Mechanisms Of Oral Tolerance Research Articles

Probiotics in Infancy and Childhood for Food Allergy Prevention and Treatment.

Food allergy represents a failure of oral tolerance mechanisms to dietary antigens. Over the past few years, food allergies have become a growing public health problem worldwide. Gut microbiota is believed to have a significant impact on oral tolerance to food antigens and in initiation and maintenance of food allergies. Therefore, probiotics have also been proposed in this field as a possible strategy for modulating both the gut microbiota and the immune system. In recent years, results from preclinical and clinical studies suggest a promising role for probiotics in food allergy prevention and treatment. However, future studies are needed to better understand the mechanisms of action of probiotics in food allergies and to design comparable study protocols using specific probiotic strains, defined doses and exposure times, and longer follow-up periods.

The Roles and Mechanisms of Gut Microbiota in Food Allergy

Recent research reveals that the increasing prevalence of food allergies (FA) is due in part to changes in the commensal microbiome. Studies in humans have shown that compared with healthy controls, individuals have distinct gut microbiomes during the onset and progression of FA. Mechanistic studies have established that the gut microbiota can affect the growth of immune tolerance to food antigens by modifying regulatory T cell differentiation, regulating basophil populations, and enhancing intestinal barrier function. New therapeutic and preventive approaches to altering the gut microbiota using diet adjustments, probiotics, prebiotics, synbiotics, postbiotics, fecal microbiota transplantation, and Chinese medicine have been developed towards FA. Herein, we summarized the latest evidence on the gut microbiota profiles and functions associated with FA, oral tolerance mechanisms, and gut microbiota-targeted therapeutic strategies for FA.

Oral tolerance to prevent anti-drug antibody formation in protein replacement therapies

Protein based therapeutics have successfully improved the quality of life for patients of monogenic disorders like hemophilia, Pompe and Fabry disease. However, a significant proportion of patients develop immune responses towards intravenously infused therapeutic protein, which can complicate or neutralize treatment and compromise patient safety. Strategies aimed at circumventing immune responses following therapeutic protein infusion can greatly improve therapeutic efficacy. In recent years, antigen-based oral tolerance induction has shown promising results in the prevention and treatment of autoimmune diseases, food allergies and can prevent anti-drug antibody formation to protein replacement therapies. Oral tolerance exploits regulatory mechanisms that are initiated in the gut associated lymphoid tissue (GALT) to promote active suppression of orally ingested antigen. In this review, we outline general perceptions and current knowledge about the mechanisms of oral tolerance, including tissue specific sites of tolerance induction and the cells involved, with emphasis on antigen presenting cells and regulatory T cells. We define several factors, such as cytokines and metabolites that impact the stability and expansion potential of these immune modulatory cells. We highlight preclinical studies that have been performed to induce oral tolerance to therapeutic proteins or enzymes for single gene disorders, such as hemophilia or Pompe disease. These studies mainly utilize a transgenic plant-based system for oral delivery of antigen in conjugation with fusion protein technology that favors the prevention of antigen degradation in the stomach while enhancing uptake in the small intestine by antigen presenting cells and regulatory T cell induction, thereby promoting antigen specific systemic tolerance.

Oral alloantigen exposure promotes donor-specific tolerance in a mouse model of minor-mismatched skin transplantation

Oral antigen exposure is a powerful, non-invasive route to induce immune tolerance to dietary antigens, and has been modestly successful at prolonging graft survival in rodent models of transplantation. To harness the mechanisms of oral tolerance for promoting long-term graft acceptance, we developed a mouse model where the antigen ovalbumin (OVA) was introduced orally prior to transplantation with skin grafts expressing OVA. Oral OVA treatment pre-transplantation promoted permanent graft acceptance and linked tolerance to skin grafts expressing OVA fused to the additional antigen 2W. Tolerance was donor-specific, as secondary donor-matched, but not third-party allografts were spontaneously accepted. Oral OVA treatment promoted an anergic phenotype in OVA-reactive CD4+ and CD8+ conventional T cells (Tconvs) and expanded OVA-reactive Tregs pre-transplantation. However, skin graft acceptance following oral OVA resisted partial depletion of Tregs and blockade of PD-L1. Mechanistically, we revealed a role for the proximal gut draining lymph nodes (gdLNs) in mediating this effect, as an intestinal infection that drains to the proximal gdLNs prevented tolerance induction. Our study extends previous work applying oral antigen exposure to transplantation and serves as proof of concept that the systemic immune mechanisms supporting oral tolerance are sufficient to promote long-term graft acceptance.

