Bradykinin is a mediator of inflammation, responsible for pain, vasodilation, and capillary permeability. Bradykinin receptor 1 (B1R) and bradykinin receptor 2 (B2R) are G protein-coupled receptors that mediate kinin effects. The latter is constitutive and rapidly desensitized; the former is induced by inflammatory cytokines and resistant to densensitization. The distribution of bradykinin receptors in human intestinal tissue was studied in patients with inflammatory bowel disease (IBD), namely ulcerative colitis (UC) and Crohn's disease (CD). Both B2R and B1R proteins are expressed in the epithelial cells of normal and IBD intestines. B1R protein is visualized in macrophages at the center of granulomas in CD. B2R protein is normally present in the apexes of enterocytes in the basal area and intracellularly in inflammatory tissue. In contrast, B1R protein is found in the basal area of enterocytes in normal intestine but in the apical portion of enterocytes in inflamed tissue. B1R protein is significantly increased in both active UC and CD intestines compared with controls. In patients with active UC, B1R mRNA is significantly higher than B2R mRNA. However, in inactive UC patients, the B1R and B2R mRNA did not differ significantly. Thus bradykinin receptors in IBD may reflect intestinal inflammation. Increased B1R gene and protein expression in active IBD provides a structural basis of the important role of bradykinin in chronic inflammation.

The distribution of tissue kallikrein (TK) and its plasma inhibitor, kallistatin in plasma and intestinal tissue, was studied in patients with active ulcerative colitis (UC) and Crohn's disease (CD). TK was localized to goblet cells and kallistatin to epithelial cells of normal human intestine. Both proteins are visualized in macrophages inside granulomas in CD as well as in plasmocytes in both CD and UC. Intestinal tissue kallikrein (ITK) and kallistatin are significantly decreased in inflamed intestine compared to noninflammatory controls. TK mRNA is significantly decreased in intestinal biopsy samples from active UC patients compared with inactive patients or controls. Immunoreactive TK is present in plasma in very low concentrations in patients and did not differ in normal subjects. Plasma kallistatin was significantly decreased in patients with active disease compared to normal controls. Our data suggest that release of TK during inflammation plays a role in inflammatory bowel disease.