These include the ability of TcdA to induce the release of the pro-inflammatory mediators IL-1β,[62] TNF-α,[63] IFN-γ,[64] CXCL1,[48] CXCL2[49] and CCL3,[65] as well as the fact that both IFN-γ−/−[64] and CCR1−/−[65] mice have a milder form of enteritis in response to TcdA injection. Despite the useful insights provided by the ileal loop model into the actions of C. difficile toxins, it should be noted that the model has some important shortcomings. First, it is a surgery-based model, which entails the injection

of C. difficile toxin preparations into the animal and not infection with the bacterium itself; second, it targets the wrong organ for disease, i.e. ileum instead of the colon; and third, it does not reflect any interaction of C. difficile with the host’s microbiota. The current Protease Inhibitor Library supplier work is the first to assess the induction of the CHIR-99021 in vitro UPR during acute C. difficile infection. A number of recent studies have implicated the UPR in the response to different forms of intestinal inflammation. These include the protective role(s) of XBP1,[17] ATF6[18] and eIF2α phosphorylation[19] against dextran sodium

sulphate-induced colitis. Despite the phosphorylation of eIF2α and the slight up-regulation of the phospho-eIF2α targets Wars and Gadd34 in the caeca and colons of C. difficile-infected mice (which serve as an early indication of phospho-eIF2α exerting its downstream effect), the lack of Xbp1 splicing and the absence of ER chaperone up-regulation in these tissues cast serious doubt on the activation of the UPR in this model of infection. Although numerous laboratories have shown that the UPR output can be modulated in a context-specific manner,[66, 67] a more likely explanation for the current set of findings is the phosphorylation of eIF2α by a kinase other than PERK. Of the four kinases that can phosphorylate Selleck Erlotinib eIF2α, Protein Kinase RNA-activated (PKR) is the most plausible candidate. The phosphorylation of AKT and STAT3, as well as eIF2α,

in the C. difficile-infected mice gives further credence to this hypothesis because, in addition to phosphorylating eIF2α, PKR is an upstream inducer of both AKT and STAT3 phosphorylation.[68] AKT plays an important role in promoting intestinal epithelial homeostasis and wound repair during intestinal inflammation.[69] Furthermore, the protective effect of lysophosphatidic acid against C. difficile toxin-induced cell death in vitro is in part due to its induction of AKT phosphorylation.[70] Therefore, the phosphorylation of AKT in the C. difficile-infected mice may be a pro-survival signal that aims to counteract and contain the inflicted epithelial damage. The phosphorylation of STAT3 in the C. difficile-infected mice should be viewed from a broader perspective. First, the use of STAT3IEC-KO mice has shown that activation of intestinal epithelial STAT3 regulates immune homeostasis in the gut by promoting IL-22-dependent mucosal wound healing.