Time matters: The circadian rhythm in intestinal homeostasis and food allergy.

Intestinal immune homeostasis and well-balanced oral tolerance mechanisms are essential for defending the host against pathogens and toxic substances while simultaneously absorbing essential nutrients to nourish the human body.

Oral tolerance:Recent advances on mechanisms and potential applications.

Oral tolerance is a type of immune hypo-responsiveness induced by oral administration of food or harmless gastrointestinal antigens. It is evident that the induction of oral tolerance can protect our body from enteric problems, such as food allergies and colitis caused by autoimmunity. Here we review the immunological mechanisms of oral tolerance, the role of T cell cytokines in generating tolerance and the impact of Peyer's patches and mesenteric lymph nodes, and discuss the part played by commensal microflora in the regulation and maintenance of the intestinal barrier. The potential clinical applications of oral tolerance in human disease therapy are also included in this review. Understanding the mechanisms of oral tolerance may lead to the development of alternative strategies for preventing or suppressing the symptoms of autoimmune diseases and allergies.

Mechanisms of Oral Tolerance.

Oral tolerance is a state of systemic unresponsiveness that is the default response to food antigens in the gastrointestinal tract, although immune tolerance can also be induced by other routes, such as the skin or inhalation. Antigen can be acquired directly by intestinal phagocytes, or pass through enterocytes or goblet cell-associated passages prior to capture by dendritic cells (DCs) in the lamina propria. Mucin from goblet cells acts on DCs to render them more tolerogenic. A subset of regulatory DCs expressing CD103 is responsible for delivery of antigen to the draining lymph node and induction of Tregs. These DCs also imprint gastrointestinal homing capacity, allowing the recently primed Tregs to home back to the lamina propria where they interact with macrophages that produce IL-10 and expand. Tregs induced by dietary antigen include Foxp3+ Tregs and Foxp3- Tregs. In addition to Tregs, T cell anergy can also contribute to oral tolerance. The microbiota plays a key role in the development of oral tolerance, through regulation of macrophages and innate lymphoid cells that contribute to the regulatory phenotype of gastrointestinal dendritic cells. Absence of microbiota is associated with a susceptibility to food allergy, while presence of Clostridia strains can suppress development of food allergy through enhancement of Tregs and intestinal barrier function. It is not clear if feeding of antigens can also induce true immune tolerance after a memory immune response has been generated, but mechanistic studies of oral immunotherapy trials demonstrate shared pathways in oral tolerance and oral immunotherapy, with a role for Tregs and anergy. An important role for IgA and IgG antibodies in development of immune tolerance is also supported by studies of oral tolerance in humans. The elucidation of key pathways in oral tolerance could identify new strategies to increase efficacy of immunotherapy treatments for food allergy.

Cellular Components and Mechanisms of Oral Tolerance Induction.

Oral tolerance can be defined as an inhibition of specific immune responsiveness to subsequent parenteral injections of proteins to which an individual or animal has been previously exposed via the oral route. Multiple mechanisms of tolerance are induced by oral-fed antigens, but induction of regulatory CD4 T-cells expressing the transcription factor Foxp3 and the membrane-bound TGF-β stands out as the major players in oral tolerance. Oral antigen administration suppresses several animal models of autoimmune disease, including experimental autoimmune encephalomyelitis, uveitis, thyroiditis, myasthenia, arthritis, and diabetes, but also nonautoimmune inflammatory conditions such as asthma, atherosclerosis, graft rejection, allergy, and stroke. However, human trials have produced mixed results, and a great deal remains to be learned about the mechanisms of oral tolerance before it can be successfully applied to people. In this review, we highlight the cellular components involved in oral tolerance induction. A deep knowledge of these intricate cell interactions will pave the way for a successful application of antigen tolerance to treat autoimmune and nonautoimmune inflammatory diseases.

