Oral tolerance: new approaches, new problems

Oral tolerance failure upon neonatal gut colonization with Escherichia coli producing the genotoxin colibactin

The intestinal barrier controls the balance between tolerance and immunity to luminal antigens. When this finely tuned equilibrium is deregulated, inflammatory disorders can occur. There is a concomitant increase, in urban populations of developed countries, of immune-mediated diseases along with a shift in Escherichia coli population from the declining phylogenetic group A to the newly dominant group B2, including commensal strains producing a genotoxin called colibactin that massively colonized the gut of neonates. Here, we showed that mother-to-offspring early gut colonization by colibactin-producing E. coli impairs intestinal permeability and enhances the transepithelial passage of luminal antigen, leading to an increased immune activation. Functionally, this was accompanied by a dramatic increase in local and systemic immune responses against a fed antigen, decreased regulatory T cell population, tolerogenic dendritic cells, and enhanced mucosal delayed-type hypersensitivity response. Conversely, the abolition of colibactin expression by mutagenesis abrogates the alteration of oral tolerance induced by neonatal colonization by E. coli. In conclusion, the vertical colonization by E. coli producing the genotoxin colibactin enhances intestinal translocation and subsequently alters oral tolerance. Thus, early colonization by E. coli from the newly dominant phylogenetic group B2, which produces colibactin, may represent a risk factor for the development of immune-mediated diseases.

Up-regulation of MDP and tuftsin gene expression in Th1 and Th17 cells as an adjuvant for an oral Lactobacillus casei vaccine against anti-transmissible gastroenteritis virus

The role of muramyl dipeptide (MDP) and tuftsin in oral immune adjustment remains unclear, particularly in a Lactobacillus casei (L. casei) vaccine. To address this, we investigated the effects of different repetitive peptides expressed by L. casei, specifically the MDP and tuftsin fusion protein (MT) repeated 20 and 40 times (20MT and 40MT), in mice also expressing the D antigenic site of the spike (S) protein of transmissible gastroenteritis virus (TGEV) on intestinal and systemic immune responses and confirmed the immunoregulation of these peptides. Treatment of mice with a different vaccine consisting of L. casei expressing MDP and tuftsin stimulated humoral and cellular immune responses. Both 20MT and 40MT induced an increase in IgG and IgA levels against TGEV, as determined using enzyme-linked immunosorbent assay. Increased IgG and IgA resulted in the activation of TGEV-neutralising antibody activity in vitro. In addition, 20MT and 40MT stimulated the differentiation of innate immune cells, including T helper cell subclasses and regulatory T (Treg) cells, which induced robust T helper type 1 and T helper type 17 (Th17) responses and reduced Treg T cell immune responses in the 20MT and 40MT groups, respectively. Notably, treatment of mice with L. casei expressing 20MT and 40MT enhanced the anti-TGEV antibody immune responses of both the humoral and mucosal immune systems. These findings suggest that L. casei expressing MDP and tuftsin possesses substantial immunopotentiating properties, as it can induce humoral and T cell-mediated immune responses upon oral administration, and it may be useful in oral vaccines against TGEV challenge.

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.

Are we getting enough allergens?

This paper proposes that reduced allergen exposure is one of the factors underlying the higher risk of IgE-mediated allergic disease in populations with an urbanized, westernized, and affluent lifestyle. This lower allergen exposure results in the failure to induce and maintain immune tolerance to common environmental allergens. The paper summarizes different lines of evidence that may support or contradict this hypothesis and points to areas where more knowledge is needed.

Perioperative management of chronic pain patients with opioid dependency

PURPOSE OF REVIEW

In this article, we discuss the perioperative anesthesia and pain management of patients with chronic pain receiving chronic opioid administration. In our practice we may expect to be confronted with opioid-dependent patients in routine anesthesia practice and should acquire specific knowledge and skills to effectively manage the perioperative and acute pain management issues that arise.

RECENT FINDINGS

The number of patients treated chronically with opioids has increased steadily over the past decade; currently about 10% of all chronic-pain patients are treated with opioids. As these patients are no longer confined to terminally ill cancer patients, growing numbers of these patients are facing surgical interventions.

