P049. Longitudinal assessment of epithelial and immune cell changes following ileostomy closure in patients with ulcerative colitis
J. Landy1, H. Omar Al-Hassi2, E. Mann2, S. Peake1, 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
The interactions between microbiota, epithelial barrier and innate immune responses are important in the pathogenesis of IBD. The ileo-anal pouch offers a unique opportunity to study these inter-relationships before the onset of disease. There are few data regarding tight junction expression or dendritic cell (DC) characteristics following restorative proctocolectomy (RPC) for ulcerative colitis (UC). We aimed to assess the relationship between changes in epithelial tight junction expression, dendritic cell phenotype and mucosal cytokine production over the first year following RPC for UC.
Mucosal biopsy samples were taken from UC patients undergoing RPC, from the ileostomy afferent loop, the pouch pre-ileostomy closure (P0) and the pouch 6 and 12 months post-ileostomy closure (n = 5). Epithelial cells and lamina propria DC were isolated from biopsy tissue. Epithelial cells were identified as pancytokeratin positive and DC were identified as an HLA DR+, lineage− (CD3−, CD14−, CD16−, CD19−, CD34−) population. Eptihelial cell expression of zona occludens (ZO)-1, claudin 1 and claudin 2 and DC expression of TLR 2 and 4, CCR9, β 7 and CD40 were measured by multicolour flow cytometry. Cytokines were assessed by multiplex ELISA of biopsy supernatants. The paired t-test was used for statistical analysis.
Epithelial expression of claudin 2 was increased (p = 0.04) at 6 months and remained elevated at 12 months. No changes were seen in ZO-1 or claudin 1 expression. There was a significant increase in β 7 expression on lamina propria DC (p = 0.02), but no differences in DC TLR or CD40 expresssion were seen at 6 months. DC expression of β 7 was further elevated (p = 0.005) as well as significantly increased TLR 4 and CD40 expression (p = 0.04). No cytokines were found to be elevated at 6 months, but at 12 months there was a trend towards increased IL6 (p = 0.05) and IL10 (p = 0.06).
In patients with UC, altered tight junction expression with increased epithelial expression of the “pore-forming” tight junction claudin 2 was an early event after ileostomy closure that preceded the onset of mucosal inflammation. In parallel, more lamina propria DC expressed gut homing markers possibly in response to increased exposure to the changing microbial signals and a more permeable epithelial barrier. These changes in parallel may lead to increased microbial stimulation of DC with increased TLR and co-stimulatory molecule expression that could predispose to the development of inflammation.