Influence of gut microbiota on mouse B2 B cell ontogeny and function

Microbiota-mediated shaping of mouse spleen structure and immune function characterized by scRNA-seq and Stereo-seq

Gut microbes exhibit complex interactions with their hosts and shape an organism's immune system throughout its lifespan. As the largest secondary lymphoid organ, the spleen has a wide range of immunological functions. To explore the role of microbiota in regulating and shaping the spleen, we employ scRNA-seq and Stereo-seq technologies based on germ-free (GF) mice to detect differences in tissue size, anatomical structure, cell types, functions, and spatial molecular characteristics. We identify 18 cell types, 9 subtypes of T cells, and 7 subtypes of B cells. Gene differential expression analysis reveals that the absence of microorganisms results in alterations in erythropoiesis within the red pulp region and congenital immune deficiency in the white pulp region. Stereo-seq results demonstrate a clear hierarchy of immune cells in the spleen, including marginal zone (MZ) macrophages, MZ B cells, follicular B cells and T cells, distributed in a well-defined pattern from outside to inside. However, this hierarchical structure is disturbed in GF mice. Ccr7 and Cxcl13 chemokines are specifically expressed in the spatial locations of T cells and B cells, respectively. We speculate that the microbiota may mediate the structural composition or partitioning of spleen immune cells by modulating the expression levels of chemokines.

Gastrointestinal Dysfunction in Stroke

Gastrointestinal (GI) complications are seen in over 50% of ischemic stroke survivors; the most common complications are dysphagia, constipation, and GI bleeding. The bidirectional relationship of the gut-brain axis and stroke has recently gained traction, wherein stroke contributes to gut dysbiosis (alterations in the normal host intestinal microbiome) and gut dysbiosis perpetuates poor functional neurologic outcomes in stroke. It is postulated that the propagation of proinflammatory cells and gut metabolites (including trimethylamine N-oxide and short-chain fatty acids) from the GI tract to the central nervous system play a central role in gut-brain axis dysfunction. In this review, we discuss the known GI complications in acute ischemic stroke, our current knowledge from experimental stroke models for gut-brain axis dysfunction in stroke, and emerging therapeutics that target the gut-brain axis.

Intestinal microbial 16S sequencing and LC-MS metabonomic analysis revealed differences between young and old cats

With the progress of society, the health problems of pets have attracted more and more attention. Recent studies have shown that intestinal microflora and related fecal metabolites play a crucial role in the healthy growth of cats. However, the potential role and related metabolic characteristics of gut microbiota in different age groups of pet cats need to be further clarified. 16S rRNA gene sequencing was used to analyze the intestinal microbial composition of young and old cats. LC-MS metabonomic analysis is used to characterize the changes in the metabolic spectrum in feces. The potential relationship between intestinal microorganisms and metabolites, as well as the differences in different age groups, were studied. The species composition of intestinal microflora in the young group and old group is significantly different, T-test algorithm shows 36 different ASVs and 8 different genuses, while the Wilcoxon algorithm shows 81 different ASVs and 17 different genuses. The metabolomics analysis identified 537 kinds of fecal metabolites, which are rich in differences between young and old cats, and may be potential biomarkers indicating the health of cats. 16S rRNA analysis showed significant differences in fructose and mannose metabolism, while metabonomics KEGG analysis showed significant difference in choline metabolism in cancer. Our study compared the differences between the intestinal microbiome and fecal metabolites in young and old cats. This difference provides a new direction for further exploring the relationship between the composition and metabolism of intestinal microbiota in cats of different age groups. It also provides a reference for cat health research.

Microbial Interventions to Improve Neonatal Gut Health

The diverse pioneer microbial community colonizing the mammalian gastrointestinal tract is critical for the developing immune system. Gut microbial communities of neonates can be affected by various internal and external factors, resulting in microbial dysbiosis. Microbial dysbiosis during early life affects gut homeostasis by changing metabolic, physiological, and immunological status, which increases susceptibility to neonatal infections and long-term pathologies. Early life is crucial for the establishment of microbiota and the development of the host immune system. Therefore, it provides a window of opportunity to reverse microbial dysbiosis with a positive impact on host health. Recent attempts to use microbial interventions during early life have successfully reversed dysbiotic gut microbial communities in neonates. However, interventions with persistent effects on microbiota and host health are still limited. This review will critically discuss microbial interventions, modulatory mechanisms, their limitations, and gaps in knowledge to understand their roles in improving neonatal gut health.

