Increased expression of protease-activated receptor-2 in mucosal mast cells in Crohn's ileitis

Background and aims: Activation of protease-activated receptor-2 (PAR-2) may stimulate various events of importance in inflammatory processes, including release of inflammatory mast cell mediators. PAR-2 is frequently up-regulated during inflammatory conditions, but it is not known if the expression is altered in Crohn's disease. The aim of the present study was to investigate the ileal mucosal PAR-2 expression in Crohn's ileitis, with particular emphasis on the expression in ileal mucosal mast cells. Methods: Surgical specimens from the distal ileum were collected from patients with Crohn's ileitis and patients with colonic cancer as controls. The overall expression of PAR-2 was investigated by Western blot, and the presence of PAR-2 expressing mucosal mast cells by immunohistochemistry and cell counting. The effect of tumor necrosis factor-alpha (TNF-alpha) on the PAR-2 expression in a human mast cell tine (HMC-1) was investigated by RT-PCR and immunocytochemistry. Results: In Crohn's specimens, the fraction of PAR-2-expressing mucosal. mast cells was increased about 2.5 times (P < 0.001; n = 14) compared with specimens from control patients (n = 6). No difference was found between inflamed (n = 6) and uninflamed Crohn's specimens (P > 0.05; n = 8). Exposure to TNF-alpha for 48 h up-regulated PAR-2 mRNA and protein expression in the HMC-1 cell line. Conclusion: PAR-2 is up-regulated on ileal mucosal mast cells in Crohn's ileitis, possibly due to the action of inflammatory cytokines, such as TNF-alpha. This may contribute to perpetuating the inflammatory process in the intestinal mucosa in Crohn's ileitis. (C) 2008 European Crohn's and Colitis Organisation. Published by Elsevier B.V. All. rights reserved.