Inhibition of specific immune responses by feeding protein antigens

Subcutaneous injection of an immunologically tolerated protein up to 5 days before skin injuries improves wound healing

Oral tolerance blocks the development of specific immune responses to proteins ingested by the oral route. One of the first registries of oral tolerance showed that guinea pigs fed corn became refractory to hypersensitivity to corn proteins. Mice fed with chow containing corn are tolerant to zein, and parenteral injection of zein plus adjuvant blocks immunization to unrelated proteins injected concomitantly and reduces unspecific inflammation. Extensive and prolonged inflammatory infiltrate in the wound bed is one of the causes of pathological wound healing. Previous research shows that intraperitoneal injection of zein concomitant with skin injuries reduces the inflammatory infiltrate in the wound bed and improves wound healing. Herein, we tested if one subcutaneous injection of zein before skin injury improves wound healing. We also investigated how long the effects triggered by zein could improve skin wound healing. Mice fed zein received two excisional wounds on the interscapular skin under anesthesia. Zein plus Al(OH)₃ was injected at the tail base at 10 min, or 3, 5, or 7 days before skin injuries. Wound healing was analyzed at days 7 and 40 after injury. Our results showed that a zein injection up to 5 days before skin injury reduced the inflammatory infiltrate, increased the number of T-cells in the wound bed, and improved the pattern of collagen deposition in the neodermis. These findings could promote the development of new strategies for the treatment and prevention of pathological healing using proteins normally found in the common diet.

Late introduction of fish and eggs is associated with increased risk of allergy development - results from the FARMFLORA birth cohort

The prevalence of allergy is markedly low in children growing up on farms. An increasing number of studies indicate that the timing of food introduction may affect allergy development. We aimed to investigate if protection against allergy in farm environments may be mediated through differences in food-introduction practices between farm and non-farm families, using an explorative approach. Twenty-eight farm and 37 non-farm children were included in the FARMFLORA birth cohort. Practices of breastfeeding and introduction of formulas and complementary foods were collected by questionnaires at 6, 12, and 18 months of age. Allergy was diagnosed by pediatricians at 3 years of age. The only difference in food-introduction practices observed between farm and non-farm children was an earlier introduction of nuts in farmers (median month: 11 [IQR: 8–6] in farmers, 15 [12–19] in non-farmers). One farm child (4%) and 10 non-farm children (27%) were allergic at 3 years of age. Lower risk of allergy development was associated with early exclusive breastfeeding (continuous variable; OR = 0.59, 95% CI: 0.39–0.89), but also having received eggs (OR = 0.08, 95% CI: 0.13–0.54) and fish (logistic regression not applicable, P = 0.01 in likelihood ratio testing [χ²]) at 10 months of age or earlier compared to later. Our results were not affected by reverse causation, as judged by a questionnaire sent to the families in retrospect. Timing of introduction of complementary foods is unlikely to contribute to the lower risk of allergy among farm children. Although early exclusive breastfeeding was associated with a lower rate of allergy development, postponed introduction of complementary foods might increase the risk of developing allergy. Owing to the limited sample size, our results are only indicative, but support prior findings.

Indirect effects of immunological tolerance to a regular dietary protein reduce cutaneous scar formation

Oral tolerance refers to the specific inhibition of immune responsiveness to T-cell-dependent antigens contacted through the oral route before parenteral immunization. Oral tolerance to one protein does not inhibit immune responses to other unrelated proteins, but parenteral injection of tolerated antigens plus adjuvant into tolerant, but not normal, mice inhibits immune responses to antigens injected concomitantly or soon thereafter. The inhibitory effect triggered by parenteral injection of tolerated proteins is known as bystander suppression or indirect effects of oral tolerance. Intraperitoneal injection of ovalbumin (OVA) plus alum adjuvant in OVA-tolerant mice soon before skin injury inhibits inflammation and improves cutaneous wound healing. However, as OVA is not a regular component of mouse chow, we tested whether indirect effects could be triggered by zein, the main protein of corn that is regularly present in mouse chow. We show that intraperitoneal injection of a single dose (10 μg) of zein plus alum adjuvant soon before skin injury in mice reduces leucocyte infiltration but increase the number of T cells and the expression of resistin-like molecule-α (a marker of alternatively activated macrophages) in the wound bed, increases the expression of transforming growth factor-β₃ in the newly formed epidermis and reduces cutaneous scar formation. These results suggest that indirect effects of oral tolerance triggered by parenteral injection of regular dietary components may be further explored as one alternative way to promote scarless wound healing.

IL-6 Inhibits Upregulation of Membrane-Bound TGF-β 1 on CD4+ T Cells and Blocking IL-6 Enhances Oral Tolerance

Oral administration of Ag induces regulatory T cells that express latent membrane-bound TGF-β (latency-associated peptide [LAP]) and have been shown to play an important role in the induction of oral tolerance. We developed an in vitro model to study modulation of LAP⁺ on CD4⁺ T cells. The combination of anti-CD3 mAb, anti-CD28 mAb, and recombinant IL-2 induced expression of LAP on naive CD4⁺ T cells, independent of Foxp3 or exogenous TGF-β. In vitro generated CD4⁺LAP⁺Foxp3^- T cells were suppressive in vitro, inhibiting proliferation of naive CD4⁺ T cells and IL-17A secretion by Th17 cells. Assessing the impact of different cytokines and neutralizing Abs against cytokines, we found that LAP induction was decreased in the presence of IL-6 and IL-21, and to a lesser extent by IL-4 and TNF-α. IL-6 abrogated the in vitro induction of CD4⁺LAP⁺ T cells by STAT3-dependent inhibition of Lrrc32 (glycoprotein A repetitions predominant [GARP]), the adapter protein that tethers TGF-β to the membrane. Oral tolerance induction was enhanced in mice lacking expression of IL-6R by CD4⁺ T cells and by treatment of wild-type mice with neutralizing anti-IL-6 mAb. These results suggest that proinflammatory cytokines interfere with oral tolerance induction and that blocking the IL-6 pathway is a potential strategy for enhancing oral tolerance in the setting of autoimmune and inflammatory diseases.

