Toll-like receptor 4 signaling by intestinal microbes influences susceptibility to food allergy

The journey toward disease modification in cow milk protein allergy

Cow milk protein allergy (CMPA) is one of the most common food allergies in the pediatric age worldwide. Prevalence, persistence, and severity of this condition are on the rise, with a negative impact on the health-related quality of life of the patients and families and on the costs related to its management. Another relevant issue is that CMPA in early life may be the first stage of the "allergic march," leading to the occurrence of other atopic manifestations later in life, especially asthma, atopic eczema, urticaria, and rhinoconjunctivitis. Thus, "disease modification" options that are able to modulate the disease course of pediatric patients affected by CMPA would be very welcomed by affected families and healthcare systems. In this review, we report the most relevant progress on this topic.

Non-Host Factors Influencing Onset and Severity of Celiac Disease

Celiac disease (CeD) is a chronic autoimmune condition driven by gluten ingestion in genetically predisposed individuals, resulting in inflammatory lesions in the proximal small intestine. Although the presence of specific HLA-linked haplotypes and gluten consumption are necessary for disease development, they alone do not account for the variable onset of CeD in susceptible individuals. This review explores the multifaceted role of non-host factors in CeD development, including dietary and microbial influences. We discuss clinical associations and observations highlighting the impact of these factors on disease onset and severity. Furthermore, we discuss studies in CeD-relevant animal models that offer mechanistic insights into how diet, the microbiome, and enteric infections modulate CeD pathogenesis. Finally, we address the clinical implications and therapeutic potential of understanding these cofactors offering a promising avenue for preventive and therapeutic interventions in CeD management.

A Lipopolysaccharide-Enriched Cow's Milk Allergy Microbiome Promotes a TLR4-Dependent Proinflammatory Intestinal Immune Response

We have previously reported that the gut microbiota of healthy infants harbors allergy-protective bacteria taxa that are depleted in infants with cow's milk allergy (CMA). Few reports have investigated the role of the gut microbiota in promoting allergic responses. In this study we selected a CMA-associated microbiota with increased abundance of Gram-negative bacteria for analysis of its proinflammatory potential. LPS is the major component of the outer membrane of Gram-negative bacteria. Colonization of mice with a global or conditional mutation of the LPS receptor TLR4 with this CMA microbiota induced expression of serum amyloid A1 (Saa1) and other Th17-, B cell-, and Th2-associated genes in the ileal epithelium in a TLR4-dependent manner. In agreement with the gene expression data, mice colonized with the CMA microbiota have expanded populations of Th17 and regulatory T cells and elevated concentrations of fecal IgA. Importantly, we used both antibiotic-treated specific pathogen-free and germ-free rederived mice with a conditional mutation of TLR4 in the CD11c+ compartment to demonstrate that the induction of proinflammatory genes, fecal IgA, and Th17 cells is dependent on TLR4 signaling. Furthermore, metagenomic sequencing revealed that the CMA microbiota has an increased abundance of LPS biosynthesis genes. Taken together, our results show that a microbiota displaying a higher abundance of LPS genes is associated with TLR4-dependent proinflammatory gene expression and a mixed type 2/type 3 response in mice, which may be characteristic of a subset of infants with CMA.

Effects of Varied Sulfamethazine Dosage and Exposure Durations on Offspring Mice

The development of antibiotics was a turning point in the history of medicine; however, their misuse and overuse have contributed to the current global epidemic of antibiotic resistance. According to epidemiological studies, early antibiotic exposure increases the risk of immunological and metabolic disorders. This study investigated the effects of exposure to different doses of sulfamethazine (SMZ) on offspring mice and compared the effects of exposure to SMZ on offspring mice in prenatal and early postnatal periods and continuous periods. Furthermore, the effects of SMZ exposure on the gut microbiota of offspring mice were analyzed using metagenome. According to the results, continuous exposure to high-dose SMZ caused weight gain in mice. IL-6, IL-17A, and IL-10 levels in the female offspring significantly increased after high-dose SMZ exposure. In addition, there was a significant gender difference in the impact of SMZ exposure on the gut microbiota of offspring: Continuous high-dose SMZ exposure significantly decreased the relative abundance of Ligilactobacillus murinus, Limosilactobacillus reuteri, Lactobacillus johnsonii, and Bifidobacterium pseudolongum (p < 0.05) in female offspring mice; however, these significant changes were not observed in male offspring mice.

What we need to know about the germ-free animal models

The gut microbiota (GM), as a forgotten organ, refers to the microbial community that resides in the gastrointestinal tract and plays a critical role in a variety of physiological activities in different body organs. The GM affects its targets through neurological, metabolic, immune, and endocrine pathways. The GM is a dynamic system for which exogenous and endogenous factors have negative or positive effects on its density and composition. Since the mid-twentieth century, laboratory animals are known as the major tools for preclinical research; however, each model has its own limitations. So far, two main models have been used to explore the effects of the GM under normal and abnormal conditions: the isolated germ-free and antibiotic-treated models. Both methods have strengths and weaknesses. In many fields of host-microbe interactions, research on these animal models are known as appropriate experimental subjects that enable investigators to directly assess the role of the microbiota on all features of physiology. These animal models present biological model systems to either study outcomes of the absence of microbes, or to verify the effects of colonization with specific and known microbial species. This paper reviews these current approaches and gives advantages and disadvantages of both models.

Complex interplay of gut microbiota between obesity and asthma in children

Obesity is an important risk factor and common comorbidity of childhood asthma. Simultaneously, obesity-related asthma, a distinct asthma phenotype, has attracted significant attention owing to its association with more severe clinical manifestations, poorer disease control, and reduced quality of life. The establishment of the gut microbiota during early life is essential for maintaining metabolic balance and fostering the development of the immune system in children. Microbial dysbiosis influences host lipid metabolism, triggers chronic low-grade inflammation, and affects immune responses. It is intimately linked to the susceptibility to childhood obesity and asthma and plays a potentially crucial transitional role in the progression of obesity-related asthma. This review article summarizes the latest research on the interplay between asthma and obesity, with a particular focus on the mediating role of gut microbiota in the pathogenesis of obesity-related asthma. This study aims to provide valuable insight to enhance our understanding of this condition and offer preliminary evidence to support the development of therapeutic interventions.

Commensal bacteria signal through TLR5 and AhR to improve barrier integrity and prevent allergic responses to food

The increasing prevalence of food allergies has been linked to reduced commensal microbial diversity. In this article, we describe two features of allergy-protective Clostridia that contribute to their beneficial effects. Some Clostridial taxa bear flagella (a ligand for TLR5) and produce indole (a ligand for the aryl hydrocarbon receptor [AhR]). Lysates and flagella from a Clostridia consortium induced interleukin-22 (IL-22) secretion from ileal explants. IL-22 production is abrogated in explants from mice in which TLR5 or MyD88 signaling is deficient either globally or conditionally in CD11c+ antigen-presenting cells. AhR signaling in RORγt+ cells is necessary for the induction of IL-22. Mice deficient in AhR in RORγt+ cells exhibit increased intestinal permeability and are more susceptible to an anaphylactic response to food. Our findings implicate TLR5 and AhR signaling in a molecular mechanism by which commensal Clostridia protect against allergic responses to food.

