Differential effects of varying concentrations of Clostridium difficile toxin A on epithelial barrier function and expression of cytokines

Background. Presentation after Clostridium difficile infection may depend on the level of epithelial exposure to toxins. We investigated epithelial barrier function and expression of interleukin (IL)-8 and transforming growth factor (TGF)-beta in response to varying concentrations of C. difficile toxin A. Methods. T84 cells were either preexposed or continuously exposed to C. difficile toxin A (0.01-1000 ng/mL). Barrier function was assessed by measurements of transepithelial electrical resistance. Results. Preexposure to less than or equal to10 ng/mL toxin A led to an increase in the release of TGF-beta1, but there was no change in the expression of IL-8. In contrast, after preexposure to >10 ng/mL toxin A, there was enhanced expression of IL-8, but release of TGF-beta1 was similar to that in control monolayers. After preexposure to >10 ng/mL toxin A, there was complete and irreversible loss of electrical resistance. At lower concentrations, loss of resistance across monolayers was followed by recovery, which was enhanced by all 3 recombinant isoforms of TGF-beta. Pretreatment with recombinant isoforms of TGF-beta or coculture with TGF-beta3-expressing colonic subepithelial myofibroblasts was also protective. Conclusions. In C. difficile infection, the development and severity of colonic inflammation may depend on the exposure of intestinal epithelial cells to toxins and the expression of proinflammatory (IL-8) and protective (TGF-beta) factors.