Systemic effects of oral tolerance reduce the cutaneous scarring

BACKGROUND

Immunological tolerance refer to the inhibition of specific immune responsiveness and the ingestion of proteins previous to immunization is a reliable method to induce (oral) tolerance. Parenteral exposure to tolerated antigens, in adjuvant, trigger indirect and systemic effects that inhibits concomitant immune responses to other unrelated antigens and also decrease unrelated inflammatory responses. Interesting, intraperitoneal (i.p.) exposure to orally-tolerated proteins soon before an incisional linear skin wound improves the healing by primary intention in mice. An important clinical and surgical objective is to identify strategies to improve wound healing and reduce scarring.

OBJECTIVE

To evaluate whether i.p. injection of an orally-tolerated protein improves wound healing by secondary intention and reduce scarring of full-thickness excisional skin injury.

METHODS

C57Bl/6 mice were turned tolerant to ovalbumin (OVA) by drinking a solution containing OVA; seven days later, they received an i.p. injection of OVA plus Al(OH)3 adjuvant immediately before two full-thickness excisional skin wounds, under anesthesia. The wound healing process was evaluated macro and microscopically after H&E, toluidine blue and Gomori's Trichrome staining. The presence of granulocytes, macrophages, miofibroblasts, fibronectin, collagen I and collagen III was investigated by immunofluorescence and the levels of cytokines by flow cytometry or ELISA. Mice not tolerant to OVA were included as controls.

RESULTS

The i.p. injection of OVA+Al(OH)3 in mice orally tolerant to OVA reduced the subsequent inflammatory response in the wound bed and the cutaneous scarring. There was a change in the pattern of collagen deposition making it more similar to the pattern observed in intact skin. In tolerant mice, mast cells and granulocytes (Ly-6C/G+), were reduced, while lymphocytes (CD3+) were increased in the wound bed. Time course analysis of Th1/Th2/Th17 cytokines and growth factors showed slightly differences between tolerant and control groups.

CONCLUSION

Parenteral injection of an orally-tolerated protein has systemic consequences that impair the inflammatory response triggered by skin injury and reduce the cutaneous scarring.

Lung transplantation: chronic allograft dysfunction and establishing immune tolerance

Despite significant medical advances since the advent of lung transplantation, improvements in long-term survival have been largely unrealized. Chronic lung allograft dysfunction, in particular obliterative bronchiolitis, is the primary limiting factor. The predominant etiology of obliterative bronchiolitis involves the recipient's innate and adaptive immune response to the transplanted allograft. Current therapeutic strategies have failed to provide a definitive treatment paradigm to improve long-term outcomes. Inducing immune tolerance is an emerging therapeutic strategy that abrogates allograft rejection, avoids immunosuppression, and improves long-term graft function. The aim of this review is to discuss the key immunologic components of obliterative bronchiolitis, describe the state of establishing immune tolerance in transplantation, and highlight those strategies being evaluated in lung transplantation.

Oral tolerance correlates with high levels of lymphocyte activity

Oral tolerance is defined as an inhibition of specific immune responsiveness to a previously ingested antigen. Paradoxically, we found an increased lymphocyte activity in tolerant mice alongside the specific inhibition. Orally-tolerant mice presented higher number of immunoglobulin secreting cells (ISC) in spleen and bone marrow; showed a greater variety of Ig classes being produced: IgM and IgA in the spleen and IgG and IgM in the bone marrow. ISC from immunized mice produced mainly IgG. Despite having the same number of regulatory and activated T cells in the spleen after immunization, these cells appeared earlier in tolerant mice, right after the primary immunization. Also, tolerant mice showed a prompt expression of regulatory cytokines (TGF-β and IL-10) and a transient expression of effector cytokines (IL-2 and IFN-γ). Thus, in addition to an inhibited specific responsiveness, orally-tolerant mice displayed an early and widespread mobilization of activated and regulatory lymphocytes.

Induced CD4+Foxp3+ regulatory T cells in immune tolerance

Regulatory T lymphocytes are essential to maintain homeostasis of the immune system, limiting the magnitude of effector responses and allowing the establishment of immunological tolerance. Two main types of regulatory T cells have been identified--natural and induced (or adaptive)-and both play significant roles in tuning down effector immune responses. Adaptive CD4(+)Foxp3(+) regulatory T (iTreg) cells develop outside the thymus under a variety of conditions. These include not only antigen presentation under subimmunogenic or noninflammatory conditions, but also chronic inflammation and infections. We speculate that the different origin of iTreg cells (noninflammatory versus inflammatory) results in distinct properties, including their stability. iTreg cells are also generated during homeostasis of the gut and in cancer, although some cancers also favor expansion of natural regulatory T (nTreg) cells. Here we review how iTreg cells develop and how they participate in immunological tolerance, contrasting, when possible, iTreg cells with nTreg cells.

The effects of TLR activation on T-cell development and differentiation

Invading pathogens have unique molecular signatures that are recognized by Toll-like receptors (TLRs) resulting in either activation of antigen-presenting cells (APCs) and/or costimulation of T cells inducing both innate and adaptive immunity. TLRs are also involved in T-cell development and can reprogram Treg cells to become helper cells. T cells consist of various subsets, that is, Th1, Th2, Th17, T follicular helper (Tfh), cytotoxic T lymphocytes (CTLs), regulatory T cells (Treg) and these originate from thymic progenitor thymocytes. T-cell receptor (TCR) activation in distinct T-cell subsets with different TLRs results in differing outcomes, for example, activation of TLR4 expressed in T cells promotes suppressive function of regulatory T cells (Treg), while activation of TLR6 expressed in T cells abrogates Treg function. The current state of knowledge of regarding TLR-mediated T-cell development and differentiation is reviewed.

