A purified diet affects intestinal epithelial proliferation and barrier functions through gut microbial alterations.

The gut microbiota plays a crucial role in maintaining epithelial barrier function. Although multiple studies have demonstrated the significance of dietary factors on the gut microbiota and mucosal barrier function, the impact of a purified diet, which has long been used in various animal experiments, on intestinal homeostasis remains to be elucidated. Here, we compared the impact of two different types of diets, a crude diet and an AIN-93G-formula purified diet, on epithelial integrity and the gut microbiota. Purified diet-fed mice exhibited shorter villi and crypt lengths and slower epithelial turnover, particularly in the ileum. In addition, antimicrobial products, including REG3γ, were substantially decreased in purified diet-fed mice. Purified diet feeding also suppressed α1,2-fucosylation on the epithelial surface. Furthermore, the purified diet induced metabolic rewiring to fatty acid oxidation and ketogenesis. 16S ribosomal RNA gene sequencing of the ileal contents and mucus layer revealed distinct gut microbiota compositions between the purified and crude diet-fed mice. Purified diet feeding reduced the abundance of segmented filamentous bacteria (SFB), which potently upregulate REG3γ and fucosyltransferase 2 (Fut2) by stimulating group 3 innate lymphoid cells (ILC3s) to produce IL-22. These observations illustrate that the intake of a crude diet secures epithelial barrier function by facilitating SFB colonization, whereas a purified diet insufficiently establishes the epithelial barrier, at least partly owing to the loss of SFB. Our data suggest that the influence of purified diets on the epithelial barrier integrity should be considered in experiments using purified diets.

α-Glucosidase inhibitors boost gut immunity by inducing IgA responses in Peyer's patches.

Peyer's patches (PPs) are specialized gut-associated lymphoid tissues that initiate follicular helper T (Tfh)-mediated immunoglobulin A (IgA) response to luminal antigens derived from commensal symbionts, pathobionts, and dietary sources. IgA-producing B cells migrate from PPs to the small intestinal lamina propria and secrete IgA across the epithelium, modulating the ecological balance of the commensal microbiota and neutralizing pathogenic microorganisms. α-glucosidase inhibitors (α-GIs) are antidiabetic drugs that inhibit carbohydrate digestion in the small intestinal epithelium, leading to alterations in the commensal microbiota composition and metabolic activity. The commensal microbiota and IgA responses exhibit bidirectional interactions that modulate intestinal homeostasis and immunity. However, the effect of α-GIs on the intestinal IgA response remains unclear. We investigated whether α-GIs affect IgA responses by administering voglibose and acarbose to mice via drinking water. We analyzed Tfh cells, germinal center (GC) B cells, and IgA-producing B cells in PPs by flow cytometry. We also assessed pathogen-specific IgA responses. We discovered that voglibose and acarbose induced Tfh cells, GCB cells, and IgA-producing B cells in the PPs of the proximal small intestine in mice. This effect was attributed to the modification of the microbiota rather than a shortage of monosaccharides. Furthermore, voglibose enhanced secretory IgA (S-IgA) production against attenuated Salmonella Typhimurium. Our findings reveal a novel mechanism by which α-GIs augment antigen-specific IgA responses by stimulating Tfh-GCB responses in PPs, and suggest a potential therapeutic application as an adjuvant for augmenting mucosal vaccines.

Dietary iodine attenuates allergic rhinitis by inducing ferroptosis in activated B cells.

Iodine-containing formulations have been widely used to treat iodine deficiency and as antiseptics. Lecithin-bound iodine (LBI) has been approved to treat allergic diseases in Japan; however, its underlying mechanism remains unknown. In this study, we show that LBI ameliorated disease symptoms in an ovalbumin (OVA)-induced allergic rhinitis mouse model. LBI suppressed OVA-specific IgE production by attenuating germinal center (GC) reaction in the draining lymph nodes. The antiallergic effect of LBI is most likely attributed to increased serum iodine levels but not thyroid hormone levels. In vitro treatment of activated B cells with potassium iodide induced ferroptosis by increasing intracellular reactive oxygen species (ROS) and ferrous iron in a concentration-dependent manner. Accordingly, LBI diets increased ROS levels in GC B cells of the draining lymph nodes. This study suggests that iodine directly promotes ferroptosis in activated B cells and attenuates GC reactions, leading to the alleviation of allergic symptoms.

