Rytkonen SH, et al. - This study was undertaken to assess a possible role of regulatory T cells (Tregs) in the pathophysiology of tubulointerstitial nephritis (TIN) with (TINU) and without uveitis. For this purpose, the presence and quantity of FOXP₃⁺ T regulatory lymphocytes in diagnostic kidney biopsies from pediatric patients was investigated. Presence of FOXP₃⁺ T cells was apparent in kidney biopsy samples from TIN and TINU patients. Compared with other patients, significantly lower density of FOXP₃⁺ T cells was seen in patients with chronic uveitis, suggesting a different pathomechanism for these clinical conditions.