Abrogation by subsequent feeding of antibody response including IgE, in parenterally immunized mice

Oral tolerance induced by continuous feeding: enhanced up-regulation of transforming growth factor-beta/interleukin-10 and suppression of experimental autoimmune encephalomyelitis

Oral administration of antigen leads to specific immune hyporesponsiveness termed as oral tolerance. Different doses and feeding regimens have been demonstrated to induce different types of tolerance and degrees of immune suppression. Herein, we compare distinct different regimens of feeding using equivalent final doses of antigen in order to investigate the role of frequency of antigen uptake in the induction of oral tolerance. We demonstrate that continuous feeding of antigen in the drinking water, as compared to a single feeding or feeding once per day over several days enhances suppression to both Th1 and Th2 type responses in B6D2F1 and BALB/c mice. Continuous feeding suppresses antibody responses in aged B6D2F1 mice, which are otherwise refractory to oral tolerance induction. Continuous feeding of ovalbumin (OVA) in high or low doses, as compared to control or single daily feeding over several days, up-regulates interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) production in both OVA TCR transgenic and BALB/c mice. In all regimens tested in wild type mice, low doses were more efficacious than high doses in inducing IL-10 and TGF-beta. Serial feeding (multiple low dose daily gavages) using OVA or myelin basic protein (MBP), also led to up-regulation of TGF-beta and IL-10 production in OVA TCR and MBP TCR transgenic mice, as well as enhanced inhibition of MBP-induced experimental autoimmune encephalomyelitis (EAE) in (PLxSJL) F1 mice. We did not find differences in the cytokine profile between serial (multiple low dose daily gavages) and continuous feeding regimens, suggesting that repetitive discrete delivery of oral antigen provides a sustained signal for the induction of oral tolerance. Thus, using different regimens of feeding that resemble natural feeding with equivalent final doses of antigen, we found enhancement of oral tolerance utilizing regimens that resemble natural feeding. Such feeding regimens may be advantageous in the application of oral tolerance for clinical purposes in the treatment of autoimmune and other inflammatory conditions.

Oral tolerance to protein antigens

Oral tolerance is an active non-response to antigens delivered via the oral route. Mechanisms governing tolerance induction have been well characterized in mouse. Similar studies in man are lacking, although there is evidence that tolerance can be induced. In disease states, tolerance is altered and this may account for the presence of mucosal inflammation. In food hypersensitivity there is evidence that allergens may be handled differently and this may play a role in disease expression.

Interruption of recently induced immune responses by oral administration of antigen

Interest in oral tolerance has been renewed in the last few years as a possibility of intervention in human autoimmune diseases. An obstacle in this direction is that, although easily induced in animals virgin of contact with the antigen, oral tolerance becomes hard to induce in previously immunized animals. The present results show that there is an early period after primary immunization in which prolonged oral exposure to the antigen may arrest ongoing immune responses. Beyond this period, oral exposures to the antigen become ineffective and may actually boost immune responses. The end of the susceptible period coincides with the emergence of free specific antibodies in serum. However, the previous administration of purified anti-ovalbumin antibodies (40 micrograms) was unable to block the induction of oral tolerance to ovalbumin in normal mice.

Prevention of lung eosinophilic inflammation by oral tolerance

Airway inflammation plays a major role in human asthma. Increasing evidence points to a close correlation between eosinophil infiltration and allergic lung disease. A new murine model of eosinophilic lung inflammation has recently been developed; it consists of immunizing mice with small fragments of solidified hen egg white implanted (EWI) into the subcutaneous tissue. In this model, which is further characterized here, mice challenged with ovalbumin (OVA) present an intense and persistent lung eosinophilia, as well as histopathological findings that resemble human asthma. In the present work, the effect of oral tolerance on the development of allergic lung inflammation in B6 mice immunized with antigen plus adjuvant or with EWI is investigated. It was found that in mice rendered orally tolerant by previous exposure to antigen in the drinking water, the T-helper type 2 cell (Th2)-associated allergic responses in both protocols of immunization were almost completely abolished. The allergic responses were assessed by pulmonary and bone marrow eosinophilia, lung histopathology and antigen-specific IgE and IgG1 production. These findings provide the first indication that Th2-associated lung pathology can be prevented by oral tolerance.

