6c), thereby ruling out the activation of the IRE1 pathway. Up-regulation of ER chaperones is the hallmark of UPR activation. When assessed by immunoblotting, the caecal and colonic protein samples from the infected mice did not show the induction of BiP, P58IPK or calreticulin as a result Volasertib mouse of infection (Fig. 6d–f). There was no indication of ER chaperone up-regulation at the mRNA level either (data not shown). The phosphorylation of eIF2α and the up-regulation of Il22 in the caeca and colons of C. difficile-infected mice, as well as the up-regulation of Reg3g in their caeca,

raises the prospect of pro-survival signalling in these tissues in response to infection. To investigate this possibility, caecal and colonic protein lysates from untreated and C. difficile-infected mice were probed for the phosphorylation levels of AKT and STAT3. Both the caeca and colons of the infected mice showed a significant increase in AKT (Fig. 7a) and STAT3 (Fig. 7b) phosphorylation levels in comparison to their untreated counterparts. These data support the induction of pro-survival signals in C. difficile-infected mice. This study contains two major novel elements. (i) It analyses the host response in the caeca and colons of C. difficile-infected mice with a panel of > 90 of the genes involved in mucosal biology, and correlates these changes with the cellular response at these sites

of infection, AP24534 order as determined by flow cytometry. (ii) It examines the

induction of the UPR and pro-survival signals at these sites in the aftermath of C. difficile infection. Collectively, the gene expression and flow cytometric results point to four main trends in the local response to C. difficile infection. First, they show an up-regulation of chemokine genes involved in recruiting effector cells of the innate immune response to the sites of infection. CXCL1 and CXCL2 are potent neutrophil chemoattractants and activators, Thymidine kinase and induce neutrophil mobilization from the bone marrow.[43, 44] CCL2 is in turn a chemoattractant for monocytes. Most nucleated cells express CCL2 in response to pro-inflammatory cytokines such as interleukin-1β (IL-1β)[45] or upon engagement of innate immune receptors by a number of microbial products. Flow cytometric analysis had shown a substantial increase in the number of neutrophils in the caeca and colons of the infected mice and up-regulated levels of CD11b on the recruited neutrophils, an indication of their potential activation.[46] It also documented that a higher fraction of cells of the monocyte/macrophage lineage express low levels of MHC II in the caeca and colons of the infected mice, further confirming monocyte recruitment to the site of infection and raising the prospect of their differentiation after exposure to cytokines and/or microbial products.[47] The up-regulation of Cxcl1, Cxcl2 and Ccl2 in the caeca and colons of C.