Translocation of Shiga toxin across polarized intestinal cells in tissue culture

Escherichia coli strains producing Shiga toxins (Stx) 1 and 2 colonize the lower gastrointestinal tract in humans and are associated with gastrointestinal and systemic diseases. Stx are detectable in the feces of infected patients, and it is likely that toxin passes from the intestinal tract lumen to underlying tissues. The objective of this study was to develop an in vitro model to study the passage of Stx across intact, polarized cell monolayers. Translocation of biologically active Stx was examined in four cell lines grown on polycarbonate filters. Stx1 translocated across intestinal cell monolayers (CaCo2A and T84 cells) in an energy-requiring and saturable manner, while the monolayers maintained a high level of electrical resistance. Stx1 had no effect on electrical resistance or inulin movement across these cell lines for at least 24 h. Induction of specific Stx receptors with sodium butyrate reduced the proportion of toxin translocated across CaCo2A monolayers but had no major effect on the movement of horseradish peroxidase or [3H]inulin. We have shown that biologically active Stx1 is capable of moving across intact polarized intestinal epithelial cells without apparent cellular disruption, probably via a transcellular pathway. The data also suggest that the presence of Stx receptors on the apical surface of intestinal epithelial cells may offer some protection against the absorption of luminal Stx1.