Diurnal changes in bacterial settlement on the Peyer's patch and surrounding mucosa in the rat ileum and its effect against the intestinal immune system

Our previous study revealed the diurnal change in the indigenous bacteria settling on the terminal region of the rat ileum. In the present study, we investigated the diurnal change in indigenous bacteria on the most distal ileal Peyer's patch (PP) and surrounding ileal mucosa and explored how stimulation from indigenous bacteria for a day affects the intestinal immune system at the beginning of the light phase. Histological measurement revealed that bacteria adjacent to the follicle-associated epithelium of PP and to the villous epithelium of the surrounding ileal mucosa are more abundant at zeitgeber time (ZT)0 and ZT18 than at ZT12. On the other hand, tissue-section 16S rRNA amplicon sequencing revealed no significant difference between ZT0 and ZT12 in the bacterial composition on the ileal tissue including the PP. One-day treatment with an antibiotic (Abx) successfully impaired the settlement of bacteria around the ileal PP. In transcriptome analysis, 1-day Abx treatment led to the downregulation of several chemokines in both PP and ordinary ileal mucosa at ZT0. Histological analysis of the 1-day Abx group revealed decreases in both CD68⁺ macrophages in PP and naphthol AS-D chloroacetate esterase stain-positive mast cells in the ileal villi. Together, these findings suggest that the colonies of indigenous bacteria on the distal ileal PP and surrounding mucosa expand during the dark phase, which might lead to the expression of genes to regulate the intestinal immune system and contribute to the homeostasis of at least macrophages in PP and mast cells in the ileal mucosa.

Common Variable Immunodeficiency Patient Fecal Microbiota Transplant Recapitulates Gut Dysbiosis

Purpose

Patients with non-infectious complications have worse clinical outcomes in common variable immunodeficiency (CVID) than those with infections-only. Non-infectious complications are associated with gut microbiome aberrations, but there are no reductionist animal models that emulate CVID. Our aim in this study was to uncover potential microbiome roles in the development of non-infectious complications in CVID.

Methods

We examined fecal whole genome shotgun sequencing from patients CVID, and non-infectious complications, infections-only, and their household controls. We also performed Fecal Microbiota transplant from CVID patients to Germ-Free Mice.

Results

We found potentially pathogenic microbes Streptococcus parasanguinis and Erysipelatoclostridium ramosum were enriched in gut microbiomes of CVID patients with non-infectious complications. In contrast, Fusicatenibacter saccharivorans and Anaerostipes hadrus, known to suppress inflammation and promote healthy metabolism, were enriched in gut microbiomes of infections-only CVID patients. Fecal microbiota transplant from non-infectious complications, infections-only, and their household controls into germ-free mice revealed gut dysbiosis patterns in recipients from CVID patients with non-infectious complications, but not infections-only CVID, or household controls recipients.

Conclusion

Our findings provide a proof of concept that fecal microbiota transplant from CVID patients with non-infectious complications to Germ-Free mice recapitulates microbiome alterations observed in the donors.

Markers of immune dysregulation in response to the ageing gut: insights from aged murine gut microbiota transplants

BACKGROUND

Perturbations in the composition and diversity of the gut microbiota are accompanied by a decline in immune homeostasis during ageing, characterized by chronic low-grade inflammation and enhanced innate immunity. Genetic insights into the interaction between age-related alterations in the gut microbiota and immune function remain largely unexplored.

METHODS

We investigated publicly available transcriptomic gut profiles of young germ-free mouse hosts transplanted with old donor gut microbiota to identify immune-associated differentially expressed genes (DEGs). Literature screening of the Gene Expression Omnibus and PubMed identified one murine (Mus musculus) gene expression dataset (GSE130026) that included small intestine tissues from young (5-6 weeks old) germ-free mice hosts that were compared following 8 weeks after transplantation with either old (~ 24-month old; n = 5) or young (5-6 weeks old; n = 4) mouse donor gut microbiota.

RESULTS

A total of 112 differentially expressed genes (DEGs) were identified and used to construct a gut network of encoded proteins, in which DEGs were functionally annotated as being involved in an immune process based on gene ontology. The association between the expression of immune-process DEGs and abundance of immune infiltrates from gene signatures in normal colorectal tissues was estimated from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) project. The analysis revealed a 25-gene signature of immune-associated DEGs and their expression profile was positively correlated with naïve T-cell, effector memory T-cell, central memory T-cell, resident memory T-cell, exhausted T-cell, resting Treg T-cell, effector Treg T-cell and Th1-like colorectal gene signatures. Conclusions These genes may have a potential role as candidate markers of immune dysregulation during gut microbiota ageing. Moreover, these DEGs may provide insights into the altered immune response to microbiota in the ageing gut, including reduced antigen presentation and alterations in cytokine and chemokine production.