The differentiation and maintenance of RORγt+ Tregs respectively require integrin αvβ8 expression by dendritic cells and commensal microbiota

Abstract The generation of RORγt+ regulatory T cells (Tregs), which regulate type 2 immune respond, is dependent on dendritic cells and microbiota, but mechanisms are poorly understood. Here we show that the differentiation of RORγt+ Tregs was critically dependented on integrin αvβ8 expressed in DCs. In mice, lack of αvβ8 in DCs resulted in loss of RORγt+ Tregs in the small intestine and mesenteric lymph nodes. Moreover, we also report that the maintenance of RORγt+ Tregs needs the existence of commensal bacteria but not DCs in small intestine. The percentage and the proliferation of RORγt+ Tregs were decreased after treated with antibiotic while these were unaffected by the absence of DCs in a short time. These date demonstrate that αvβ8 expressed in small intestinal DCs play a critical role in the induction of RORγt+ Tregs and microbiota act as a key factor on maintenance of RORγt+ Tregs, respectively. Our results may help to explain the mechanisms of oral tolerance via αvβ8 in DCs and commensal microbiota regulate the generation of RORγt+ Tregs to suppress type 2 immune respond.

Plant-based vaccines for oral delivery of type 1 diabetes-related autoantigens: Evaluating oral tolerance mechanisms and disease prevention in NOD mice

Autoantigen-specific immunological tolerance represents a central objective for prevention of type 1 diabetes (T1D). Previous studies demonstrated mucosal antigen administration results in expansion of Foxp3+ and LAP+ regulatory T cells (Tregs), suggesting oral delivery of self-antigens might represent an effective means for modulating autoimmune disease. Early preclinical experiments using the non-obese diabetic (NOD) mouse model reported mucosal administration of T1D-related autoantigens [proinsulin or glutamic acid decarboxylase 65 (GAD)] delayed T1D onset, but published data are conflicting regarding dose, treatment duration, requirement for combinatorial agents, and extent of efficacy. Recently, dogma was challenged in a report demonstrating oral insulin does not prevent T1D in NOD mice, possibly due to antigen digestion prior to mucosal immune exposure. We used transplastomic plants expressing proinsulin and GAD to protect the autoantigens from degradation in an oral vaccine and tested the optimal combination, dose, and treatment duration for the prevention of T1D in NOD mice. Our data suggest oral autoantigen therapy alone does not effectively influence disease incidence or result in antigen-specific tolerance assessed by IL-10 measurement and Treg frequency. A more aggressive approach involving tolerogenic cytokine administration and/or lymphocyte depletion prior to oral antigen-specific immunotherapy will likely be required to impart durable therapeutic efficacy.

Effect of a synbiotic containing Lactobacillus rhamnosus GG and fructooligosaccharides on the dynamics of the level of fecal calprotectin in children of first year of life

Rationale: As clinical efficacy of probiotics and prebiotics is determined by their joint effects both on the mechanism of immune tolerance, gut inflammation and intestinal wall permeability, one of the objective methods to assess efficacy of probiotic strain-containing agents could be based on measurement of fecal calprotectin levels. Aim: To evaluate changes in fecal calprotectin as an efficacy parameter of treatment with the Lactobacillus rhamnosus GG – fructooligosacсharide complex for prevention of atopic dermatitis in infants. Materials and methods: Sixty healthy newborns from the risk group for allergic disorders were randomized (envelope randomization) into two groups: the infants from the control group (n = 31) were given widely used recommendations to prevent atopic dermatitis, whereas the infants from the study group (n = 29) were additionally administered a synbiotic containing Lactobacillus rhamnosus GG with fructooligosaccharides. The efficacy of the synbiotic therapy was assessed by measurement of fecal calprotectin levels at 3 and 6 months of the follow-up. Results: The first measurement of fecal calprotectin levels at 3 months showed its significant increase in all infants (mean 276.9 ± 128.8 mcg/G), compared to the normal range (below 50 mcg/G). The second measurement at 6 months demonstrated a decrease in fecal calprotectin in infants from both groups (mean 75.8 ± 55.3 mcg/G). However, mean levels of fecal calprotectin in the infants from the study group who had been administered the synbiotic, was significantly lower than that in the control group (48.6 ± 38.5 and 99.7 ± 57.4 mcg/G, respectively; р < 0.05). Conclusion: The observed changes in fecal calprotectin levels support the positive role of synbiotics and lyophilized complex of Lactobacillus rhamnosus GG with fructooligosaccharides in the growth of gut microbiota in infants and in the reduction of inflammation, all of this being an important prerequisite for development of the oral tolerance mechanisms.

An update on oral immunotherapy for the treatment of food allergy

Abstract Food allergy is an important public health concern, affecting 10% of infants, 5–6% of children and 2% of adults in westernized countries. Current management involves food avoidance, education of patients and carers in the emergency management of allergic reactions and in some cases provision of an adrenaline autoinjector. Oral immunotherapy (OIT) has recently been explored as a potential treatment for food allergy. This review will discuss mechanisms of oral tolerance and summarize clinical and immunologic effects of OIT.

