The capacity of cholera toxin (CT) and of the heat-labile enterotoxin produced by Escherichia coli isolated from humans (LTh) to interact with glycolipids bearing ABO(H) blood group determinants isolated from different sources and separated by thin layer chromatography was studied. Toxin binding to the ABO(H)-related glycolipids depends on the glycolipid source, the type of the blood group activity, and the toxin. LTh and CT were capable of interacting with several blood group-active glycolipids from pig intestinal mucosa and both toxins preferentially recognize glycolipids isolated from animals carrying A-blood group antigenic determinants compared to those isolated from animals lacking these antigens. In contrast, LTh but not CT was able to interact with ABO(H)-active glycolipids from human erythrocytes. LTh preferentially binds to glycolipids isolated from A, B, and AB compared to O red cells. Results from competition experiments between CT and LTh for binding to the blood group-active glycolipids suggest that the carbohydrate structure requirements for the interaction of each toxin are different. The present findings may help to understand the results of clinical studies indicating an association between ABO(H) blood groups and the severity of diarrheal diseases produced by some toxigenic enterobacteria.
The ability of membrane ABH blood group-active glycoconjugates to act as receptors of the heat-labile enterotoxin of Escherichia coli (LTh) was studied in vitro and in vivo when GM1 was blocked by the cholera toxin B subunit. Rabbits were classified as AB or H based on intestinal ABH-antigenic activities. Brush border membranes from AB rabbits contained 4 times more LTh binding sites than the H ones. LTh interaction could be inhibited by lectins that recognize ABH determinants. LTh induced a similar dose-dependent secretory response in ligated ileal loops of both types of animals. Anti-AB antibodies and Ulex europaeus I lectin could significantly reduce the fluid accumulation in AB and H rabbits, respectively. LTh caused adenylate cyclase activation even when GM1 was blocked, and this effect was abolished by the addition of specific ABH ligands. These results suggest that ABH glycoconjugates are involved in the host secretory response to LTh in rabbit intestine.
We examined the ability of blood group A-active glycoconjugates to act as receptors for Escherichia coli heat-labile type I enterotoxin (LT-I) in HT-29 cells. These cells contained ~4 times more specific binding sites for LT-I than for cholera toxin (CT). Binding of LT-I could not be blocked by the B subunit of CT (CT-B), indicating the existence of LT-I receptors in addition to the glycosphingolipid GM1. LT-I was able to increase levels of cyclic adenosine monophosphate (AMP), even in the presence of CT-B. Helix pomatia and anti-blood group A antibody caused a dose-dependent inhibition of binding of LT-I to cells and production of cyclic AMP. LT-I recognized several complex blood group A-active glycosphingolipids from cells, and this interaction was also interfered with by H. pomatia. Treatment of cells with D,L-threo-1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol diminished surface expression of blood group A-active glycosphingolipids and binding of LT-I to non-GM1 receptors. These observations suggest that blood group A-active glycosphingolipids can function as alternative receptors for LT-I in HT-29 cells.
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