To investigate whether the gene expression profile of human Treg cells in an inflammatory environment is different from circulating human Treg cells, CD3+CD4+CD25+CD127low Treg cells and CD3+CD4+CD25−CD127+ non-Treg cells were isolated from: synovial exudate obtained from inflamed joints of juvenile idiopathic arthritis (JIA) patients, peripheral blood (PB) from JIA patients with active and inactive disease, and PB from healthy children and healthy adults (Supplementary Fig. 1a for gating strategy). Here, IL2RA is linked to juvenile idiopathic arthritis.