Treatment of peanut allergy and colitis in mice via the intestinal release of butyrate from polymeric micelles

The microbiome modulates host immunity and aids the maintenance of tolerance in the gut, where microbial and food-derived antigens are abundant. Yet modern dietary factors and the excessive use of antibiotics have contributed to the rising incidence of food allergies, inflammatory bowel disease and other non-communicable chronic diseases associated with the depletion of beneficial taxa, including butyrate-producing Clostridia. Here we show that intragastrically delivered neutral and negatively charged polymeric micelles releasing butyrate in different regions of the intestinal tract restore barrier-protective responses in mouse models of colitis and of peanut allergy. Treatment with the butyrate-releasing micelles increased the abundance of butyrate-producing taxa in Clostridium cluster XIVa, protected mice from an anaphylactic reaction to a peanut challenge and reduced disease severity in a T-cell-transfer model of colitis. By restoring microbial and mucosal homoeostasis, butyrate-releasing micelles may function as an antigen-agnostic approach for the treatment of allergic and inflammatory diseases.

Pentraxin 3 Facilitates Shrimp-Allergic Responses in IgE-Activated Mast Cells

Background. Since food avoidance is currently the only way to prevent allergic reactions to shrimp, a better understanding of molecular events in the induction and progression of allergy, including food allergy, is needed for developing strategies to inhibit allergic responses. Pentraxin 3 (PTX3) is rapidly produced directly from inflammatory or damaged tissues and is involved in acute immunoinflammatory responses. However, the role of PTX3 in the development of immediate IgE-mediated shrimp allergy remains unknown. Methods. Wild-type BALB/c mice were immunized intraperitoneally and were challenged with shrimp extract. Serum IgE and PTX3 levels were analyzed. RBL-2H3 cells were stimulated with either dinitrophenyl (DNP) or serum of shrimp-allergic mice, and markers of degranulation, proinflammatory mediators, and phosphorylation of signal proteins were analyzed. We further examined the effect of PTX3 in shrimp extract-induced allergic responses in vitro and in vivo. Results. Mice with shrimp allergy had increased PTX3 levels in the serum and small intestine compared with healthy mice. PTX3 augmented degranulation, the production of proinflammatory mediators, and activation of the Akt and MAPK signaling pathways in mast cells upon DNP stimulation. Furthermore, the expression of transcription factor CCAAT/enhancer-binding protein delta (CEBPD) was elevated in PTX3-mediated mast cell activation. Finally, the PTX3 inhibitor RI37 could attenuate PTX3-induced degranulation, proinflammatory mediator expression, and phosphorylation of the Akt and MAPK signaling. Conclusions. The results suggested that PTX3 can facilitate allergic responses. Our data provide new insight to demonstrate that PTX3 is a cause of allergic inflammation and that RI37 can serve as a therapeutic agent in shrimp allergy.

Manipulating the microbiome to enhance oral tolerance in food allergy

Loss of oral tolerance (OT) to food antigens results in food allergies. One component of achieving OT is the symbiotic microorganisms living in the gut (microbiota). The composition of the microbiota can drive either pro-tolerogenic or pro-inflammatory responses against dietary antigens though interactions with the local immune cells within the gut. Products from bacterial fermentation, such as butyrate, are one of the main communication molecules involved in this interaction, however, this is released by a subset of bacterial species. Thus, strategies to specifically expand these bacteria with protolerogenic properties have been explored to complement oral immunotherapy in food allergy. These approaches either provide digestible biomolecules to induce beneficial bacteria species (prebiotics) or the direct administration of live bacteria species (probiotics). While this combined therapy has shown positive outcomes in clinical trials for cow's milk allergy, more research is needed to determine if this therapy can be extended to other food allergens.

The Role of the Gut Microbiome in Cow's Milk Allergy: A Clinical Approach

Cow's milk allergy (CMA) is the most prevalent food allergy (FA) in infancy and early childhood and can be present with various clinical phenotypes. The significant increase in FA rates recorded in recent decades has been associated with environmental and lifestyle changes that limit microbial exposure in early life and induce changes in gut microbiome composition. Gut microbiome is a diverse community of microbes that colonize the gastrointestinal tract (GIT) and perform beneficial functions for the host. This complex ecosystem interacts with the immune system and has a pivotal role in the development of oral tolerance to food antigens. Emerging evidence indicates that alterations of the gut microbiome (dysbiosis) in early life cause immune dysregulation and render the host susceptible to immune-mediated diseases later in life. Therefore, the colonization of the gut by "healthy" microbes that occurs in the first years of life determines the lifelong health of the host. Here, we present current data on the possible role of the gut microbiome in the development of CMA. Furthermore, we discuss how gut microbiome modification might be a potential strategy for CMA prevention and treatment.

Bifidobacterium animalis KV9 and Lactobacillus vaginalis FN3 alleviated β-lactoglobulin-induced allergy by modulating dendritic cells in mice

Food allergy is a serious public health problem because of its high incidence and risk. Probiotics can induce immune regulation in patients with allergic diseases, but its mechanism is not fully clear. In this paper, β-lactoglobulin (β-LG)-sensitized mice were used as models to explore the mechanism of Bifidobacterium animalis KV9 (KV9) and Lactobacillus vaginalis FN3 (FN3) on reducing allergic reactions and regulating immune cell function. The results showed that oral administration of KV9 and FN3 significantly reduced the scores of allergic symptoms, hypothermia symptoms, and serum levels of β-LG-specific immunoglobulins E (β-LG-sIgE), histamine, and mast cell protease in allergic mice. Flow cytometry analysis of intestinal dendritic cells (DCs) showed that the proportion of CD11c+major histocompatibility complex (MHC)-II+DCs, CD11c+CD80+DCs, and CD11c+ CD86+DCs increased after KV9 and FN3 intervention, indicating that the strains induced immature DCs and decreased the antigen-presenting capacity of DCs. Meanwhile, the toll-like receptor 4 (TLR4)-NF-κB signaling pathway was activated in DCs. The secretion of interleukin-12 (IL-12) was significantly increased, while interleukin-4 (IL-4) was decreased by DCs after KV9 and FN3 intervention, indicating that DCs have the potential to promote T-cell differentiation into T helper type 1 (Th1) cells. Furthermore, the proportion of CD3+CD8−IFN-γ+ T cells in the spleen increased, while CD3+CD8−IL-4+T cells decreased after oral administration of KV9 and FN3, correcting the T helper type 2 (Th2)-skewed immune responses. These results indicate that KV9 and FN3 reduce β-LG-induced allergic symptoms in mice, and suggest that the two potential probiotics might be used as an alternative therapeutic agent for mitigating food allergy.

