RABBIT SUCRASE-ISOMALTASE CONTAINS A FUNCTIONAL INTESTINAL RECEPTOR FOR CLOSTRIDIUM-DIFFICILE TOXIN-A

The intestinal effects of Clostridium difficile toxin A are initiated by toxin binding to luminal enterocyte receptors. We reported previous ly that the rabbit heal brush border (BE) receptor is a glycoprotein w ith an alpha-d-galactose containing trisaccharide in the toxin-binding domain (1991. J. Clin. Invest. 88:119-125). In this study we characte rized the rabbit ileal BE receptor for this toxin. Purified toxin rece ptor peptides of 19 and 24 amino acids showed 100% homology with rabbi t sucrase-isomaltase (SI). Guinea pig receptor antiserum reacted in We stern blots with rabbit SI and with the purified toxin receptor. Antir eceptor IgG blocked in vitro binding of toxin A to rabbit ileal villus cell BE. Furthermore, anti-SI IgG inhibited toxin A-induced secretion (by 78.1%, P < 0.01), intestinal permeability (by 80.8%, P < 0.01), a nd histologic injury (P < 0.01) in rabbit deal loops in vivo. Chinese hamster ovary cells transfected with SI cDNA showed increased intracel lular calcium increase in response to native toxin (holotoxin) or to a recombinant 873-amino acid peptide representing the receptor binding domain of toxin A. These data suggest that toxin A binds specifically to carbohydrate domains on rabbit ileal SI, and that such binding is r elevant to signal transduction mechanisms that mediate in vitro and in vivo toxicity.