The mammalian intestinal tract is colonized by trillions of beneficial commensal bacteria that are anatomically restricted to specific niches. However, the mechanisms that regulate anatomical containment remain unclear. Here we identify that interleukin (IL)-22-producing innate lymphoid cells (ILCs) are present in intestinal tissues of healthy mammals. Depletion of ILCs resulted in peripheral dissemination of commensal bacteria and systemic inflammation, which was prevented by administration of IL-22. Disseminating bacteria were identified as Alcaligenes species originating from host lymphoid tissues. Alcaligenes was sufficient to promote systemic inflammation following ILC-depletion in mice, and Alcaligenes-specific systemic immune responses were associated with Crohn's disease and progressive HCV infection in patients. Collectively, these data indicate that ILCs regulate selective containment of lymphoid-resident bacteria to prevent systemic inflammation associated with chronic diseases.

Fucosylation of intestinal epithelial cells, catalyzed by fucosyltransferase 2 (Fut2), is a major glycosylation mechanism of host–microbiota symbiosis. Commensal bacteria induce epithelial fucosylation, and epithelial fucose is used as a dietary carbohydrate by many of these bacteria. However, the molecular and cellular mechanisms that regulate the induction of epithelial fucosylation are unknown. Here, we show that type 3 innate lymphoid cells (ILC3) induced intestinal epithelial Fut2 expression and fucosylation in mice. This induction required the cytokines interleukin-22 and lymphotoxin in a commensal bacteria–dependent and –independent manner, respectively. Disruption of intestinal fucosylation led to increased susceptibility to infection by Salmonella typhimurium. Our data reveal a role for ILC3 in shaping the gut microenvironment through the regulation of epithelial glycosylation.

The development of protein-based vaccines remains a major challenge in the fields of immunology and drug delivery. Although numerous protein antigens have been identified that can generate immunity to infectious pathogens, the development of vaccines based on protein antigens has had limited success because of delivery issues. In this article, an acid-sensitive microgel material is synthesized for the development of protein-based vaccines. The chemical design of these microgels is such that they degrade under the mildly acidic conditions found in the phagosomes of antigenpresenting cells (APCs). The rapid cleavage of the microgels leads to phagosomal disruption through a colloid osmotic mechanism, releasing protein antigens into the APC cytoplasm for class I antigen presentation. Ovalbumin was encapsulated in microgel particles, 200 -500 nm in diameter, prepared by inverse emulsion polymerization with a synthesized acid-degradable crosslinker. Ovalbumin is released from the acid-degradable microgels in a pH-dependent manner; for example, microgels containing ovalbumin release 80% of their encapsulated proteins after 5 h at pH 5.0, but release only 10% at pH 7.4. APCs that phagocytosed the acid-degradable microgels containing ovalbumin were capable of activating ovalbumin-specific cytoxic T lymphocytes. The aciddegradable microgels developed in this article should therefore find applications as delivery vehicles for vaccines targeted against viruses and tumors, where the activation of cytoxic T lymphocytes is required for the development of immunity.polymer ͉ crosslinker ͉ encapsulation ͉ vaccination ͉ cytotoxic T lymphocyte

T he huge intestinal surface area is physically protected by a layer of tightly joined epithelial cells, which prevent most enteric environmental antigens from penetrating the host (1). However, entry into the host is made possible by a special gateway, comprised of M cells, located over organized mucosal lymphoid follicles such as Peyer's patches (PP). The M cells, characterized by an irregular brush border and reduced glycocalyx, efficiently take up and transport a wide variety of macromolecules and microorganisms from the gut lumen to the inside of the PP (2-6), which contain all of the necessary lymphoid cells for the induction and regulation of antigen-specific IgA responses (7). However, the origin of M cells and the regulation of their development are not understood. A previous study (8) The common mucosal immune system (CMIS), which connects the inductive (e.g., PP) and effector (e.g., lamina propria; LP) sites, has been shown to be a central pathway for the induction of antigen-specific IgA immune responses in the gastrointestinal tract (7). For example, oral administration of Salmonella typhimurium leads to the transport of the bacterial antigen from the lumen of the intestinal tract into the PP by means of M cells for the initial priming of antigen-specific CD4 ϩ T cells and IgA-committed B cells (12). These antigen-sensitized cells leave the PP and contribute to the subsequent induction of Salmonella-specific IgA response in the distant intestinal LP by means of CMIS. In addition to the wellcharacterized CMIS-dependent IgA induction pathway, recent evidence suggests the presence of an additional IgA induction pathway that is independently operated from the PP-originated CMIS (13-15). Interestingly, it also has been reported that induction of intestinal mucosal IgA against the commensal bacteria was independent from T cell help and organized lymphoid tissue (16). Further, our recent study (17) has demonstrated that antigenspecific IgA antibody responses can be induced in the absence of PP. These studies imply the existence of a PP-independent mucosal immune pathway for dietary antigen and bacteria uptake.A recent study (18) has suggested that the invasion gene (SPI1)-deficient S. typhimurium can be disseminated from the intestinal epithelium to the systemic compartment in the absence of PPassociated M cells by means of the CD18-dependent pathway. Further, dendritic cells in the lamina propria of the small intestine expressing tight junction protein offer another possible antigen uptake site (19). Thus, intestinal DCs are capable of extending dendrites to the lumen side by opening the tight junction. However, the exact mechanism for inducing Ag-specific immune responses independently of PP requires further elucidation.In this study, we have discovered intestinal villous M cells, which serve as an antigen gateway for the sampling of gut bacteria and subsequent induction of Ag-specific immune responses in a PPindependent manner. These lines of study are crucial for understanding the mechanisms of antige...