Oral tolerance in EAE: reversal of tolerance by T helper cell cytokines

Oral administration of myelin basic protein (MBP) inhibits clinical and histopathological manifestations of experimental autoimmune encephalomyelitis (EAE), but only partially reduces serum anti-MBP antibody titers. We report here that orally administered MBP alters the isotypic distribution of anti-MBP antibody-forming cells (AFC) among various lymphoid tissues, with the most profound differences seen in mucosal tissues. We observed an isotype-selective reduction in anti-MBP IgA but not IgM AFC frequencies in Peyer's patches. The anti-MBP IgA AFC frequencies could be reconstituted by addition of interleukin 4 (IL-4) and interleukin 5(IL-5). The cytokines did not appear to generate de novo responses since no increases in anti-MBP lgA AFC frequencies were observed in control cultures. These results indicate that decreased antibody production, as a result of oral antigen administration, can be reversed by exposure to the appropriate cytokines.

Chemical denaturation of ovalbumin abrogates the induction of oral tolerance of specific IgG antibody and DTH responses in mice

We have examined the effects of ingestion of chemically denatured ovalbumin (OVA) in mice. Both 8 M urea-denatured OVA (UD-OVA) and carboxymethylated UD-OVA (CM-OVA) were purified by gel filtration. Specific IgG antibody and systemic delayed-type hypersensitivity (DTH) responses to OVA were not suppressed by CM-OVA fed prior to or after immunization with OVA in complete Freund's adjuvant (CFA). When CM-OVA was used instead of OVA, for immunization, serum IgG and DTH responses to CM-OVA were orally tolerized by OVA, but not by UD-OVA or CM-OVA. Studies of antigen uptake in mice using sandwich ELISA tests showed that OVA, but not CM-OVA, was absorbed after antigen ingestion. In vitro studies further demonstrated that CM-OVA was digested much more rapidly than OVA. Moreover, studies using bovine serum albumin (BSA) demonstrated that both IgG and DTH responses to BSA were orally tolerant to BSA, but not to denatured BSA. Finally, studies using human gamma-globulin (HGG), a well-known tolerogen, also found that the IgG antibody response to HGG was not orally tolerized by denatured HGG. These results suggest that complete denaturation of globular proteins may affect their processing and absorption in the gut and thus abrogates oral tolerance induction.

Secretory IgA response in oral immunotherapy. Investigation in birch pollinosis

A rationale for oral immunotherapy (OIT) might be founded on two potential mechanisms: induction of a mucosal secretory IgA response, or induction of systemic hyporesponsiveness (oral tolerance). Previous studies have shown clinically that there is a beneficial effect of OIT in birch pollinosis, in both children and adults. During OIT, birch pollen antigens in enterocoated capsules were given to 20 adults (participating in a double-blind, placebo-controlled trial) and 10 children, all suffering from birch pollinosis. Saliva and tears (only adults) samples were collected before, during, and after OIT. Each sample was assayed for both IgA antibodies against birch pollen antigens and total IgA by enzyme-linked immunosorbent assay. IgA antibody levels were also expressed in relation to total IgA concentrations, to correct for variations in secretion and flow rate between subjects and at different times. Changes in birch-specific secretory IgA antibodies in saliva and tears could not explain the beneficial effect of OIT in birch pollinosis. Further studies in this field are warranted.

Role of new allergens and of allergens consumption in the increased incidence of food sensitizations in France

Food allergy is a group of distinct clinico-pathological entities that have an immunological basis in common, and in which an abnormal or exaggerated immunological response to a specific food leads to disease. Some clinical pictures involving multiple organ system (anaphylaxis) are potentially fatal. The data on the incidence, prevalence, mortality rate and food products involved in food-induced anaphylaxis and the evolution of food sensitization compared with changes in eating habits are not very reliable. In the present study we analysed, over a period of 9 years (1984-1992), a group of 580 patients with pathological reactions to foods, 60 of which presented severe, near-fatal reactions. We sought the etiologic components and food sensitization in comparison with the principal tendencies of food consumption in France. Food products most frequently incriminated in anaphylactic reactions are not of a primary nutritional importance: celery (30%), crustaceans (17%), fish (13%), peanuts (12%), mango (6%), mustard (3%), but they are often hidden allergens in commercial foods. The sensitization to food products in the group of 580 patients reveals, in decreasing order of frequency: wheat (39%), peanuts (37%), crab (34%), celery (30%), soy (30%). Compared with previous data, the frequency of sensitization to different foods has changed; for instance, the sensitizations to wheat, soy, peanuts, celery, mustard, rice, are definitely increasing. The increased consumption and more attentive clinical research may be the reasons for this evolution. For products such as egg and pork, the data are stable and parallel with consumption, whilst for other products like milk and other dairy products, the increased consumption is accompanied by a decrease of the incidence of sensitization. The reactivity to some allergens may be affected by the way of preparing the food.

