Carbohydrate expression in the intestinal mucosa.

UNLABELLED: The understanding of mechanisms responsible for alterations in mucin synthesis and secretions is essential in elucidating the aetiology of intestinal disorders. The existence of distinct mucins and M-cell transport mechanisms, and their beneficial effects, have long been recognised. Since nutritional and bacterial factors alter the mucin characteristics and are relevant to planning preventative strategies for intestinal diseases, the studies described in this monograph were designed to test the hypothesis that mucin composition and endocrine status of the intestinal tract are altered by dietary constituents and microbial flora. A study of gut-associated lymphoid tissue (GALT) was undertaken to test the hypothesis that lymphocyte-epithelial interactions influence the glycosylation of cells overlying Peyer's patches. The effects of diet and microbial flora were analysed by comparing the data from male Wistar germ-free rats, with conventional or human flora. Such rats were fed either a commercial diet, containing crude fibre, or a purified diet. Bone marrow transfers from syngeneic Balb/c mice to severe combined immunodeficient (SCID) mice were made to induce the formation of GALT. A comparison was made of the glycoconjugate profile of Peyer's patches in the guts of mice and humans. The results of the study showed that feeding a fibre-rich diet to germ-free rats resulted in increased villus-crypt lengths, decreased carboxylated mucin content of goblet cells, increased N-acetylglucosamine and sialic acid residues in the surface goblet cells, and a reduction in the number of endocrine cells in the small intestine. The lectin markers revealed M-cell development in the dome epithelium of the reconstituted SCID mice. Mouse M cells were labelled by fucose-specific lectins but in human Peyer's patches no distinct M-cell-staining pattern was observed.
CONCLUSIONS: (1) the interactions between diet and flora alter the mucosal architecture and the activity of endocrine cells; (2) the dietary changes are influential in modifying the epithelial mucin predominantly in the small intestine while the microbial flora influences the mucosal architecture predominantly in the large intestine; (3) the use of bone marrow transplantation from syngeneic mice into SCID mice along with lectin markers for M cells can be used to study the histogenesis of Peyer's patches; (4) the distinct differences between mouse and human Peyer's patches suggest that when considering cell surface glycoconjugates as target molecules appropriate lectin should be used for each species. A future challenge in intestinal epithelial cell biology is identifying the nature and distribution of cell surface receptors for specific dietary components and bacteria.