In the representative gut bacterium Lactobacillus plantarum, we identified genes encoding the enzymes involved in a saturation metabolism of polyunsaturated fatty acids and revealed in detail the metabolic pathway that generates hydroxy fatty acids, oxo fatty acids, conjugated fatty acids, and partially saturated transfatty acids as intermediates. Furthermore, we observed these intermediates, especially hydroxy fatty acids, in host organs. Levels of hydroxy fatty acids were much higher in specific pathogen-free mice than in germ-free mice, indicating that these fatty acids are generated through polyunsaturated fatty acids metabolism of gastrointestinal microorganisms. These findings suggested that lipid metabolism by gastrointestinal microbes affects the health of the host by modifying fatty acid composition.biohydrogenation | hydratase | fatty acid isomerase | conjugated linoleic acid | lipid nutrition

Mast cells are known effector cells in allergic and inflammatory diseases, but their precise roles in intestinal inflammation remain unknown. Here we show that activation of mast cells in intestinal inflammation is mediated by ATP-reactive P2X7 purinoceptors. We find an increase in the numbers of mast cells expressing P2X7 purinoceptors in the colons of mice with colitis and of patients with Crohn's disease. Treatment of mice with a P2X7 purinoceptor-specific antibody inhibits mast cell activation and subsequent intestinal inflammation. Similarly, intestinal inflammation is ameliorated in mast cell-deficient KitW-sh/W-sh mice, and reconstitution with wild-type, but not P2x7−/− mast cells results in susceptibility to inflammation. ATP-P2X7 purinoceptor-mediated activation of mast cells not only induces inflammatory cytokines, but also chemokines and leukotrienes, to recruit neutrophils and subsequently exacerbate intestinal inflammation. These findings reveal the role of P2X7 purinoceptor-mediated mast cell activation in both the initiation and exacerbation of intestinal inflammation.

Vitamins are micronutrients that have physiological effects on various biological responses, including host immunity. Therefore, vitamin deficiency leads to increased risk of developing infectious, allergic, and inflammatory diseases. Since B vitamins are synthesized by plants, yeasts, and bacteria, but not by mammals, mammals must acquire B vitamins from dietary or microbial sources, such as the intestinal microbiota. Similarly, some intestinal bacteria are unable to synthesize B vitamins and must acquire them from the host diet or from other intestinal bacteria for their growth and survival. This suggests that the composition and function of the intestinal microbiota may affect host B vitamin usage and, by extension, host immunity. Here, we review the immunological functions of B vitamins and their metabolism by intestinal bacteria with respect to the control of host immunity.

The indigenous bacteria create natural cohabitation niches together with mucosal Abs in the gastrointestinal (GI) tract. Here we report that opportunistic bacteria, largely Alcaligenes species, specifically inhabit host Peyer's patches (PPs) and isolated lymphoid follicles, with the associated preferential induction of antigen-specific mucosal IgA Abs in the GI tract. Alcaligenes were identified as the dominant bacteria on the interior of PPs from naïve, specific-pathogen-free but not from germ-free mice. Oral transfer of intratissue uncultured Alcaligenes into germ-free mice resulted in the presence of Alcaligenes inside the PPs of recipients. This result was further supported by the induction of antigen-specific Ab-producing cells in the mucosal (e.g., PPs) but not systemic compartment (e.g., spleen). The preferential presence of Alcaligenes inside PPs and the associated induction of intestinal secretory IgA Abs were also observed in both monkeys and humans. Localized mucosal Ab-mediated symbiotic immune responses were supported by Alcaligenes-stimulated CD11c + dendritic cells (DCs) producing the Ab-enhancing cytokines TGF-β, B-cell-activating factor belonging to the TNF family, and IL-6 in PPs. These CD11c + DCs did not migrate beyond the draining mesenteric lymph nodes. In the absence of antigen-specific mucosal Abs, the presence of Alcaligenes in PPs was greatly diminished. Thus, indigenous opportunistic bacteria uniquely inhabit PPs, leading to PP-DCsinitiated, local antigen-specific Ab production; this may involve the creation of an optimal symbiotic environment on the interior of the PPs.Alcaligenes | intratissue habitation | Peyer's patch