Oral tolerance

Role of tolerance in the development of eosinophilic gastrointestinal diseases

Although the precise link is not completely understood, eosinophilic gastrointestinal diseases have been shown to be highly associated with atopy. Oral tolerance describes the specific suppression of immune responses to an antigen by prior administration of the antigen by the oral route. Like other allergic gastrointestinal diseases, eosinophilic gastrointestinal disorders may result from a loss of oral tolerance or a failure in the induction of tolerance. Further study to clarify the role of tolerance in the development of eosinophilic gastrointestinal diseases can help identify potential prevention strategies and therapeutic targets.

Evading the immune response upon in vivo gene therapy with viral vectors

Gene therapy has the potential to provide minimally invasive and long-term treatment for many inherited disorders that otherwise have poor prognoses and limited treatment options. The sustained therapeutic correction of genetic disease by viral gene transfer has been accomplished in patients with severe immune deficiencies, or by the transduction of an immune privileged site for the treatment of ocular disease. For other diseases and target tissues, immune responses to vectors or transgene products often present major obstacles for therapy. Innate and adaptive immunity, sometimes including pre-existing or memory responses, may contribute by varying degrees to immune-mediated rejection and immunotoxicity. This review provides an overview of the immune responses to in vivo gene transfer with the most commonly used viral gene therapy vectors, and discusses strategies and protocols employed in evading the immune system in order to provide optimal gene therapy.

Therapeutic effects of mucosal tolerance on experimental colitis in rats

OBJECTIVE

To analyze the therapeutic effect of oral tolerance and nasal tolerance singly and in combination with mucosal adjuvant on experimental colitis in rats.

METHODS

Rat models were established using trinitrobenzenesulphonic acid enemas. Ovalbumin was used as inducing antigen and lipopolysaccharide as adjuvant. Colonic scores, splenic mononuclear cell proliferation, and expressions of Toll-like receptors (TLR) and regulatory T cells were determined.

RESULTS

Colonic scores decreased most significantly after ovalbumin and lipopolysaccharide nasal administration (P<0.05). Colonic expression of forkhead box P3 in rats after ovalbumin and lipopolysaccharide oral (P<0.05) and nasal administration (P<0.01) were both significantly higher than untreated rats. TLR2 expression on CD4(+)CD25(+) T cells decreased most significantly after ovalbumin and lipopolysaccharide nasal therapies (P<0.01). TLR4 colonic expression decreased significantly after ovalbumin and lipopolysaccharide oral administration (P<0.05) and lipopolysaccharide oral administration (P<0.05).

CONCLUSION

Although experimental colitis prevented oral tolerance, nasal tolerance was successfully induced. The therapeutic effect of nasal tolerance combined with adjuvant produced the best results. TLR downregulation and CD4(+)CD25(+) T cells upregulation were involved in mucosal tolerance.

Downregulation of T helper cell type 3 in patients with acute coronary syndrome

BACKGROUND AND AIMS

There is an imbalance between Th1 and Th2 in the development and progression of atherosclerosis and in patients with acute coronary syndrome (ACS) including acute myocardial infarction (AMI) and unstable angina. T helper cell type 3 (Th3), which primarily secretes transforming growth factor beta-1 (TGF-beta1), has been shown to inhibit both Th1 and Th2 cells. The present study was designed to investigate whether Th3 cells are involved in plaque destabilization and the onset of ACS.

METHODS

Ninety one patients who underwent diagnostic catheterization were classified into four groups (AMI group, unstable angina group, stable angina group and chest pain syndrome group). The cell frequencies of Th1, Th2 and Th3 were detected using flow cytometry, and the concentrations of their related cytokines IFN-gamma, IL-4 and TGF-beta1 were studied by ELISA.

RESULTS

Apart from the imbalance between Th1 and Th2, results revealed a significant decrease in peripheral Th3 number and levels of TGF-beta1 in patients with ACS as compared with those in patients with stable angina and chest pain syndrome (p<0.01).

CONCLUSIONS

Downregulation of Th3 cells in patients with ACS may play a potential role in plaque destabilization and the onset of ACS.

The role of NF-kappaB and Smad3 in TGF-beta-mediated Foxp3 expression

The transcription factor Foxp3 is essential for the development of functional, natural Treg (nTreg), which plays a prominent role in self-tolerance. Suppressive Foxp3(+) Treg cells can be generated from naïve T cells ex vivo, following TCR and TGF-beta1 stimulations. However, the molecular contributions from the different arms of these pathways leading to Foxp3 expression are not fully understood. TGF-beta1-activated Smad3 plays a major role in the expression of Foxp3, since TGF-beta1-induced-Treg generation from Smad3(-/-) mice is markedly reduced and abolished by inactivating Smad2. In the TCR pathway, deletion of Bcl10, which activates NF-kappaB, markedly reduces both IL-2 and Foxp3 production. However, partial rescue of Foxp3 expression occurs on addition of exogenous IL-2. TGF-beta1 significantly attenuates NF-kappaB binding to the Foxp3 promoter, while inducing Foxp3 expression. Furthermore, deletion of p50, a NF-kappaB subunit, results in increased Foxp3 expression despite a decline in the IL-2 production. We posit several TCR-NF-kappaB pathways, some increasing (Bcl10-IL-2-Foxp3) while others decreasing (p50-Foxp3) Foxp3 expression, with the former predominating. A better understanding of Foxp3 regulation could be useful in dissecting the cause of Treg dysfunction in several autoimmune diseases and for generating more potent TGF-beta1-induced-Treg cells for therapeutic purposes.

