Lactobacillus delbrueckii subsp. bulgaricus 2038 and Streptococcus thermophilus 1131 Induce the Expression of the REG3 Family in the Small Intestine of Mice via the Stimulation of Dendritic Cells and Type 3 Innate Lymphoid Cells

Gut microbiota as a key regulator of intestinal mucosal immunity

Gut microbiota is a complex microbial community with the ability of maintaining intestinal health. Intestinal homeostasis largely depends on the mucosal immune system to defense external pathogens and promote tissue repair. In recent years, growing evidence revealed the importance of gut microbiota in shaping intestinal mucosal immunity. Therefore, according to the existing findings, this review first provided an overview of intestinal mucosal immune system before summarizing the regulatory roles of gut microbiota in intestinal innate and adaptive immunity. Specifically, this review delved into the gut microbial interactions with the cells such as intestinal epithelial cells (IECs), macrophages, dendritic cells (DCs), neutrophils, and innate lymphoid cells (ILCs) in innate immunity, and T and B lymphocytes in adaptive immunity. Furthermore, this review discussed the main effects of gut microbiota dysbiosis in intestinal diseases and offered future research prospects. The review highlighted the key regulatory roles of gut microbiota in intestinal mucosal immunity via various host-microbe interactions, providing valuable references for the development of microbial therapy in intestinal diseases.

Immune cell-intrinsic Ah receptor facilitates the expression of antimicrobial REG3G in the small intestine

The intestinal epithelial layer is susceptible to damage by chemical, physiological and mechanical stress. While it is essential to maintain the integrity of epithelium, the biochemical pathways that contribute to the barrier function have not been completely investigated. Here we demonstrate an aryl hydrocarbon receptor (AHR)-dependent mechanism facilitating the production of the antimicrobial peptide AMP regenerating islet-derived protein 3 gamma (REG3G), which is essential for intestinal homeostasis. Genetic ablation of AHR in mice impairs pSTAT3-mediated REG3G expression and increases bacterial numbers of Segmented filamentous bacteria (SFB) and Akkermansia muciniphila in the small intestine. Studies with tissue-specific conditional knockout mice revealed that the presence of AHR in the epithelial cells of the small intestine is not required for the production of REG3G through the phosphorylated STAT3-mediated pathway. However, immune-cell-specific AHR activity is necessary for normal expression of REG3G in all regions of the small intestine. A diet rich in broccoli, capable of inducing AHR activity, increases REG3G production when compared to a semi-purified diet that is devoid of ligands that can potentially activate the AHR, thus highlighting the importance of AHR in antimicrobial function. Overall, these data suggest that homeostatic antimicrobial REG3G production is increased by an AHR pathway intrinsic to the immune cells in the small intestine.

Interleukin-22 enhanced the mucosal barrier and inhibited the invasion of Salmonella enterica in human-induced pluripotent stem cell-derived small intestinal epithelial cells

Human-induced pluripotent stem cell-derived small intestinal epithelial cell (hiPSC-SIEC) monolayers are useful in vitro models for evaluating the gut mucosal barrier; however, their reactivity to cytokines, which are closely related to the regulation of mucosal barrier function, remains unclear. Interleukin (IL)-22 is a cytokine that contributes to regulate the mucosal barrier in the intestinal epithelia. Using microarray and gene set enrichment analysis, we found that hiPSC-SIEC monolayers activate the immune response and enhance the mucosal barrier in response to IL-22. Moreover, hiPSC-SIEC monolayers induced the gene expression of antimicrobials, including the regenerating islet-derived protein 3 family. Furthermore, IL-22 stimulation upregulated Mucin 2 secretion and gene expression of an enzyme that modifies sugar chains, suggesting alteration of the state of the mucus layer of hiPSC-SIEC monolayers. To evaluate its physiological significance, we measured the protective activity against Salmonella enterica subsp. enterica infection in hiPSC-SIEC monolayers and found that prestimulation with IL-22 reduced the number of viable intracellular bacteria. Collectively, these results suggest that hiPSC-SIEC monolayers enhance the mucosal barrier and inhibit infection by pathogenic bacteria in response to IL-22, as previously reported. These results can contribute to the further application of hiPSC-SIECs in evaluating mucosal barriers.