The role of the intestinal context in the generation of tolerance and inflammation

The mucosal surface of the intestine alone forms the largest area exposed to exogenous antigens as well as the largest collection of lymphoid tissue in the body. The enormous amount of nonpathogenic and pathogenic bacteria and food-derived antigens that we are daily exposed sets an interesting challenge to the immune system: a protective immune activity must coexist with efficient regulatory mechanisms in order to maintain a health status of these organisms. This paper discusses how the immune system assimilates the perturbations from the environment without generating tissue damage.

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.

Induction of mucosal tolerance in SLE: a sniff or a sip away from ameliorating lupus?

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by aberrant immune responses against intracellularly derived self antigens. Treatment for SLE relies on the use of aggressive immunosuppressants and steroids that are nonspecific and can cause serious adverse effects. The observation that a systemic immune tolerance to self antigens or generation of regulatory T cells may follow mucosal (nasal or oral) exposure to self proteins or monoclonal antibody against CD3 respectively suggests that induction of mucosal tolerance offers the basis of a side effect-free therapy that could re-establish the ability to distinguish self from non-self and restore peripheral tolerance in individuals susceptible to developing autoimmune diseases. Here I review studies on mucosal tolerance in autoimmune diseases and discuss the therapeutic potential of inducing tolerance for the treatment of SLE.

Cell-mediated immune response to unrelated proteins and unspecific inflammation blocked by orally tolerated proteins

Oral tolerance promotes a generalized decrease in specific immune responsiveness to proteins previously encountered via the oral route. In addition, parenteral immunization with a tolerated protein also triggers a significant reduction in the primary responsiveness to a second unrelated antigen. This is generally explained by 'innocent bystander suppression', suggesting that the transient and episodic effects of inhibitory cytokines released by contact with the tolerated antigen would block responses to the second antigen. In disagreement with this view, we have previously shown that: (i) these inhibitory effects do not require concomitance or contiguity of the injections of the two proteins; (ii) that intravenous or intragastric exposures to the tolerated antigen are not inhibitory; and (iii) that the inhibitory effect, once triggered, persists in the absence of further contact with the tolerated protein, possibly by inhibition of secondary responsiveness (immunological memory). The present work confirms that immunological memory of the second unrelated antigen is hindered by exposure to the tolerated antigen and, in addition, shows that this exposure: (i) inhibits the inflammation triggered by an unrelated antigen through the double effect of inhibiting production of leucocytes in the bone marrow and blocking their migration to inflammed sites; and (ii) significantly blocks footpaw swelling triggered by carrageenan. Taken together, these results conclusively demonstrate that inhibitory effects of parenteral injection of tolerated antigens are much more general than suggested by the 'innocent bystander suppression' hypothesis.

Modulation of Oral Tolerance to Ovalbumin by Dietary Protein in Mice

This study sought to determine whether oral tolerance to ovalbumin (OVA), responsible for food allergy, is affected by different amounts of protein intake. For this, 6-wk-old BALB/c mice were fed with low protein (5%, LP), normal protein (20%, NP) and high protein (40%, HP) diets, orally given either OVA (OVA-fed) or water (Water-fed) for 4 d, and then immunized intraperitoneally twice at a 3-wk interval with alum-precipitated OVA. After the last immunization, sera were collected to measure total and OVA-specific IgE by enzyme assay (ELISA). Splenocytes were cultured and stimulated with concanavalin A (Con A), lipopolysaccharide (LPS) or OVA and assayed for 3H-thymidine incorporation. The culture supernatants from their splenocytes stimulated with OVA were analyzed for interleukin (IL)-4, interferon (IFN)-gamma, and IL-12. Total IgE was significantly higher in OVA-fed HP groups as compared to NP and LP groups (p<0.05). The highest and the lowest OVA-specific IgE were observed in HP and LP diet groups, respectively (p<0.05). OVA-fed mice receiving the LP diet demonstrated significantly lower IL-4 as compared to the other two groups (p<0.05), while IFN-gamma was significantly higher in the LP compared to the HP group (p<0.05). Levels of IL-12 did not differ among the OVA-fed groups. Splenocytes of OVA-fed mice kept on the LP and HP diet showed significant impairment of proliferation to OVA as compared to the NP group (p<0.01). Proliferation against Con A was impaired in the LP group compared to the NP group (p<0.05) but not in Water-fed groups. However, it was higher against LPS in the HP than the LP group (p<0.05) both in Water-fed and OVA-fed animals. All these findings indicate that established oral tolerance to OVA is clearly affected by the amount of protein diet. They support the suggestion that dietary protein plays an important role(s) in IgE-mediated food allergies.

The ratio of n-6 to n-3 fatty acids in maternal diet influences the induction of neonatal immunological tolerance to ovalbumin

Prevalence of allergy is increasing in many countries and might be related to changed environmental factors, such as dietary fatty acids (FA). The present study investigates whether dietary ratio of n-6 to n-3 FA influences the induction of immunological tolerance to ovalbumin (OA) in neonatal rats. During late gestation and throughout lactation Sprague-Dawley rats were fed a diet containing 7% linseed oil (n-3 diet), sunflower oil (n-6 diet) or soybean oil (n-6/n-3 diet). At 10-16 days of age the rat offspring were subsequently exposed, or not, to OA via the milk. The offspring were weaned onto the same diets as the mothers and immunized with OA and the bystander antigen human serum albumin (HSA). In the offspring on the n-3 diet exposure to OA via the milk resulted in lower delayed type hypersensitivity reaction (DTH) and antibody responses against both OA and HSA, compared to those in the offspring not exposed to OA, indicating the induction of oral tolerance. In the offspring on the n-6 diet, the exposure to OA led to depressed specific immune responses against only OA, not HSA. In the offspring on the n-6/n-3 diet oral exposure to OA did not influence immune responses against OA, or HSA. The results indicate that the dietary ratio of n-6/n-3 FA is important for the induction of neonatal oral tolerance. Thus nonoptimal feeding may have effects on the development of immunological tolerance to dietary antigen ingested by the mother. The ratio of n-6/n-3 FA in the diet may be considered in the context of increased prevalence of allergy.

