Colonic Mucosal Immune Activity in Irritable Bowel Syndrome: Comparison with Healthy Controls and Patients with Ulcerative Colitis

Mucosal immune activity may participate in irritable bowel syndrome (IBS) pathogenesis. Mast- and T cell numbers from patients with IBS or ulcerative colitis (UC) and healthy controls were determined. Between November 2007 and May 2012, patients with diarrhea-predominant IBS (D-IBS, n = 83), 49 patients with UC, and 25 healthy controls were recruited. Of the UC group, 28 were in remission and 21 had mildly active UC. Biopsies from each colon segment were subjected to immunohistochemical analysis. The mast cells, intraepithelial lymphocytes (IELs), and lamina proprial lymphocytes (LPLs) were counted. Compared to the healthy controls, the patients with D-IBS, UC in remission, and mildly active UC had significantly higher mean colorectal mucosal mast-cell, IEL, and LPL counts. Comparison with the colon segments (ascending, transverse, descending, and sigmoid segments) that had once been involved in UC (in the patients with remission) revealed that the D-IBS colons had similar immune-cell counts. However, they had significantly fewer immune cells than the colon segments that presently showed involvement in the patients with mildly-activated UC. The mast-cell and IEL counts were similar in the D-IBS rectums and once-involved UC rectums but significantly higher in the presently-involved UC rectums. However, both the once-involved and presently-involved UC rectums had significantly higher LPL counts than the D-IBS rectums. Patients with D-IBS had significantly higher colonic mucosal immune-cell counts than healthy controls but had similar counts to patients with UC in remission. The symptoms in both conditions may originate from low-grade inflammation in the colonic mucosa.