Mechanisms of Oral Tolerance

Mechanisms of Oral Tolerance

3,3'-Diindolylmethane Inhibits Flt3L/GM-CSF-induced-bone Marrow-derived CD103+Dendritic Cell Differentiation Regulating Phosphorylation of STAT3 and STAT5

The intestinal immune system maintains oral tolerance to harmless antigens or nutrients. One mechanism of oral tolerance is mediated by regulatory T cell (Treg)s, of which differentiation is regulated by a subset of dendritic cell (DC)s, primarily CD103+ DCs. The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, plays an important role in regulating immunity. The intestines are exposed to various AhR ligands, including endogenous metabolites and phytochemicals. It was previously reported that AhR activation induced tolerogenic DCs in mice or in cultures of bone marrow-derived DCs. However, given the variety of tolerogenic DCs, which type of tolerogenic DCs is regulated by AhR remains unknown. In this study, we found that AhR ligand 3,3'-diindolylmethane (DIM) inhibited the development of CD103+ DCs from mouse bone marrow cells stimulated with Flt3L and GM-CSF. DIM interfered with phosphorylation of STAT3 and STAT5 inhibiting the expression of genes, including Id2, E2-2, IDO-1, and Aldh1a2, which are associated with DC differentiation and functions. Finally, DIM suppressed the ability of CD103+ DCs to induce Foxp3+ Tregs.

Construction of a Der p2-transgenic plant for the alleviation of airway inflammation

In clinical therapy, the amount of antigen administered to achieve oral tolerance for allergic diseases is large, and the cost is a major consideration. In this study, we used tobacco plants to develop a large-scale protein production system for allergen-specific immunotherapy, and we investigated the mechanisms of oral tolerance induced by a transgenic plant-derived antigen. We used plants (tobacco leaves) transgenic for the Dermatophagoides pteronyssinus 2 (Der p2) antigen to produce Der p2. Mice received total protein extract from Der p2 orally once per day over 6 days (days 0-2 and days 6-8). Mice were also sensitized and challenged with yeast-derived recombinant Der p2 (rDer p2), after which the mice were examined for airway hyper-responsiveness and airway inflammation. After sensitization and challenge with rDer p2, mice that were fed with total protein extracted from transgenic plants showed decreases in serum Der p2-specific IgE and IgG1 titers, decreased IL-5 and eotaxin levels in bronchial alveolar lavage fluid, and eosinophil infiltration in the airway. In addition, hyper-responsiveness was also decreased in mice that were fed with total protein extracted from transgenic plants, and CD4(+)CD25(+)Foxp3(+) regulatory T cells were significantly increased in mediastinal and mesenteric lymph nodes. Furthermore, splenocytes isolated from transgenic plant protein-fed mice exhibited decreased proliferation and increased IL-10 secretion after stimulation with rDer p2. The data here suggest that allergen-expressing transgenic plants could be used for therapeutic purposes for allergic diseases.

Antigen-specific regulatory T cells are detected in Peyer's patches after the interaction between T cells and dendritic cells loaded with orally administered antigen

Systemic immune tolerance is induced for orally administered antigen, and this phenomenon is called oral tolerance. However, the mechanism of oral tolerance has not been completely elucidated. It has been suggested that antigen presentation and generation of regulatory T cells in Peyer's patches (PPs) are important for induction of oral tolerance. Hence, we orally administered fluorescence-labelled antigen to mice and examined kinetics of the antigen and interaction between antigen-loaded dendritic cells and T cells. It was visualized that dendritic cells in PP rapidly take up antigen. We next transferred antigen-specific naïve T cells from T cell receptor transgenic mice and administered the antigen orally. Antigen-specific T cells accumulated in IFR in PP and DCs that have ingested antigen come in contact with antigen-specific T cells in IFR. The accumulated T cells were then collected and analyzed for the pattern of gene expression by real-time PCR, which revealed a gene expression pattern similar to that of FoxP3-positive regulatory T (T reg) cells. CCR9, an intestinal homing marker, was also strongly expressed. These results suggest that DCs that have captured oral antigens in PPs locally induce antigen-specific naïve T cells to differentiate into T reg cells with the intestinal homing phenotype.