E3 ubiquitin ligase GRAIL controls primary T cell activation and oral tolerance

T cell unresponsiveness or anergy is one of the mechanisms that maintain inactivity of self-reactive lymphocytes. E3 ubiquitin ligases are important mediators of the anergic state. The RING finger E3 ligase GRAIL is thought to selectively function in anergic T cells but its mechanism of action and its role in vivo are largely unknown. We show here that genetic deletion of Grail in mice leads not only to loss of an anergic phenotype in various models but also to hyperactivation of primary CD4(+) T cells. Grail(-/-) CD4(+) T cells hyperproliferate in vitro to TCR stimulation alone or with concomitant anti-CD28 costimulation, with transient increased survival. In vitro differentiated T helper 1 cells show slight but significant hypersecretion of IFN-gamma in Grail(-/-) mice whereas Th2 and Th17 cytokine secretions are unchanged. Consistent with defective in vitro anergy, oral tolerance is abolished in vivo in OT-II TCR transgenic Grail(-/-) mice fed with ovalbumin. In experimental allergic encephalitis, a model of organ-specific autoimmunity, oral tolerization with myelin basic protein was abrogated as well in Grail(-/-) mice. On the protein level, Grail(-/-) naïve T cells show no significant differences of total and phosphorylated levels of ZAP70, phospholipase Cgamma1, and MAP kinases p38 and JNK but elevated baseline levels of MAP kinase ERK1/2. In summary, we define a role for GRAIL in primary T cell activation, survival, and differentiation. In addition, we formally prove an indispensable role for GRAIL in T cell anergy and oral tolerance-a promising, antigen-specific strategy to treat autoimmune diseases.

Oral administration of OKT3 monoclonal antibody to human subjects induces a dose-dependent immunologic effect in T cells and dendritic cells

INTRODUCTION

Parenteral OKT3 is used to treat transplant rejection and a humanized anti-CD3 Mab has shown positive clinical effects in new onset diabetes. Oral administration of anti-CD3 has not been tested in humans, but suppresses autoimmunity in animal models. Beta-glucosylceramide enhances NKT cell and regulatory T cell activity and enhances the effects of oral anti-CD3 in animals.

MATERIALS AND METHODS

Fifteen healthy volunteers (three per group) received orally administered OKT3 over a dose range of 0.2 to 5.0 mg daily with or without beta-glucosylceramide 7.5 mg for 5 days. Safety and immune parameters were measured on days 5, 10, and 30.

RESULTS AND DISCUSSION

Oral OKT3 enhanced T cell proliferation, suppressed Th1 and Th17 responses by 43% and 41%, respectively, increased TGF-beta/IL-10 expression and decreased IL-23/IL-6 expression by dendritic cells, and affected the IgG repertoire as measured by antigen arrays. Co-administration of oral beta-glucosylceramide induced similar effects. No side effects were observed and no subjects developed human anti-mouse antibodies.

CONCLUSION

These findings demonstrate that oral anti-CD3 monoclonal antibody is safe and biologically active in humans and presents a new avenue for the treatment of autoimmune diseases.

Suppression of Th1 and Th17, but not Th2, responses in a CD8(+) T cell-mediated model of oral tolerance

The role of CD8(+) T cells in oral tolerance remains unclear. To address this, we developed a model to induce CD8(+) Tregs by feeding the major histocompatibility complex class I immunodominant epitope of OVA, OVA((257-264)). OVA((257-264)) feeding induced tolerance similar to that observed in OVA protein-fed mice, capable of suppressing the production of Th1 and Th17 cytokines and inhibiting a Th1-driven delayed-type hypersensitivity response following immunization with whole OVA (wOVA) protein. OVA((257-264)) peptide-induced suppression could be transferred to naive mice with CD8(+) cells, but not CD8-depleted cells, isolated from mesenteric lymph nodes of peptide-fed mice. Interestingly, while capable of inhibiting Th1 and Th17 responses, OVA((257-264)) feeding could not suppress any feature of a Th2 inflammatory response, though OVA protein feeding could, suggesting that these cells function through a different mechanism than their CD4(+) counterparts generated in response to feeding with wOVA. Thus, CD8(+) T cells are functionally capable of mediating tolerance to Th1 and Th17 responses.

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.

Immunomodulatory gene therapy prevents antibody formation and lethal hypersensitivity reactions in murine pompe disease

Infantile Pompe disease progresses to a lethal cardiomyopathy in absence of effective treatment. Enzyme-replacement therapy (ERT) with recombinant human acid alpha-glucosidase (rhGAA) has been effective in most patients with Pompe disease, but efficacy was reduced by high-titer antibody responses. Immunomodulatory gene therapy with a low dose adeno-associated virus (AAV) vector (2 x 10(10) particles) containing a liver-specific regulatory cassette significantly lowered immunoglobin G (IgG), IgG1, and IgE antibodies to GAA in Pompe disease mice, when compared with mock-treated mice (P < 0.05). AAV-LSPhGAApA had the same effect on GAA-antibody production whether it was given prior to, following, or simultaneously with the initial GAA injection. Mice given AAV-LSPhGAApA had significantly less decrease in body temperature (P < 0.001) and lower anaphylactic scores (P < 0.01) following the GAA challenge. Mouse mast cell protease-1 (MMCP-1) followed the pattern associated with hypersensitivity reactions (P < 0.05). Regulatory T cells (Treg) were demonstrated to play a role in the tolerance induced by gene therapy as depletion of Treg led to an increase in GAA-specific IgG (P < 0.001). Treg depleted mice were challenged with GAA and had significantly stronger allergic reactions than mice given gene therapy without subsequent Treg depletion (temperature: P < 0.01; symptoms: P < 0.05). Ubiquitous GAA expression failed to prevent antibody formation. Thus, immunomodulatory gene therapy could provide adjunctive therapy in lysosomal storage disorders treated by enzyme replacement.

Allergen-specific antibody and cytokine responses, mast cell reactivity and intestinal permeability upon oral challenge of sensitized and tolerized mice

BACKGROUND

Food allergy has reached an epidemic level in westernized countries and although central mechanisms have been described, the variability associated with genetic diversity underscores the still unresolved complexity of these disorders.

OBJECTIVE

To develop models of food allergy and oral tolerance, both strictly induced by the intestinal route, and to compare antigen-specific responses.