Impact of aging on animal models of Parkinson's disease

Aging is the biggest risk factor for developing Parkinson's disease (PD), the second most common neurodegenerative disorder. Several animal models have been developed to explore the pathophysiology underlying neurodegeneration and the initiation and spread of alpha-synuclein-related PD pathology, and to investigate biomarkers and therapeutic strategies. However, bench-to-bedside translation of preclinical findings remains suboptimal and successful disease-modifying treatments remain to be discovered. Despite aging being the main risk factor for developing idiopathic PD, most studies employ young animals in their experimental set-up, hereby ignoring age-related cellular and molecular mechanisms at play. Consequently, studies in young animals may not be an accurate reflection of human PD, limiting translational outcomes. Recently, it has been shown that aged animals in PD research demonstrate a higher susceptibility to developing pathology and neurodegeneration, and present with a more disseminated and accelerated disease course, compared to young animals. Here we review recent advances in the investigation of the role of aging in preclinical PD research, including challenges related to aged animal models that are limiting widespread use. Overall, current findings indicate that the use of aged animals may be required to account for age-related interactions in PD pathophysiology. Thus, although the use of older animals has disadvantages, a model that better represents clinical disease within the elderly would be more beneficial in the long run, as it will increase translational value and minimize the risk of therapies failing during clinical studies. Furthermore, we provide recommendations to manage the challenges related to aged animal models.

Gut Microbiota and Their Metabolites in Stroke: A Double-Edged Sword

Besides damaging the brain, stroke causes systemic changes, including to the gastrointestinal system. A growing body of evidence supports the role of the gut and its microbiota in stroke, stroke prognosis, and recovery. The gut microbiota can increase the risk of a cerebrovascular event, playing a role in the onset of stroke. Conversely, stroke can induce dysbiosis of the gut microbiota and epithelial barrier integrity. This has been proposed as a contributor to systemic infections. In this review, we describe the role of the gut microbiota, microbiome and microbiota-derived metabolites in experimental and clinical stroke, and their potential use as therapeutic targets. Fourteen clinical studies have identified 62 upregulated (eg, Streptococcus, Lactobacillus, Escherichia) and 29 downregulated microbial taxa (eg, Eubacterium, Roseburia) between stroke and healthy participants. The majority found that stroke patients have reduced gut microbiome diversity. However, other nonbacterial microorganisms are yet to be studied. In experimental stroke, severity is dependent on gut microbiome composition, whereas the latter can greatly change with antibiotics, age, and diet. Consumption of foods rich in choline and L-carnitine are positively associated with stroke onset via production of trimethylamine N-oxide in experimental and clinical stroke. Conversely, in mice, consumption of dietary fiber improves stroke outcome, likely via gut microbiota-derived metabolites called short-chain fatty acids, such as acetate, propionate, and butyrate. The majority of the evidence, however, comes from experimental studies. Clinical interventions targeted at gut microbiota-derived metabolites as new therapeutic opportunities for stroke prevention and treatment are warranted.

Gut Microbiota: Critical Controller and Intervention Target in Brain Aging and Cognitive Impairment

The current trend for the rapid growth of the global aging population poses substantial challenges for society. The human aging process has been demonstrated to be closely associated with changes in gut microbiota composition, diversity, and functional features. During the first 2 years of life, the gut microbiota undergoes dramatic changes in composition and metabolic functions as it colonizes and develops in the body. Although the gut microbiota is nearly established by the age of three, it continues to mature until adulthood, when it comprises more stable and diverse microbial species. Meanwhile, as the physiological functions of the human body deteriorated with age, which may be a result of immunosenescence and "inflammaging," the guts of elderly people are generally characterized by an enrichment of pro-inflammatory microbes and a reduced abundance of beneficial species. The gut microbiota affects the development of the brain through a bidirectional communication system, called the brain-gut-microbiota (BGM) axis, and dysregulation of this communication is pivotal in aging-related cognitive impairment. Microbiota-targeted dietary interventions and the intake of probiotics/prebiotics can increase the abundance of beneficial species, boost host immunity, and prevent gut-related diseases. This review summarizes the age-related changes in the human gut microbiota based on recent research developments. Understanding these changes will likely facilitate the design of novel therapeutic strategies to achieve healthy aging.