SUMMARY

In our clinical practice, we should employ multimodal pain management therapy by using an around-the-clock regimen of nonsteroidal anti-inflammatory drugs, cyclooxygenase-2 inhibitors, acetaminophen, and regional blockade. Dosing regimens should be individualized to optimize efficacy while minimizing the risk of adverse events.

Basic science for the clinician 26: Tolerance--mechanisms and manifestations

Usually the immune system monitors our internal milieu, protecting us from external and internal risks, silently watching over the rest. Pathologic autoimmunity is usually avoided, except in certain animal models and certain immunogenetically predisposed people. On the other hand, "salutary autoimmunity" occurs in the interaction of immune systems with themselves or other immune pathways as part of control or recognition mechanisms, eg, idiotype network, epitope-MHC complex binding with B- or T-cell antigen receptors. There are means by which dangerous autoimmune reactants are eliminated from the repertoire before birth; some of these are described here. However, potentially dangerous autoimmune effectors can be identified in the immunologic repertoire of certain adult animal strains but not damage the animal; these latent autoimmune effector pathways are held in check in adult animals/humans by active suppressive mechanisms.The identification and control of autoimmunity may well be the holy grail of rheumatology. Autoimmunity may also be an active participant in a number of other organ systems and diseases, so lessons learned in immunology may apply broadly throughout medicine. Once a better understanding of the normal processes and aberrancies that lead to disease are had, one can look forward to interventions to reestablish tolerance, perhaps by something as simple as a capsule containing the appropriate self antigen-containing molecules--"oral tolerizing" as a cure for autoimmune diseases! There is much promising evidence in favor of the efficacy of oral tolerance in animal models, but as of yet, human disease has proven a harder nut to crack. Although the concept of oral tolerance is nearing its centennial, there is still much to learn!

Seafood allergy: lessons from clinical symptoms, immunological mechanisms and molecular biology

Food allergy consists of a wide range of disorders that result from adverse immune responses to dietary antigens. Manifestations of allergic response includes acute, potentially fatal anaphylactic reactions and a variety of chronic diseases that mainly affect the gastrointestinal tract, skin, and respiratory tract. Tools for clinical diagnosis and management, which have not changed much in the past two decades, include the clinical history, tests for specific IgE antibody to suspected foods, elimination diets, oral food challenges, and provision of medications such as epinephrine for emergency treatment. On the other hand, recent immunological and molecular biological research have enhanced our understanding of the mechanisms of these disorders and revealed the identities of many food allergens. Here, we will discuss seafood allergies with respect to the clinical manifestations, diagnosis, immunological mechanisms, and molecular biology of seafood allergens. Furthermore, potential applications and future directions in the clinical management of seafood allergies are discussed.

A novel model of sensitization and oral tolerance to peanut protein

The prevalence of food allergic diseases is rising and poses an increasing clinical problem. Peanut allergy affects around 1% of the population and is a common food allergy associated with severe clinical manifestations. The exact route of primary sensitization is unknown although the gastrointestinal immune system is likely to play an important role. Exposure of the gastrointestinal tract to soluble antigens normally leads to a state of antigen-specific systemic hyporesponsiveness (oral tolerance). A deviation from this process is thought to be responsible for food-allergic diseases. In this study, we have developed a murine model to investigate immunoregulatory processes after ingestion of peanut protein and compared this to a model of oral tolerance to chicken egg ovalbumin (OVA). We demonstrate that oral tolerance induction is highly dose dependent and differs for the allergenic proteins peanut and OVA. Tolerance to peanut requires a significantly higher oral dose than tolerance to OVA. Low doses of peanut are more likely to induce oral sensitization and increased production of interleukin-4 and specific immunoglobulin E upon challenge. When tolerance is induced both T helper 1 and 2 responses are suppressed. These results show that oral tolerance to peanut can be induced experimentally but that peanut proteins have a potent sensitizing effect. This model can now be used to define regulatory mechanisms following oral exposure to allergenic proteins on local, mucosal and systemic immunity and to investigate the immunomodulating effects of non-oral routes of allergen exposure on the development of allergic sensitization to peanut and other food allergens.