METHODS

BALB/c mice were mucosally sensitized to ovalbumin (OVA) in the presence of the mucosal adjuvant cholera toxin, or tolerized by intra-gastric administrations of OVA alone. Antibody titres and cytokines were determined by ELISA, and allergic status was determined through several physiologic parameters including decline in temperature, diarrhoea, mast cell degranulation and intestinal permeability.

RESULTS

OVA-specific antibodies (IgE, IgGs and IgA in serum and feces) were produced in sensitized mice exclusively. Upon intra-gastric challenge with OVA, sensitized mice developed anaphylactic reactions associated with a decline of temperature, diarrhoea, degranulation of mast cells, which were only moderately recruited in the small intestine, and increased intestinal permeability. Cytokines produced by immune cells from sensitized mice included T-helper type 2 cytokines (IL-5, IL-13), but also IL-10, IFN-gamma and IL-17. In contrast, all markers of allergy were totally absent in tolerized animals, and yet the latter were protected from subsequent sensitization, demonstrating that oral tolerance took place efficiently.

CONCLUSION

This work allows for the first time an appropriate comparison between sensitized and tolerized BALB/c mice towards OVA. It highlights important differences from other models of allergy, and thus questions some of the generally accepted notions of allergic reactions, such as the protective role of IFN-gamma, the importance of antigen-specific secretory IgA and the role of mucosal mast cells in intestinal anaphylaxis. In addition, it suggests that IL-17 might be an effector cytokine in food allergy. Finally, it demonstrates that intestinal permeability towards the allergen is increased during challenge.

Is there a feudal hierarchy amongst regulatory immune cells? More than just Tregs

Nature has provided the developing immune system with several checkpoints important for the maintenance of tolerance and the prevention of autoimmunity. The regulatory mechanisms operating in the periphery of the system are mediated by subsets of regulatory cells, now considered principal contributors to peripheral tolerance. Regulatory T cells (Tregs) have received titanic interest in the past decade, placing them at the centre of immuno-suppressive reactions. However, it has become clearer that other immune suppressive cells inhibit auto-reactivity as effectively as Tregs. The function of Tregs and other regulatory cells in rheumatoid arthritis will be discussed in this review.

Immunotherapy for the Prevention and Treatment of Type 1 Diabetes

A major effort has been on-going to develop immunotherapies to prevent and/or treat type 1 diabetes (T1D). This autoimmune disease is characterized by the selective loss of the insulin-producing beta cells via the cumulative effects of autoantigen-specific CD4(+) and CD8(+) T cells, autoantibodies, and activated antigen-presenting cells. To be applicable in a clinical setting, immunotherapies must suppress established beta-cell autoimmunity. Preclinical studies and recent clinical findings suggest that antigen-specific and systemic-based strategies can be effective in this regard. However, either approach alone may not be sufficient to block the diabetogenic response and establish long-term protection in the clinic. In this review, we will discuss the importance of both strategies and how a combinatorial approach to treat T1D is appealing.

Might the use of acid-suppressive medications predispose to the development of eosinophilic esophagitis?

The prevalence of eosinophilic esophagitis, a manifestation of food allergy, has increased in recent years for reasons that are not clear. The gastrointestinal mucosa is regularly exposed to food antigens with the potential to evoke immunological reactions. Studies have shown that some food allergens that ordinarily would be degraded by peptic digestion are not degraded when the pH of gastric fluid is raised to levels commonly found in the stomachs of patients treated with proton pump inhibitors (PPIs). Other studies have shown that PPIs increase gastrointestinal mucosal permeability, which might facilitate the uptake of undegraded peptide allergens. Mice treated with antisecretory medications while being fed a diet of caviar have been found to develop caviar-specific immunoglobulin E (IgE) antibodies, T-cell reactivity, and gastric eosinophilia. Adult patients treated with antisecretory medications for 3 months have been found to develop a rise in their IgE antibody levels and new, food-specific IgE antibodies. These data establish a plausible mechanism whereby acid-suppressive medications, by interfering with the peptic digestion of food allergens and increasing mucosal permeability, might lead to the development of food allergy. The time course of the introduction and subsequent widespread usage of PPIs with the emergence of eosinophilic esophagitis fits well with the hypothesis that PPIs may play an etiological role. Although the mere demonstration of a plausible association does not establish cause and effect, further studies on the role of acid suppression in the development of eosinophilic esophagitis clearly are warranted.

Oral administration of low doses of plant-based HBsAg induced antigen-specific IgAs and IgGs in mice, without increasing levels of regulatory T cells

Plant-based oral vaccines run the risk of activating regulatory T cells (Tregs) and suppressing the antigen-specific immune response via oral tolerance. Mice humanized for two HLA alleles (HLA-A2.1 and HLA-DR1) were used to measure changes in Tregs and antigen-specific immune responses induced by the oral administration of tobacco (Nicotiana tabacum), expressing the hepatitis B surface antigen (HBsAg). Antigen-specific CD8+ T cell activation was not detected, but the plant-based oral immunization, without adjuvant, resulted in humoral responses comparable to those obtained by adjuvanted DNA immunization. Treg titers did not increase with DNA immunization. In contrast, with plant immunization, Tregs increased linearly to reach a plateau at high antigen doses. The highest humoral IgA and IgG responses correlated with the lowest plant antigen dose (0.5 ng), while for DNA immunization the best antibody responses were obtained at higher antigen doses. These experiments suggest that plant-based oral vaccines could be adjusted to minimize tolerance, while still inducing an immune response. Oral tolerance and adjuvant engineering in plants are discussed.