Gut microbiota as the key controllers of "healthy" aging of elderly people

Extrinsic factors, such as lifestyle and diet, are shown to be essential in the control of human healthy aging, and thus, longevity. They do so by targeting at least in part the gut microbiome, a collection of commensal microorganisms (microbiota), which colonize the intestinal tract starting after birth, and is established by the age of three. The composition and abundance of individual microbiota appears to continue to change until adulthood, presumably reflecting lifestyle and geographic, racial, and individual differences. Although most of these changes appear to be harmless, a major shift in their composition in the gut (dysbiosis) can trigger harmful local and systemic inflammation. Recent reports indicate that dysbiosis is increased in aging and that the gut microbiota of elderly people is enriched in pro-inflammatory commensals at the expense of beneficial microbes. The clinical consequence of this change remains confusing due to contradictory reports and a high degree of variability of human microbiota and methodologies used. Here, we present the authors’ thoughts that underscore dysbiosis as a primary cause of aging-associated morbidities, and thus, premature death of elderly people. We provide evidence that the dysbiosis triggers a chain of pathological and inflammatory events. Examples include alteration of levels of microbiota-affected metabolites, impaired function and integrity of the gastrointestinal tract, and increased gut leakiness. All of these enhance systemic inflammation, which when associated with aging is termed inflammaging, and result in consequent aging-associated pathologies.

Mechanistic insight into the gut microbiome and its interaction with host immunity and inflammation

The intestinal tract is a host to 100 trillion of microbes that have co-evolved with mammals over the millennia. These commensal organisms are critical to the host survival. The roles that symbiotic microorganisms play in the digestion, absorption, and metabolism of nutrients have been clearly demonstrated. Additionally, commensals are indispensable in regulating host immunity. This is evidenced by the poorly developed gut immune system of germ-free mice, which can be corrected by transplantation of specific commensal bacteria. Recent advances in our understanding of the mechanism of host–microbial interaction have provided the basis for this interaction. This paper reviews some of these key studies, with a specific focus on the effect of the microbiome on the immune organ development, nonspecific immunity, specific immunity, and inflammation.

Gut microbiota alterations affect glioma growth and innate immune cells involved in tumor immunosurveillance in mice

Glioma is a CNS tumor with few therapeutic options. Recently, host microbiota has been involved in the immune modulation of different tumors, but no data are available on the possible effects of the gut–immune axis on brain tumors. Here, we investigated the effect of gut microbiota alteration in a syngeneic (GL261) mouse model of glioma, treating mice with two antibiotics (ABX) and evaluating the effects on tumor growth, microbe composition, natural killer (NK) cells and microglia phenotype. We report that ABX treatment (i) altered the intestinal microbiota at family level, (ii) reduced cytotoxic NK cell subsets, and (iii) altered the expression of inflammatory and homeostatic proteins in microglia. All these findings could contribute to the increased growth of intracranial glioma that was observed after ABX treatment. These results demonstrate that chronic ABX administration alters microbiota composition and contributes to modulate brain immune state paving the way to glioma growth.

Host Microbe Interactions in the Lactating Mammary Gland

The bacteria present in human milk constitute the human milk microbiome (hMM). Both the older culture-based work and the more recent studies using molecular detection of bacterial DNA have reached similar conclusions: the hMM mostly consists of commensal staphylococci such as Staphylococcus epidermidis, and streptococci. The prevalence of other bacterial groups such lactobacilli varies widely, while the abundance and prevalence of bifidobacteria is generally low. Recently, the hMM became accepted as a part of a physiologically normal state with suggested potential health benefits. Most research on the hMM has focused on its composition and potential effect on the breastfed infant. A major role as a microbiome inoculum for the infant gut has been proposed, but remains to be clearly demonstrated. Herein, we also discuss the emerging connection between the hMM and mammary gland physiology and lactation. Similarities between the mammary gland and mucosal interfaces are considerable, and in particular mucosal-like immune attributes of mammary gland. The potential role of hMM-host interactions in the mammary gland in maternal health is explored with a primary focus on lactational mastitis.

