Innate Immune Environment in Ileal Pouch Mucosa: α5 Defensin Up-regulation as Predictor of Chronic/Relapsing Pouchitis

Defensins are small cationic peptides with antibacterial activity expressed in Paneth cells (α-defensins) or generally in intestinal epithelial cells (β-defensins) that have a profound effect on gut microbiota. Chronic pouchitis, which occurs in 5% of patients after restorative proctocolectomy and can cause pouch failure, is associated to a significant increase of Clostridiaceae spp. The aim of this study was to gain further insight in the pathogenesis of pouch dysbiosis by exploring defensin expression. Thirty-two consecutive patients coming for follow-up endoscopy were recruited. On pouch biopsies, we cultured bacteria adherent to the mucosa and determined α- and β-defensins and toll-like receptor-4 and −2 mRNA 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 analysed 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. During the follow-up, chronic/relapsing pouchitis was diagnosed in six patients. The mucosal level of α-5 and α-6 defensins correlated with chronic/relapsing pouchitis onset (τ = 0.30, p = 0.034 and τ = 0.28, p = 0.053, respectively). High levels of α-5 defensin resulted to be predictive of chronic/relapsing pouchitis [AUC = 74% (95% CI = 53–89%), p = 0.052]. Patients with high levels 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, the 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 [β = 0.46 (0.18), p = 0.024 and β = 0.44 (0.18), p = 0.027, respectively]. In conclusion, chronic/relapsing pouchitis is associated to increased expression of mucosal HD-5 and to increased antimicrobial activity against Escherichia coli. In patients with chronic/relapsing pouchitis, HD-5 and TLR-4 over-expression is likely to create a hostile environment against Enterobacteriaceae, thus favouring Clostridiaceae spp by decreasing competing bacteria families.