Lipopolysaccharide-Induced Immunological Tolerance in Monocyte-Derived Dendritic Cells

Bacterial lipopolysaccharides (LPS), also referred to as endotoxins, are major outer surface membrane components present on almost all Gram-negative bacteria and are major determinants of sepsis-related clinical complications including septic shock. LPS acts as a strong stimulator of innate or natural immunity in a wide variety of eukaryotic species ranging from insects to humans including specific effects on the adaptive immune system. However, following immune stimulation, lipopolysaccharide can induce tolerance which is an essential immune-homeostatic response that prevents overactivation of the inflammatory response. The tolerance induced by LPS is a state of reduced immune responsiveness due to persistent and repeated challenges, resulting in decreased expression of pro-inflammatory modulators and up-regulation of antimicrobials and other mediators that promote a reduction of inflammation. The presence of environmental-derived LPS may play a key role in decreasing autoimmune diseases and gut tolerance to the plethora of ingested antigens. The use of LPS may be an important immune adjuvant as demonstrated by the promotion of IDO1 increase when present in the fusion protein complex of CTB-INS (a chimera of the cholera toxin B subunit linked to proinsulin) that inhibits human monocyte-derived DC (moDC) activation, which may act through an IDO1-dependent pathway. The resultant state of DC tolerance can be further enhanced by the presence of residual E. coli lipopolysaccharide (LPS) which is almost always present in partially purified CTB-INS preparations. The approach to using an adjuvant with an autoantigen in immunotherapy promises effective treatment for devastating tissue-specific autoimmune diseases like multiple sclerosis (MS) and type 1 diabetes (T1D).

The modulation and mechanism of probiotic-derived polysaccharide capsules on the immune response in allergic diseases

Allergic diseases, derived from the dysregulation of immune tolerance mechanisms, have been rising in the last two decades. Recently, increasing evidence has shown that probiotic-derived polysaccharide capsules exhibit a protective effect against allergic diseases, involving regulation of Th1/Th2 balance, induction of differentiation of T regulatory cells and activation of dendritic cells (DCs). DCs have a central role in controlling the immune response through their interaction with gut microbiota via their pattern recognition receptors, including Toll-like receptors and C-type-lectin receptors. This review discusses the effects and critical mechanism of probiotic-derived polysaccharide capsules in regulating the immune system to alleviate allergic diseases. We first describe the development of immune response in allergic diseases and recent relevant findings. Particular emphasis is placed on the effects of probiotic-derived polysaccharide capsules on allergic immune response. Then, we discuss the underlying mechanism of the impact of probiotic-derived polysaccharide capsules on DCs-mediated immune tolerance induction.

Amoxicillin does not affect the development of cow’s milk allergy in a Brown Norway rat model

The use of antibiotics as well as changes in the gut microbiota have been linked to development of food allergy in childhood. It remains unknown whether administration of a single clinically relevant antibiotic directly promotes food allergy development when administrated during the sensitisation phase in an experimental animal model. We investigated whether the antibiotic amoxicillin affected gut microbiota composition, development of cow's milk allergy (CMA) and frequencies of allergic effector cells and regulatory T cells in the intestine. Brown Norway rats were given daily oral gavages of amoxicillin for six weeks and whey protein concentrate (WPC) with or without cholera toxin three times per week for the last five weeks. Microbiota composition in faeces and small intestine was analysed by 16S rRNA sequencing. The development of CMA was assessed by WPC‐specific IgE in serum, ear swelling response to WPC and body hypothermia following oral gavage of WPC. Allergic effector cells were analysed by histology, and frequencies of regulatory and activated T cells were analysed by flow cytometry. Amoxicillin administration reduced faecal microbiota diversity, reduced the relative abundance of Firmicutes and increased the abundance of Bacteroidetes and Proteobacteria. Despite these effects, amoxicillin did not affect the development of CMA, nor the frequencies of allergic effector cells or regulatory T cells. Thus, amoxicillin does not carry a direct risk for food allergy development when administrated in an experimental model of allergic sensitisation to WPC via the gut. This finding suggests that confounding factors may better explain the epidemiological link between antibiotic use and food allergy.

Oral anaphylaxis to peanut in a mouse model is associated with gut permeability but not with Tlr4 or Dock8 mutations

BACKGROUND

The etiology of food allergy is poorly understood; mouse models are powerful systems to discover immunologic pathways driving allergic disease. C3H/HeJ mice are a widely used model for the study of peanut allergy because, unlike C57BL/6 or BALB/c mice, they are highly susceptible to oral anaphylaxis. However, the immunologic mechanism of this strain's susceptibility is not known.

OBJECTIVE

We aimed to determine the mechanism underlying the unique susceptibility to anaphylaxis in C3H/HeJ mice. We tested the role of deleterious Toll-like receptor 4 (Tlr4) or dedicator of cytokinesis 8 (Dock8) mutations in this strain because both genes have been associated with food allergy.

METHODS

We generated C3H/HeJ mice with corrected Dock8 or Tlr4 alleles and sensitized and challenged them with peanut. We then characterized the antibody response to sensitization, anaphylaxis response to both oral and systemic peanut challenge, gut microbiome, and biomarkers of gut permeability.

RESULTS

In contrast to C3H/HeJ mice, C57BL/6 mice were resistant to anaphylaxis after oral peanut challenge; however, both strains undergo anaphylaxis with intraperitoneal challenge. Restoring Tlr4 or Dock8 function in C3H/HeJ mice did not protect from anaphylaxis. Instead, we discovered enhanced gut permeability resulting in ingested allergens in the bloodstream in C3H/HeJ mice compared to C57BL/6 mice, which correlated with an increased number of goblet cells in the small intestine.

CONCLUSIONS

Our work highlights the potential importance of gut permeability in driving anaphylaxis to ingested food allergens; it also indicates that genetic loci outside of Tlr4 and Dock8 are responsible for the oral anaphylactic susceptibility of C3H/HeJ mice.

Baby's skin bacteria: first impressions are long-lasting

Early life is a dynamic period for skin microbial colonization and immune development. We postulate that microbial exposures in this period durably alter the skin immune trajectory and later disease susceptibility. Bacteria contribute to infant skin immune imprinting via interactions with microbes as well as with cutaneous epithelial and immune cells. Excellent research is underway at the skin microbiome-immune interface, both in deciphering basic mechanisms and implementing their therapeutic applications. As emphasized herein, focusing on the unique opportunities and challenges presented by microbial immune modulation in early life will be important. In our view, only through dedicated study of skin-microbe crosstalk in this developmental window can we elucidate the molecular underpinnings of pivotal events that contribute to sustained host-microbe symbiosis.

Partially Hydrolysed Whey Has Superior Allergy Preventive Capacity Compared to Intact Whey Regardless of Amoxicillin Administration in Brown Norway Rats

Background

It remains largely unknown how physicochemical properties of hydrolysed infant formulas influence their allergy preventive capacity, and results from clinical and animal studies comparing the preventive capacity of hydrolysed infant formula with conventional infant formula are inconclusive. Thus, the use of hydrolysed infant formula for allergy prevention in atopy-prone infants is highly debated. Furthermore, knowledge on how gut microbiota influences allergy prevention remains scarce.

Objective

To gain knowledge on (1) how physicochemical properties of hydrolysed whey products influence the allergy preventive capacity, (2) whether host microbiota disturbance influences allergy prevention, and (3) to what extent hydrolysed whey products influence gut microbiota composition.