Gut-Brain Psychology: Rethinking Psychology From the Microbiota-Gut-Brain Axis

Mental disorders and neurological diseases are becoming a rapidly increasing medical burden. Although extensive studies have been conducted, the progress in developing effective therapies for these diseases has still been slow. The current dilemma reminds us that the human being is a superorganism. Only when we take the human self and its partner microbiota into consideration at the same time, can we better understand these diseases. Over the last few centuries, the partner microbiota has experienced tremendous change, much more than human genes, because of the modern transformations in diet, lifestyle, medical care, and so on, parallel to the modern epidemiological transition. Existing research indicates that gut microbiota plays an important role in this transition. According to gut-brain psychology, the gut microbiota is a crucial part of the gut-brain network, and it communicates with the brain via the microbiota-gut-brain axis. The gut microbiota almost develops synchronously with the gut-brain, brain, and mind. The gut microbiota influences various normal mental processes and mental phenomena, and is involved in the pathophysiology of numerous mental and neurological diseases. Targeting the microbiota in therapy for these diseases is a promising approach that is supported by three theories: the gut microbiota hypothesis, the "old friend" hypothesis, and the leaky gut theory. The effects of gut microbiota on the brain and behavior are fulfilled by the microbiota-gut-brain axis, which is mainly composed of the nervous pathway, endocrine pathway, and immune pathway. Undoubtedly, gut-brain psychology will bring great enhancement to psychology, neuroscience, and psychiatry. Various microbiota-improving methods including fecal microbiota transplantation, probiotics, prebiotics, a healthy diet, and healthy lifestyle have shown the capability to promote the function of the gut-brain, microbiota-gut-brain axis, and brain. It will be possible to harness the gut microbiota to improve brain and mental health and prevent and treat related diseases in the future.

Intestinal Microbiota Composition in Sudden Infant Death Syndrome and Age-Matched Controls

OBJECTIVE

To assess whether features of the infant intestinal microbiome, including the carriage of toxigenic bacteria, are associated with sudden infant death syndrome (SIDS).

STUDY DESIGN

We undertook a case-controlled analysis of fecal microbiology in SIDS. Fecal material was obtained from 44 cases and 44 aged-matched controls. Microbiota composition was determined by 16S ribosomal RNA gene amplicon sequencing and comparisons between cases and controls made based on both bacterial alpha diversity measures and unconstrained ordination. Specific quantitative polymerase chain reaction assays were used to determine intestinal carriage of Staphylococcus aureus, toxigenic Clostridium difficile, and pathogenic and nonpathogenic Escherichia coli.

RESULTS

The microbial composition for the study population as a whole was consistent with previous studies of infants <12 months of age, with a correlation between alpha diversity and age (r² = 0.08; P = .007). However, no difference was observed in alpha diversity between SIDS cases and controls (P > .4). Nonmetric multidimensional scaling also revealed no evidence of differences in microbiota dispersal between SIDS cases and controls (P = .4, permutational multivariate ANOVA test; Pseudo-F = 0.9), nor was a difference observed in microbiota dispersion (P = .19, PERMDISP test; F = 1.9). There were no significant intergroup differences in the carriage of S aureus, toxigenic C difficile, total E coli, or pathogenic E coli.

CONCLUSIONS

We found no evidence of an association between altered intestinal microbiology and SIDS, or to support the development of strategies to reduce the incidence of SIDS that target intestinal microbiology.

New Insights in Anorexia Nervosa

Anorexia nervosa (AN) is classically defined as a condition in which an abnormally low body weight is associated with an intense fear of gaining weight and distorted cognitions regarding weight, shape, and drive for thinness. This article reviews recent evidences from physiology, genetics, epigenetics, and brain imaging which allow to consider AN as an abnormality of reward pathways or an attempt to preserve mental homeostasis. Special emphasis is put on ghrelino-resistance and the importance of orexigenic peptides of the lateral hypothalamus, the gut microbiota and a dysimmune disorder of neuropeptide signaling. Physiological processes, secondary to underlying, and premorbid vulnerability factors-the "pondero-nutritional-feeding basements"- are also discussed.