Induction of antigen-specific tolerance by oral administration of Lactococcus lactis delivered immunodominant DQ8-restricted gliadin peptide in sensitized nonobese diabetic Abo Dq8 transgenic mice

Active delivery of recombinant autoantigens or allergens at the intestinal mucosa by genetically modified Lactococcus lactis (LL) provides a novel therapeutic approach for the induction of tolerance. Celiac disease is associated with either HLA-DQ2- or HLA-DQ8-restricted responses to specific antigenic epitopes of gliadin, and may be treated by induction of Ag-specific tolerance. We investigated whether oral administration of LL-delivered DQ8-specific gliadin epitope induces Ag-specific tolerance. LL was engineered to secrete a deamidated DQ8 gliadin epitope (LL-eDQ8d) and the induction of Ag-specific tolerance was studied in NOD AB degrees DQ8 transgenic mice. Tolerance was assessed by delayed-type hypersensitivity reaction, cytokine measurements, eDQ8d-specific proliferation, and regulatory T cell analysis. Oral administration of LL-eDQ8d induced suppression of local and systemic DQ8-restricted T cell responses in NOD AB degrees DQ8 transgenic mice. Treatment resulted in an Ag-specific decrease of the proliferative capacity of inguinal lymph node (ILN) cells and lamina propria cells. Production of IL-10 and TGF-beta and a significant induction of Foxp3(+) regulatory T cells were associated with the eDQ8d-specific suppression induced by LL-eDQ8d. These data provide support for the development of effective therapeutic approaches for gluten-sensitive disorders using orally administered Ag-secreting LL. Such treatments may be effective even in the setting of established hypersensitivity.

Homeostatic (IL-7) and effector (IL-17) cytokines as distinct but complementary target for an optimal therapeutic strategy in inflammatory bowel disease

PURPOSE OF REVIEW

This review focuses on CD4+ T cells involved in the mediation of inflammatory tissue damage in murine models of inflammatory bowel diseases (IBDs). In particular, we describe the distinct roles of the homeostatic cytokine IL-7, which is essential to the maintenance of colitogenic memory CD4+ cells, and the newly discovered effector cytokine IL-17. We also discuss the close correlation between colitogenic Th17-type CD4+ T cells and inducible CD4+CD25+Foxp3+ regulatory T cells.

RECENT FINDINGS

IBDs are characterized by wasting and chronic intestinal inflammation induced by many different cytokine-mediated pathways. It is clearly recognized that medical and surgical interventions do not cure Crohn's disease because relapse is the rule after remission. Until a few years ago, IBD was classified into Th1-dependent, that is, Crohn's disease, and Th2-dependent, that is, ulcerative colitis, phenotypes. However, in recent years, it has been shown that new T-cell subclasses, that is, Th17 and regulatory T cells (T(R)), exist independently of Th1 and Th2 and that they play a central role in modulating IBD.

SUMMARY

The persistence of IL-7-dependent colitogenic memory CD4+ T cells is critical to the maintenance of experimental colitis. On the other hand, though Th1 and Th2 colitogenic memory CD4+ cells exist, in recent years the central role of IL-17-producing Th17-type cells in IBD has attracted renewed interest. The development of molecularly targeted therapies aimed at a variety of different Th-dependent pathogenic mechanisms may represent a novel approach to IBD therapy.

Oral tolerance: can we make it work?

Mucosal tolerance remains an attractive approach for the treatment of autoimmune and inflammatory diseases. The agents used in these treatments lack toxicity, can be easily administered, and enable the promotion of antigen-specific immune responses. The limited success of clinical trials over the past 2 decades has led to the fear that the beneficial effect observed in animal models cannot be repeated in humans. Successful application of mucosal tolerance for the treatment of human diseases will depend on strategies that target the correct cells in the gut-liver axis, improve antigen presentation, alter the administered dose and formulations, utilize potent mucosal adjuvants, develop immune biomarkers enabling follow-up of the effect, utilize combination therapies with other immune modulatory agents, and target the right patient populations. Here, we discuss 12 of the major questions related to oral tolerance and its clinical application to humans with immune-mediated disorders.

Fc receptor-like 3 protein expressed on IL-2 nonresponsive subset of human regulatory T cells

Fc receptor-like 3 (FCRL3) is a cell surface protein homologous to Fc receptors. The FCRL3 gene is present in humans but not in mice. We found that FCRL3 protein is expressed on 40% of human naturally occurring CD4(+) regulatory T (nTreg) cells (CD4(+)CD25(+)CD127(low)). Sorted nTreg cells with the surface phenotype FCRL3(+) and FCRL3(-) were both hypoproliferative to TCR stimulation and both suppressive on proliferation of conventional T cells (CD4(+)CD25(-)) in vitro. They both expressed forkhead box p3 (Foxp3) protein, the intracellular regulatory T cell marker. However, in contrast to FCRL3(-) nTreg cells, FCRL3(+) nTreg cells were not stimulated to proliferate by the addition of exogenous IL-2. In addition, Foxp3(+) cells induced from conventional T cells by TGF-beta treatment did not exhibit FCRL3 expression. These results suggest that the FCRL3(+) subset of human nTreg cells identified in this study arise in vivo and Foxp3 expression alone is not sufficient to induce FCRL3 expression. FCRL3 may be involved in human-specific mechanisms to control the generation of nTreg cells.

Natural and adaptive foxp3+ regulatory T cells: more of the same or a division of labor?

Adaptive Foxp3(+)CD4(+) regulatory T (iTreg) cells develop outside the thymus under subimmunogenic antigen presentation, during chronic inflammation, and during normal homeostasis of the gut. iTreg cells are essential in mucosal immune tolerance and in the control of severe chronic allergic inflammation, and most likely are one of the main barriers to the eradication of tumors. The Foxp3(+) iTreg cell repertoire is drawn from naive conventional CD4(+) T cells, whereas natural Treg (nTreg) cells are selected by high-avidity interactions in the thymus. The full extent of differences and similarities between iTreg and nTreg cells is yet to be defined. We speculate that iTreg cell development is driven by the need to maintain a noninflammatory environment in the gut, to suppress immune responses to environmental and food allergens, and to decrease chronic inflammation, whereas nTreg cells prevent autoimmunity and raise the activation threshold for all immune responses.

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.