Methods

The preventive capacity of four different ad libitum administered whey products was investigated in Brown Norway rats with either a conventional or an amoxicillin-disturbed gut microbiota. The preventive capacity of products was evaluated as the capacity to reduce whey-specific sensitisation and allergic reactions to intact whey after intraperitoneal post-immunisations with intact whey. Additionally, the direct effect of the whey products on the growth of gut bacteria derived from healthy human infant donors was evaluated by in vitro incubation.

Results

Two partially hydrolysed whey products with different physicochemical characteristics were found to be superior in preventing whey-specific sensitisation compared to intact and extensively hydrolysed whey products. Daily oral amoxicillin administration, initiated one week prior to intervention with whey products, disturbed the gut microbiota but did not impair the prevention of whey-specific sensitisation. The in vitro incubation of infant faecal samples with whey products indicated that partially hydrolysed whey products might confer a selective advantage to enterococci.

Conclusions

Our results support the use of partially hydrolysed whey products for prevention of cow’s milk allergy in atopy-predisposed infants regardless of their microbiota status. However, possible direct effects of partially hydrolysed whey products on gut microbiota composition warrants further investigation.

The human milk oligosaccharide 2'-fucosyllactose attenuates β-lactoglobulin-induced food allergy through the miR-146a-mediated toll-like receptor 4/nuclear factor-κB signaling pathway

Our previous experiments have confirmed that human milk oligosaccharides (HMO) and its main component 2'-fucosyllactose (2'-FL), as prebiotics, could effectively alleviate cow milk allergy by regulating the intestinal microecology. This study intended to further explore the molecular mechanism of HMO regulating intestinal immunity. The results of the allergic mouse model showed that oral administration of 2'-FL or HMO reduced β-lactoglobulin (β-LG)-induced serum-specific IgE secretion and mast cell degranulation, while reducing the inflammatory cytokines, TNF-α, IL-4, and IL-6 production and promoting the miR-146a expression. In vitro results further confirmed that 2'-FL or HMO treatment reduced allergen-induced secretion of iNOS, NO, pro-inflammatory cytokines and reactive oxygen species in RAW264.7 cells. At the same time, in contrast to the β-LG group, 2'-FL dose-dependently inhibited the TLR4/NF-κB inflammatory pathway and upregulated miR-146a expression, and the effect of the 2'-FL mid-dose group was similar to that of the HMO intervention group. In particular, adding miR-146a inhibitors to macrophages attenuated the inhibitory effect of 2'-FL on the expression of TRAF6 and IRAKI in the TLR4 pathway, suggesting that miR-146a might be involved in the immune regulation of 2'-FL. The above results indicated that 2'-FL had a similar effect to HMOs, and its effect of reducing β-LG allergy might be related to the regulation of miR-146a to inhibit TLR4/NF-κB signaling pathway.

Emerging role of nutritional short-chain fatty acids (SCFAs) against cancer via modulation of hematopoiesis

The understanding of gut microbiota has emerged as a significant frontier in development of strategies to maintain normal human body's homeostasis and preventing the disease development over the last decade. The composition of the gut microbiota influences the clinical benefit of immune checkpoints in patients with advanced cancer, but the mechanisms underlying this relationship are unclear. Cancer is among the leading causes of mortality worldwide. So far, there is no universal treatment for cancer and despite significant advances, a lot of improvement on cancer therapy is required. Owing to its role in preserving the host's health and maintaining cellular integrity, the human gut microbiome has recently drawn a lot of interest as a target for cancer treatment. Dietary fiber is fermented by the gut microbiota to generate short-chain fatty acids (SCFAs), such as acetate, butyrate, and propionate, which are physiologically active metabolites. SCFAs can modulate the pathophysiology of the tumor environment through various critical signaling pathways. In addition, SCFAs can bind to carcinogens and other toxic chemicals, thus facilitating their biotransformation and elimination through different excretory mechanisms. This review discusses the mechanisms of action of short-chain fatty acids in modulating hematopoiesis of various immune system cells and the resultant beneficial anti-cancer effects. It also provides future perspectives on cancer therapy.

Gut Microbiota, Probiotics, and Their Interactions in Prevention and Treatment of Atopic Dermatitis: A Review

Atopic dermatitis (AD) is a public health concern and is increasing in prevalence in urban areas. Recent advances in sequencing technology have demonstrated that the development of AD not only associate with the skin microbiome but gut microbiota. Gut microbiota plays an important role in allergic diseases including AD. The hypothesis of the “gut-skin” axis has been proposed and the cross-talk mechanism between them has been gradually demonstrated in the research. Probiotics contribute to the improvement of the intestinal environment, the balance of immune responses, regulation of metabolic activity. Most studies suggest that probiotic supplements may be an alternative for the prevention and treatment of AD. This study aimed to discuss the effects of probiotics on the clinical manifestation of AD based on gut microbial alterations. Here we reviewed the gut microbial alteration in patients with AD, the association between gut microbiota, epidermal barrier, and toll-like receptors, and the interaction of probiotics and gut microbiota. The potential mechanisms of probiotics on alleviating AD via upregulation of epidermal barrier and regulation of immune signaling had been discussed, and their possible effective substances on AD had been explored. This provides the supports for targeting gut microbiota to attenuate AD.

Role of innate immunity and myeloid cells in susceptibility to allergic disease

Allergic diseases, including asthma, food allergy, eczema, and allergic rhinitis, are common diseases increasing in prevalence. Allergy, a failure of immune tolerance to innocuous environmental allergens, is characterized by allergen-specific immune responses, including IgE antibodies and T helper and T follicular helper cells producing type 2 cytokines. Despite the central role of adaptive immunity in pathophysiology of allergy, there is a growing body of evidence indicating an important role for the innate immune system in allergic disease. In this review, we focus on epithelial-mononuclear phagocyte communication in the control of allergy and tolerance. We discuss studies on early life environmental exposures and allergy susceptibility, and the evidence for innate training of mononuclear phagocytes as the mechanistic link between exposure and health or disease.

Probiotics in food allergy

PURPOSE OF REVIEW

To perform a nonsystematic review of the literature on the possible role of probiotics for food allergy (FA).

RECENT FINDINGS

Animal model and in vitro evidence suggest that the gut microbiome could protect against FA and that probiotics could be a valid instrument. There is no consistent evidence in identifying the specific species, the dosage, and the optimal duration to obtain the correct immunomodulation. Early life supplementation with specific 'missing' immunomodulatory microbes - derived from machine learning approach to birth cohort studies - might represent a novel approach to the primary prevention of multiple human atopic diseases. However, further studies are needed.

SUMMARY

Currently, there is no positive recommendation from the main scientific societies to use probiotics neither for the treatment nor for the prevention of FA.

Vaccines as therapies for food allergies

Food allergy is a growing public health epidemic with few available treatments beyond allergen avoidance and rescue medications for accidental exposures. A major focus of therapeutic development for food allergies is allergen-specific immunotherapy (AIT) in which patients are exposed to increasing amounts of allergen in controlled dosing to induce desensitization or tolerance. The work of the past few decades has culminated in the recent FDA approval of a peanut product for oral AIT for peanut allergies. Despite these advances, current AIT protocols are cumbersome, take a long time to reach clinical benefit and often have significant side effects. Therefore, there is a great need to develop new therapeutics for food allergy. One area of research aims to improve AIT through the use of adjuvants which are substances traditionally added to vaccines to stimulate or direct a specific immune response. Adjuvants that induce Th1-polarized and regulatory immune responses while suppressing Th2 immunity have shown the most promise in animal models. The addition of adjuvants to AIT may reduce the amount and frequency of allergen required to achieve clinical benefit and may induce more long-lasting immune responses. In this chapter, we highlight examples of adjuvanted AIT and vaccines in development to treat food allergies.