Yogurt starter strains ameliorate intestinal barrier dysfunction via activating AMPK in Caco-2 cells

Lactic acid bacteria (LAB) are commonly used probiotics that improve human health in various aspects. We previously reported that yogurt starter strains, Lactobacillus delbrueckii subsp. bulgaricus 2038 and Streptococcus thermophilus 1131, potentially enhance the intestinal epithelial barrier function by inducing the expression of antimicrobial peptides in the small intestine. However, their effects on physical barrier functions remain unknown. In this study, we found that both strains ameliorated the decreased trans-epithelial resistance and the increased permeability of fluorescein isothiocyanate-dextran induced by tumor necrosis factor (TNF)-α and interferon (IFN)-γ in Caco-2 cells. We also demonstrated that LAB prevented a decrease in the expression and disassembly of tight junctions (TJs) induced by TNF-α and IFN-γ. To assess the repair activity of TJs, a calcium switch assay was performed. Both strains were found to promote the reassembly of TJs, and their activity was canceled by the inhibitor of AMP-activated protein kinase (AMPK). Moreover, these strains showed increased AMPK phosphorylation. These observations suggest that the strains ameliorated physical barrier dysfunction via the activation of AMPK. The activities preventing barrier destruction induced by TNF-α and IFN-γ were strain-dependent. Several strains containing L. bulgaricus 2038 and S. thermophilus 1131 significantly suppressed the barrier impairment, and L. bulgaricus 2038 showed the strongest activity among them. Our findings suggest that the intake of L. bulgaricus 2038 and S. thermophilus 1131 is a potential strategy for the prevention and repair of leaky gut.

In Vivo Functional Properties of Dairy Bacteria

This literature review aimed to collect investigations on the in vivo evidence for bacteria associated with fermented dairy foods to behave as probiotics with beneficial effects in the prevention and treatment of various diseases. All main bacterial groups commonly present in high numbers in fermented milks or cheeses were taken into account, namely starter lactic acid bacteria (SLAB) Lactobacillus delbrueckii subsp. bulgaricus and lactis, L. helveticus, Lactococcus lactis, Streptococcus thermophilus, non-starter LAB (NSLAB) Lacticaseibacillus spp., Lactiplantibacillus plantarum, dairy propionibacteria, and other less frequently encountered species. Only studies regarding strains of proven dairy origin were considered. Studies in animal models and clinical studies showed that dairy bacteria ameliorate symptoms of inflammatory bowel disease (IBD), mucositis, metabolic syndrome, aging and oxidative stress, cancer, bone diseases, atopic dermatitis, allergies, infections and damage caused by pollutants, mild stress, and depression. Immunomodulation and changes in the intestinal microbiota were the mechanisms most often involved in the observed effects. The results of the studies considered indicated that milk and dairy products are a rich source of beneficial bacteria that should be further exploited to the advantage of human and animal health.

Lactiplantibacillus plantarum OLL2712 Induces Autophagy via MYD88 and Strengthens Tight Junction Integrity to Promote the Barrier Function in Intestinal Epithelial Cells

