The significantly expressed genes were selected by a standard cut-off at twofold increased expression compared with the values on day 0. These differentially expressed genes were then classified based on Gene Ontology (GO) software specifically for genes implicated in the ‘regulation of inflammatory response’ as well as the ‘cytokines and chemokines’ in the colonic epithelium of DSS-induced colitis in mice. Analysis using PLX4032 Student’s t-test was applied to in vitro studies. Analysis between

individuals in groups in vivo was by analysis of variance followed by Student’s t-test. Results are expressed as mean ± SEM, and are representative of at least two individual experiments. P < 0·05, was considered Fulvestrant molecular weight significant. While it has been suggested that IL33 and ST2 are expressed in colonic tissue and in epithelial cells in clinical colitis,[20-23] the kinetics of their expression and relative expression compared with other DSS-induced

genes in inflamed colonic tissue is unknown. To understand the inflammatory process associated with the initiation of colitis, we systematically studied the early colon gene expression profile of DSS-induced colitis by analysing the publicly available microarray datasets deposited in the GEO using a meta-analysis approach.[26, 27] We specifically focused on the expression of cytokines and chemokines, and genes implicated in the regulation of inflammation using the Gene Ontology Analysis module in genespring gx11. Hierarchical clustering analysis showed that IL33 was the strongest of the 40 differentially expressed cytokine Thymidylate synthase and chemokine genes expressed early in the colonic tissue (see Supplementary material, Fig. S1A). Furthermore, IL33 and its receptor; the ST2 gene (IL1RL1) were the most highly induced

genes, among the 28 genes, involved in the regulation of the inflammatory response (Fig. S1B). The induced IL33 message in colonic tissue was detectable from day 4, and ST2 from day 6 after DSS administration (Fig. 1a and Fig. S1A,B). The expression levels of several other key inflammatory cytokine and chemokines, including IL-1β, IL-6, CXCL9 and CXCL10 were also significantly up-regulated (> 2-log fold) by DSS in the acute inflamed colonic tissue (Fig. 1a). However, Th2 (IL-4 and IL-5), Th1 (IFN-γ), IL-17 and the ‘alarmin’ (IL-1β and HMGB1) cytokine genes were not significantly induced (Fig. S1A,B, and data not shown). We further determined IL-33 protein levels in vitro in the cultured colonic tissue from mice that had received DSS or PBS as control as described in the Materials and methods. Consistent with the induction of IL33 message (Fig.