Direct evidence for anergy in T lymphocytes tolerized by oral administration of ovalbumin

The present study investigated bystander suppression, specific suppression and anergy as mechanisms for oral tolerance. Oral tolerance was induced in mice by a single gastric intubation of 20 mg ovalbumin (OVA) and was evaluated in vitro by the absence of T lymphocyte proliferative responses to OVA after priming by OVA-complete Freund's adjuvant (CFA). T lymphocyte unresponsiveness was antigen specific, systemic and was not affected by the vehicle used for immunization. T lymphocytes derived from tolerant popliteal lymph nodes (PLN) responded to an acetone precipitate (AP) of mycobacteria present in CFA; this response was not suppressed by co-culture with OVA, thereby arguing against a mechanism of bystander suppression in our system. Responses of PLN T lymphocytes derived from OVA-CFA primed, non-tolerant mice, or those of an OVA-specific T lymphocyte line, were not suppressed by PLN or spleen cells derived from OVA tolerant mice. These results excluded the possibility that oral tolerance was induced and maintained by a mechanism of specific suppression. At the cellular level, we found that OVA-tolerant T lymphocytes did not produce interleukin-2 (IL-2) nor express IL-2 receptor in response to OVA stimulation in vitro; both observations are indicative of a state of anergy. Incubation of OVA-tolerant PLN T lymphocytes together with murine recombinant IL-2 for 5 days, released anergic T lymphocytes and a concomitant OVA-specific proliferative response of CD4+ T cells was detected. Taken together, our experimental system excludes the involvement of bystander or specific suppression in the induction of oral tolerance to OVA, and provides direct evidence to show that oral tolerance results from specific T lymphocyte anergy.

Dietary manipulation and induction of tolerance

Clinical observations have suggested that the development of atopic diseases in childhood may be influenced by breast-feeding and the timing of first exposure to foreign protein, but the controversy is far from being resolved. Early weaning and introduction of foreign proteins (i.e., cow milk) have been associated with an increased prevalence of atopic symptoms in infants with a family history of atopy. Opposite results have been reported, and the effects of early protein introduction in infants not at risk of having atopic symptoms are poorly documented. Research in rodents suggests that perinatal antigen exposure is more likely to prime the immune system than to induce tolerance. Continuous feeding beyond the critical neonatal period leads to induction of tolerance. The immunologic response is dependent on the antigen dose. Protein transfer by breast-feeding can induce tolerance, though in a dose range otherwise associated with priming. The protective effect of antigen avoidance in infancy on the development of cow milk allergy and also on subsequent atopic symptoms is well documented. Protective effects have been observed in infants at risk who either were breast fed or received a hydrolyzed infant formula. Several clinical studies suggest a causative role of neonatal milk exposure in the development of cow milk allergy. Prospective, population-based studies are required to assess the true incidence of food-allergic diseases in childhood.

Could specific oral tolerance be a therapy for autoimmune disease?

Several experimental autoimmune diseases have been successfully suppressed by the induction of specific oral tolerance. Here, Stephen Thompson and Norman Staines review the nature and mechanisms of this form of tolerance and discuss its possible applications in the control of human autoimmune diseases.

The kinetics of oral hyposensitization to a protein antigen are determined by immune status and the timing, dose and frequency of antigen administration

We have investigated the immunological consequences of feeding a protein antigen to previously immunized animals. BALB/c mice were systemically primed with ovalbumin (OVA) in complete Freund's adjuvant (CFA) and fed with high (10 mg/g body weight), medium (1 mg/g body weight) or low (1 microgram/g body weight) doses of OVA once (Day 1, 7 or 14) or sequentially for 5 days (Days 1-5, 7-11, 14-18). The specific IgG antibody response was suppressed only by early feeds of high-dose OVA (Days 1-5). Medium-dose OVA fed on Day 14 or low-dose OVA fed at any stage after immunization enhanced the IgG antibody response. In contradistinction, systemic delayed-type hypersensitivity responses (DTH) were usually suppressed by early feeds of high or medium doses of OVA but never after feeding low-dose OVA. The results suggest that systemic DTH and IgG antibody responses to oral antigen are subject to different control mechanisms in previously primed animals. Such responses depend on the immune status of the animal and are controlled by antigen dose, time and frequency of feeding. The immunological effects observed are also demonstrable following adoptive transfer of spleen cells collected 14 days after multiple feeds of high-dose OVA to immunized mice. Our findings suggest that oral hyposensitization after systemic immunization is regulated by (suppressor) spleen cells which are activated by gut-processed antigen.