Duration of breast feeding and bovine serum albumin antibody levels in type 1 diabetes: a case-control study

OBJECTIVE

To compare the levels of bovine serum albumin (BSA) antibodies and their relationship with duration of breast feeding, age of exposure to cow's milk, and human leukocyte antigen (HLA-DQ) genotype in children with and without type 1 diabetes.

METHODS

Serum samples from 143 (0.3-14.7 yr) newly diagnosed children with type 1 diabetes and 107 unrelated control children (0.8-13.5 yr) were evaluated for BSA antibodies. Duration of breast feeding and exposure to cow's milk were recorded on questionnaires. HLA-DQ typing was determined by polymerase chain reaction.

RESULTS

One hundred percent of the diabetic children were positive for BSA antibodies compared to 1.9% for healthy controls (p < 0.001). Diabetic children also had higher levels of immunoglobulin G antibodies than unrelated controls (55.1 vs. 17.8 ng/mL, p < 0.0001). Duration of breast feeding (5.4 vs. 7.6 months, p < 0.02), but not age of exposure to cow's milk (8.3 vs. 9.2 months, p = 0.11), differed between cases and controls. There was no difference in antibody titer by duration of breast feeding or age of exposure to cow's milk in the cases or controls.

CONCLUSION

Higher levels of antibodies to BSA were found in children recently diagnosed with type 1 diabetes compared to the controls, particularly those with high or moderate HLA-DQ genotypes. The BSA profile, however, does not seem to depend on duration of breast feeding or age of exposure to cow's milk in this population.

Development of sensitisation or tolerance following repeated OVA inhalation in BALB/cJ mice. Dose-dependency and modulation by the Al(OH)3 adjuvant

Anthropogenically induced exposures may, due to their adjuvant effect, promote development of sensitisation to commonly occurring aeroallergens. No generally accepted model exists for determination of adjuvant effect of airborne substances. Therefore, BALB/cJ mice were exposed for 10 consecutive days with ovalbumin (OVA) solution, 25 mg/l-10 g/l (0.0025-1%) for 20 min/day, with and without the Al(OH)(3) adjuvant (0.5%). Four days after the last aerosol exposure, no OVA specific IgE and only low IgG1 were produced. Subsequent parenteral OVA administration showed that the 10 g/l solution induced full tolerance of the IgE response, whereas only partial tolerance was apparent with 25 mg/l OVA. The Al(OH)(3) adjuvant counteracted development of tolerance that was fully prevented at the 25 mg/l OVA concentration. Development of IgG1 was increased in a concentration-dependent manner with 500 mg/l-10 g/l OVA. No increase occurred at the 25 mg/l level, but addition of Al(OH)(3) increased IgG1 production to the same level as the higher OVA concentrations. Concentrations from 1.25 mg/l to 10 g/l OVA were studied with ten exposures followed by once-weekly aerosol exposure for uptil 6 weeks. In the range from 1.25 mg/l to 10 g/l, IgE production was time- and concentration-dependent. Both the IgE and IgG1 production were markedly promoted by Al(OH)(3). However, with aerosol exposures, the IgE antibody productions were not sufficient to increase the level of inflammatory cells in broncho-alveolar lavage fluid. Overall, this study showed that airborne Al(OH)(3) was able to counteract tolerance and increase specific IgE and IgG1 production.