Animal models in food allergy: assessment of allergenicity and preventive activity of infant formulas

Food allergies occur in about 5-10% of the overall infant and small-child population. Cow's milk protein allergy (CMPA) is the most common in young infants, with a 2-4% incidence. When breastfeeding is not possible, hypoallergenic (HA) cow's milk based formulas are usually given during the first months of life for prevention of CMPA. Depending on primary (sensitization) or secondary (triggering) prevention, the requested quality of HA formulas may be different. Besides in vitro methods, in vivo and ex vivo animal models are helpful in assessing residual allergenicity and the preventive effect of HA formulas. The sensitizing capacity of a formula can be examined by either the parenteral rat (IgE), the guinea pig (IgG1a mediated) or the oral mouse (IgE) models. The triggering IgE mediated allergenicity is tested by a parenteral rat model with oral gavage for intestinal mast cell protease (RMCPII) release. These animal models are also used for testing the oral tolerance inducing capacities of formulas. Together with cellular in vitro assays, animal models are very helpful in predicting allergenicity and the tolerogenic potential of HA infant formulas.

Orally tolerized T cells are only able to enter B cell follicles following challenge with antigen in adjuvant, but they remain unable to provide B cell help

Although it is well documented that feeding Ag can tolerize or prime systemic humoral and cell-mediated immune responses, the mechanisms involved remain unclear. Elucidation of these mechanisms remains, in part, complicated by the inability to assess responses by individual lymphocyte populations. In the past, in vivo studies have examined T cell responses at the gross level by examining their ability to support B cell Ab production. However, as the fed Ag has the capacity to affect B cells directly, analyzing the functional capacity of a single Ag-specific T cell population in vivo has been difficult. Using a double-adoptive transfer system, we have primed or tolerized T cells, independently of B cells with a high dose of fed Ag, and examined the ability of these primed or tolerized T cells to support B cell clonal expansion in response to a conjugated Ag in vivo. We have been able to show that primed T cells support B cell clonal expansion and Ab production whereas tolerized T cells do not. Thus, we have provided direct evidence that tolerized T cells are functionally unable to help B cells in vivo. Furthermore, we have shown that this inability of tolerized T cells to support fulminant B cell responses is not a result of defective clonal expansion or follicular migration, since following challenge tolerized T cells are similar to primed T cells in both of these functions.

Predictive testing for autoimmunity

Many chemicals, in particular drugs, cause systemic allergy or autoimmune-like disorders. Due to complex pathogenesis and strong dependence on genetic make-up, these immunotoxicological effects are usually missed in standard toxicity testing. Besides, animal studies that demonstrate chemically induced systemic allergy or autoimmune-like disorders are scarce. Here, animal models are presented that would fit into a predictive two-tiered strategy, designed to allow screening for immunostimulatory potential in the first tier, and more elaborate testing for allergenic or autoimmunogenic potential of selected chemicals in the second tier. The popliteal lymph node assay (PLNA), with or without reporter antigens, would fit in the first tier, and relevant route of exposure protocols with selected strains of mice or rats may be further developed to compose the second tier. To date, the relevant route of exposure models mentioned here (with 'normal' inbred mice and/or Brown Norway rats) has been tested with only a few chemicals, and the PLNA, although tested with over 100 chemicals, is not validated as yet. Conceivably, a major challenge in immunotoxicology is to incorporate the present knowledge on chemical-induced systemic allergy and autoimmunity in further development and validation of predictive models and strategies.

Stabilization of serum antibody responses triggered by initial mucosal contact with the antigen independently of oral tolerance induction

Initial contacts with a T-dependent antigen by mucosal routes may result in oral tolerance, defined as the inhibition of specific antibody formation after subsequent parenteral immunizations with the same antigen. We describe here an additional and permanent consequence of these initial contacts, namely, the blockade of secondary-type responsiveness to subsequent parenteral contacts with the antigen. When repeatedly boosted ip with small doses (3 microg) of ovalbumin (OVA) (or lysozyme), primed B6D2F1 mice showed progressively higher antibody responses. In contrast, mice primed after a single oral exposure to the antigen, although repeatedly boosted, maintained their secondary antibody titers on a level which was inversely proportional to the dose of antigen in the oral pretreatment. This phenomenon also occurred in situations in which oral tolerance was not induced. For example, senile 70-week-old B6D2F1 mice pretreated with a single gavage of 20 mg OVA did not become tolerant, i.e., they formed the same secondary levels of anti-OVA antibodies as non-pretreated mice. However, after 4 weekly challenges with 3 microg OVA ip, orally pretreated mice maintained the same anti-OVA serum levels, whereas the levels of control mice increased sequentially. This "stabilizing" effect of mucosal exposure was dose dependent, occurred with different proteins and was triggered by single or multiple oral or nasal exposures to the antigen.

Vaginal mucosa serves as an inductive site for tolerance

These data demonstrate that tolerance can be induced by vaginal Ag exposure. In these experiments, mice were given vaginal agarose gel suppositories containing either 5 mg OVA or saline for 6 h. Mice were given suppositories either during the estrous (estrogen dominant) or diestrous (progesterone dominant) stage of the estrous cycle. Mice were restrained during the inoculation period to prevent orovaginal transmission of the Ag. After 1 wk, mice were immunized s. c. with OVA in CFA. After 3 wk, mice were tested for delayed-type hypersensitivity responses by measuring footpad swelling and measuring in vitro proliferation of lymphocytes to Ag. Using ELISA, the magnitude of the serum Ab response was also measured. In some mice, FITC conjugated to OVA was used to track the dissemination of the protein into the systemic tissues. The magnitude of footpad swelling was significantly reduced in mice receiving OVA-containing suppositories during estrus compared with mice receiving saline suppositories. Concomitant decreases in the Ag-specific proliferative response were also observed in lymph node lymphocytes and splenocytes. Conversely, mice inoculated during diestrus did not show a decreased response to Ag by either footpad response or in vitro proliferation. Serum Ab titers in the estrus-inoculated mice did not decrease significantly. These data demonstrate that the reproductive tract can be an inductive site for mucosally induced tolerance. However, unlike other mucosal sites such as the lung and gastrointestinal tract, reproductive tract tolerance induction is hormonally regulated.