Spi-B alleviates food allergy by securing mucosal barrier and immune tolerance in the intestine.

Food allergy is a type I allergic reaction induced by mast cells and is mainly activated by allergen-specific immunoglobulin (Ig)E. Spi-B is an E26-transformation-specific (Ets) family transcription factor essential for the differentiation and functional maturation of several immune cell subsets, including mast cells. However, the possible involvement of Spi-B in food allergy remains unclear. In this study, we found that Spi-B-deficient mice were highly susceptible to food allergy to ovalbumin (OVA), as indicated by the exacerbation of diarrhea and elevation of serum IgE levels. These pathological changes were associated with enhanced mast cell infiltration into the intestinal lamina propria. Activation of mast cells in the intestinal mucosa was observed in Spib -/- mice, even under physiological conditions. Accordingly, Spi-B deficiency increased the translocation of fluorescently labeled dextran from the lumen to the serum, suggesting increased intestinal permeability in Spib -/- mice. Moreover, Spib -/- mice showed defects in oral tolerance induction to OVA. These data illustrate that Spi-B suppresses the development of food allergies by controlling the activation of intestinal mast cells and by inducing immune tolerance to food allergens.

Profiling of tumour-associated microbiota in human hepatocellular carcinoma.

Liver cancer is the fourth leading cause of cancer-related death. Hepatocellular carcinoma (HCC) is a primary liver cancer that results from chronic hepatitis caused by multiple predisposing factors such as viral infection, alcohol consumption, and non-alcoholic fatty liver disease. Accumulating studies have indicated that dysfunction of the gut epithelial barrier and hepatic translocation of gut microbes may be implicated in the pathogenesis of HCC. However, the translocated bacteria in HCC patients remains unclear. Here, we characterised tumour-associated microbiota in patients with liver cancer and focused on HCC. We observed that the number of amplicon sequence variants in tumour-associated microbiota was significantly higher compared with that in non-tumour regions of the liver. The tumour-associated microbiota consisted of Bacteroidetes, Firmicutes, and Proteobacteria as the dominant phyla. We identified an unclassified genus that belonged to the Bacteroides, Romboutsia, uncultured bacterium of Lachnospiraceae as a signature taxon for primary liver cancer. Additionally, we identified Ruminococcus gnavus as a signature taxon for HCC patients infected with hepatitis B and/or hepatitis C viruses. This study suggests that tumour microbiota may contribute to the pathology of HCC.

Fasting-Refeeding Impacts Immune Cell Dynamics and Mucosal Immune Responses.

Nutritional status potentially influences immune responses; however, how nutritional signals regulate cellular dynamics and functionality remains obscure. Herein, we report that temporary fasting drastically reduces the number of lymphocytes by ∼50% in Peyer's patches (PPs), the inductive site of the gut immune response. Subsequent refeeding seemingly restored the number of lymphocytes, but whose cellular composition was conspicuously altered. A large portion of germinal center and IgA+ B cells were lost via apoptosis during fasting. Meanwhile, naive B cells migrated from PPs to the bone marrow during fasting and then back to PPs during refeeding when stromal cells sensed nutritional signals and upregulated CXCL13 expression to recruit naive B cells. Furthermore, temporal fasting before oral immunization with ovalbumin abolished the induction of antigen-specific IgA, failed to induce oral tolerance, and eventually exacerbated food antigen-induced diarrhea. Thus, nutritional signals are critical in maintaining gut immune homeostasis.