Zinc deficiency suppresses the development of oral tolerance in rats

Oral tolerance is a specific immune unresponsiveness to food antigens to prevent hypersensitivity reactions. We investigated whether zinc deficiency affects oral tolerance. Rats were fed a control (C) or zinc-deficient (ZD) diet, or pair-fed (PF) to ZD rats for 28 d. Beginning on d 7, rats were administered ovalbumin (OVA) orally to induce tolerance, or PBS 3 times/wk, and were then immunized by OVA injection. The proliferation of mesenteric lymph node (MLN) and spleen lymphocytes after in vitro OVA stimulation and the delayed-type hypersensitivity were higher in OVA-fed ZD than in OVA-fed C rats and not different between OVA- and PBS-fed ZD rats, indicating a suppression of tolerance. Lymphocyte proliferation did not differ between PF and C rats. Expressions of cytokines involved in oral tolerance, i.e., interleukin (IL)-4, IL-10 and transforming growth factor-beta, were higher in OVA- than in PBS-fed C rats, but not in ZD rats. Apoptosis was higher in OVA- than in PBS-fed C rats but not different between OVA- and PBS-fed ZD rats. Inflammation and ulcerations that were not present in ZD rats on d 7 (ZD(7)) developed in OVA- or PBS-fed ZD rats. Compared with ZD(7) rats, tumor necrosis factor-alpha and cytokine-induced neutrophil chemoattractant were higher in OVA- and PBS-fed ZD rats, whereas interferon-gamma increased only in OVA-fed ZD rats. In conclusion, zinc deficiency suppresses oral tolerance through dysregulation of cytokine expression and lack of antigen-specific clonal deletion. We suggest that abrogation of tolerance may lead to development of mucosal inflammation and damage.

Mucosal immunity: its role in defense and allergy

The interface between the organism and the outside world, which is the site of exchange of nutrients, export of products and waste components, must be selectively permeable and at the same time, it must constitute a barrier equipped with local defense mechanisms against environmental threats (e.g. invading pathogens). The boundaries with the environment (mucosal and skin surfaces) are therefore covered with special epithelial layers which support this barrier function. The immune system, associated with mucosal surfaces covering the largest area of the body (200-300 m(2)), evolved mechanisms discriminating between harmless antigens and commensal microorganisms and dangerous pathogens. The innate mucosal immune system, represented by epithelial and other mucosal cells and their products, is able to recognize the conserved pathogenic patterns on microbes by pattern recognition receptors such as Toll-like receptors, CD14 and others. As documented in experimental gnotobiotic models, highly protective colonization of mucosal surfaces by commensals has an important stimulatory effect on postnatal development of immune responses, metabolic processes (e.g. nutrition) and other host activities; these local and systemic immune responses are later replaced by inhibition, i.e. by induction of mucosal (oral) tolerance. Characteristic features of mucosal immunity distinguishing it from systemic immunity are: strongly developed mechanisms of innate defense, the existence of characteristic populations of unique types of lymphocytes, colonization of the mucosal and exocrine glands by cells originating from the mucosal organized tissues ('common mucosal system') and preferential induction of inhibition of the responses to nondangerous antigens (mucosal tolerance). Many chronic diseases, including allergy, may occur as a result of genetically based or environmentally induced changes in mechanisms regulating mucosal immunity and tolerance; this leads to impaired mucosal barrier function, disturbed exclusion and increased penetration of microbial, food or airborne antigens into the circulation and consequently to exaggerated and generalized immune responses to mucosally occurring antigens, allergens, superantigens and mitogens.

Phenotypic analysis of oral tolerance to alloantigens: evidence that the indirect pathway of antigen presentation is involved

BACKGROUND

Oral administration of alloantigens induces down-regulation of Th1 immune responses and reduces the incidence of corneal graft rejection. This study examined the role of Th1 and Th2 cytokines, accessory cells, and lymphoid organs that are known to be instrumental in other forms of antigen-specific tolerance.

METHODS

Allogeneic dendritic cells (DC) were administered orally using a protocol that is known to reduce the incidence of corneal allograft rejection and prevent the generation of allospecific delayed-type hypersensitivity (DTH). Hosts included normal mice and gene knockout (KO) mice, including B cell-deficient (mu)MT, interleukin (IL)-4 KO, IL-10 KO, and interferon (IFN)-gamma KO mice. The requirement for either an intact spleen or thymus was also examined. Orally administered paraformaldehyde-fixed, UVB-treated, or sonicated allogeneic cells were tested to determine if dead cells were capable of inducing tolerance.

RESULTS

Studies on gene KO mice indicated that a Th1 cytokine (IFN-gamma) and a Th2 cytokine (IL-4) were needed for the development of oral tolerance to alloantigens. By contrast, IL-10 was not required. Although an intact spleen was necessary for the development of tolerance, removal of the thymus did not affect down-regulation of DTH.

