HMGB1 and juvenile idiopathic arthritis: In that context, our finding of increased amounts of HMGB1 in inflamed joints of children with oligoarticular and polyarticular JIA led us to the hypothesis that the another possible origin of HMGB1 in JIA could have been the inflamed joints and that serum HMGB1 was not synthesised only by the circulating leukocytes.