Plasmacytoid dendritic cells are crucial in Bifidobacterium adolescentis-mediated inhibition of Yersinia enterocolitica infection

The Potential Immunomodulatory Effect of Bifidobacterium longum subsp. longum BB536 on Healthy Adults through Plasmacytoid Dendritic Cell Activation in the Peripheral Blood

The interaction between the gut microbiota and the host can influence the host's immune system. Bifidobacterium, a commensal genus of gut bacteria, seems to have positive effects on host health. Our previous clinical research showed that B. longum subsp. longum BB536 enhanced innate and adaptive immune responses in elderly individuals with a lower grade of immunity, but the immunomodulatory mechanism is still unclear. In this study, dendritic cell (DC) surface markers in peripheral blood mononuclear cells isolated from healthy individuals were evaluated through coculture with heat-killed BB536. DC markers, innate immune activity and cytokine levels in plasma were also evaluated by a randomized, double-blind, placebo-controlled, parallel-group study (UMIN000045564) with 4 weeks of continuous live BB536 intake. BB536 significantly increased the expression of CD86 and HLA-DR on plasmacytoid DCs (pDCs) in vitro. Compared to placebo (n = 48), a significant increase in the expression of CD86 on peripheral pDCs was detected at week 4 of live BB536 intake (n = 49; 1 × 1010 CFU/day). Furthermore, coculture with hk-BB536 significantly increased the IFNγ expression level and demonstrated trends of increased IFNα1 and IFNβ expression. These findings suggest that consumption of BB536 has potential immunomodulatory effects on healthy individuals through the activation of peripheral pDCs.

Strain-specific alterations in gut microbiome and host immune responses elicited by tolerogenic Bifidobacterium pseudolongum

The beneficial effects attributed to Bifidobacterium are largely attributed to their immunomodulatory capabilities, which are likely to be species- and even strain-specific. However, their strain-specificity in direct and indirect immune modulation remain largely uncharacterized. We have shown that B. pseudolongum UMB-MBP-01, a murine isolate strain, is capable of suppressing inflammation and reducing fibrosis in vivo. To ascertain the mechanism driving this activity and to determine if it is specific to UMB-MBP-01, we compared it to a porcine tropic strain B. pseudolongum ATCC25526 using a combination of cell culture and in vivo experimentation and comparative genomics approaches. Despite many shared features, we demonstrate that these two strains possess distinct genetic repertoires in carbohydrate assimilation, differential activation signatures and cytokine responses signatures in innate immune cells, and differential effects on lymph node morphology with unique local and systemic leukocyte distribution. Importantly, the administration of each B. pseudolongum strain resulted in major divergence in the structure, composition, and function of gut microbiota. This was accompanied by markedly different changes in intestinal transcriptional activities, suggesting strain-specific modulation of the endogenous gut microbiota as a key to immune modulatory host responses. Our study demonstrated a single probiotic strain can influence local, regional, and systemic immunity through both innate and adaptive pathways in a strain-specific manner. It highlights the importance to investigate both the endogenous gut microbiome and the intestinal responses in response to probiotic supplementation, which underpins the mechanisms through which the probiotic strains drive the strain-specific effect to impact health outcomes.

Study on the additive protective effect of PGLYRP3 and Bifidobacterium adolescentis Reuter 1963 on severity of DSS-induced colitis in Pglyrp3 knockout (Pglyrp3 -/-) and wild-type (WT) mice

BACKGROUND AND AIMS

Pglyrp3 is a bactericidal innate immunity protein known to sustain the habitual gut microbiome and protect against experimental colitis. Intestinal inflammation and metaflammation are commonly associated with a marked reduction of commensal bifidobacteria. Whether Pglyrp3 and bifidobacteria interact synergistically or additively to alleviate metaflammation is unknown. We investigated the extent to which Pglyrp3 and bifidobacteria regulate metaflammation and gut bacterial dysbiosis in DSS-induced mouse models of intestinal inflammation.

MATERIAL & METHODS

8-10 weeks old male mice were used. In both WT and Pglyrp3 -/- experiments, the mice were randomly divided into three groups of 16 mice per group: (1) a control group receiving sterile tap water, (2) an experimental group receiving sterile tap water supplemented with only 5% DSS, and (3) an experimental group receiving sterile tap water supplemented with 5% DSS and 1 × 10⁹ CFU/ml of Bifidobacterium adolescentis (B.a.) for 7 days. Wild-type (WT) littermates of the respective gene (i.e. Pglyrp3) were used as controls throughout the study. Clinical signs of general health and inflammation were monitored daily. Faecal pellet samples were analysed by qRT-PCR for microbial composition. Histology of relevant organs was carried out on day 8. Metabolic parameters and liver inflammation were determined in serum samples.