CONCLUSIONS

Oral tolerance induced with allogeneic cells shares characteristics with antigen-specific unresponsiveness induced by other routes, yet there are some noteworthy differences. The capacity of killed or sonicated allogeneic cells to induce oral tolerance and enhance corneal graft survival indicates that oral tolerance to alloantigens can occur via the indirect pathway of alloantigen presentation. These results also emphasize the remarkable redundancy in the mechanisms that the immune system employs to produce antigen-specific unresponsiveness.

Prevention of bronchiolitis obliterans in rat lung allografts by type V collagen-induced oral tolerance

BACKGROUND

We have reported that feeding type V collagen (col(V)) to lung allograft recipients induces immune tolerance that prevents acute lung allograft rejection. Repeated acute rejection is a risk factor for or associated with chronic rejection, known as bronchiolitis obliterans (BO), the leading cause of death in lung allograft recipients. The current study examines if col(V)-induced oral tolerance prevents BO.

METHODS

WKY rats (RT1l) were fed either col(V) or diluent before orthotopic transplantation of F344 (RT1lvl) lung allografts. No rats received any immunosuppression. At 10 weeks posttransplantation the time to onset of BO, delayed type hypersensitivity (DTH) responses to donor antigens, and col(V) were examined. In addition, proliferative responses of recipient T lymphocytes to donor antigens, and ability of recipient antigen presenting cells to present alloantigens in lung allografts were evaluated.

RESULTS

The data show that recipient rats have sustained DTH responses to donor antigens and col(V). T lymphocytes from col(V)-fed lung allograft recipients were unable to proliferate in response to donor antigens, but feeding col(V) had no effect on the presentation of donor alloantigens by recipient antigen presenting cells. All diluent fed rats developed BO, but only mild acute rejection (grade 2) was present in all rats fed col(V). Transforming growth factor (TGF)-beta production was up-regulated systemically in col(V)-fed, but not diluent fed, lung allograft recipients, and neutralizing TGF-beta [corrected] recovered the DTH response to donor antigens in col(V)-fed rats.

CONCLUSIONS

Collectively these data show that col(V)-induces oral tolerance that prevents BO, and that tolerance may be mediated by systemic production of TGF-beta [corrected].

A revisit of mucosal IgA immunity and oral tolerance

Induction of mucosal immunity by oral immunization with protein antigen alone is difficult: potent mucosal adjuvants, vectors, or other special delivery systems are required. Cholera toxin (CT) has been shown to be an effective adjuvant for the development of mucosal vaccines and, when given with vaccine, induces both mucosal and systemic immune responses via a Th2 cell-dependent pathway. However, and in addition to potential type-I hypersensitivity, a major concern for use of mucosal adjuvants such as CT is that this molecule is not suitable for use in humans because of its inherent toxicity. When we examined the potential toxicity of CT for the central nervous system, both CT and CT-B accumulated in the olfactory nerves/epithelium and olfactory bulbs of mice when given by the nasal route. The development of effective mucosal vaccines for the elderly is also an important issue; however, only limited information is available. When mucosal adjuvanticity of CT was evaluated in aged mice, an early immune dysregulation was evident in the mucosal immune system. The present review discusses these potential problems for effective mucosal vaccine development. Tolerance represents the most common and important response of the host to environmental antigens, including food and commensal bacterial components, for the maintenance of an appropriate immunological homeostasis. We have examined whether Peyer patches could play a more important role for the maintenance of oral tolerance. Using Peyer patch-null mice, we found that mice lacking this gut-associated lymphoid tissue retained their capability to produce secretory IgA antibodies but did not develop normal oral tolerance to protein antigens.