Nasal vaccination with troponin reduces troponin specific T-cell responses and improves heart function in myocardial ischemia-reperfusion injury

Myocardial ischemia with subsequent reperfusion (MI/R) can lead to significant myocardial damage. Ischemia initiates inflammation at the blood-microvascular endothelial cell interface and contributes significantly to both acute injury and repair of the damaged tissue. We have found that MI/R injury in mice is associated with a cellular immune response to troponin. Myocardial cells exclusively synthesize troponin and release the troponin into the bloodstream following injury. Mucosally administered proteins induce T cells that secrete anti-inflammatory cytokines such as IL-10 and transforming growth factor beta at the anatomical site where the protein localizes. We found that nasal administration of the three subunits of troponin (C, I and T isoforms), given prior to or 1 h following MI/R, decreased infarct size by 40% measured 24 h later. At 1.5 months following MI/R, there was a 50% reduction in infarct size and improvement in cardiac function as measured by echocardiography. Protection was associated with a reduction of cellular immunity to troponin. Immunohistochemistry demonstrated increased IL-10 and reduced IFN-gamma in the area surrounding the ischemic infarct following nasal troponin. Adoptive transfer of CD4+ T cells to mice from nasally troponin-treated mice 1 h after the MI/R decreased infarct size by 72%, whereas CD4+ T cells from IL-10-/- mice or nasally BSA-treated mice had no effect. Our results demonstrate that IL-10-secreting CD4+ T cells induced by nasal troponin reduce injury following MI/R. Modulation of cardiac inflammation by nasal troponin provides a novel treatment to decrease myocardial damage and enhance recovery after myocardial ischemia.

T regulatory cells in contact hypersensitivity

PURPOSE OF REVIEW

The review summarizes the recent investigations focused on T regulatory cells in hapten diseases.

RECENT FINDINGS

Multiple mechanisms ensure tolerance to small chemicals penetrating the skin. Among these, specific T regulatory cells play a major role in controlling harmful immune responses to environmental antigens. Most of the T regulatory cells involved in this process belongs to the CD4 subset and suppress hapten-specific immune response through the release of IL-10 and through direct interaction with effector T cells, blocking their function.

SUMMARY

Methods for in-vitro and in-vivo expansion of specific T regulatory cells may represent an innovative approach for the cure of contact hypersensitivity.

Mucosal tolerance induced by an immunodominant peptide from rat alpha3(IV)NC1 in established experimental autoimmune glomerulonephritis

Experimental autoimmune glomerulonephritis (EAG), an animal model of Goodpasture's disease, can be induced in Wistar Kyoto (WKY) rats by immunization with the noncollagenous domain of the alpha 3 chain of type IV collagen, alpha3(IV)NC1. Recent studies have identified an immunodominant peptide, pCol (24-38), from the N-terminus of rat alpha3(IV)NC1; this peptide contains the major B- and T-cell epitopes in EAG and can induce crescentic nephritis. In this study, we investigated the mechanisms of mucosal tolerance in EAG by examining the effects of the nasal administration of this peptide after the onset of disease. A dose-dependent effect was observed: a dose of 300 microg had no effect, a dose of 1000 microg resulted in a moderate reduction in EAG severity, and a dose of 3000 microg produced a marked reduction in EAG severity accompanied by diminished antigen-specific, T-cell proliferative responses. These results demonstrate that mucosal tolerance in EAG can be induced by nasal administration of an immunodominant peptide from the N-terminus of alpha3(IV)NC1 and should be of value in designing new therapeutic strategies for patients with Goodpasture's disease and other autoimmune disorders.

Regulatory lymphocytes and intestinal inflammation

The immune system is pivotal in mediating the interactions between host and microbiota that shape the intestinal environment. Intestinal homeostasis arises from a highly dynamic balance between host protective immunity and regulatory mechanisms. This regulation is achieved by a number of cell populations acting through a set of shared regulatory pathways. In this review, we summarize the main lymphocyte subsets controlling immune responsiveness in the gut and their mechanisms of control, which involve maintenance of intestinal barrier function and suppression of chronic inflammation. CD4(+)Foxp3(+) T cells play a nonredundant role in the maintenance of intestinal homeostasis through IL-10- and TGF-beta-dependent mechanisms. Their activity is complemented by other T and B lymphocytes. Because breakdown in immune regulatory networks in the intestine leads to chronic inflammatory diseases of the gut, such as inflammatory bowel disease and celiac disease, regulatory lymphocytes are an attractive target for therapies of intestinal inflammation.

IL-10 and IL-27 producing dendritic cells capable of enhancing IL-10 production of T cells are induced in oral tolerance

Oral tolerance is a key feature of intestinal immunity, generating systemic tolerance to ingested antigens (Ag). Dendritic cells (DC) have been revealed as important immune regulators, however, the precise role of DC in oral tolerance induction remains unclear. We investigated the characteristics of DC in spleen, mesenteric lymph node (MLN), and Peyer's patch (PP) after oral Ag administration in a TCR-transgenic mouse model. DC from PP and MLN of tolerized mice induced IL-10 production but not Foxp3 expression in cocultured T cells. IL-10 production was markedly increased after 5-7-day Ag administration especially in PP DC. On the other hand, IL-27 production was increased after 2-5-day Ag administration. CD11b(+) DC, which increased after ingestion of Ag, prominently expressed IL-10 and IL-27 compared with CD11b(-) DC. These results suggest that IL-10 and IL-27 producing DC are increased by interaction with antigen specific T cells in PP, and these DC act as an inducer of IL-10 producing T cells in oral tolerance.

Back to the future for multiple sclerosis therapy: focus on current and emerging disease-modifying therapeutic strategies

The last decade has seen numerous advances in the treatment of multiple sclerosis with six immunotherapeutic agents licensed for use. Although these therapeutic agents have powerful effects upon the inflammatory phase of disease, they have limitations in treating the progression of disability and in their safety profile. This review focuses on our current understanding of first- and second-line treatments for multiple sclerosis, including combination therapies, and also discusses the most promising novel therapeutic strategies on the horizon. Such agents include orally administered immunosuppressive drugs, monoclonal antibodies, antigen-specific tolerance, and neural protection and repair strategies. The challenge ahead lies in the delivery of potent drugs to inhibit inflammation and neurodegeneration while limiting side effects. Further elucidation of the pathophysiology of disease may provide new clinical targets and disease-relevant biomarkers that, in combination with proteomics, may help personalize treatment to individual patients.

