22 (the Th17 subset) is enriched in the joints, compared with the blood, of children with JIA, and that this cell type is found in significantly higher numbers in the joints of children with extended oligoarticular JIA than in those with persistent oligoarticular JIA (8).