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 characterise 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 [seven with active inflammation, 22 without inflammation]. Expression of adhesion molecule MAdCAM-1 was assessed using immunohistochemistry, and flow cytometry was used to characterise 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.