Food allergy. Part 1: immunopathogenesis and clinical disorders

Up to 8% of children less than 3 years of age and approximately 2% of the adult population experience food-induced allergic disorders. A limited number of foods are responsible for the vast majority of food-induced allergic reactions: milk, egg, peanuts, fish, and tree nuts in children and peanuts, tree nuts, fish, and shellfish in adults. Food-induced allergic reactions are responsible for a variety of symptoms involving the skin, gastrointestinal tract, and respiratory tract and may be caused by IgE-mediated and non-IgE-mediated mechanisms. In part 1 of this series, immunopathogenic mechanisms and clinical disorders of food allergy are described.

Active suppression in orally tolerized rats coincides with in situ transforming growth factor-beta (TGF-beta) expression in the draining lymph nodes

Adult rats were fed pellets containing ovalbumin (OvA) during 4 weeks, and were 2 weeks thereafter immunized subcutaneously with a mixture of OvA and human serum albumin (HSA) in Freund's complete adjuvant (day 0). As a result of the immunization, the draining lymph nodes of the nontolerized (control) rats were heavily enlarged from day 10 to day 18; however, this size increase was absent in the OvA-fed rats. This manifestation of active suppression in the tolerized rats was preceded by the appearance of scattered CD4+ TGF-beta-expressing T cells in the T cell area of their lymph nodes (days 5-8); correspondingly, the levels of TGF-beta mRNA in the nodes were elevated in the tolerant rats compared with the control rats. The anti-OvA antibody levels in sera from the rats revealed that there was an initial B cell priming in the OvA-fed group, with levels higher than in the control group during the first week. Thereafter, suppression governed the response, and from day 10 onwards the anti-OvA levels were considerably lower than in the controls. When other groups of animals were pretreated with neutralizing anti-TGF-beta antibodies 1 day before the immunization, the anti-OvA response of the OvA-fed rats was restored to the levels of the control group, demonstrating the importance of TGF-beta in the maintenance of suppression. In conclusion, we demonstrate that TGF-beta-producing cells appear in the draining lymph nodes shortly after immunization in rats made orally tolerant using a relatively high-dose feeding regime; these cells are probably responsible for the down-regulation of the immune response observed in the OvA-fed rats.

Priming or tolerization of the B- and Th2-dependent immune response by the oral administration of OVA-DNP is determined by the antigen dosage

In the present report we established antigen dosages that induce oral tolerance of Th1 and Th2 lymphocytes or instead prime B- and Th2-dependent immune response and induce the tolerance of Th1 lymphocytes. Using different hapten-carrier systems, we found that low doses of OVA-DNP administered orally primed B and Th2 cells. On the other hand, no priming of B or Th2 cells was found in high-dose-OVA-DNP-fed rats. Low-dose-OVA-DNP-fed rats showed a strong mucosal immune response, with a high number of IgA anti-DNP antibody-forming cells in the lamina propria, while no mucosal immune response was observed in high-dose-OVA-DNP-fed rats. Thirty days after the immunization, tolerization of Th1 lymphocytes was confirmed in low- and high-dose-OVA-DNP-fed rats by diminished antigen-specific proliferation in vitro, reduced titers of anti-DNP IgG2a in serum, reduced expression of CD25 and CD134 molecules in cultured cells exposed to the antigen, reduced DTH reaction, and reduced IL-2 synthesis in culture. On the other hand, a high dose of OVA-DNP led to Th1 and Th2 tolerance, with an inhibition of specific IgG1 and IgG2a anti-DNP antibodies in serum after a parenteral challenge with OVA in CFA. This functional evidence was supported by the direct examination of IL-2 and IL-4 production. Furthermore, whereas in vitro assays seem to indicate that active suppression could be the responsible for Th1 tolerization in low-dose-OVA-DNP-fed rats, the results obtained after the transference of spleen or MLN cells to naive recipients support the idea that a subtractive mechanism is behind the tolerization of Th1 lymphocytes.

Urotherapy for patients with cancer

Cancer cells release various antigens, some of which appear in the urine. Oral autourotherapy is suggested as a new treatment modality for cancer patients. It will provide the intestinal lymphatic system with the many tumor antigens against which antibodies may be produced. These antibodies may be pierced through the blood stream and attack the tumor and its cells.

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.

