MFG-E8 (milk fat globule-epidermal growth factor 8) deficiency is strongly associated with acquisition of immune-mediated disorders due to the loss of tissue homeostasis. However, comparatively little is known regarding its functions in gastrointestinal tract disorders, in which immune homeostasis is a major concern. Herein, we report altered MFG-E8 expression in inflamed colons during the acute phase of murine experimental colitis and found that treatment with recombinant MFG-E8, but not its arginine-glycine-aspartate mutant counterpart, ameliorated colitis by reducing inflammation and improving disease parameters. To reveal the MFG-E8-mediated antiinflammatory mechanism, we employed an in vitro system, which showed the down-regulation of NF-κB in an LPS-dependent manner. Additionally, MFG-E8 altered αvβ3 integrin-mediated focal adhesion kinase phosphorylation by impeding the binding of one of its potent ligands osteopontin, which becomes activated during colitis. Taken together, our results indicated that MFG-E8 has a novel therapeutic potential for treatment of colitis.

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We evaluated whether a simplified human microbiota consortium (SIHUMI) induces colitis in germfree (GF) 129S6/SvEv (129) and C57BL/6 (B6) interleukin-10-deficient (IL-10 ؊/؊ ) mice, determined mouse strain effects on colitis and the microbiota, examined the effects of inflammation on relative bacterial composition, and identified immunodominant bacterial species in "hu-

To prevent excessive inflammatory responses to commensal microbes, intestinal macrophages, unlike their systemic counterparts, do not produce inflammatory cytokines in response to enteric bacteria. Consequently, loss of macrophage tolerance to the enteric microbiota plays a central role in the pathogenesis of inflammatory bowel diseases. Therefore, we examined whether the hyporesponsive phenotype of intestinal macrophages is programmed by prior exposure to the microbiota. IL-10, but not in vivo exposure to the microbiota, programs intestinal macrophage tolerance, because wild-type (WT) colonic macrophages from germ-free and specific pathogen-free (SPF)-derived mice produce IL-10, but not IL-12 p40, when activated with enteric bacteria. Basal and activated IL-10 expression is mediated through a MyD88-dependent pathway. Conversely, colonic macrophages from germ-free and SPF-derived colitis-prone Il10−/− mice demonstrated robust production of IL-12 p40. Next, mechanisms through which IL-10 inhibits Il12b expression were investigated. Although Il12b mRNA was transiently induced in LPS-activated WT bone marrow-derived macrophages (BMDMs), expression persisted in Il10−/− BMDMs. There were no differences in nucleosome remodeling, mRNA stability, NF-κB activation, or MAPK signaling to explain prolonged transcription of Il12b in Il10−/− BMDMs. However, acetylated histone H4 transiently associated with the Il12b promoter in WT BMDMs, whereas association of these factors was prolonged in Il10−/− BMDMs. Experiments using histone deacetylase (HDAC) inhibitors and HDAC3 short hairpin RNA indicate that HDAC3 is involved in histone deacetylation of the Il12b promoter by IL-10. These results suggest that histone deacetylation on the Il12b promoter by HDAC3 mediates homeostatic effects of IL-10 in macrophages.

SummarySeveral negative regulatory mechanisms control Toll-like receptor (TLR)-mediated inflammatory responses and restore immune system balance, including the zinc-finger protein A20, a negative regulator of TLR signalling that inhibits nuclear factor kappa B (NF-kB) activity. In the present study, we investigated TLR-5-mediated A20 expression and its role in intestinal epithelial cells (IECs) during inflammation. HCT-15 and HT-29 cells were stimulated with flagellin, then the expressions of A20, interleukin-1 receptorassociated kinase (IRAK-M) and Tollip were evaluated using RNase protection assay. Furthermore, experimental colitis was induced in tlr4-deficient CH3/HeJ mice by administration of dextran sodium sulphate (DSS), then flagellin was injected anally, and the colonic expression of A20 was examined by real-time polymerase chain reaction (PCR) and immunohistochemistry. To confirm flagellin-induced expression of A20, we employed an organ culture system. The role of A20 in flagellin-induced tolerance induction was evaluated in vitro, using a gene knock-down method targeting A20. A20 expression increased rapidly and peaked at 1 h after flagellin stimulation in cultured IECs, then declined gradually to the basal level. In vivo, anal injection of flagellin induced epithelial expression of A20 in injured colonic tissue, whereas flagellin did not cause a significant increase in A20 expression in non-injured normal tissue, which was also confirmed in vitro using the organ culture system. Gene knock-down using A20 siRNA did not influence tolerance induced by restimulation with flagellin. A20 is an early response negative regulator of TLR-5 signalling in IECs that functions during intestinal inflammation. Our results provide new insights into the negative feedback regulation of TLR-5 signalling that maintains the innate immune system in the gut.

Altered intestinal microbial composition (dysbiosis) and metabolic products activate aggressive mucosal immune responses that mediate inflammatory bowel diseases (IBD). This dysbiosis impairs the function of regulatory immune cells, which normally promote mucosal homeostasis. Normalizing and maintaining regulatory immune cell function by correcting dysbiosis provides a promising approach to treat IBD patients. However, existing microbe-targeted therapies, including antibiotics, prebiotics, probiotics, and fecal microbial transplantation, provide variable outcomes that are not optimal for current clinical application. This review discusses recent progress in understanding the dysbiosis of IBD and the basis for therapeutic restoration of homeostatic immune function by manipulating an individual patient's microbiota composition and function. We believe that identifying more precise therapeutic targets and developing appropriate rapid diagnostic tools will guide more effective and safer microbebased induction and maintenance treatments for IBD patients that can be applied in a personalized manner.

The p110δ subunit of class IA phosphoinositide 3-kinase modulates signaling in innate immune cells. We previously demonstrated that mice harboring a kinase-dead p110δ subunit (p110δKD) develop spontaneous colitis. Macrophages contributed to the Th1/Th17 cytokine bias in p110δKD mice through increased IL-12 and IL-23 expression. Here, we show that the enteric microbiota is required for colitis development in germ free p110δKD mice. Colonic tissue and macrophages from p110δKD mice produce significantly less IL-10 compared to wild type (WT) mice. p110δKD APC co-cultured with naïve CD4+ antigen-specific T cells also produce significantly less IL-10, and induce more IFN-γ- and IL-17A-producing CD4+ T cells compared to WT APC. Illustrating the importance of APC – T cell interactions in colitis pathogenesis in vivo, Rag1-/-/p110δKD mice develop mild colonic inflammation and produced more colonic IL-12p40 compared to Rag1-/- mice. However, CD4+CD45RBhigh/low T cell Rag1-/-/p110δKD recipient mice develop severe colitis with increased percentages of IFN-γ- and IL-17A-producing lamina propria CD3+CD4+ T cells compared to Rag1-/- recipient mice. Intestinal tissue samples from patients with Crohn’s disease reveal significantly lower expression of PIK3CD compared to intestinal samples from non-IBD control subjects (p<0.05). PIK3CD expression inversely correlated with the ratio of IL12B:IL10 expression. In conclusion, the PI3K subunit p110δ controls homeostatic APC – T cell interactions by altering the balance between IL-10 and IL-12/23. Defects in p110δ expression and/or function may underlie the pathogenesis of human IBD and lead to new therapeutic strategies.