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P071. Alterations in epithelial and dendritic cell tight junction proteins expression in the ileo-anal pouch following ileostomy closure

J. Landy1, H.O. Al-Hassi2, E. Ronde2, S. Peake1, N. English2, E. Mann2, D. Bernardo2, C. Tee2, P.J. Ciclitira3, R.J. Nicholls4, S.K. Clark5, S. Knight2, A.L. Hart1

1St Mark's Hospital, IBD Unit, London, United Kingdom; 2Antigen Presentation Research Group, Imperial College, London, United Kingdom; 3St Thomas' Hospital, Gastroenterology, London, United Kingdom; 4Imperial College, Department of Biosurgery and Surgical Technology, London, United Kingdom; 5St Mark's Hospital, Colorectal Surgery, London, United Kingdom

Background: Epithelial barrier function is controlled by tight junction proteins (TJP). Barrier properties of pouch mucosa in pouchitis are altered, with decreased tightening TJP claudin‑1 and increased pore-forming claudin‑2 expression [1]. Dendritic cells (DCs) also affect barrier function and express TJPs to interact with the microbiota. We hypothesize that changes in the microbiota following ileostomy closure modulates TJP which may predispose to the development of pouchitis. We performed a longitudinal study to assess changes in TJP expression of the pouch epithelium and lamina propria DC following ileostomy closure.

Methods: Mucosal biopsy samples were taken from UC patients undergoing restorative proctocolectomy (RPC), from the ileostomy afferent loop, the pouch pre-ileostomy closure (P0) and the pouch 6 months post-ileostomy closure (in the same patients). Epithelial cells were isolated from biopsy tissue by EDTA. Lamina propria DC were isolated by collagenase digestion. Epithelial cells were identified as pancytokeratin positive and DCs were identified as an HLA DR+, lineage-(CD3‑, CD14‑, CD16‑, CD19‑, CD34‑, CD56‑) population. Expression of ZO‑1, claudin‑1 and claudin‑2 in epithelial cell and DC was measured by flow cytometry. Paired t‑tests were performed for statistical analysis.

Results: See Table 1.

Table 1
UC ileostomy (n = 5)81%34%8%79%35%3%
Pre-ileostomy closure pouch (P0) (n = 5)84%44%25%74%55%32%
6 month pouch (n = 5)91%40%66%87%57%47%

ZO‑1 and claudin‑1 expression remained stable following closure of the ileostomy in both epithelial cells and DC. Claudin‑2 expression was not significantly increased in both epithelium (p = 0.26) and dendritic cells (p = 0.06) in P0 samples compared to ileostomy samples. In the pouch 6 months post-ileostomy, epithelial expression of claudin‑2 increased significantly compared to ileostomy (p = 0.008) and P0 (p = 0.012) samples and DC claudin‑2 expression increased compared to ileostomy (p = 0.048) and P0 samples (p = 0.19).

Conclusions: Increased expression of Claudin‑2 after ileostomy closure, favours barrier dysfunction and may increase the interactions between the microbiota and mucosal immune responses. Changes in TJP expression following ileostomy closure may be a critical step in UC RPC patients' predisposition to pouchitis.

1. Amasheh S et al. (2009), Inflamed pouch mucosa possesses altered tight junctions indicating recurrence of inflammatory bowel disease, Int J Colorectal Dis, 1149–56, 24.