Oral tolerance: mechanisms and possible role in inflammatory joint diseases

Decreased systemic immune responsiveness to a specific antigen following exposure to that antigen by the enteric route is termed 'oral tolerance.' Oral tolerance is revealed when attempts are made to parenterally immunize the host to the same antigen that was previously administered orally or intragastrically. A similar phenomenon is also seen following antigen exposure via the nasal mucosa and a related phenomenon is seen following antigen exposure in the upper respiratory tract. There has been a marked renewal of interest in the mechanisms that underlie oral tolerance because of its potential role for preventing and treating autoimmune and inflammatory diseases and IgE-mediated allergic disorders. The specific factors that determine whether or not the host develops mucosal tolerance to an antigen administered by the mucosal route are also of substantial importance for those involved in mucosal vaccine development. Furthermore, putative abnormalities in the ability of the host to develop mucosal tolerance may play a pathogenetic role in certain autoimmune and allergic diseases and disorders. Several well-defined immunological mechanisms mediate oral tolerance. These include the induction, following mucosal antigen exposure, of regulatory populations of T-cells that can down-regulate specific immune responses (e.g. DTH) via the production of specific cytokines (e.g. TGF-beta 1, IL-10 and IL-4). In addition, clonal anergy, clonal deletion and antibody-mediated suppression can be shown to play a role in the induction and maintenance of mucosal tolerance in several experimental systems. In animal studies, the onset of collagen-induced, adjuvant-induced, antigen-induced and pristane-induced arthritis has been delayed and the severity of ongoing disease diminished following feeding collagen type II. Mucosal tolerance has been clearly demonstrated in humans and clinical studies have been undertaken to treat rheumatoid arthritis using a similar approach. Results of initial clinical studies in rheumatoid arthritis indicated a modest improvement and further studies are ongoing in this and other autoimmune diseases (e.g. multiple sclerosis, autoimmune uveitis and insulin-dependent diabetes). This approach, if successful, could offer a new and novel therapeutic modality for preventing autoimmune and allergic disorders, and modulating ongoing disease.

Indirect effects of oral tolerance in mice

Anti-DNP antibody formation resulting from intraperitoneal (i.p.) immunization with DNP-KLH may be blocked by simultaneous (i.p.) injection of DNP-Ova or native Ova in mice orally tolerant to Ova, but not in normal mice. In Ova-tolerant mice the inhibition of anti-DNP antibody formation also occurred when DNP-Ova and DNP-KLH were given by separate routes of immunization: subcutaneous (s.c.) and i.p. A second exposure to Ova by gastric intubation (gavage) or intravenous administration simultaneously with i.p. immunization with DNP-KLH failed to inhibit anti-DNP antibody formation. There was inhibition of responses to DNP-KLH i.p. by DNP-Ova given 24 h before, but not 24 h after, and in the Ova-tolerant mice, addition of DNP-Ova only to the primary immunization with DNP-KLH inhibited secondary and tertiary responses to DNP-KLH in the absence of further exposures to DNP-Ova. These results suggest that the indirect effects of parenteral exposure of tolerant mice to the tolerated immunogen may inhibit unrelated immune responses. This inhibition is not due to 'innocent bystanding' suppression, i.e., to inhibitory cytokines provided locally by specific suppressor lymphocytes; it may derive from more durable perturbations of immune system.

CO2 anesthesia facilitates a serum antibody response to orally-administered antigens

Under most experimental circumstances, mice fed a protein antigen produce a smaller serum antibody response than the response elicited in mice that are parenterally immunized with that same antigen. In our experiments, mice fed keyhole limpet hemocyanin or herpes simplex virus type 1 had low, if any, serum IgG antibody responses regardless of whether antigen consumption was voluntary (in drinking fluids) or involuntary (force-fed by pipette). However, when force-feeding occurred during CO2 anesthesia, mice produced significantly higher serum antibody responses, which were comparable to those elicited in mice injected intraperitoneally with the same antigen. Although its mechanism of action is unclear, this potentiating effect does not appear to be mediated by possible CO2-mediated entry of the antigens into the respiratory tract, since mice fed antigen immediately before CO2 anesthesia also had a substantial antibody response.

Split tolerance of Th1 and Th2 cells in tolerance to Theiler's murine encephalomyelitis virus

Theiler's murine encephalomyelitis virus (TMEV) produces a chronic, inflammatory demyelinating disease in susceptible mouse strains that is used as a model for multiple sclerosis. Because disease susceptibility correlates temporally with the development of virus-specific delayed-type hypersensitivity (DTH) responses, we studied methods and mechanisms by which virus-specific DTH could be specifically inhibited. The intravenous injection of UV-inactivated TMEV coupled to syngeneic splenocytes via a carbodiimide linkage (TMEV-SP), prior to immunization, induced a significant degree of tolerance in virus-specific helper (Th) cells as determined by decreased DTH and T cell proliferative responses, and decreased interleukin (IL)-2 and interferon (IFN)-gamma protein and mRNA levels. In contrast to the reduced levels of Th1-specific lymphokine mRNA levels, IL-4-specific mRNA levels in response to virus stimulation were not affected in tolerant mice. Surprisingly, the total anti-TMEV antibody response in DTH tolerant mice was enhanced 20-100-fold over sham-tolerized controls and was composed of reduced levels of anti-virus IgG2a, but dramatically increased levels of anti-virus IgG1. The "split-tolerance" was antigen specific, dependent on the concentrations of TMEV and carbodiimide used in the coupling procedure, and varied with the number of coupled syngeneic splenocytes administered. The fixative effects of carbodiimide on antigen-presenting function were necessary for the induction of DTH tolerance with TMEV-SP, since intravenous administration of virus coupled to splenocytes via a biotin-avidin linkage led to enhanced virus-specific antibody responses, but was unable to inhibit DTH unless concomitantly fixed with carbodiimide. Collectively, the data indicate that Th1 cells (mediating DTH, IL-2 and IFN-gamma production, and helper function for IgG2a production) were specifically anergized, with concomitant stimulation of Th2 cells (producing IL-4 and mediating helper function for IgG1 antibody production).

Comparison of antibody and cell-mediated immune responses in horses following feeding of a novel dietary antigen, ovalbumin, and rotavirus

Adult ponies which were fed ovalbumin (OVA) daily for 2 weeks had significantly greater serum anti-OVA IgG (P = 0.001) and antigen specific lymphocyte responses (P = 0.031) after intramuscular injection with OVA given with saponin than control ponies which had not been fed the antigen. This suggests that, despite the lack of evidence of B- or T-cell activation in peripheral blood during the period of OVA feeding, the animals were primed for an active secondary immune response. Adult ponies were challenged with equine rotavirus, strain H-2, but no statistically significant differences were found in serum IgG-associated antibody responses or antigen-specific lymphocyte responses between the rotavirus-challenged group and the control group, either following rotavirus challenge or intramuscular injection of rotavirus antigen given with saponin. Our findings, that feeding the non-replicating protein antigen OVA appeared to prime for an increased immune response rather than inducing oral tolerance, may be of relevance to future studies on the way the equine gastrointestinal tract handles usually harmless antigens.