Specific IgE, IgG, and IgA antibody response to oral immunotherapy in birch pollinosis

Thirty-nine patients with birch pollinosis participated in a double-blind, placebo-controlled trial of oral immunotherapy (OIT) for 18 months. They were treated with increasing doses of freeze-dried birch-pollen antigens for 16 months, reaching a cumulative dose of 280 x 10(6) biologic units. This is about 200 times more than the dose used in conventional subcutaneous immunotherapy (IT). In the placebo-treated group, but not in the actively treated group, there was a rise in postseasonal birch-specific IgE antibody levels. A significant decline in postseasonal values after 1 year of treatment was recorded in the actively treated, but not in the placebo-treated, group. Compared to the placebo treatment, there was a significant rise in birch-specific IgG antibodies in patients administered active treatment; however, the rise was less than that usually observed during subcutaneous IT. No significant change in birch-specific serum IgA was found in either group. The changes in IgE and IgG antibody levels demonstrate that OIT affects the immune system. This supports our recent findings that OIT demonstrates a beneficial effect in the treatment of birch pollinosis in adults. But, as with subcutaneous IT, there was no clear relationship between antibody response and clinical findings in the patients. The underlying mechanisms responsible for the relief of symptoms thus remain unknown.

Adjuvant activity of Escherichia coli heat-labile enterotoxin and effect on the induction of oral tolerance in mice to unrelated protein antigens

The ability of Escherichia coli heat-labile enterotoxin (LT) to influence the induction and maintenance of tolerance was examined in animals primed orally with a soluble protein antigen, ovalbumin (OVA), or in animals primed orally with two unrelated protein antigens administered simultaneously, OVA and bovine serum albumin (BSA). LT is immunologically and structurally related to the cholera enterotoxin (CT), which has been shown to be capable of abrogating oral tolerance to protein antigens when delivered simultaneously with the antigens. In this study, simultaneous administration of LT with OVA was shown to prevent the induction of tolerance to OVA and to increase the serum anti-OVA IgG response 30- to 90-fold over OVA-primed and PBS-primed animals, respectively. This effect was determined to be a function of the enzymatically active A subunit of the toxin since the B (binding) subunit alone was unable to influence tolerance induction. Animals fed LT with OVA after the initial OVA prime developed a significantly lower serum IgG and mucosal IgA anti-OVA response than those fed LT with OVA in the initial immunization, indicating that prior exposure to the antigen reduces the effectiveness of LT to influence tolerance and its ability to act as an adjuvant. LT was not able to abrogate tolerance once it had been established. Serum IgG and mucosal IgA responses in animals receiving LT on only a single occasion, that being upon first exposure to antigen, were equivalent to responses after three OVA/LT primes, indicating that commitment to responsiveness occurs early and upon first exposure to antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of an established DTH response to ovalbumin in mice by feeding antigen after immunization

Experiments were designed to examine whether systemic delayed-type hypersensitivity responses (DTH) to ovalbumin (OVA) can be suppressed when antigen is fed after immunization, and to investigate the immunological mechanisms involved. A single 25 mg feed of OVA given 7 or 14 days after immunization with OVA in complete Freund's adjuvant (CFA) suppressed the DTH response of BDF1 mice, but had no significant effect on the serum IgG antibody response. DTH suppression was greatest when antigen was fed soon after immunization, and became less pronounced as the time interval between feeding and immunization increased. The phenomenon was also demonstrated in mice of the BALB/c strain. Cell transfer experiments suggested that the post-immunization suppression was not due to a population of suppressor cells that have been described previously in association with classical oral tolerance for DTH. We conclude that there are separate and distinct mechanisms for the prevention of induction of DTH by antigen feeding in naive mice and the suppression of expression of DTH in sensitized animals.

A genetically determined lack of oral tolerance to ovalbumin is due to failure of the immune system to respond to intestinally derived tolerogen

In this study we have examined whether differences between mouse strains in the induction of tolerance after feeding ovalbumin (OVA) are due to differences in intestinal processing of OVA or are determined by the systemic immune system. Compared with major histocompatibility complex (MHC)-congenic BALB/c mice, BALB/B mice develop much less tolerance of systemic delayed-type hypersensitivity (DTH) and humoral immunity after feeding OVA and this defect is also expressed partially in (BALB/B x BALB/c)F1 animals. Serum taken from either BALB/c or BALB/B mice fed OVA 1 h before produced significant suppression of systemic DTH responses in BALB/c, but not in BALB/B mice. Although OVA-fed BALB/B serum was slightly less tolerogenic than BALB/c serum, we conclude that the defective induction of oral tolerance in BALB/B mice is due primarily to a MHC-influenced defect with the immune system. These findings support the idea that clinical food-sensitive enteropathy reflects an immune response gene-controlled defect in tolerance to dietary proteins.

