Expression of MAdCAM-1 and gut-homing T-cells in inflamed pouch mucosa.

BACKGROUND AND AIMS Pouchitis is a common complication following formation of an ileal pouch-anal anastomosis (IPAA) after proctocolectomy for ulcerative colitis (UC). Gut-specific lymphocyte trafficking mechanisms have been identified as players in the pathogenesis of UC. In the present study, we aimed to characterize the presence of lymphocyte subsets expressing gut-homing molecules in pouches and peripheral blood of UC patients with and without pouchitis. METHODS Biopsy samples and peripheral blood were collected from 29 patients with an IPAA (7 with active inflammation, 22 without inflammation). Expression of adhesion molecule MAdCAM-1 was assessed using immunohistochemistry, and flow cytometry was used to characterize expression of integrin α4β7, C-chemokine receptor 9 (CCR9) and CD103 on T-cell subsets. RESULTS MAdCAM-1 expression was significantly increased in case of active inflammation in the pouch. T-cells expressing integrin α4β7 were abundant in the pouch mucosa, but the frequency of integrin α4β7 expressing T-cells was decreased on CD4 + lymphocytes during inflammation. Co-expression of gut-homing markers CCR9 and α4β7 was more pronounced in biopsies compared with peripheral blood, but was not enhanced upon active inflammation. CONCLUSIONS Gut-homing T-cells are abundant in pouch mucosa, but the classic hypothesis that the chronic inflammatory state is maintained by an accumulation of α4β7-expressing effector T-cells is not supported by our data.