RESULTS

Intestinal inflammation in mice of group 2 were significantly increased compared to those of control group 1. There was a significant difference in mean scores for inflammation severity between DSS-treated WT and DSS-treated Pglyrp3 -/- mice. Buildup of key serum metabolic markers (cholesterol, triglyceride and glucose) was set off by colonic inflammation. qRT-PCR quantification showed that DSS significantly decreased the Clostridium coccoides and Bifidobacterium cell counts while increasing those of Bacteroides group in both WT and Pglyrp3 -/- mice. These manifestations of DSS-induced dysbiosis were significantly attenuated by feeding B.a. Both the local and systemic ill-being of the mice alleviated when they received B.a.

DISCUSSION

This study shows that Pglyrp3 facilitates recognition of bifidobacterial cell wall-derived peptidoglycan, thus leading additively to a reduction of metaflammation through an increase in the number of bifidobacteria, which were able to mitigate intestinal immunopathology in the context of Pglyrp3 blockade.

Terminal Ileitis due to Yersinia Infection: An Underdiagnosed Situation

Endoscopy is currently the gold standard for the diagnosis of inflammatory bowel disease (IBD). The presence of macroscopic lesions along with the microscopic detection of inflammatory infiltration in the terminal ileum often leads the gastroenterologist to the diagnosis of Crohn's disease (CD). However, some of these cases could be, in fact, an infection caused by Yersinia spp., accompanied or not with CD, which could be easily diagnosed with the identification of serum antibodies against Yersinia outer protein antigens (YOP antigens). Since Yersiniosis is considered to be an uncommon situation, food and water are not usually checked for the possibility of contamination by Yersinia. Therefore, it is reasonable to assume that the true prevalence of Yersinia infection in patients with terminal ileitis is probably underestimated. In this article, we review the most important data regarding the various aspects of Yersinia infection with special focus on its pathophysiology and diagnosis. We recommend testing for serum antibodies against YOP antigens in all patients with an endoscopic and histological image of terminal ileitis in order to identify Yersiniosis in conjunction or not with terminal ileum CD.

The Role of Plasmacytoid Dendritic Cells in Gut Health

Plasmacytoid dendritic cells (pDCs) are a unique subset of cells with different functional characteristics compared to classical dendritic cells. The pDCs are critical for the production of type I IFN in response to microbial and self-nucleic acids. They have an important role for host defense against viral pathogen infections. In addition, pDCs have been well studied as a critical player for breaking tolerance to self-nucleic acids that induce autoimmune disorders such as systemic lupus erythematosus. However, pDCs have an immunoregulatory role in inducing the immune tolerance by generating Tregs and various regulatory mechanisms in mucosal tissues. Here, we summarize the recent studies of pDCs that focused on the functional characteristics of gut pDCs, including interactions with other immune cells in the gut. Furthermore, the dynamic role of gut pDCs will be investigated with respect to disease status including gut infection, inflammatory bowel disease, and cancers.

Bifidobacteria and Their Molecular Communication with the Immune System

Bifidobacterium represents a genus within the phylum Actinobacteria which is one of the major phyla in the healthy intestinal tract of humans. Bifidobacterium is one of the most abundant genera in adults, but its predominance is even more pronounced in infants, especially during lactation, when they can constitute the majority of the total bacterial population. They are one of the pioneering colonizers of the early gut microbiota, and they are known to play important roles in the metabolism of dietary components, otherwise indigestible in the upper parts of the intestine, and in the maturation of the immune system. Bifidobacteria have been shown to interact with human immune cells and to modulate specific pathways, involving innate and adaptive immune processes. In this mini-review, we provide an overview of the current knowledge on the immunomodulatory properties of bifidobacteria and the mechanisms and molecular players underlying these processes, focusing on the corresponding implications for human health. We deal with in vitro models suitable for studying strain-specific immunomodulatory activities. These include peripheral blood mononuclear cells and T cell-mediated immune responses, both effector and regulatory cell responses, as well as the modulation of the phenotype of dendritic cells, among others. Furthermore, preclinical studies, mainly germ-free, gnotobiotic, and conventional murine models, and human clinical trials, are also discussed. Finally, we highlight evidence supporting the immunomodulatory effects of bifidobacterial molecules (proteins and peptides, exopolysaccharides, metabolites, and DNA), as well as the role of bifidobacterial metabolism in maintaining immune homeostasis through cross-feeding mechanisms.