The Peyer's patch microenvironment suppresses T cell responses to chemokines and other stimuli

Immunosurveillance of mucosal sites presents immune cells with challenges not encountered in the periphery. T cells in the gut must distinguish enteric pathogens from innocuous non-self Ag derived from food or commensal bacteria. The mechanisms that regulate T cells in the gut remain incompletely understood. We assessed the effect of the Peyer's patch microenvironment on T cell responses to chemokines. Chemokines are believed to play an important role during T cell priming by facilitating T cell migration into and within lymphoid tissues as well as T cell encounter and interaction with APCs. We found a profound suppression of chemokine-stimulated T cell chemotaxis and actin polymerization in Peyer's patch relative to lymph node. Chemokine hyporesponsiveness is imposed upon T cells within hours of their entry into Peyer's patches and is reversed following their removal. Suppression was not restricted to chemokine stimulation, as T cell responses to Con A and PMA were also suppressed. The global nature of this defect is further underscored by an impairment in calcium mobilization. Evidence indicates that a soluble factor contributes to this hyporesponsiveness, and comparison of Peyer's patches and lymph nodes revealed striking differences in their chemokine and cytokine constitution, indicating a marked Th2 bias in the Peyer's patches. The role of the Th2 microenvironment in mediating suppression is suggested by the ability of Nippostrongylus brasiliensis to elicit hyporesponsiveness in lymph node T cells. The suppressive milieu encountered by T cells in Peyer's patches may be critical for discouraging undesired immune responses and promoting tolerance.

Oral tolerance induction by type V collagen downregulates lung allograft rejection

Immunization with specific proteins or peptides has been used to induce immunologic tolerance to allografts other than the lung. Recently, we have reported that the immune response to lung alloantigen also involves an immune response to type V collagen [col(V)]. The purpose of the current study was to determine if oral administration of col(V) to lung allograft recipients before transplantation downregulates acute rejection episodes. The data show that, compared with controls, col(V)-fed recipients had fewer polymorphonuclear cells and lymphocytes in allograft bronchoalveolar lavage fluid, and reduced rejection pathology. Data showing that col(V)- fed allograft recipients had diminished delayed-type hypersensitivity (DTH) responses to donor alloantigens suggest that feeding col(V) prevented allograft rejection by inducing tolerance to donor antigens. Systemic production of transforming growth factor (TGF)-beta, interleukin (IL)-4, or IL-10 has been reported to be a mechanism for oral tolerance-induced suppression of immune responses. Feeding col(V) induced upregulated production of TGF-beta, but not IL-4 or IL-10 in serum. Neutralizing TGF-beta recovered the DTH response to donor antigen in tolerant allograft recipients. Collectively, these data show that oral administration of col(V) is a novel approach to induce immunologic tolerance to lung allografts, and that TGF-beta contributed to suppression of the rejection response.

Peyer's patches are required for oral tolerance to proteins

To clarify the role of Peyer's patches in oral tolerance induction, BALB/c mice were treated in utero with lymphotoxin beta-receptor Ig fusion protein to generate mice lacking Peyer's patches. When these Peyer's patch-null mice were fed 25 mg of ovalbumin (OVA) before systemic immunization, OVA-specific IgG Ab responses in serum and spleen were seen, in marked contrast to low responses in OVA-fed normal mice. Further, high T-cell-proliferative- and delayed-type hypersensitivity responses were seen in Peyer's patch-null mice given oral OVA before systemic challenge. Higher levels of CD4(+) T-cell-derived IFN-gamma, IL-4, IL-5, and IL-10 syntheses were noted in Peyer's patch-null mice fed OVA, whereas OVA-fed normal mice had suppressed cytokine levels. In contrast, oral administration of trinitrobenzene sulfonic acid (TNBS) to Peyer's patch-null mice resulted in reduced TNBS-specific serum Abs and splenic B cell antitrinitrophenyl Ab-forming cell responses after skin painting with picryl chloride. Further, when delayed-type hypersensitivity and splenic T cell proliferative responses were examined, Peyer's patch-null mice fed TNBS were unresponsive to hapten. Peyer's patch-null mice fed trinitrophenyl-OVA failed to induce systemic unresponsiveness to hapten or protein. These findings show that organized Peyer's patches are required for oral tolerance to proteins, whereas haptens elicit systemic unresponsiveness via the intestinal epithelial cell barrier.