Contribution of microbiota to the intestinal physicochemical barrier

The large number of intestinal microorganisms, which exceeds the total number of human cells by ten folds, alludes to a significant contribution to human health. This is vivid in enteric and some systemic diseases emanating from disruption of the microbiota. As life style keeps shifting towards disruption of the microbiota in most societies worldwide, interest in the contribution of the microbiota to gut health has grown enormously. Many studies have been conducted to elucidate the exact contribution of the microbiota to human health. The knowledge gained from these studies indicates that the microbiota interacts with the intestinal milieu to maintain gut health. In this review, the crosstalk of microbiota with the intestinal physicochemical barrier pivotal to the gut innate immunity is highlighted. In particular, the review focuses on the role of the microbiota on competitive exclusion of pathogens, intestinal pH, epithelial mechanical barrier integrity, apical actin cytoskeleton, antimicrobial peptides, and the mucus layer. Understanding this microbe-host relationship will provide useful insight into overcoming some diseases related to the disruption of the host microbiota.

Precision respiratory medicine and the microbiome

A decade of rapid technological advances has provided an exciting opportunity to incorporate information relating to a range of potentially important disease determinants in the clinical decision-making process. Access to highly detailed data will enable respiratory medicine to evolve from one-size-fits-all models of care, which are associated with variable clinical effectiveness and high rates of side-effects, to precision approaches, where treatment is tailored to individual patients. The human microbiome has increasingly been recognised as playing an important part in determining disease course and response to treatment. Its inclusion in precision models of respiratory medicine, therefore, is essential. Analysis of the microbiome provides an opportunity to develop novel prognostic markers for airways disease, improve definition of clinical phenotypes, develop additional guidance to aid treatment selection, and increase the accuracy of indicators of treatment effect. In this Review we propose that collaboration between researchers and clinicians is needed if respiratory medicine is to replicate the successes of precision medicine seen in other clinical specialties.

Diversity of gut microflora is required for the generation of B cell with regulatory properties in a skin graft model

B cells have been reported to promote graft rejection through alloantibody production. However, there is growing evidence that B cells can contribute to the maintenance of tolerance. Here, we used a mouse model of MHC-class I mismatched skin transplantation to investigate the contribution of B cells to graft survival. We demonstrate that adoptive transfer of B cells prolongs skin graft survival but only when the B cells were isolated from mice housed in low sterility "conventional" (CV) facilities and not from mice housed in pathogen free facilities (SPF). However, prolongation of skin graft survival was lost when B cells were isolated from IL-10 deficient mice housed in CV facilities. The suppressive function of B cells isolated from mice housed in CV facilities correlated with an anti-inflammatory environment and with the presence of a different gut microflora compared to mice maintained in SPF facilities. Treatment of mice in the CV facility with antibiotics abrogated the regulatory capacity of B cells. Finally, we identified transitional B cells isolated from CV facilities as possessing the regulatory function. These findings demonstrate that B cells, and in particular transitional B cells, can promote prolongation of graft survival, a function dependent on licensing by gut microflora.

Harnessing the Microbiome to Enhance Cancer Immunotherapy

The microbiota plays a key role in regulating the innate and adaptive immune system. Herein, we review the immunological aspects of the microbiota in tumor immunity in mice and man, with a focus on toll-like receptor (TLR) agonists, vaccines, checkpoint modulators, chemotherapy, and adoptive T cell transfer (ACT) therapies. We propose innovative treatments that may safely harness the microbiota to enhance T cell-based therapies in cancer patients. Finally, we highlight recent developments in tumor immunotherapy, particularly novel ways to modulate the microbiome and memory T cell responses to human malignancies.

Effect of a protein-free diet in the development of food allergy and oral tolerance in BALB/c mice

The aim of the present study was to investigate the effect of a protein-free diet in the induction of food allergy and oral tolerance in BALB/c mice. The experimental model used was mice that were fed, since weaning up to adulthood, a balanced diet in which all dietary proteins were replaced by amino acid diet (Aa). The absence of dietary proteins did not prevent the development of food allergy to ovalbumin (OVA) in these mice. However, Aa-fed mice produced lower levels of IgE, secretory IgA and cytokines. In addition, when compared with mice from control group, Aa-fed mice had a milder aversive reaction to the allergen measured by consumption of OVA-containing solution and weight loss during food allergy development. In addition, mice that did not have dietary proteins in their diets were less susceptible to induction of oral tolerance. One single oral administration was not enough to suppress specific serum Ig and IgG1 levels in the Aa-fed group, although it was efficient to induce suppression in the control group. The present results indicate that the stimulation by dietary proteins alters both inflammatory reactivity and regulatory immune reactivity in mice probably due to their effect in the maturation of the immune system.

