A Controlled Study of Colonic Immune Activity and β7+ Blood T Lymphocytes in Patients With Irritable Bowel Syndrome

Background & Aims: The mechanisms behind irritable bowel syndrome (IBS) are incompletely understood. Recently several studies have suggested a low-grade colonic inflammation as initiator of the gut dysfunctions recorded in this patient group. The aim of this study was to characterize the phenotype and homing properties of colonic and peripheral blood lymphocytes in patients with IBS. Methods: Patients with IBS (n = 33), defined by the Rome II criteria, were compared with UC patients (n = 23) and control subjects (n = 15) without gastrointestinal symptoms. Colonic and peripheral blood lymphocytes were analyzed by flow cytometry. Secretion of IFN-γ from intestinal biopsies was determined by enzyme-linked immunosorbent assay, and immunohistochemical staining of colonic biopsies was performed. Results: IBS patients displayed an increased frequency of peripheral blood CD4+ and CD8+ T cells expressing the gut homing integrin β7. Accordingly, IBS and UC patients had an augmented frequency of lamina propria CD8+ T cells in the ascending colon as compared with control subjects. The frequency of intestinal T cells expressing integrin β7+ was unaltered in IBS and UC patients, although the expression of mucosal addressin cell adhesion molecule-1+ endothelium, the ligand for integrin β7, was increased in the ascending colon of IBS and UC patients as compared with control subjects. Conclusions: Patients with IBS exhibit an enhanced immune activity in the gut and an increased frequency of integrin β7+ T lymphocytes in the peripheral blood. Our data further support the hypothesis of IBS being at least partially an inflammatory disorder.