Enriched CD45RA⁻CD62L⁺ central memory T and decreased CD3⁺CD56⁺ natural killer T lymphocyte subsets in the rectum of ulcerative colitis patients

Objectives: To investigate the distinctive features of lymphocytes promoting inflammation in ulcerative colitis. Methods: We performed flow cytometric analysis of peripheral blood mononuclear cells (PBMCs) and colorectal mucosa lymphocytes in ulcerative colitis patients (n = 13) and control patients (n = 5). Results: CD62L⁺/CD3⁺CD4⁺ (35.7 ± 14.0% vs. 19.9 ± 6.4%) and CD62L⁺/CD3⁺CD4⁻ cells (17.1 ± 17.4% vs. 2.4 ± 3.9%) were higher in the rectum of ulcerative colitis patients than in control patients. Subpopulation analysis revealed that CD45RA⁻CD62L⁺/CD3⁺CD4⁺, that is, central memory T cell fraction in CD4⁺ T cells, was significantly increased in the rectum of ulcerative colitis, compared to that in control patients (23.3 ± 10.5% vs. 8.2 ± 4.0%). Comparison of rectum and colon samples in ulcerative colitis patients indicated that CD56⁺/CD3⁺ was decreased in the rectum compared to that in the colon (11.3 ± 12.5% vs. 21.3 ± 16.5%). The ratio of CD56⁺/CD3⁺ was also decreased in the rectum of active ulcerative colitis patients compared to that in ulcerative colitis patients at the endoscopic remission stages (2.8 ± 1.7% vs. 18.5 ± 13.3%). Conclusion: We demonstrated that CD62L⁺ T lymphocytes, particularly the CD45RA⁻CD62L⁺ T cell subset that represents central memory T cells, were increased in the rectum of patients with ulcerative colitis. In addition, the CD56⁺/CD3⁺ subset (natural killer T cells) was decreased in the rectum compared to that of less inflamed colonic mucosa. These results suggest that the enrichment of central memory T lymphocytes and the reduction of natural killer T cells in the gut mucosa are involved in the pathogenesis of ulcerative colitis.