Autophagy is an important system conserved in eukaryotes that maintains homeostasis by degrading abnormal proteins. Autophagy incompetence in intestinal epithelial cells causes the abnormal function of intestinal stem cells and other cells and damages intestinal barrier function. The disruption of the intestinal barrier causes chronic inflammation throughout the body, followed by impaired glucose and lipid metabolism. Lactiplantibacillus plantarum OLL2712 (OLL2712) is a lactic acid bacterium that induces interleukin-10 production from immune cells, alleviates chronic inflammation, and improves glucose and lipid metabolism. In this study, we hypothesized that OLL2712 exerts anti-inflammatory effects by inducing autophagy and ameliorating intestinal barrier dysfunction, and we investigated its autophagy-inducing activities and functions. Caco-2 cells stimulated with OLL2712 for 24 h showed an increased number of autolysosomes per cell, compared with unstimulated cells. Therefore, the permeability of fluorescein isothiocyanate dextran 4000 (FD-4) was suppressed by inducing autophagy. In contrast, mucin secretion in HT-29-MTX-E12 cells was also increased by OLL2712 but not via autophagy induction. Finally, the signaling pathway involved in autophagy induction by OLL2712 was found to be mediated by myeloid differentiation factor 88 (MYD88). In conclusion, our findings suggest that OLL2712 induces autophagy in intestinal epithelial cells via MYD88, and that mucosal barrier function is strengthened by inducing autophagy.

Lactobacillus for the treatment and prevention of atopic dermatitis: Clinical and experimental evidence

Atopic dermatitis (AD) is a chronic inflammatory skin disease, accompanied by itching and swelling. The main pathological mechanism of AD is related to the imbalance between Type 2 helper cells (Th2 cells) and Type 1 helper cells (Th1 cells). Currently, no safe and effective means to treat and prevent AD are available; moreover, some treatments have side effects. Probiotics, such as some strains of Lactobacillus, can address these concerns via various pathways: i) facilitating high patient compliance; ii) regulating Th1/Th2 balance, increasing IL-10 secretion, and reducing inflammatory cytokines; iii) accelerating the maturation of the immune system, maintaining intestinal homeostasis, and improving gut microbiota; and iv) improving the symptoms of AD. This review describes the treatment and prevention of AD using 13 species of Lactobacillus. AD is commonly observed in children. Therefore, the review includes a higher proportion of studies on AD in children and fewer in adolescents and adults. However, there are also some strains that do not improve the symptoms of AD and even worsen allergies in children. In addition, a subset of the genus Lactobacillus that can prevent and relieve AD has been identified in vitro. Therefore, future studies should include more in vivo studies and randomized controlled clinical trials. Given the advantages and disadvantages mentioned above, further research in this area is urgently required.

Resistant Potato Starch Alters the Cecal Microbiome and Gene Expression in Mice Fed a Western Diet Based on NHANES Data

Several studies indicate that the four major types of resistant starch (RS1-4) are fermented in the cecum and colon to produce short-chain fatty acids (SCFAs) and can alter the microbiome and host physiology. However, nearly all these studies were conducted in rodents fed with a diet that does not approximate what is typically consumed by humans. To address this, mice were fed a Total Western Diet (TWD) based on National Health and Nutrition Examination Survey (NHANES) data that mimics the macro and micronutrient composition of a typical American diet for 6 weeks and then supplemented with 0, 2, 5, or 10% of the RS2, resistant potato starch (RPS), for an additional 3 weeks. The cecal microbiome was analyzed by 16S sequencing. The alpha-diversity of the microbiome decreased with increasing consumption of RPS while a beta-diversity plot showed four discreet groupings based on the RPS level in the diet. The relative abundance of various genera was altered by feeding increasing levels of RPS. In particular, the genus Lachnospiraceae NK4A136 group was markedly increased. Cecal, proximal, and distal colon tissue mRNA abundance was analyzed by RNASeq. The cecal mRNA abundance principal component analysis showed clear segregation of the four dietary groups whose separation decreased in the proximal and distal colon. Differential expression of the genes was highest in the cecum, but substantially decreased in the proximal colon (PC) and distal colon (DC). Most differentially expressed genes were unique to each tissue with little overlap in between. The pattern of the observed gene expression suggests that RPS, likely through metabolic changes secondary to differences in microbial composition, appears to prime the host to respond to a range of pathogens, including viruses, bacteria, and parasites. In summary, consumption of dietary RPS led to significant changes to the microbiome and gene expression in the cecum and to a lesser extent in the proximal and distal colon.