Plant vaccines: an immunological perspective

The advent of technologies to express heterologous proteins in planta has led to the proposition that plants may be engineered to be safe, inexpensive vehicles for the production of vaccines and possibly even vectors for their delivery. The immunogenicity of a variety of antigens of relevance to vaccination expressed in different plants has been assessed. The purpose of this article is to examine the utility of plant-expression systems in vaccine development from an immunological perspective.

Preconditioning and tolerance against cerebral ischaemia: from experimental strategies to clinical use

Neuroprotection and brain repair in patients after acute brain damage are still major unfulfilled medical needs. Pharmacological treatments are either ineffective or confounded by adverse effects. Consequently, endogenous mechanisms by which the brain protects itself against noxious stimuli and recovers from damage are being studied. Research on preconditioning, also known as induced tolerance, over the past decade has resulted in various promising strategies for the treatment of patients with acute brain injury. Several of these strategies are being tested in randomised clinical trials. Additionally, research into preconditioning has led to the idea of prophylactically inducing protection in patients such as those undergoing brain surgery and those with transient ischaemic attack or subarachnoid haemorrhage who are at high risk of brain injury in the near future. In this Review, we focus on the clinical issues relating to preconditioning and tolerance in the brain; specifically, we discuss the clinical situations that might benefit from such procedures. We also discuss whether preconditioning and tolerance occur naturally in the brain and assess the most promising candidate strategies that are being investigated.

Cutting edge: A critical role of B and T lymphocyte attenuator in peripheral T cell tolerance induction

T cell activation and tolerance are delicately regulated by costimulatory molecules. Although B and T lymphocyte attenuator (BTLA) has been shown as a negative regulator for T cell activation, its role in peripheral T cell tolerance induction in vivo has not been addressed. In this study, we generated a novel strain of BTLA-deficient mice and used three different models to characterize the function of BTLA in controlling T cell tolerance. In an oral tolerance model, BTLA-deficient mice were found resistant to the induction of T cell tolerance to an oral Ag. Moreover, compared with wild-type OT-II cells, BTLA(-/-) OT-II cells were less susceptible to tolerance induction by a high-dose OVA peptide administered i.v. Finally, BTLA(-/-) OT-I cells caused autoimmune diabetes in RIP-mOVA recipient mice. Our results thus demonstrate an important role for BTLA in the induction of peripheral tolerance of both CD4(+) and CD8(+) T cells in vivo.

B-1 cells modulate oral tolerance in mice

Although the origin and functions of B-1 cells are controversial, they are considered as a cellular element of innate immunity due to their ability to produce natural autoantibodies of the IgM type. These antibodies are encoded by a relatively limited repertoire of V genes, and their resulting diversity is smaller than that produced by conventional B cells. B-1 cells constitute the larger fraction of B cells in the peritoneal cavity and migrate to non-specific inflammation sites. In addition, they contribute to the production of IgA antibodies in the intestinal lamina propria. It has been demonstrated that they participate in the induction and maintenance of peripheral tolerance. Herein, the participation of B-1 cells in inducing oral tolerance is evaluated. Unexpectedly, BALB/Xid mice, the animals deficient in B-1 cells, are not tolerized to OVA but instead are responsive to oral immunization. Conversely, BALB/c mice respond to oral tolerance to this antigen. We used these biological characteristics of these animals to investigate whether B-1 cells are involved in the induction of oral tolerance to OVA. Results show that B-1 cells from BALB/c mice, treated orally with OVA and adoptively transferred to BALB/Xid mice were able to suppress local hypersensitivity reaction and lymphoproliferative cellular response observed in BALB/Xid mice. These data demonstrate that B-1 cells have regulatory properties and are involved in the induction of oral tolerance.

T cell-mediated immunoregulation in the gastrointestinal tract

In the intestinal tract, only a single layer of epithelial cells separates innate and adaptive immune effector cells from a vast amount of antigens. Here, the immune system faces a considerable challenge in tolerating commensal flora and dietary antigens while preventing the dissemination of potential pathogens. Failure to tightly control immune reactions may result in detrimental inflammation. In this respect, 'conventional' regulatory CD4(+) T cells, including naturally occurring and adaptive CD4(+) CD25(+) Foxp3(+) T cells, Th3 and Tr1 cells, have recently been the focus of considerable attention. However, regulatory mechanisms in the intestinal mucosa are highly complex, including adaptations of nonhaematopoietic cells and innate immune cells as well as the presence of unconventional T cells with regulatory properties such as resident TCRgammadelta or TCRalphabeta CD8(+) intraepithelial lymphocytes. This review aims to summarize the currently available knowledge on conventional and unconventional regulatory T cell subsets (Tregs), with special emphasis on clinical data and the potential role or malfunctioning of Tregs in four major human gastrointestinal diseases, i.e. inflammatory bowel diseases, coeliac disease, food allergy and colorectal cancer. We conclude that the clinical data confirms some but not all of the findings derived from experimental animal models.

The biocompatible polysaccharide chitosan enhances the oral tolerance to type II collagen

Chitosan is a mucoadhesive polysaccharide that promotes the transmucosal absorption of peptides and proteins. At mucosal sites chitosan exhibits immunomodulatory activities and stimulates the release of regulatory cytokines. Herein we evaluated the effect of the co-administration of chitosan in the tolerance to type II collagen (CII) using an experimental model of arthritis. Rats were fed diluent (acetic acid), 1 mg CII, 1 mg chitosan or 1 mg CII + 1 mg chitosan during 5 days before immunization with CII in Freund's complete adjuvant. Systemic effects were evaluated in draining lymph nodes after antigenic challenge or during the clinical evolution of arthritis. Specific antibodies, proliferation against CII and the production of interferon (IFN)-gamma and interleukin-10 were assessed. Clinical signs were observed 13-15 days after primary immunization. The CII : chitosan group presented the lowest incidence and developed moderate arthritis, with reduced levels of immunoglobulin (Ig)G2a anti-CII, a limited proliferation in draining lymph nodes and a lower release of IFN-gamma after restimulation with CII. Our results demonstrate that chitosan enhances the tolerance to an articular antigen with a decrease in the inflammatory responses and, as a consequence, an improvement in clinical signs.

