Clostridium difficile Toxin-Induced Inflammation and Intestinal Injury Are Mediated by the Inflammasome

BACKGROUND & AIMS: Clostridium difficile-associated disease (CDAD) is the leading cause of nosocomial diarrhea in the United States. C difficile toxins TcdA and TcdB breach the intestinal barrier and trigger mucosal inflammation and intestinal damage. The inflammasome is an intracellular danger sensor of the innate immune system. In the present study, we hypothesize that TcdA and TcdB trigger inflammasome-dependent interleukin (IL)-1 beta production, which contributes to the pathogenesis of CDAD. METHODS: Macrophages exposed to TcdA and TcdB were assessed for IL-1 beta production, an indication of inflammasome activation. Macrophages deficient in components of the inflammasome were also assessed. Truncated/mutated forms of Tcd3 were assessed for their ability to activate the inflammasome. The role of inflammasome signaling in vivo was assessed in ASC-deficient and IL-1 receptor antagonist-treated mice. RESULTS: TcdA and TcdB triggered inflammasome activation and IL-1 beta secretion in macrophages and human mucosal biopsy specimens. Deletion of Nlrp3 decreased, whereas deletion of ASC completely abolished, toxin-induced IL-1 beta release. TcdB-induced IL-1 beta release required recognition of the full-length toxin but not its enzymatic function. In vivo, deletion of ASC significantly reduced toxin-induced inflammation and damage, an effect that was mimicked by pretreatment with the IL-1 receptor antagonist anakinra. CONCLUSIONS: TcdA and TcdB trigger IL-1 beta release by activating an ASC-containing inflammasome, a response that contributes to toxin-induced inflammation and damage in vivo. Pretreating mice with the IL-1 receptor antagonist anakinra afforded the same level of protection that was observed in ASC(-/-) mice. These data suggest that targeting inflammasome or IL-1 beta signaling may represent new therapeutic targets in the treatment of CDAD.