Probiotic supplements induce immunological responses in the host, and dietary fructooligosaccharides (FOS) stimulate the growth of selected intestinal microflora. In this study we investigated the immunological influences of orally administrated FOS. BALB/c mice were orally administered 0-7.5% FOS for 6 weeks, and the intestinal mucosal immune responses were measured. In the 2.5%-FOS group, fecal IgA was significantly increased. IgA secretion by Peyer's patch (PP) cells was upregulated in a dose-dependent way in response to FOS and CD4+ T cells from PP showed a dose-dependent increase in production of interferon-gamma and interleukin (IL) 10, and a high response in production of IL-5 and IL-6. In contrast, FOS suppressed serum IgG1. Our findings suggest that FOS supplementation changes the intestinal environment of microflora, and leads to upregulation of IgA secretion in CD4+ PP cells in intestinal mucosa, and to suppression of the systemic immune response to type 2 helper T (Th2) dominant.

Intestinal epithelial cells (IECs) are continuously exposed to large numbers of commensal bacteria but are relatively insensitive to them, thereby averting an excessive inflammatory reaction. In this study, we show that the low responsiveness of human IEC lines to LPS was mainly brought about by a down-regulation of TLR4 gene transcription. Additionally, the presence of an IEC-specific repressor element in the 5′ region of the TLR4 gene and binding of a NF to the element was shown. The transcription factor ZNF160, which was expressed more abundantly in a LPS-low responder IEC line than in a LPS-high responder IEC line, repressed TLR4 gene transcription. ZNF160 is known to interact with the scaffold protein KAP1 via its N terminus to recruit histone deacetylase. Histone deacetylation, as well as DNA methylation, at the 5′ region of the TLR4 gene was significantly higher in LPS-low responder IEC lines than in a monocyte line or a LPS-high responder IEC line. It was demonstrated that TLR4 gene transcription was repressed by these epigenetic regulations, which were, at least in part, dependent on ZNF160. Down-regulaton of TLR4 gene expression by these mechanisms in IECs possibly contributes to the maintainance of homeostasis in the intestinal commensal system.

Background:Intestinal epithelial cells (IECs) express low levels of TLR4 and are hyporesponsive to commensal bacteria. Results: TLR4 gene is methylated in IECs, and this process is dependent on commensal bacteria in the large intestine. Conclusion: Commensal bacteria control epigenetic modification of the host gene. Significance: This study shows a novel mechanism underlying the maintenance of intestinal symbiosis.

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The intestinal tract contains many commensal bacteria that modulate various physiological host functions. Dysbiosis of commensal bacteria triggers dysfunction of the intestinal epithelial barrier, leading to the induction or aggravation of intestinal inflammation. To elucidate whether microRNA plays a role in commensal microbiome-dependent intestinal epithelial barrier regulation, we compared transcripts in intestinal epithelial cells (IECs) from conventional and germ-free mice and found that commensal bacteria induced the expression of miR-21-5p in IECs. miR-21-5p increased intestinal epithelial permeability and up-regulated ADP ribosylation factor 4 (ARF4), a small GTPase, in the IEC line Caco-2. We also found that ARF4 expression was up-regulated upon suppression of phosphatase and tensin homolog () and programmed cell death 4 (), which are known miR-21-5p targets, by RNAi. Furthermore, ARF4 expression in epithelial cells of the large intestine was higher in conventional mice than in germ-free mice. ARF4 suppression in the IEC line increased the expression of tight junction proteins and decreased intestinal epithelial permeability. These results indicate that commensal microbiome-dependent miR-21-5p expression in IECs regulates intestinal epithelial permeability via ARF4, which may therefore represent a target for preventing or managing dysfunction of the intestinal epithelial barrier.