Antibody response reveal differences in oral tolerance to wheat and maize grain protein fractions

The influence of diet on humoral immune responses to gluten- and maize-derived proteins was examined using ELISA and protein blotting techniques. Mice raised on the maize-based (gluten-free) diet responded well to parenteral immunization with each of six gluten-derived protein preparations (whole gliadin, two omega-gliadin fractions, wheat salt-soluble proteins, a peptic-tryptic digest and a subtilisin digest of gluten), as serum antibody levels increased at least 300-fold in each case. In contrast, mice raised on the wheat-based diet responded poorly to immunization with either whole gliadin or omega-gliadin and were virtually non-responsive to enzymic digest of gluten. Diet had little effect on the magnitude of the antibody response to wheat salt-soluble proteins, with both groups showing a 300-fold increase in titre. Similarly, tolerance to alpha-zeins, the alcohol-soluble proteins of maize, did not occur on either diet. However, some oral tolerance was observed to maize glutelin. The specificity of the various antibody responses was then analysed by immunoblotting. Following immunization with gluten proteins or digests, antibodies from the maize-fed mice bound more or less equally to each of the main gliadin bands and to the glutenins while the mice on the wheat-based diet had antibody specific for omega-gliadin proteins. Serum antibodies from the maize-fed mice, immunized with either alpha-zein or maize glutelin, showed even labelling of the major maize endosperm proteins while antibodies from mice on the wheat diet showed strong labelling of the Mr 27,000 and 58,000 bands. These results show that diet influenced the specificity, as well as the magnitude of serum antibody responses to cereal proteins. In addition, oral tolerance appeared to affect the humoral response to some cereal proteins more than others. Both of these findings have important implications for our understanding of coeliac disease.

Immunologic outcome of enteric administration of ovalbumin to neonatal rats is anatomic-site specific

An important immunologic response to the oral ingestion of a protein antigen is systemic tolerance to subsequent parenteral encounter with the same antigen. In the newborn intestine, ileal epithelial cells nonspecifically take up macromolecules and degrade them in lysosomal enzyme-containing vacuoles. We speculated that processing of protein antigens by the ileal cells helps mediate systemic immunologic tolerance to the antigens. Therefore, we developed a neonatal rat model in which ovalbumin (OVA) was administered either by gastric gavage or by infusion into surgically constructed loops of jejunum or ileum. We also administered OVA to other groups of animals by injection into the intact jejunum or ileum. Two and 4 weeks later, animals were challenged with OVA measured. Whereas animals that received OVA by gastric gavage were made tolerant to the protein (produced no detectable serum IgG anti-OVA antibodies after parenteral challenge), the animals given OVA into the jejunum or ileum did not show tolerance; indeed, some of those given OVA into the ileum were immunized by the enteric exposure. From these data we postulate that the development of systemic immunologic tolerance to a protein antigen in the newborn requires "upstream" processing of the antigen by gastric or pancreatic secretions and that exposure of the distal intestine to intact protein antigens can result in systemic sensitization to the antigens. The latter response might be causally linked to food allergies or autoimmune diseases.

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.

Transfer of protein antigens into milk after intravenous injection into lactating mice

We investigated the transfer of bovine serum 125I-albumin (125I-BSA), bovine 125I-gamma-globulin (125I-BGG), 125I-ovalbumin (125I-OVA), and 125I-beta-lactoglobulin (125I-BLG) from the blood into the milk of lactating mice. Equal amounts (by weight) of the radiolabeled proteins were injected intravenously into mice 1 wk postpartum. Total radioactivity, trichloroacetic acid-precipitable radioactivity, and specifically immunoprecipitable radioactivity were measured in serum, mammary gland homogenate, and milk. Clearance of immunoreactive OVA (iOVA) and iBLG from the circulation was more rapid than iBSA and iBGG. The radioactivity in mammary tissue associated with BSA and BGG was greater than 70% immunoprecipitable throughout the 4-h test interval; 125I-OVA and 125I-BLG were less than 12% precipitable 1 and 4 h after injection. In milk obtained at 4 h, there was an approximately 10-fold greater accumulation of iBSA or iBGG than of iOVA or iBLG. These experiments demonstrate that protein antigens differ in their ability to transfer from maternal circulation into milk. The transfer into milk appeared to be in proportion to persistence of the antigens in the maternal circulation.

Immune dysfunction in rabbits associated with chronic administration of enemas and rectal insemination

NZ rabbits were treated with various combinations of enemas and intrarectal insemination (1 or 3 ml of semen a week) to investigate the effects of intestinal uptake and immunogenicity of seminal components and of an unrelated antigen, bovine serum albumin (BSA), given simultaneously. For 5 months the treatment was limited to enemas and/or semen, and total immunoglobulins and antisperm and antilymphocyte antibodies were determined. Then, without interruption of the treatments, the animals received two courses of three consecutive daily intrarectal administrations of BSA, and the humoral response was determined 7 days after each course of administration. Only 1 of 18 intrarectally inseminated animals responded with production of antisperm antibodies; none had antilymphocyte antibodies. Total immunoglobulins, however, were significantly increased in animals receiving enemas alone (p less than 0.02) or followed by insemination (p less than 0.05). The humoral response to BSA was significantly (p less than 0.01) enhanced by prior administration of enemas but was moderately reduced by simultaneous administration of semen, in a dose-related fashion.