Oral tolerance in protein-deprived mice. I. Profound antibody tolerance but impaired DTH tolerance after antigen feeding

We have examined the effects of protein deprivation on the induction of oral tolerance for systemic antibody and DTH responses to the protein antigen ovalbumin (OVA). Mice were fed 4% or 24% protein diets from weaning and given a single feed of OVA 2 weeks later (short-term deprivation) or after 10 weeks (long-term deprivation). Tolerance for serum antibody responses was more profound in protein-deprived animals than in 24% protein-fed control groups. Conversely, tolerance for DTH responses was impaired in protein-deprived mice. This was demonstrated both for short-term deprivation, where nutritional rehabilitation after OVA feeding was necessary to demonstrate this effect on DTH, and for long-term deprivation. Furthermore, the effect of short-term deprivation on tolerance for DTH responses was similar to that observed after cyclophosphamide pretreatment of OVA-fed mice. Protein deprivation has disparate effects on the humoral and cell-mediated limbs of oral tolerance, and our results support the hypothesis that this regime selectively depletes a population of suppressor T cells responsible for the fine control of DTH tolerance.

The regulation of immune responses to dietary protein antigens

Hypersensitivity reactions to food proteins are rare, probably because the intestinal immune system has evolved efficient means of preventing such responses. In this article Allan Mowat reviews the mechanisms underlying the induction of immunological tolerance after feeding proteins and suggests how a breakdown in oral tolerance may lead to potentially harmful hypersensitivity in the intestine.

Suppression of type II collagen-induced arthritis by intragastric administration of soluble type II collagen

Although oral administration of protein antigens may lead to specific immunologic unresponsiveness, this method of immunoregulation has not been applied to models of autoimmune disease. Type II collagen-induced arthritis is an animal model of polyarthritis induced in susceptible mice and rats by immunization with type II collagen, a major component of cartilage. Intragastric administration of soluble type II collagen, prior to immunization with type II collagen in adjuvant, suppresses the incidence of collagen-induced arthritis. Administration of denatured type II collagen has no observable effect on the incidence or severity of the disease. The overall magnitude of the antibody response is not significantly reduced in collagen-fed mice as compared to controls. While the isotype distribution of the anti-collagen antibodies is similar in the two groups, there is a tendency toward reduced IgG2 responses in the collagen-fed mice.

Oral administration of grass pollen to hay fever patients. An efficacy study in oral hyposensitization

Oral hyposensitization is still widely used in the treatment of allergic diseases, but controlled studies proving a beneficial effect are lacking. Fifty-eight hay fever patients were admitted to a double-blind placebo efficacy study in oral hyposensitization. An enterosoluble tablet containing timothy whole pollen or placebo was taken daily. Preseasonally, the actively treated patients received 4,315,000 PNU (880,260 AUR) and totally for 6 months 8,915,000 PNU (1,818,660 AUR). Such high doses have never been tried in similar studies. A new principle has been used - "the pollen count interval method" - in the evaluation of symptom and medication score. The study failed to prove any beneficial effect of oral hyposensitization measured by symptom score, medication score, nasal provocation test or skin prick test. There was no change in timothy specific IgE and IgG which could be caused by the treatment. The possibility that oral hyposensitization might be an effective treatment of hay fever in the future is discussed, but it is concluded that the present regimens cannot be recommended.

Effect of prior intragastric antigen administration on primary and secondary anti-ovalbumin responses of C57BL/6 and NZB mice

We evaluated the effect of antigen feeding on the subsequent primary and secondary anti-ovalbumin (OVA) responses of C57BL/6 and NZB mice. When C57BL/6 mice were given a single 20-mg dose of OVA intragastrically, profound tolerance was observed after challenge, 7 d later, with 125 micrograms of OVA in complete adjuvant or after two injections of 5 micrograms of OVA adsorbed to alum given 7 and 21 d after antigen feeding. OVA-fed NZB mice failed to become tolerant to a primary challenge with OVA in complete adjuvant, but showed a degree of tolerance similar to that of C57BL/6 mice when challenged two or three times with OVA in alum. These studies demonstrate that NZB mice fail to show tolerance at the level of the primary response after antigen feeding; however, they are normally tolerant when a secondary response to a lower dose of antigen is evaluated. This study suggests that, after antigen feeding, different mechanisms of tolerance may be involved in the regulation of primary and secondary responses.