DIETARY PLANT LECTINS AND THE SMALL INTESTINE

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Edible legumes contain several growth inhibitory factors which cause intestinal malabsorption and weight loss in animals: adverse effects which are ameliorated in the germ free state and by antibiotic therapy. Purified phytohemagglutinin (PHA) and the erythroagglutinating (E4) and mitogenic (L4) isolectins have been isolated from red kidney beans by sepharosethyroglobulin affinity and ion exchange chromatography. Impaired lipid, nitrogen and vitamin B12 absorption which develop when PHA is incorporated in the diet, is associated with intestinal bacterial overgrowth. The effects may result from (a) binding of the PHA to the intestinal microvillus membrane and (b) subsequent adhesive interaction with a specific bacterial flora adjacent to the mucosal surface. Utilizing this in vivo model of PHA lectin induced diarrheal disease, the types and distribution of adherent small intestinal bacteria will be defined using bacterial culture and immunofluorescent staining, and an agar gel morphometric technique to isolate adherent microorganisms. The mechanism of the PHA-induced bacterial adherence and role of surface components of specific adherent bacteria will be defined to determine whether PHA recognizes similar saccharrides residues at the mucosal and bacterial surfaces and cross bridges them. Components of the mucus layer will be examined for evidence of PHA and/or specific bacterial adherence. Intestinal microvillus membrane receptors for E4 and L4 will be isolated using solubilization of membrane proteins and separation by affinity chromatography. Identification and isolation will utilize the electroblotting technique of Southern and SDS-PAGE electrophoresis. Purified soy lectin will be studied in a manner similar to PHA to detect malabsorption of nitrogen, lipid and vitamin B12 in association with an adherent microbial flora. Changes in populations of microorganisms in the mucus layer may be a factor of importance in chronic human intestinal disorders. Intestinal biopsy tissue on which the mucus layer is retained will be studied by special morphological techniques to enumerate and map the distribution and extent of microbial colonization. Patients with tropical sprue will be compared to indigenous and emigrant control subjects to study differences in the mucus layer. Tissue of patients will be examined before and after antibiotic administration and other modes of therapy.