The accessory cell function of murine Peyer's patches

The cellular composition and certain functional characteristics of murine Peyer's patches (PP) were examined and compared with other lymphoid tissues. The composition of PP resembled most closely that of the spleen with the exception of a significant decrease in the number of adherent and phagocytic cells. Very few cells with dendritic morphology could be identified in Peyer's patches. Whole PP (and the nonadherent population) were capable of presenting antigen ovalbumin, human gammaglobulin, and purified protein derivative in a T proliferative assay to sensitized lymph node cells and to an antigen-specific T-cell clone. The antigen-presenting cell in both the spleen and PP was concentrated in the low-density population which floated on 1.080 bovine plasma albumin. However, equal numbers of whole and PP floaters were deficient in their capacity to present antigen compared with similar populations from spleen. Moreover, in PP the antigen-presenting cell appeared in the nonadherent rather than the adherent population as found with other lymphoid tissues. Similar results were obtained with (B6A)F1, CBA, A.TFR-1 and B10.S (12R) mice, suggesting that the inability of adherent cells from PP to present antigen effectively was not genetically determined. Whole and nonadherent PP contained cells capable of stimulating an allogeneic MLR, although again they were generally inferior to those of the spleen when comparable numbers of cells were employed. The adherent population of PP did not elicit an MLR. However, whole PP contained accessory cells needed for mitogen-induced proliferation since passage over nylon-wool columns resulted in a nonadherent fraction which did not respond to concanavalin A or phytohemagglutinin and the addition of adherent peritoneal exudate cells restored the lectin response. The differences noted in the accessory cell function in PP and other lymphoid tissues suggest the possibility that quantitative or qualitative differences in the function of these cells may explain some of the previously observed characteristics of PP, such as the inability to detect a primary antibody response in this tissue. The possibility that the development of gut-associated suppressor cells and their migration to peripheral tissues may be involved in the systemic tolerance that follows oral immunization and that these may be related to numerical and/or functional differences in macrophages or accessory cells is discussed.

Induction and control of the gastrointestinal immune system

The stimulation of cells in gut associated lymphoid tissue (GALT) by intestinal antigens can result either in immunity or tolerance to that antigen. The factors that determine which effect predominates are not understood, but the answer seems to lie in a better understanding of the cellular interactions and regulatory mechanisms in GALT. Induction of an immune response in GALT involves the same macrophage-T cell, T cell-T cell, and T cell-B cell interactions that have been described in other lymphoid tissues. Regulatory T cells have now been shown to play an important role in controlling the immune response to intestinal antigens. The presence of helper T cells specific for the IgA isotype in Peyer's patches may partly explain the old observation that the intestinal route is preferential for this antibody class. The stimulation of suppressor T cells in GALT is responsible for many instances in which tolerance rather than immunisation has followed antigen feeding. Although there is experimental evidence supporting the idea that mucosal IgA immunity and systemic IgG tolerance can occur concomitantly after antigen feeding, recent data obtained after the feeding of a variety of protein antigens indicate that this is not the usual result. More commonly either immunity or tolerance occurs concomitantly in both mucosal and systemic systems after antigen feeding, suggesting that the suppressor cells mediating oral tolerance also suppress mucosal IgA responses.

Influence of breast feeding on subsequent reactivity to a related renal allograft

In a previous report the hypothesis that exposure of the neonate to maternal allogeneic cells via the process of breast feeding would result in hyporesponsiveness to a subsequent maternal donor-related renal transplant was examined. Support for this hypothesis was obtained after correlating results of maternal donor-related renal transplantation with the breast feeding status of the transplant recipient. In the present report this observation has been expanded upon and it was asked if a history of breast feeding was associated with improved results in a different patient population (HLA semi-identical sibling donors). Breast-fed patients showed dramatic improvements in graft function rates compared to non-breast-fed counterparts at all intervals studied (P less than or equal to 0.001). Because a history of breast feeding correlated with improved results after sibling donor as well as maternal donor transplantation, it was concluded that the breast feeding effect is not entirely specific for maternal antigens. These observations underscore the importance of breast feeding as a variable in clinical-related renal transplantation.

Immunologic suppression after oral administration of antigen. III. Activation of suppressor-inducer cells in the Peyer's patches

Mice were orally administered sheep erythrocytes (SRBC) in a regimen previously known to produce systemic tolerance to SRBC. Cellular interactions and movement from the gut-associated lymphoid tissue (GALT) to the spleen were found to occur using both in vivo and in vitro transfer systems. The cell in the GALT which initiates the suppression circuit migrates from the GALT to the spleen shortly after contacting antigen. This cell is a T suppressor-inducer (Tsi) cell which interacts with splenic lymphocytes to induce the formation of an effector T suppressor cell (Ts). The Tsi and Ts can be separated from each other by their differential sensitivities to cyclophosphamide. In addition, the Tsi can be separated from other GALT T cells by its inability to bind the lectin, peanut agglutinin. Thus, cell migration and cellular interaction among T cells must occur to result in orally induced tolerance.

Specifically induced suppression of T cell and NK-like cytolytic activity by ingested soluble antigens

The effect of feeding xenoserum (xs) on cytolytic cell activity induced by parenteral injection was examined in C3H/N mice. Spleen cells were cultured with xs and then assayed for cytolytic activity against a panel of 51Cr-labeled YAC-1, AKR-A, or P815 target cells. Prior feeding resulted in significant suppression of responses stimulated by injection and culture. The induction of these responses was antigen specific for xs whereas the effector stage represented polyclonal activation of cytolytic cells. Some effector cells were lysed by either anti-Lyt 2 or anti-NK- 1.2 and complement and some were blocked by anti-Lyt 2 or anti-T200 in the cytotoxicity assay. Thus, both cytolytic T and NK-like cells were suppressed by antigen feeding. Activity of TH cell-derived factors which enhance cytolytic activity ("promoter" factor, interferon, and interleukin 2) also was diminished in culture supernatants of cells from mice fed soluble antigens. The conclusion that polyclonal cytolytic responses induced by soluble antigen can be regulated by prior enteric stimulation is made.