Post-translational suppression of the high affinity IgE receptor expression on mast cells by an intestinal bacterium

Mast cells, which express the high-affinity IgE receptor (FcεRI) on their surface, play a crucial role in inducing allergic inflammation. Since mast cells are activated by crosslinking of FcεRI with IgE and allergens, the cell surface expression level of FcεRI is an important factor in determining the sensitivity to allergens. Recently, the involvement of gut microbiota in the prevalence and regulation of allergy has attracted attention but the precise underlying mechanisms are not fully understood. In this study, the effect of intestinal bacteria on cell surface expression of FcεRI was examined. Bacteroides acidifaciens type A 43 specifically suppressed cell surface expression of FcεRI on mouse bone marrow-derived mast cells (BMMCs) without reduction in FcεRI α and β-chain mRNA and total protein expression. The suppressive effect required sustained exposure to this bacterium, with a corresponding reduction in Erk activation. Inhibition of Erk decreased cell surface distribution of FcεRI in BMMCs, at least in part, through facilitated endocytosis of FcεRI. These results indicate that B. acidifaciens type A 43 suppresses cell surface expression of FcεRI on mast cells in a post-translational manner via inhibition of Erk. The suppression of FcεRI expression on mast cells by specific bacteria might be the underlying mechanism involved in the regulation of allergy by gut microbiota.

Low-Dose Exposure to Ganglioside-Mimicking Bacteria Tolerizes Human Macrophages to Guillain-Barré Syndrome-Associated Antigens

Early in life, commensal bacteria play a major role in immune development, helping to guide the host response toward harmful stimuli while tolerating harmless antigens to prevent autoimmunity. Guillain-Barré syndrome (GBS) is an autoimmune disease caused by errant immune attack of antibody-bound ganglioside receptors on host nerve cells, resulting in paralysis. Lipooligosaccharides enveloping the prevalent enteric pathogen, Campylobacter jejuni, frequently mimic human gangliosides and can trigger GBS by stimulating the autoimmune response. In low- to middle-income countries, young children are consistently exposed to C. jejuni, and it is not known if this impacts GBS susceptibility later in life. Using a macrophage model, we examined the effect of training these cells with low doses of ganglioside-mimicking bacteria prior to challenge with GBS-associated antigens. This training caused decreased production of proinflammatory cytokines, suggesting tolerance induction. We then screened Campylobacter isolates from 154 infant fecal samples for GM1 ganglioside mimicry, finding that 23.4% of strains from both symptomatic and asymptomatic infants displayed GM1-like structures. Training macrophages with one of these asymptomatic carrier isolates also induced tolerance against GBS-associated antigens, supporting that children can be exposed to the tolerizing antigen early in life. RNA interference of Toll-like receptor 2 (TLR2) and TLR4 suggests that these receptors are not involved in tolerance associated with decreases in tumor necrosis factor (TNF), interleukin-6 (IL-6), or IL-1β levels. The results of this study suggest that exposure to ganglioside-mimicking bacteria early in life occurs naturally and impacts host susceptibility to GBS development. IMPORTANCE In this study, we demonstrated that it is possible to tolerize immune cells to potentially dampen the autoreactive proinflammatory immune response against Guillain-Barré syndrome (GBS)-associated antigens. The innate immune response functions to arm the host against bacterial attack, but it can be tricked into recognizing the host's own cells when infectious bacteria display sugar structures that mimic human glycans. It is this errant response that leads to the autoimmunity and paralysis associated with GBS. By presenting immune cells with small amounts of the bacterial glycan mimic, we were able to suppress the proinflammatory immune response upon subsequent high exposure to glycan-mimicking bacteria. This suggests that individuals who have already been exposed to the glycan mimics in small amounts are less sensitive to autoimmune reactions against these glycans, and this could be a factor in determining susceptibility to GBS.

Changes in inflammatory factors in the Brown Norway rat model of food allergy

BACKGROUND

The role of serum S100A8/A9 in intestinal inflammation has been confirmed, and its role in food allergy is currently being investigated.

OBJECTIVE

To explore the levels of S100A8/A9 and inflammatory factors, including Toll-like receptors 4 (TLR4), Nuclear transcription factors (NF-κB) and Tumor necrosis factor α (TNF-α), in mild food allergies.

METHODS

Eighty 3-week-old male Brown Norway rats were used. Forty rats were randomly assigned to the ovalbumin-sensitized experimental group, while 40 rats were assigned to the normal saline sham-sensitized control group. Body weight and length and the levels of serum ovalbumin-specific IgE (OVA-IgE), histamine, Th1-associated and Th2-associated factors, S100A8/A9 and inflammation-associated cytokines were compared.

RESULTS

Through the evaluation of OVA-IgE level and Th1/Th2 balance in the experimental group, a successful IgE-mediated food allergy model was constructed. Compared with the control group, the experimental group had higher serum S100A8/A9 levels on days 21, 28, 35 and 42 (all P < 0.05); higher TLR4 levels on days 28, 35 and 42 (all P < 0.05); higher TNF-α levels on days 28, 35 and 42 (all P < 0.05); higher NF-κB levels on days 35 and 42 (all P < 0.05); and higher IL-1β and IL-6 levels on days 7 to 42 (all P < 0.05). Moreover, positive correlations were found between the serum levels of S100A8/A9 and inflammation-associated cytokines [TNF-α: r = 0.378, P = 0.039; IL-1β: r = 0.679, P = 0.000; IL-6: r = 0.590, P = 0.001].

CONCLUSION

S100A8/A9 and inflammatory-related factors, including TLR4, NF-κB, TNF-α, IL-6 and IL-1β, is closely related to food allergies. Moreover, immune and inflammatory factors interact with each other in food allergies, which may provide insight into food allergy causes and treatments.

B cells and the microbiota: a missing connection in food allergy

Food allergies are a major public health concern due to their widespread and rising prevalence. The increase in food allergy is partially due to Western lifestyle habits which deplete protective commensal microbiota. These microbial perturbations can result in adverse host-microbe interactions, altering the phenotype of various immune cells and instigating allergic sensitization. Although B cells are critical to allergic pathology, microbial influences on B cells have been somewhat overlooked. Here, we focus on direct and indirect interactions between bacteria and B cells and how such interactions regulate B-cell phenotype, namely antibody production (IgA, IgE, IgG1, and IgG4) and regulatory B-cell (Breg) function. Understanding how microbes modulate B-cell activity in the context of food allergies is critical to both tracing the development of disease and assessing future treatment options.