Enhancement of Oral Tolerance Induction in DO11.10 Mice by Lactobacillus gasseri OLL2809 via Increase of Effector Regulatory T Cells

Food allergy is a serious problem for infants and young children. Induction of antigen-specific oral tolerance is one therapeutic strategy. Enhancement of oral tolerance induction by diet is a promising strategy to prevent food allergy in infants. Thus, in this study, we evaluate the effect of probiotic Lactobacillus gasseri OLL2809 (LG2809) on oral tolerance induction in a mouse model. The degree of oral tolerance induction was evaluated by measuring the proliferation and level of IL-2 production of splenic CD4⁺ T cells from DO11.10 mice fed ovalbumin (OVA) alone or OVA with LG2809. Oral administration of LG2809 significantly decreased the rate of proliferation and IL-2 production by CD4⁺ T cells from OVA-fed mice. LG2809 increased a ratio of CD4⁺ T-cell population, producing high levels of IL-10 and having strong suppressive activity. Moreover, LG2809 increased a ratio of plasmacytoid dendritic cells (pDCs) among the lamina propria (LP) in small intestine. When used as antigen presenting cells to naïve CD4⁺ T cells from DO11.10 mice, LP cells from BALB/c mice fed LG2809 induced higher IL-10 production and stronger suppressive activity than those from non-treated mice. These results suggest that oral administration of LG2809 increases the population of pDCs in the LP, resulting in the enhancement of oral tolerance induction by increasing the ratio of effector regulatory T cells. LG2809 could, therefore, act as a potent immunomodulator to prevent food allergies by promoting oral tolerance.

Crosstalk between microbiota, pathogens and the innate immune responses

Research in the last decade has convincingly demonstrated that the microbiota is crucial in order to prime and orchestrate innate and adaptive immune responses of their host and influence barrier function as well as multiple developmental and metabolic parameters of the host. Reciprocally, host reactions and immune responses instruct the composition of the microbiota. This review summarizes recent evidence from experimental and human studies which supports these arms of mutual relationship and crosstalk between host and resident microbiota, with a focus on innate immune responses in the gut, the role of cell death pathways and antimicrobial peptides. We also provide some recent examples on how dysbiosis and pathogens can act in concert to promote intestinal infection, inflammatory pathologies and cancer. The future perspectives of these combined research efforts include the discovery of protective species within the microbiota and specific traits and factors of microbes that weaken or enforce host intestinal homeostasis.

A Lactobacillus plantarum strain isolated from kefir protects against intestinal infection with Yersinia enterocolitica O9 and modulates immunity in mice

Lactobacillus plantarum C4, previously isolated from kefir and characterized as a potential probiotic strain, was tested for its protective and immunomodulatory capacity in a murine model of yersiniosis. The inoculation of BALB/c mice with a low pathogenicity serotype O9 strain of Yersinia enterocolitica results in a prolonged intestinal infection with colonization of Peyer's patches. Pretreatment with C4 was without effect on fecal excretion of yersiniae, but shortened the colonization of Peyer's patches. This protective effect was associated with pro-inflammatory status in the intestinal mucosa (TNF-α production in infected mice was increased by C4) and an increase in total IgA secretion. At a systemic level, C4 did not promote a pro-inflammatory response, although production of the immunoregulatory cytokine IFN-γ was enhanced. These findings suggest that L. plantarum C4 can increase resistance to intestinal infections through its immunomodulatory activity.

TLR signaling-induced CD103-expressing cells protect against intestinal inflammation

BACKGROUND

Toll-like receptor (TLR) expression in patients with inflammatory bowel disease is increased when compared with healthy controls. However, the impact of TLR signaling during inflammatory bowel disease is not fully understood.

METHODS

In this study, we used a murine model of acute phase inflammation in bone marrow chimeric mice to investigate in which cell type TLR2/4 signal induction is important in preventing intestinal inflammation and how intestinal dendritic cells are influenced. Mice were either fed with wild-type bacteria, able to initiate the TLR2/4 signaling cascade, or with mutant strains with impaired signal induction capacity.

RESULTS

The induction of the TLR2/4 signal cascade in epithelial cells resulted in inflammation in bone marrow chimeric mice, whereas induction in hematopoietic cells had an opposed function. Furthermore, feeding of wild-type bacteria prevented disease; however, differing signal induction of bacteria had no effect on lamina propria dendritic cell activation. In contrast, functional TLR2/4 signals resulted in increased frequencies of CD103-expressing lamina propria and mesenteric lymph node dendritic cells, which were able to ameliorate disease.

CONCLUSIONS

The TLR-mediated amelioration of disease, the increase in CD103-expressing cells, and the beneficial function of TLR signal induction in hematopoietic cells indicate that the increased expression of TLRs in patients with inflammatory bowel disease might result in counterregulation of the host and serve in preventing disease.