Immunohistochemical study of chymase-positive mast cells in inflammatory bowel disease

Mast cell-derived chymase promotes inflammatory responses and tissue fibrosis. Although previous studies have reported changes in the number of mucosal mast cells in inflammatory bowel disease (IBD), the behaviour of chymase immunopositive mast cells has not been studied. In this study, we immunohistochemically investigated chymase immunopositive mast cells in the inflamed mucosa of IBD patients. Surgically-obtained or biopsy specimens from 10 patients with ulcerative colitis (UC), 10 patients with Crohn's disease (CD) and 10 normal colorectal tissue specimens were used. The chymase immunopositive cells were identified by immunohistochemical analysis using a monoclonal anti-human chymase antibody. In the normal colonic mucosa, a small number of chymase immunopositive mast cells were detected at the basal sites of the mucosa. There were no immunopositive cells in the submucosa. Chymase immunopositive mast cells were similarly observed in the inactive UC mucosa, but these cells decreased significantly in number in the active UC mucosa. In the inactive CD mucosa, the number of chymase immunopositive mast cells increased significantly (P < 0.05), and this was more clearly observed in the active CD mucosa. Furthermore, in the active CD mucosa, these cells were detected in the submucosa, propria muscularis, and surrounding fatty tissue. These observations suggest a crucial role for chymase immunopositive mast cells in the pathophysiology of CD. Since intestinal fibrotic changes such as stricture formation are a characteristic feature of CD, chymase immunopositive mast cells may act as a stimulus for the process of tissue fibrosis and tissue remodelling in the pathophysiology of CD.