Objective: The pathogenesis of ulcerative colitis and Crohn's disease is still unclear. Vascular injury has been suggested as a potential pathogenetic mechanism. Serum thrombomodulin is a marker of endothelial cell injury. The aim of this study was to determine the relevance of increased serum thrombomodulin levels for assessing disease activity in inflammatory bowel disease. As a potential cause of serum thrombomodulin level increase, the loss of local vascular thrombomodulin expression was investigated immunohistochemically.

Methods: Thrombomodulin levels were determined by enzyme-linked immunosorbent assay in sera from patients with ulcerative colitis, Crohn's disease, Schistosoma mansoni infection, and infectious diarrhea and controls. The vascular expression of thrombomodulin was investigated immunohistochemically in fresh frozen transmural specimens of normal, Crohn's, and ulcerative colitis bowel samples.

Results: Significantly elevated serum thrombomodulin levels were only detected in active ulcerative colitis and infectious diarrhea complicated by septicemia. A marked and general loss of vascular endothelial cell thrombomodulin expression was found immunohistochemically in inflamed bowel tissues. Graded by a newly established thrombomodulin staining index, this was significantly more marked in ulcerative colitis than Crohn's disease.

Conclusions: Serum thrombomodulin proved to be a novel marker of disease activity in ulcerative colitis closely related to local vascular endothelial cell damage, which might be a relevant pathophysiological feature of ulcerative colitis.