What do cytokine profiles tell us about subsets of juvenile idiopathic arthritis?

Classification of juvenile idiopathic arthritis is an ongoing process and up to now has been predominantly based on clinical manifestations--mainly number of joints at onset of disease. In the meantime, basic studies have advanced our knowledge regarding the disease pathogenesis. Unfortunately, studies of cytokines and cytokine polymorphisms have not followed the predominantly clinical International League of Associations for Rheumatology classification in that no significant biological differences among the different disease categories have been demonstrated with robust associations. Only systemic-onset disease seems to be quite different from other disease categories with regard to biologic mechanisms; indeed, it now seems closer to autoinflammatory than to classic autoimmune diseases. New players in the immunologic basis of juvenile idiopathic arthritis (eg, interleukin-17 and regulatory T cells) are also discussed in this review.