Innate Immune Environment in Ileal Pouch Mucosa: α-5 Defensin Up-Regulation as Predictor of Chronic/Relapsing Pouchitis

Background Defensins are small cationic peptides with antibacterial activity expressed only in Paneth cells (α-defensins) or generally in intestinal epithelial cells (β-defensins) that have a profound effect on gut microbiota. We have recently shown that chronic pouchitis, that occurs in 5% of patients after restorative proctocolectomy and can cause pouch failure, is associated to a significant increase Clostridiaceae spp. The aim of this study was to gain further insight in the pathogenesis of chronic/relapsing pouchitis by exploring the interplay between the microbiota adherent to the ileal pouch mucosa and defensin expression. Patients and methods Thirty-two consecutive patients coming for follow up endoscopy, were recruited. On pouch biopsies we determined bacteria adherent to the mucosa, by culture method, and mRNA for α-and β-defensins and Toll Like Receptor-4 and -2, by quantitative Real Time RT-PCR. Serum and mucosal levels of IL-1β, IL-6 and TNF-α were measured with immunometric assays. Faecal lactoferrin was analyzed by quantitative ELISA. After a median follow up of 23 (IQR 20-24) months the patients were contacted for a reassessment of current and past disease activity. Results During the follow up chronic/relapsing pouchitis was diagnosed in 6 patients. Mucosal level of α-5 and α-6 defensins correlated with chronic/ relapsing pouchitis onset (tau=0.30, p=0.034 and tau=0.28, p=0.053, respectively). High levels of α-5 defensin resulted predictive of chronic/relapsing pouchitis [AUC=74%(95% CI=53-89%), p=0.052]. Patients with high level of α-5 and α-6 defensins had earlier pouchitis relapses (p=0.009 and p=0.034, respectively). High levels of α-5 defensin were associated to a significant risk of chronic/relapsing pouchitis [OR=10.6(95% CI=1.2-97.6), p=0.027]. At multivariate analysis mucosal levels of α-5 defensin and the number of CFU of mucosa- associated Clostridiaceae spp resulted to be independent predictors of chronic/relapsing pouchitis [tau=0.46(0.18), p=0.024 and tau=0.44(0.18), p=0.027, respectively]. Conclusion Chronic/relapsing pouchitis is associated to increased expression of mucosal α-5 defensin. High levels of α-5 defensin may be the response to challenge of Clostridiaceae spp antigens or, alternatively they may favour Clostridiaceae spp decreasing other competing bacteria familiae.