The role of antigen processing and suppressor T cells in immune responses to dietary proteins in mice

Deficiency of 6B11+ invariant NK T-cells in celiac disease

Immunoregulatory NK T-cells are deficient in certain autoimmune diseases. The purpose of this study was to investigate any deficiency of immunoregulatory NK T-cells in celiac disease. NK T-cells were identified by flow cytometry with 6B11 and V alpha 24 markers in blood from 18 normal and 12 celiac subjects. Blood mononuclear cells were stimulated with anti-CD3/CD28 antibodies and intracellular cytokines assessed at 4 h in seven normal and eight celiac subjects. V alpha 24/GAPDH mRNA was quantitated in duodenal biopsies by real time PCR in 17 control and 13 celiac subjects. NK T-cells in celiac subjects were reduced to 30% of those in normal subjects. Intracellular IL-4, IL-10 and IL-13 increased significantly by 33-41% in normal subjects, but did not change in celiac subjects. V alpha 24/GAPDH mRNA from celiac subjects was reduced to 5% of levels in control subjects. We conclude that immunoregulatory NK T-cells are deficient in celiac disease.

Initiating mechanisms of food allergy: Oral tolerance versus allergic sensitization

Immediately after birth the mucosa of the gastrointestinal tract, which represents the greatest body surface area exposed to the outside environment, is confronted with a large variety of foreign antigens. The immune system of the intestine now has to meet the task of discriminating between pathogens and harmless antigens, such as food proteins and commensal bacteria, and to respond accordingly. This important job is fulfilled by cells of the gut-associated lymphoid tissue, the largest immunologic organ in the body. Despite the large extent of food antigen exposure, only a small percentage of individuals experience adverse immunologic reactions to food. This is due to the fact that the normal immune response to dietary proteins is associated with the induction of oral tolerance, which refers to a state of active inhibition of immune responses to an antigen by means of prior exposure to that antigen via the oral route. Abrogation of oral tolerance or failure to induce oral tolerance may result in the development of food hypersensitivity. In the present review, factors that may play a role in the outcome of oral tolerance versus sensitization to food proteins are discussed.

Autoimmune-mediated intestinal inflammation-impact and regulation of antigen-specific CD8+ T cells

BACKGROUND & AIMS

Few data exist regarding mechanisms of mucosal CD8+ T-cell reactivity to epithelial-specific antigen. To dissect the immunologic mechanisms underlying CD8+ T-cell dysregulation, reactivity to a self-antigen expressed in intestinal epithelium of mice bearing a major histocompatibility complex class I-restricted T-cell receptor specific for this antigen was studied. In addition, antigen-specific regulatory CD4+ T cells induced in vivo were tested to control these autoreactive CD8+ T cells.

METHODS

Transgenic VILLIN-HA mice were mated with CL4-TCR transgenic mice. Alternatively, adoptive transfer of CL4-TCR transgenic CD8+ T cells into VILLIN-HA transgenic mice was performed to mimic spontaneous encounter of neoantigen. Mucosal CD8+ T cells were characterized under different conditions of tolerance, immunopathology, and active immunosuppression.

RESULTS

Transgenic CD8+ T cells from VILLIN-HA x CL4-TCR transgenic mice preferentially migrated and expanded in mucosal lymphoid tissues. Although transgenic CD8+ T cells showed signs of T-cell activation, they failed to cause tissue damage. This was accompanied by the induction/expansion of CD4+ and CD8+, Foxp3-expressing T cells. In contrast, adoptive transfer of naive transgenic CD8+ T cells from CL4-TCR transgenic mice into VILLIN-HA transgenic mice induced severe intestinal inflammation with poor clinical course of disease. Transgenic CD8+ T cells secreted vigorous amounts of proinflammatory cytokines like interferon gamma/tumor necrosis factor alpha. Strikingly, this acute wasting disease was significantly ameliorated by cotransfer of antigen-specific regulatory CD4+ T cells.

