CD25brightCD4+ T cells suppressed both proliferation and cytokine secretion of synovial responder cells. CD25brightCD4+ T cells and CD25- CD4+ T cells (RSF) from two patients with psoriatic arthritis (PsA), two with spondyloarthopathies (SpA), two with juvenile idiopathic arthritis (JIA), and two with rheumatoid arthritis (RA) were sorted by flow cytometry. Increasing numbers of CD25brightCD4+ T cells were added to a fixed number of autologous RSF in coculture. Proliferation was measured after 6 days of culture with anti-CD3 stimulation (filled symbols). Culture supernatants were analyzed for cytokine content (open symbols). A response of 100% equals a proliferation/cytokine secretion of CD4+ RSF on their own. IFN, interferon; IL, interleukin; TNF, tumor necrosis factor.