Development of the early mucosal lesions in experimental inflammatory bowel disease--implications for pathogenesis.

The purpose of this study was to better establish the morphologic basis of the early mucosal lesions of experimental inflammatory bowel disease because understanding the development of these lesions has important pathogenetic implications. Sprague-Dawley rats were given 1.5% hydrolyzed lambda-carrageenan orally for 30 days. This produced small intestinal lesions which were then evaluated. Light microscopy showed an increased amount of inflammatory cells in the gut wall with prominent Peyer's patches, microgranulomas, crypt abscesses, pin-point ulcerations, and a repair reaction. Scanning electron microscopy revealed pin-point ulcerations in relation to Peyer's patches. Transmission electron microscopy, in addition to the above findings, showed disruptions of enterocyte microvilli and terminal webs. Follicle-associated epithelium appeared to be a predictive site for the development of crypt abscesses and pin-point ulcerations. Enzyme-linked immunoadsorbent assays indicated that orally administered carrageenan elicited a systemic antibody response. Our results suggest that damage to enterocyte microvilli and terminal webs may be important early events in the morphogenesis of the lesions.