Applications of Mouse Models to the Study of Food Allergy

Mouse models of allergic disease offer numerous advantages when compared to the models of other animals. However, selection of appropriate mouse models is critical to advance the field of food allergy by revealing mechanisms of allergy and for testing novel therapeutic approaches. All current mouse models for food allergy have weaknesses that may limit their applicability to human disease. Aspects such as the genetic predisposition to allergy or tolerance from the strain of mouse used, allergen dose, route of exposure (oral, intranasal, intraperitoneal, or epicutaneous), damage of the epithelial barrier, use of adjuvants, food matrix effects, or composition of the microbiota should be considered prior to the selection of a specific murine model and contemplated according to the intended purpose of the study. This chapter reviews our current knowledge on the application of mouse models to food allergy research and the variables that may influence the successful development of each type of model.

Antibiotic-induced gut dysbiosis and barrier disruption and the potential protective strategies

The oral antibiotic therapies administered widely to people and animals can cause gut dysbiosis and barrier disruption inevitably. Increasing attention has been directed toward antibiotic-induced gut dysbiosis, which involves a loss of diversity, changes in the abundances of certain taxa and consequent effects on their metabolic capacity, and the spread of antibiotic-resistant bacterial strains. Treatment with beta-lactam, glycopeptide, and macrolide antibiotics is associated with the depletion of beneficial commensal bacteria in the genera Bifidobacterium and Lactobacillus. The gut microbiota is a reservoir for antibiotic resistance genes, the prevalence of which increases sharply after antibiotic ingestion. The intestinal barrier, which comprises secretory, physical, and immunological barriers, is also a target of antibiotics. Antibiotic induced changes in the gut microbiota composition could induce weakening of the gut barrier through changes in mucin, cytokine, and antimicrobial peptide production by intestinal epithelial cells. Reports have indicated that dietary interventions involving prebiotics, probiotics, omega-3 fatty acids, and butyrate supplementation, as well as fecal microbiota transplantation, can alleviate antibiotic-induced gut dysbiosis and barrier injuries. This review summarizes the characteristics of antibiotic-associated gut dysbiosis and barrier disruption, as well as the strategies for alleviating this condition. This information is intended to provide a foundation for the exploration of safer, more efficient, and affordable strategies to prevent or relieve antibiotic-induced gut injuries.

Gut Microbiome Modulation for Preventing and Treating Pediatric Food Allergies

The increasing prevalence and severity of pediatric food allergies (FA) demands innovative preventive and therapeutic strategies. Emerging evidence suggests a pivotal role for the gut microbiome in modulating susceptibility to FA. Studies have demonstrated that alteration of gut microbiome could precede FA, and that particular microbial community structures early in life could influence also the disease course. The identification of gut microbiome features in pediatric FA patients is driving new prevention and treatment approaches. This review is focused on the potential role of the gut microbiome as a target for FA prevention and treatment.

B Cell Responses in the Development of Mammalian Meat Allergy

Studies of meat allergic patients have shown that eating meat poses a serious acute health risk that can induce severe cutaneous, gastrointestinal, and respiratory reactions. Allergic reactions in affected individuals following meat consumption are mediated predominantly by IgE antibodies specific for galactose-α-1,3-galactose (α-gal), a blood group antigen of non-primate mammals and therefore present in dietary meat. α-gal is also found within certain tick species and tick bites are strongly linked to meat allergy. Thus, it is thought that exposure to tick bites promotes cutaneous sensitization to tick antigens such as α-gal, leading to the development of IgE-mediated meat allergy. The underlying immune mechanisms by which skin exposure to ticks leads to the production of α-gal-specific IgE are poorly understood and are key to identifying novel treatments for this disease. In this review, we summarize the evidence of cutaneous exposure to tick bites and the development of mammalian meat allergy. We then provide recent insights into the role of B cells in IgE production in human patients with mammalian meat allergy and in a novel mouse model of meat allergy. Finally, we discuss existing data more generally focused on tick-mediated immunomodulation, and highlight possible mechanisms for how cutaneous exposure to tick bites might affect B cell responses in the skin and gut that contribute to loss of oral tolerance.

Synergistic depletion of gut microbial consortia, but not individual antibiotics, reduces amyloidosis in APPPS1-21 Alzheimer's transgenic mice

In preceding efforts, we demonstrated that antibiotic (ABX) cocktail-mediated perturbations of the gut microbiome in two independent transgenic lines, termed APP_SWE/PS1_ΔE9 and APPPS1-21, leads to a reduction in Aβ deposition in male mice. To determine whether these observed reductions of cerebral Aβ amyloidosis are specific to any individual antibiotic or require the synergistic effects of several antibiotics, we treated male APPPS1-21 transgenic mice with either individual ABX or an ABX cocktail and assessed amyloid deposition. Specifically, mice were subject to oral gavage with high dose kanamycin, gentamicin, colistin, metronidazole, vancomycin, individually or in a combination (ABX cocktail) from postnatal days (PND) 14 to 21, followed by ad libitum, low-dose individual ABX or ABX cocktail in the drinking water until the time of sacrifice. A control group was subject to gavage with water from PND 14 to 21 and received drinking water till the time of sacrifice. At the time of sacrifice, all groups showed distinct cecal microbiota profiles with the highest differences between control and ABX cocktail-treated animals. Surprisingly, only the ABX cocktail significantly reduced brain Aβ amyloidosis compared to vehicle-treated animals. In parallel studies, and to assess the potential exposure of ABX to the brain, we quantified the levels of each ABX in the brain by liquid chromatography-mass spectrometry (LC-MS) at PND 22 or at 7 weeks of age. With the exception of metronidazole (which was observed at less than 3% relative to the spiked control brains), we were unable to detect the other individual ABX in brain homogenates. Our findings suggest that synergistic alterations of gut microbial consortia, rather than individual antimicrobial agents, underlie the observed reductions in brain amyloidosis.

The gut microbiota, environmental factors, and links to the development of food allergy

Food allergy appears to have its roots in an insufficient exposure to a diverse range of environmental microbiota during early life. Microbial exposure ensures the colonization of the gastrointestinal tract with commensal microbes, which is necessary for the induction of a balanced and tolerogenic immune function. High-throughput sequencing technology has facilitated in-depth studies of the gut microbiota as well as bacterial-derived metabolites. Although the role of the microbiota in allergies is now widely studied, its importance for food allergy was only recently noted. Studies in human cohorts have shown that there is an association of dysbiosis and pathogenesis of food allergy, while studies from animal models have demonstrated the capacity of specific species in the gut microbiota to alter immune response, which may lead to the desensitization of food allergy. This article reviews the role of the gut microbiota in food allergy, and discusses the influence of environmental factors as well as prevention and management strategies relating to such regulatory mechanism.

