HSP60 specific T cells in the synovium of juvenile idiopathic arthritis (JIA) patients are IL-10-producing CD30+ regulatory T cell (Treg)-like cells. (a) HSP60 (stained brown and marked by red arrows) is highly expressed in synovial lining membranes in the inflamed joints of JIA patients. (b) HSP60 is released by the synovial tissues in the inflamed joint. In the synovial fluid, CD4+ T cells are present. T cells that react to the self-HSP60 or HSP60 epitopes produce IL-10 [13, 68] and express CD30. Presence of these HSP60-reactive T cells correlates with a mild disease course . Therefore, we hypothesize that these T cells could be CD25- and FOXP3-expressing naturally occurring Tregs , or IL-10-producing T regulatory 1 cells. Altogether, HSP60 may induce Tregs in the joints of JIA patients and thereby regulate the inflammation of these JIA patients, as is seen in oligoarticular JIA. HSP, heat shock protein.