Immune and genetic gardening of the intestinal microbiome

The mucosal immune system - consisting of adaptive and innate immune cells as well as the epithelium - is profoundly influenced by its microbial environment. There is now growing evidence that the converse is also true, that the immune system shapes the composition of the intestinal microbiome. During conditions of health, this bidirectional interaction achieves a homeostasis in which inappropriate immune responses to non-pathogenic microbes are averted and immune activity suppresses blooms of potentially pathogenic microbes (pathobionts). Genetic alteration in immune/epithelial function can affect host gardening of the intestinal microbiome, contributing to the diversity of intestinal microbiota within a population and in some cases allowing for unfavorable microbial ecologies (dysbiosis) that confer disease susceptibility.

Alterations of gut barrier and gut microbiota in food restriction, food deprivation and protein-energy wasting

Increasing evidence shows that gut microbiota composition is related to changes of gut barrier function including gut permeability and immune function. Gut microbiota is different in obese compared to lean subjects, suggesting that gut microbes are also involved in energy metabolism and subsequent nutritional state. While research on gut microbiota and gut barrier has presently mostly focused on intestinal inflammatory bowel diseases and more recently on obesity and type 2 diabetes, this review aims at summarizing the present knowledge regarding the impact, in vivo, of depleted nutritional states on structure and function of the gut epithelium, the gut-associated lymphoid tissue (GALT), the gut microbiota and the enteric nervous system. It highlights the complex interactions between the components of gut barrier in depleted states due to food deprivation, food restriction and protein energy wasting and shows that these interactions are multidirectional, implying the existence of feedbacks.

Bacterial ClpB heat-shock protein, an antigen-mimetic of the anorexigenic peptide α-MSH, at the origin of eating disorders

The molecular mechanisms at the origin of eating disorders (EDs), including anorexia nervosa (AN), bulimia and binge-eating disorder (BED), are currently unknown. Previous data indicated that immunoglobulins (Igs) or autoantibodies (auto-Abs) reactive with α-melanocyte-stimulating hormone (α-MSH) are involved in regulation of feeding and emotion; however, the origin of such auto-Abs is unknown. Here, using proteomics, we identified ClpB heat-shock disaggregation chaperone protein of commensal gut bacteria Escherichia coli as a conformational antigen mimetic of α-MSH. We show that ClpB-immunized mice produce anti-ClpB IgG crossreactive with α-MSH, influencing food intake, body weight, anxiety and melanocortin receptor 4 signaling. Furthermore, chronic intragastric delivery of E. coli in mice decreased food intake and stimulated formation of ClpB- and α-MSH-reactive antibodies, while ClpB-deficient E. coli did not affect food intake or antibody levels. Finally, we show that plasma levels of anti-ClpB IgG crossreactive with α-MSH are increased in patients with AN, bulimia and BED, and that the ED Inventory-2 scores in ED patients correlate with anti-ClpB IgG and IgM, which is similar to our previous findings for α-MSH auto-Abs. In conclusion, this work shows that the bacterial ClpB protein, which is present in several commensal and pathogenic microorganisms, can be responsible for the production of auto-Abs crossreactive with α-MSH, associated with altered feeding and emotion in humans with ED. Our data suggest that ClpB-expressing gut microorganisms might be involved in the etiology of EDs.

The effects of the microbiota on the host immune system

The human gastrointestinal track harbors hundreds of species of commensal organisms, collectively known as microbiota. The composition of the intestinal microbiota is changeable by various factors, such as host genotype, diet, antibiotics, pathogen infections, among others. Changes in these factors can cause microbiome disruption known as dysbiosis, leading to the outgrowth of potential pathogenic bacteria or decrease in the number of beneficial bacteria. Dysbiosis has been implicated in numerous inflammatory and autoimmune diseases. This review is focused on host-microbiota interactions, specifically on influence of bacterial-derived signals on immune cell function and the mechanisms by which these signals modulate the development and progression of inflammatory and autoimmune diseases.

Intestinal microbiota and its effects on the immune system

The microbiota colonizes every surface exposed to the external world and in the gut, it plays important roles in physiological functions such as the maturation of the immune system, the degradation of complex food macromolecules and also behaviour. As such, the immune system has developed tools to cohabit with the microbiota, but also to keep it under control. When this control is lost, dysbiosis, i.e. deregulation in bacterial communities, can occur and this can lead to inflammatory disorders, including inflammatory bowel disease, obesity, diabetes and autism. For these reasons, the analysis of the microbiota, its interactions with the host and its composition in disease, have been intensively investigated in the last few years. In this review, we summarize the major findings in the interaction of the microbiota with the host immune system.