Short-Term Amoxicillin-Induced Perturbation of the Gut Microbiota Promotes Acute Intestinal Immune Regulation in Brown Norway Rats

The intestinal gut microbiota is essential for maintaining host health. Concerns have been raised about the possible connection between antibiotic use, causing microbiota disturbances, and the increase in allergic and autoimmune diseases observed during the last decades. To elucidate the putative connection between antibiotic use and immune regulation, we have assessed the effects of the antibiotic amoxicillin on immune regulation, protein uptake, and bacterial community structure in a Brown Norway rat model. Daily intra-gastric administration of amoxicillin resulted in an immediate and dramatic shift in fecal microbiota, characterized by a reduction of within sample (α) diversity, reduced variation between animals (β diversity), increased relative abundance of Bacteroidetes and Gammaproteobacteria, with concurrent reduction of Firmicutes, compared to a water control group. In the small intestine, amoxicillin also affected microbiota composition significantly, but in a different way than observed in feces. The small intestine of control animals was vastly dominated by Lactobacillus, but this genus was much less abundant in the amoxicillin group. Instead, multiple different genera expanded after amoxicillin administration, with high variation between individual animals, thus the small intestinal α and β diversity were higher in the amoxicillin group compared to controls. After 1 week of daily amoxicillin administration, total fecal IgA level, relative abundance of small intestinal regulatory T cells and goblet cell numbers were higher in the amoxicillin group compared to controls. Several bacterial genera, including Escherichia/Shigella, Klebsiella (Gammaproteobacteria), and Bifidobacterium, for which the relative abundance was higher in the small intestine in the amoxicillin group than in controls, were positively correlated with the fraction of small intestinal regulatory T cells. Despite of epidemiologic studies showing an association between early life antibiotic consumption and later prevalence of inflammatory bowel diseases and food allergies, our findings surprisingly indicated that amoxicillin-induced perturbation of the gut microbiota promotes acute immune regulation. We speculate that the observed increase in relative abundance of small intestinal regulatory T cells is partly mediated by immunomodulatory lipopolysaccharides derived from outgrowth of Gammaproteobacteria.

Imprinting of the immune system by the microbiota early in life

The ontogeny and maturation of the immune system is modulated by the microbiota. During fetal life, the mother's microbiota produces compounds that are transferred to the fetus and offspring, and enhance the generation of innate immune cells. After birth, the colonizing microbiota induces the development of intestinal lymphoid tissues and maturation of myeloid and lymphoid cells, and imprints the immune system with a reactivity level that persists long after weaning into adulthood. When the cross-talk between host and microbiota is perturbed early in life, a pathological imprinting may develop that is characterized by excessive immune reactivity in adulthood, which translates into increased susceptibility to inflammatory pathologies. In this review, we discuss the recent data that demonstrate the existence of a time window of opportunity early in life during which mice and human have to be exposed to microbiota in order to develop a balanced immune system. We also discuss the factors involved in imprinting, such as the microbiota, immune cells and stromal cells, as well as the nature of imprinting.

Food allergy and the microbiome: Current understandings and future directions

Growing evidence points to an important role for the commensal microbiota in susceptibility to food allergy. Epidemiologic studies demonstrate associations between exposures known to modify the microbiome and risk of food allergy. Direct profiling of the gut microbiome in human cohort studies has demonstrated that individuals with food allergy have distinct gut microbiomes compared to healthy control subjects, and dysbiosis precedes the development of food allergy. Mechanistic studies in mouse models of food allergy have confirmed that the composition of the intestinal microbiota can imprint susceptibility or resistance to food allergy on the host and have identified a unique population of microbially responsive RORγt-positive FOXp3-positive regulatory T cells as critical for the maintenance of tolerance to foods. Armed with this new understanding of the role of the microbiota in food allergy and tolerance, therapeutics aimed at modifying the gastrointestinal microbiota are in development. In this article we review key milestones in the development of our current understanding of how the gastrointestinal microbiota contributes to food allergy and discuss our vision for the future of the field.

Cutaneous Exposure to Clinically Relevant Lone Star Ticks Promotes IgE Production and Hypersensitivity through CD4+ T Cell- and MyD88-Dependent Pathways in Mice

Tick-borne allergies are a growing public health concern and have been associated with the induction of IgE-mediated food allergy to red meat. However, despite the increasing prevalence of tick bite-induced allergies, the mechanisms by which cutaneous exposure to ticks leads to sensitization and the production of IgE Abs are poorly understood. To address this question, an in vivo approach was used to characterize the IgE response to lone star tick proteins administered through the skin of mice. The results demonstrated that tick sensitization and challenge induced a robust production of IgE Abs and supported a role for IgE-mediated hypersensitivity reactions in sensitized animals following oral administration of meat. The induction of IgE responses was dependent on cognate CD4⁺ T cell help during both the sensitization phase and challenge phase with cutaneous tick exposure. In addition, IgE production was dependent on B cell-intrinsic MyD88 expression, suggesting an important role for TLR signaling in B cells to induce IgE responses to tick proteins. This model of tick-induced IgE responses could be used to study the factors within tick bites that cause allergies and to investigate how sensitization to food Ags occurs through the skin that leads to IgE production.

The Microbiome and Food Allergy

The gut-associated lymphoid tissue (GALT) faces a considerable challenge. It encounters antigens derived from an estimated 1014 commensal microbes and greater than 30 kg of food proteins yearly. It must distinguish these harmless antigens from potential pathogens and mount the appropriate host immune response. Local and systemic hyporesponsiveness to dietary antigens, classically referred to as oral tolerance, comprises a distinct complement of adaptive cellular and humoral immune responses. It is increasingly evident that a functional epithelial barrier engaged in intimate interplay with innate immune cells and the resident microbiota is critical to establishing and maintaining oral tolerance. Moreover, innate immune cells serve as a bridge between the microbiota, epithelium, and the adaptive immune system, parlaying tonic microbial stimulation into signals critical for mucosal homeostasis. Dysregulation of gut homeostasis and the subsequent disruption of tolerance therefore have clinically significant consequences for the development of food allergy.

Association between extrauterine growth restriction and changes of intestinal flora in Chinese preterm infants

The aim of the study was to investigate any association between extrauterine growth restriction (EUGR) and intestinal flora of <30-week-old preterm infants. A total of 59 preterm infants were assigned to EUGR (n=23) and non-EUGR (n=36) groups. Intestinal bacteria were compared by using high-throughput sequencing of bacterial rRNA. The total abundance of bacteria in 344 genera (7568 v. 13,760; P<0.0001) and 456 species (10,032 v. 18,240; P<0.0001) was significantly decreased in the EUGR group compared with the non-EUGR group. After application of a multivariate logistic model and adjusting for potential confounding factors, as well as false-discovery rate corrections, we found four bacterial genera with higher and one bacterial genus with lower abundance in the EUGR group compared with the control group. In addition, the EUGR group showed significantly increased abundances of six species (Streptococcus parasanguinis, Bacterium RB5FF6, two Klebsiella species and Microbacterium), but decreased frequencies of three species (one Acinetobacter species, Endosymbiont_of_Sphenophorus_lev and one Enterobacter_species) compared with the non-EUGR group. Taken together, there were significant changes in the intestinal microflora of preterm infants with EUGR compared to preterm infants without EUGR.

The gut microbiome in food allergy

OBJECTIVE

To review observational human, murine, and interventional trial studies that have examined the gut microbiome in food allergy, and to provide perspective on future investigations in this field.

DATA SOURCES

A review of the published literature was performed with PubMed, and clinical studies catalogued at ClinicalTrials.gov were also reviewed.

STUDY SELECTIONS

The most recent relevant studies, seminal works, and topical clinical trials were selected.

