AIM: To investigate the role of local colonic mucosal NK receptor-positive T (NKR+ T) cells in the regulation of intestinal inflammation, we analyzed the population and function of these cells in ulcerative colitis (UC).METHODS: Colonic mucosal tissues were obtained from colonoscopic biopsies of the descending colon from 96 patients with UC (51 endoscopically uninflamed, 45 inflamed) and 18 normal controls. Endoscopic appearance and histologic score at the biopsied site were determined by Matts' classification. A single cell suspension was prepared from each biopsy by collagenase digestion.Two NKR+ T cell subsets, CD56+ (CD56+CD3+) T cells and CD161+(CD161+CD3+) T cells, were detected by flow cytometric analysis.Intracellular cytokine analysis for anti-inflammatory cytokine interleukin-10 (IL-10) was performed by in vitro stimulation with phorbol-myristate acetate (PMA) and ionomycin.RESULTS: CD56+ T cells and CD161+ T cells are present in the normal human colon and account for 6.7% and 21.3% of all mononuclear cells, respectively. The populations of both CD56+ T cells and CD161+ T cells were decreased significantly in the inflamed mucosa of UC. In contrast, the frequency of conventional T cells CD56-CD3+cells and CD161-CD3+ cells) was similar among the patient and control groups. The populations of NKR+ T cells were correlated inversely with the severity of inflammation, which was classified according to the endoscopic and histologic Matts' criteria.Interestingly, approximately 4% of mucosal NKR+ T cells expressing IL-10 were detected by in vitro stimulation with PMA and ionomycin.CONCLUSION: Selective reduction in the population of colonic mucosal NKR+T cells may contribute to the development of intestinal inflammation in UC.