From the diet to the nucleus: vitamin A and TGF-beta join efforts at the mucosal interface of the intestine

The vitamin A metabolites, including retinoic acid (RA), form ligands for retinoic acid-related nuclear receptors and together they play pleiotropic roles in various biological processes. Recently, we described that RA also functions as a key modulator of transforming growth factor-beta (TGF-beta)-driven immune deviation, capable of suppressing the differentiation of interleukin-17 secreting T helper cells (T(H)17) and conversely promoting the generation of Foxp3(+) T regulatory (Treg) cells. This review will focus on the role of RA in the reciprocal TGF-beta-driven differentiation of T(H)17 and Treg and on the importance of such regulatory mechanism to control a functional immune system, in particular at the mucosal interface of the intestine.

Atopic dermatitis and allergic reactions to individual fragrance chemicals

BACKGROUND

Allergic contact dermatitis prevalence is reported as equal in atopic and nonatopic dermatitis. Atopic dermatitis is under-represented in those with allergic contact dermatitis to agents having cutaneous and dietary exposure. We compared rates of atopic dermatitis between patients with allergic contact dermatitis arising out of individual fragrance chemicals with known oral/cutaneous exposure against exclusively cutaneous exposure.

METHODS

Between 1982 and 2007, 37 065 dermatitis patients were tested with Fragrance mix I. Those who were positive were tested for individual fragrance allergy. Chemicals were categorized according to whether their exposure pattern was solely cutaneous, oral or mixed. Current and past atopic dermatitis rates were compared between the whole population and groups allergic to individual fragrances. Age and gender were controlled.

RESULTS

Cinnamic alcohol and cinnamal allergy groups had reduced rates of both 'current' [24/266 (9.0%) P = 0.0008, 38/364 (10.4%) P = 0.0005] and 'past' atopic dermatitis [44/266 (16.5%) P = 0.009, 70/346 (19.2%) P = 0.037]. Atopic dermatitis rates in groups allergic to Evernia prunastri and hydroxycitronellal (cutaneous exposure only) were not reduced [120/597 (20.1%) and 41/153 (26.8%)]. Groups allergic to cinnamic alcohol (P < 0.0001, P < 0.0001) and cinnamal (P < 0.0001, P < 0.004) had reductions in 'current' and 'past' atopic dermatitis, compared with Evernia prunastri.

CONCLUSIONS

Patients allergic to individual fragrances with dietary exposure have reduced rates of atopic dermatitis. This suggests that patients with atopic dermatitis have heightened oral tolerance to dietary haptens, in contrast to the known close association of atopic dermatitis with food-protein allergy. Haptens may interfere with food protein tolerance by binding to soluble protein to alter its configuration and immunogenic profile.

Should digestion assays be used to estimate persistence of potential allergens in tests for safety of novel food proteins?

Food allergies affect an estimated 3 to 4% of adults and up to 8% of children in developed western countries. Results from in vitro simulated gastric digestion studies with purified proteins are routinely used to assess the allergenic potential of novel food proteins. The digestion of purified proteins in simulated gastric fluid typically progresses in an exponential fashion allowing persistence to be quantified using pseudo-first-order rate constants or half lives. However, the persistence of purified proteins in simulated gastric fluid is a poor predictor of the allergenic status of food proteins, potentially due to food matrix effects that can be significant in vivo. The evaluation of the persistence of novel proteins in whole, prepared food exposed to simulated gastric fluid may provide a more correlative result, but such assays should be thoroughly validated to demonstrate a predictive capacity before they are accepted to predict the allergenic potential of novel food proteins.

Mucosal immunity and protection against HIV/SIV infection: strategies and challenges for vaccine design

To date, most HIV vaccine strategies have focused on parenteral immunization and systemic immunity. These approaches have not yielded the efficacious HIV vaccine urgently needed to control the AIDS pandemic. As HIV is primarily mucosally transmitted, efforts are being re-focused on mucosal vaccine strategies, in spite of complexities of immune response induction and evaluation. Here, we outline issues in mucosal vaccine design and illustrate strategies with examples from the recent literature. Development of a successful HIV vaccine will require in-depth understanding of the mucosal immune system, knowledge that ultimately will benefit vaccine design for all mucosally transmitted infectious agents.

A DNA vaccine for multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a disease in which safety is of paramount importance when developing a potential therapeutic. Antigen-specific treatments provide a method for achieving efficacy while maintaining safety. DNA vaccines are one such form of treatment that have been tested in clinical trials

OBJECTIVE

To determine if a DNA vaccine is a viable method of antigen-specific treatment of MS.

RESULTS/CONCLUSION

Phase I and II trials of BHT-3009, a DNA vaccine encoding myelin basic protein, demonstrated that it was safe, well-tolerated, and caused antigen-specific immune tolerance. BHT-3009 showed efficacy in reducing brain lesion activity as well as clinical relapses in patients that were immunologically active at baseline. BHT-3009 is a promising therapy in development for MS, and may prove to be one of the first antigen-specific treatments for this disease.

Autoimmune pathology accounts for common manifestations in a wide range of neuro-psychiatric disorders: the olfactory and immune system interrelationship

Smell has traditionally been considered a less important sense when compared to sight or hearing, but recent research has unraveled important features inherent to the sense of smell. Once considered just a chemical sensor for sampling the environment, data from animal models and human studies currently imply numerous and complex effects of smell on behavior, mood, and on the immune response. In this review we discuss a possible inter-relationship between olfactory impairment, autoimmunity and neurological/psychiatric symptoms in several diseases affecting the central nervous system (CNS) such as Parkinson, Alzheimer's disease, autism, schizophrenia, multiple sclerosis and neuropsychiatric lupus erythematosus. We suggest that common manifestations are not mere coincidences. Current data from animal models show that neuropsychiatric manifestations are intimately associated with smell impairment, and autoimmune dysregulation, via autoantibodies (anti-NMDAR, anti-ribosomal P) or other mechanisms. From clues of pathological manifestations, we propose a novel approach to the understanding of the interactions between the CNS, the smell and the immune system.