Type II collagen oral tolerance; mechanism and role in collagen-induced arthritis and rheumatoid arthritis

Oral tolerance means a diminished immune response to previously fed antigens. Repeated oral administrations of type II collagen (CII) induce oral tolerance and inhibit the development of collagen-induced arthritis (CIA). Dendritic cells (DCs) in the gut-associated lymphoid tissue (GALT) take up the CII and then present it to T cells to generate regulatory T cells (Tregs), which induce systemic immune tolerance to CII. Inhibitory cytokines, such as transforming growth factor (TGF)-beta and interleukin (IL)-10, and several immune regulatory molecules, including indoleamine 2,3-dioxygenase (IDO) and retinoic acid, play an important role in Treg generation. Each DC subset may play different roles, and CD11c+CD11b+DCs and IDO+DCs are important in the generation of antigen-inducible Tregs in CII oral tolerance. Upon stimulation with the antigen involved in its generation, Treg is activated and regulates the immune response through inhibitory cytokine production, cell-to-cell contact-dependent mechanisms, DC modification, and bystander suppression. The DCs and Tregs are deeply involved in oral tolerance through reciprocal interactions. Several clinical trials have been conducted in RA patients to examine the efficacy of CII oral tolerance. An understanding the mechanism of oral tolerance to CII would give clinicians new insights into the development of natural immune tolerance and new therapeutic approaches for the treatment of autoimmune diseases.

On the aetiopathogenesis of type 1 diabetes: key roles for innate immunity and dietary antigens?

A key characteristic of human “auto”immune disease is the focus on a few target autoantigens. This phylogenetically conserved antigenic restriction is consistent with the concept that the non adaptive innate immune system is critical to disease development. Indeed, defects of macrophages, dendritic cells or NK T cells have been reported for type 1 diabetes or its animal models. Products of the innate immune system, such as IL-12, IL-15 and IL-18 have been shown to drive destructive insulitis. Besides the modulatory impact of infections a key environmental factor appears to be the diet. Wheat, soy and cow milk may contain diabetogenic proteins, as judged from animal experiments. These findings indicate a key role of the gut immune system which probably exhibits deficient oral tolerance mechanisms and therefore would mount a proinflammatory response when challenged with putative diabetogenic compounds in the diet. Dietary intervention studies to modulate the natural course of type 1 diabetes are underway.

Oral immunotherapy for food allergy

Food allergy is an increasingly prevalent disorder with potentially life-threatening complications that requires life-altering changes in dietary habits and psychosocial interactions. The standard of care presently includes strict dietary elimination of the implicated allergen and ready access to injectable epinephrine; however, no active, definitive therapeutic options exist for food-allergic patients. Although the detailed immunologic mechanisms underlying the development of food allergy are still being fully defined, food allergy appears to be the direct result of a breakdown in oral tolerance. Thus, current therapeutic approaches to food allergy are focused on modulating the immunologic response to food proteins to promote induction of oral tolerance. In this review, we examine gastrointestinal mucosal immunity and the mechanisms of oral tolerance, as well as the breakdown in oral tolerance that promotes food allergy, and we also explore novel therapeutic interventions for treatment of food allergy.

The Gut Mucosa as a Site for Induction of Regulatory T-Cells

Regulatory T lymphocytes (Tregs) are specialized for immune suppression and are important regulators of the immune response in various settings. Tregs actively suppress enteroantigen-reactive cells and contribute to the maintenance of intestinal immune homeostasis. Distinct Treg subsets coexist in the intestinal mucosa and mesenteric lymph nodes. Disturbances in Treg number and function are associated with immune-mediated disorders. Therefore, Tregs are potential targets for immunotherapies. The gut mucosal immune system is the largest lymphoid organ in the body. This site has continuous antigenic challenges from food antigens, antigens of the abundant normal bacterial flora, and pathogens. Despite this constant antigenic stimulation, controlled inflammatory responses and suppression of inflammation appear to be the rule. The gut immune system differentiates the antigenic signals from the high background noise of food and bacterial antigens. This tight regulation required to maintain homeostasis is achieved through multiple non-immune and immune factors. Oral tolerance is a mechanism in which the gastrointestinal immune system inhibits or promotes its reaction toward an orally administered antigen. Mucosal tolerance is attractive as an approach to the treatment of autoimmune and inflammatory diseases; the benefits of using an oral tolerance approach are: lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. Multiple mechanisms of tolerance are induced by oral antigen administration. Recent data suggest that oral antigen administration of antigens may promote activation of different types of regulatory T lymphocytes, enabling treatment of immune mediated disorders. This review summarizes the recent data on induction of regulatory T-cells by oral antigen administration as a possible mechanism of oral tolerance.