Safety and efficacy of using heat-killed Lactobacillus plantarum L-137: High-dose and long-term use effects on immune-related safety and intestinal bacterial flora

Heat-killed Lactobacillus plantarum L-137 (HK L-137) promotes immune function in animals. In healthy people, T-cell proliferation was shown to be enhanced by taking 10 mg HK L-137 daily for 12 weeks. However, the safety and efficacy of higher doses or longer treatments have not yet been investigated in humans. To investigate the high-dose and long-term use effects of HK L-137 on immune-related safety and on host intestinal bacterial flora, 15 healthy volunteers took a daily HK L-137 (50 mg) preparation for 4 weeks. An additional 29 participants who regularly visited a clinic for health care took HK L-137 (10 mg) daily for 12 months. Measures for anthropometrics, hematology, biochemistry, and urinalysis were taken at scheduled timepoints for all participants. Stool and blood samples were also collected and evaluated for microbes and short-chain fatty acids (SCFA); isolated T-cells were assessed for levels of proliferation induced by phytohemagglutinin in the long-term study. Adverse events or shifts in clinical measures from normal ranges due to the dietary intervention were not observed in the high-dose or long-term studies. Long-term intake also did not result in immune exhaustion due to any chronic immunostimulation; ex vivo T-cell proliferation was significantly greater at 12 months than at baseline (p < 0.01). In addition, the Firmicutes/Bacteroidetes ratio in stool samples was significantly lower at 12 months than at baseline (p < 0.05) due to the long-term intake of the HK L-137. Lastly, fecal SCFA concentrations were significantly greater (p < 0.05) at 6 months than at baseline. From these data, it can be concluded that the efficacy of HK L-137 is maintained with no overt adverse effects as a result of high-dose and/or long-term consumption.

Harnessing the potential of Lactobacillus species for therapeutic delivery at the lumenal-mucosal interface

Lactobacillus species have been studied for over 30 years in their role as commensal organisms in the human gut. Recently there has been a surge of interest in their abilities to natively and recombinantly stimulate immune activities, and studies have identified strains and novel molecules that convey particular advantages for applications as both immune adjuvants and immunomodulators. In this review, we discuss the recent advances in Lactobacillus-related activity at the gut/microbiota interface, the efforts to probe the boundaries of the direct and indirect therapeutic potential of these bacteria, and highlight the continued interest in harnessing the native capacity for the production of biogenic compounds shown to influence nervous system activity. Taken together, these aspects underscore Lactobacillus species as versatile therapeutic delivery vehicles capable of effector production at the lumenal-mucosal interface, and further establish a foundation of efficacy upon which future engineered strains can expand.

Colonic Mucosal Microbiota and Association of Bacterial Taxa with the Expression of Host Antimicrobial Peptides in Pediatric Ulcerative Colitis

Inflammatory bowel diseases (IBD), ulcerative colitis (UC) and Crohn's disease (CD), are chronic debilitating disorders of unknown etiology. Over 200 genetic risk loci are associated with IBD, highlighting a key role for immunological and epithelial barrier functions. Environmental factors account for the growing incidence of IBD, and microbiota are considered as an important contributor. Microbiota dysbiosis can lead to a loss of tolerogenic immune effects and initiate or exacerbate inflammation. We aimed to study colonic mucosal microbiota and the expression of selected host genes in pediatric UC. We used high-throughput 16S rDNA sequencing to profile microbiota in colonic biopsies of pediatric UC patients (n = 26) and non-IBD controls (n = 27). The expression of 13 genes, including five for antimicrobial peptides, in parallel biopsies was assessed with qRT-PCR. The composition of microbiota between UC and non-IBD differed significantly (PCoA, p = 0.001). UC children had a decrease in Bacteroidetes and an increase in several family-level taxa including Peptostreptococcaceae and Enterobacteriaceae, which correlated negatively with the expression of antimicrobial peptides REG3G and DEFB1, respectively. Enterobacteriaceae correlated positively with the expression siderophore binding protein LCN2 and Betaproteobacteria negatively with DEFB4A expression. The results indicate that reciprocal interaction of epithelial microbiota and defense mechanisms play a role in UC.