RESULTS

Gut dysbiosis likely precedes the development of food allergy, and the timing of such dysbiosis is critical. Gut microbiota associated with individual food allergies may be distinct. Murine models support the importance of gut microbiota in shaping immune maturation and tolerance. Gut microbiota may affect food allergy susceptibility by modulating type 2 immunity, influencing immune development and tolerance, regulating basophil populations, and promoting intestinal barrier function. Ongoing and future interventional trials of probiotics, prebiotics, synbiotics, and fecal microbiota transfer will help translate our understanding of the gut microbiome in food allergy to clinical practice. Future work in this area will include deepening of current research foci, as well as expansion of efforts to include the virome, mycobiome, and interactions between the microbiome, host, and environment. Robust and consistent study designs, multidimensional profiling, and systems biology approaches will enable this future work.

CONCLUSION

By advancing research on the microbiome in food allergy, we can further our understanding of food allergy and derive new approaches for its prevention and therapy.

Influences on allergic mechanisms through gut, lung, and skin microbiome exposures

In industrialized societies the incidence of allergic diseases like atopic dermatitis, food allergies, and asthma has risen alarmingly over the last few decades. This increase has been attributed, in part, to lifestyle changes that alter the composition and function of the microbes that colonize the skin and mucosal surfaces. Strategies that reverse these changes to establish and maintain a healthy microbiome show promise for the prevention and treatment of allergic disease. In this Review, we will discuss evidence from preclinical and clinical studies that gives insights into how the microbiota of skin, intestinal tract, and airways influence immune responses in the context of allergic sensitization.

Gut Microbiome as Target for Innovative Strategies Against Food Allergy

The dramatic increase in food allergy prevalence and severity globally requires effective strategies. Food allergy derives from a defect in immune tolerance mechanisms. Immune tolerance is modulated by gut microbiota function and structure, and microbiome alterations (dysbiosis) have a pivotal role in the development of food allergy. Environmental factors, including a low-fiber/high-fat diet, cesarean delivery, antiseptic agents, lack of breastfeeding, and drugs can induce gut microbiome dysbiosis, and have been associated with food allergy. New experimental tools and technologies have provided information regarding the role of metabolites generated from dietary nutrients and selected probiotic strains that could act on immune tolerance mechanisms. The mechanisms are multiple and still not completely defined. Increasing evidence has provided useful information on optimal bacterial species/strains, dosage, and timing for intervention. The increased knowledge of the crucial role played by nutrients and gut microbiota-derived metabolites is opening the way to a post-biotic approach in the stimulation of immune tolerance through epigenetic regulation. This review focused on the potential role of gut microbiome as the target for innovative strategies against food allergy.

Healthy infants harbor intestinal bacteria that protect against food allergy

There has been a striking generational increase in life-threatening food allergies in Westernized societies^1,2 One hypothesis to explain this rising prevalence is that 21^st century lifestyle practices, including misuse of antibiotics, dietary changes, and higher rates of Caesarean birth and formula feeding have altered intestinal bacterial communities; early life alterations may be particularly detrimental.^3,4 To better understand how commensal bacteria regulate food allergy in humans we colonized germ free (GF) mice with feces from healthy or cow’s milk allergic (CMA) infants ⁵. We show here that GF mice colonized with bacteria from healthy, but not CMA, infants were protected against anaphylactic responses to a cow’s milk allergen. Differences in bacterial composition separated the healthy and CMA populations in both the human donors and the colonized mice. Healthy and CMA colonized mice also exhibited unique transciptome signatures in the ileal epithelium. Correlation of ileal bacteria with genes upregulated in the ileum of healthy or CMA colonized mice identified a Clostridial species, Anaerostipes caccae, that protected against an allergic response to food. Our findings demonstrate that intestinal bacteria are critical for regulating allergic responses to dietary antigens and suggest that interventions that modulate bacterial communities may be therapeutically relevant for food allergy.

Mechanisms by which gut microorganisms influence food sensitivities

Finely tuned mechanisms enable the gastrointestinal tract to break down dietary components into nutrients without mounting, in the majority of cases, a dysregulated immune or functional host response. However, adverse reactions to food have been steadily increasing, and evidence suggests that this process is environmental. Adverse food reactions can be divided according to their underlying pathophysiology into food intolerances, when, for instance, there is deficiency of a host enzyme required to digest the food component, and food sensitivities, when immune mechanisms are involved. In this Review, we discuss the clinical and experimental evidence for enteric infections and/or alterations in the gut microbiota in inciting food sensitivity. We focus on mechanisms by which microorganisms might provide direct pro-inflammatory signals to the host promoting breakdown of oral tolerance to food antigens or indirect pathways that involve the metabolism of protein antigens and other dietary components by gut microorganisms. Better understanding of these mechanisms will help in the development of preventive and therapeutic strategies for food sensitivities.

Perinatal antibiotic exposure alters composition of murine gut microbiota and may influence later responses to peanut antigen

Background

Accumulating evidence suggests that the gut microbiota shapes developmental processes within the immune system. Early life antibiotic use is one factor which may contribute to immune dysfunction and the recent surge in allergies by virtue of its effects on gut microbiota.

Objective and methods

As a first step towards determining whether a relationship exists between perinatal antibiotic induced changes in the gut microbiota and the later development of a peanut allergy, we exposed newborn mice to either the broad-spectrum antibiotic vancomycin or to a vehicle for 6 weeks and then used a novel murine model of peanut allergy.

Results

Early-life treatment with vancomycin resulted in a significant shift in the gut microbiota community characterized by a reduction in the abundance of firmicutes and preponderance of inflammatory proteobacteria. Mice with an antibiotic-altered microbiota, showed a localized allergic-like response characterized by ear swelling and scratching following intra-dermal peanut antigen challenge. Likewise, circulating IgE levels were increased in antibiotic-treated mice, but no evidence of a systemic allergic or anaphylactic-like response was observed. Importantly, we utilized the naturally occurring pro-inflammatory cytokine, tumor necrosis factor-α (TNF-α), rather than the more commonly used cholera toxin, as an adjuvant together with the peanut antigen.

Conclusion

Our data suggest that early antibiotic exposure promotes a shift in the gut microbiota community that may in turn, influence how mice later respond to a TNF-α + antigen challenge. However, further studies verifying the capacity of microbiota restoration to protect against allergic responses will be needed to confirm a causal role of antibiotic-induced microbiota variations in promoting allergic disease phenotypes.

Mouse Microbiota Models: Comparing Germ-Free Mice and Antibiotics Treatment as Tools for Modifying Gut Bacteria

As the intestinal microbiota has become better appreciated as necessary for maintenance of physiologic homeostasis and also as a modulator of disease processes, there has been a corresponding increase in manipulation of the microbiota in mouse models. While germ-free mouse models are generally considered to be the gold standard for studies of the microbiota, many investigators turn to antibiotics treatment models as a rapid, inexpensive, and accessible alternative. Here we describe and compare these two approaches, detailing advantages and disadvantages to both. Further, we detail what is known about the effects of antibiotics treatment on cell populations, cytokines, and organs, and clarify how this compares to germ-free models. Finally, we briefly describe recent findings regarding microbiota regulation of infectious diseases and other immunologic challenges by the microbiota, and highlight important future directions and considerations for the use of antibiotics treatment in manipulation of the microbiota.