Background & aims: Collagenous colitis is a rare diarrheal disease of unknown pathophysiology that is histologically defined by subepithelial bandlike structures. The objective of this study was to elucidate the biochemical composition and the origin of the bandlike structures in collagenous colitis.
Methods: Immunohistochemical and in situ hybridization analyses were performed on endoscopic specimens using specific antibodies and riboprobes for collagen types I, III, IV, and VI and for the glycoprotein tenascin.
Results: In collagenous colitis, the mucosal matrix with the exception of the bands retained a normal architecture and extracellular matrix composition. The bands stained most prominently for type VI collagen and tenascin. Less abundant staining for both proteins was also found in the subepithelial matrix of the normal mucosa. In situ hybridization showed no significant increase in collagen type VI messenger RNA expression in cells around and entrapped in the bands in collagenous colitis compared with normal specimens.
Conclusions: The results support the suggestion that collagenous colitis is a localized alteration of the extracellular matrix, which involves the pericryptal-subepithelial myofibroblast sheath. The data suggest that reduced matrix degradation and not overactivation of matrix synthesis may be the reason for the subepithelial accumulation of matrix proteins.