Effects of increase in fish oil intake on intestinal eicosanoids and inflammation in a mouse model of colitis

BACKGROUND

Inflammatory bowel diseases (IBD) are chronic intestinal inflammatory diseases affecting about 1% of western populations. New eating behaviors might contribute to the global emergence of IBD. Although the immunoregulatory effects of omega-3 fatty acids have been well characterized in vitro, their role in IBD is controversial.

METHODS

The aim of this study was to assess the impact of increased fish oil intake on colonic gene expression, eicosanoid metabolism and development of colitis in a mouse model of IBD. Rag-2 deficient mice were fed fish oil (FO) enriched in omega-3 fatty acids i.e. EPA and DHA or control diet for 4 weeks before colitis induction by adoptive transfer of naïve T cells and maintained in the same diet for 4 additional weeks. Onset of colitis was monitored by colonoscopy and further confirmed by immunological examinations. Whole genome expression profiling was made and eicosanoids were measured by HPLC-MS/MS in colonic samples.

RESULTS

A significant reduction of colonic proinflammatory eicosanoids in FO fed mice compared to control was observed. However, neither alteration of colonic gene expression signature nor reduction in IBD scores was observed under FO diet.

CONCLUSION

Thus, increased intake of dietary FO did not prevent experimental colitis.

Microbiome and immunological interactions

The healthy human gut supports a complex and diverse microbiota, dominated by bacterial phylotypes belonging to Bacteroidetes and Firmicutes. In the inflamed gut, overall diversity decreases, coincident with a greater representation of Proteobacteria. There is growing evidence supporting an important role for human gut bacteria in mucosal immunity; interactions at the level of both intestinal and colonic epithelial cells, dendritic cells, and T and B immune cells have been documented. These interactions influence gut barrier and defense mechanisms that include antimicrobial peptide and secretory IgA synthesis. The functional effects of commensal bacteria on T helper cell differentiation have led to the emerging concept that microbiota composition determines T effector- and T regulatory-cell balance, immune responsiveness, and homeostasis. The importance of this biology in relation to immune homeostasis, inflammatory bowel disease, and the rising incidence of autoimmune diseases will be discussed. The detailed description of the human gut microbiota, integrated with evidence-based mechanisms of immune modulation, provides an exciting platform for the identification of next-generation probiotics and related pharmaceutical products.

Proteomics at the interface of psychology, gut physiology and dysfunction: an underexploited approach that deserves expansion

Gut functions such as digestion and absorption are essential to life and the emerging insights into the gut-brain axis - that is, the cross talk between the enteric and CNS - point towards critical links between (eating) behavior, psychology, whole body and gut physiology, and digestive and overall health. While proteomics is ideally positioned to shed more light on these interactions, be it applied to the periphery (e.g., blood) or the locus of action (i.e., the gut), it is to date largely underexploited, mainly because of challenging sampling and tissue complexity. In view of the contrast between potential and current delivery of proteomics in the context of intestinal health, this article briefs the reader on the state-of-the-art of molecular intestinal research, reviews current proteomic studies (explicitly focusing on the most recent ones that target inflammatory bowel disease patient samples) and argues for an expansion of this research field.

The intestinal flora is required to support antibody responses to systemic immunization in infant and germ free mice

The presence of a complex and diverse intestinal flora is functionally important for regulating intestinal mucosal immune responses. However, the extent to which a balanced intestinal flora regulates systemic immune responses is still being defined. In order to specifically examine whether the acquisition of a less complex flora influences responses to immunization in the pre-weaning stages of life, we utilize a model in which infant mice acquire an intestinal flora from their mothers that has been altered by broad-spectrum antibiotics. In this model, pregnant dams are treated with a cocktail of antibiotics that alters both the density and microbial diversity of the intestinal flora. After challenge with a subcutaneous immunization, the antibiotic altered flora infant mice have lower antigen specific antibody titers compared to control age-matched mice. In a second model, we examined germ free (GF) mice to analyze how the complete lack of flora influences the ability to mount normal antibody responses following subcutaneous immunization. GF mice do not respond well to immunization and introduction of a normal flora into GF mice restores the capacity of these mice to respond. These results indicate that a gastrointestinal flora reduced in density and complexity at critical time points during development adversely impacts immune responses to systemic antigens.