Antigen-specific tolerogenic and immunomodulatory strategies for the treatment of autoimmune arthritis

OBJECTIVES

To review various antigen-specific tolerogenic and immunomodulatory approaches for arthritis in animal models and patients in regard to their efficacy, mechanisms of action, and limitations.

METHODS

We reviewed the published literature in Medline (PubMed) on the induction of antigen-specific tolerance and its effect on autoimmune arthritis, as well as the recent work on B-cell-mediated tolerance from our laboratory. The prominent key words used in different combinations included arthritis, autoimmunity, immunotherapy, innate immunity, tolerance, treatment, and rheumatoid arthritis (RA). Although this search spanned the years 1975 to 2007, the majority of the short-listed articles belonged to the period 1990 to 2007. The relevant primary as well as cross-referenced articles were then collected from links within PubMed and reviewed.

RESULTS

Antigen-specific tolerance has been successful in the prevention and/or treatment of arthritis in animal models. The administration of soluble native antigen or an altered peptide ligand intravenously, orally, or nasally, and the delivery of the DNA encoding a particular antigen by gene therapy have been the mainstay of immunomodulation. Recently, the methods for in vitro expansion of CD4+CD25+ regulatory T-cells have been optimized. Furthermore, interleukin-17 has emerged as a promising new therapeutic target in arthritis. However, in RA patients, non-antigen-specific therapeutic approaches have been much more successful than antigen-specific tolerogenic regimens.

CONCLUSION

An antigen-specific treatment against autoimmune arthritis is still elusive. However, insights into newly emerging mechanisms of disease pathogenesis provide hope for the development of effective and safe immunotherapeutic strategies in the near future.

Impairing oral tolerance promotes allergy and anaphylaxis: a new murine food allergy model

BACKGROUND

Food allergy is a disorder in which antigenic food proteins elicit immune responses. Animal models of food allergy have several limitations that influence their utility, including failure to recapitulate several key immunologic hallmarks. Consequently, little is known regarding the pathogenesis and mechanisms leading to food allergy. Staphylococcus aureus-derived enterotoxins, a common cause of food contamination, are associated with antigen responses in atopic dermatitis.

OBJECTIVE

We hypothesized that S aureus-derived enterotoxins might influence the development of food allergy. We examined the influence of administration of staphylococcal enterotoxin B (SEB) with food allergens on immunologic responses and compared these responses with those elicited by a cholera toxin-driven food allergy model.

METHODS

Oral administration of ovalbumin or whole peanut extract with or without SEB was performed once weekly. After 8 weeks, mice were challenged with oral antigen alone, and the physiologic and immunologic responses to antigen were studied.

RESULTS

SEB administered with antigen resulted in immune responses to the antigen. Responses were highly T(H)2 polarized, and oral challenge with antigen triggered anaphylaxis and local and systemic mast cell degranulation. SEB-driven sensitization induced eosinophilia in the blood and intestinal tissues not observed with cholera toxin sensitization. SEB impaired tolerance specifically by impairing expression of TGF-beta and regulatory T cells, and tolerance was restored with high-dose antigen.

CONCLUSIONS

We demonstrate a new model of food allergy to oral antigen in common laboratory strains of mice that recapitulates many features of clinical food allergy that are not seen in other models. We demonstrate that SEB impairs oral tolerance and permits allergic responses.

In vivo switch to IL-10-secreting T regulatory cells in high dose allergen exposure

High dose bee venom exposure in beekeepers by natural bee stings represents a model to understand mechanisms of T cell tolerance to allergens in healthy individuals. Continuous exposure of nonallergic beekeepers to high doses of bee venom antigens induces diminished T cell-related cutaneous late-phase swelling to bee stings in parallel with suppressed allergen-specific T cell proliferation and T helper type 1 (Th1) and Th2 cytokine secretion. After multiple bee stings, venom antigen-specific Th1 and Th2 cells show a switch toward interleukin (IL) 10-secreting type 1 T regulatory (Tr1) cells. T cell regulation continues as long as antigen exposure persists and returns to initial levels within 2 to 3 mo after bee stings. Histamine receptor 2 up-regulated on specific Th2 cells displays a dual effect by directly suppressing allergen-stimulated T cells and increasing IL-10 production. In addition, cytotoxic T lymphocyte-associated antigen 4 and programmed death 1 play roles in allergen-specific T cell suppression. In contrast to its role in mucosal allergen tolerance, transforming growth factor beta does not seem to be an essential player in skin-related allergen tolerance. Thus, rapid switch and expansion of IL-10-producing Tr1 cells and the use of multiple suppressive factors represent essential mechanisms in immune tolerance to a high dose of allergens in nonallergic individuals.

New potential treatments for protection of pancreatic B-cell function in Type 1 diabetes

Type 1 diabetes mellitus results from the progressive and specific autoimmune destruction of insulin-secreting pancreatic B-cells, which develops over a period of years and continues after the initial clinical presentation. The ultimate goal of therapeutic intervention is prevention or reversal of the disease by the arrest of autoimmunity and by preservation/restoration of B-cell mass and function. Recent clinical trials of antigen-specific or non-specific immune therapies have proved that modulation of islet specific autoimmunity in humans and prevention of insulin secretion loss in the short term after the onset of disease is achievable. The identification of suitable candidates for therapy, appropriate dosage and timing, specificity of intervention and the side-effect profile are crucial for the success of any approach. Considering the complexity of the disease, it is likely that a rationally designed approach of combined immune-based therapies that target suppression of B-cell specific autoreactivity and maintenance of immune tolerance, coupled with islet regeneration or replacement of the destroyed B-cell mass, will prove to be most effective in causing remission/reversal of disease in a durable fashion.