CONCLUSIONS

Epithelial-specific antigen expression is sufficient to trigger severe antigen-specific CD8+ T-cell-mediated intestinal inflammation; this might be controlled by antigen-specific regulatory T cells under physiological conditions.

Intestinal Epithelial Antigen Induces CD4+ T Cells with Regulatory Phenotype in a Transgenic Autoimmune Mouse Model

Regulatory T cells play a crucial role in the control of immune responses in the intestinal mucosa and their absence may predispose to inflammatory bowel disease (IBD). However, the induction of regulatory T cells at sites of mucosal inflammation is not yet fully understood and may involve antigen presentation by local immature dendritic cells and/or intestinal epithelial cells (IECs). VILLIN-HA mice, which express the hemagglutinin (HA) from influenza virus A exclusively in enterocytes of the intestinal epithelium, were matched with T cell receptor (TCR)-HA mice expressing an alphabeta-TCR which recognizes a major histocompatibility complex (MHC) class II-restricted epitope of HA in order to determine the impact of antigen presentation by IECs on CD4(+) T cell immunity. In VILLIN-HA x TCR-HA mice, peripheral HA-specific lymphocytes showed an activated phenotype and increased infiltration into the intestinal mucosa without destruction of the intestinal epithelium. Mucosal lymphocytes from VILLIN-HA x TCR-HA mice secreted lower amounts of interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) and exhibited an increased expression of interleukin-10 (IL-10), Nrp-1, and Foxp3, molecules published as markers for regulatory T cells. IECs can take up and process antigen but the antigen presentation capacity of these cells is often inefficient. Functional and molecular characterization of IECs from VILLIN-HA and VILLIN-HA x TCR-HA transgenic mice revealed a direct role in the induction of CD4(+) T cells with a regulatory phenotype that maintain intestinal homeostasis.

Oral tolerance: lessons on treatment of food allergy

Oral tolerance is the active non-response by the immune system to an antigen administered through the oral route. It is postulated that food hypersensitivity results from a breakdown in oral tolerance induction, and the importance of oral tolerance in food hypersensitivity can be traced back to classic experiments from 1911 in which guinea pigs were protected from anaphylaxis by prior feeding of antigen. Host and antigenic factors play a role in determining the pathways and mechanisms to which a fed antigen can gain tolerance. Recent studies have demonstrated the potential of using oral tolerance to treat food allergies, and additional studies are necessary to further our understanding of mechanisms of oral tolerance induction.

Impaired B cell responses to orally administered antigens in lamina propria but not Peyer's patches of Galphai2-deficient mice prior to colitis

Despite numerous studies on the intestinal immune system in patients with inflammatory bowel disease (IBD) and animal models of IBD, very little is known about the immune reactivity of mucosal lymphocytes following oral immunizations under these circumstances. The reactivity of Peyer's patch (PP) and lamina propria (LP) T and B lymphocytes in inhibitory G-protein alpha2 subunit-deficient (Galphai2-/-) mice developing an IBD resembling ulcerative colitis was investigated following repeated oral immunizations with keyhole limpet haemocyanin (KLH), together with the adjuvant cholera toxin, prior to colitis. The antigen-specific B-cell response in the LP of both the small and the large intestines was significantly reduced in Galphai2-/- as compared to wild-type mice. In contrast, the frequency of KLH-specific immunoglobulin (Ig)-producing cells in the PP did not differ between Galphai2-/- and wild-type mice, whereas the total frequency of Ig-producing cells as well as the frequency of enteric flora-specific Ig-producing cells in the PP was significantly increased in Galphai2-/- as compared to wild-type mice. Analysis of T cell responses following restimulation ex vivo with KLH revealed a dramatic increase in the production of interferon-gamma in mesenteric lymph node, PP and LP lymphocytes from Galphai2-deficient as compared to wild-type mice, together with decreased production of interleukin-10 in all locations except the PP.

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.

Children at risk for asthma: home allergen levels, lymphocyte proliferation, and wheeze

BACKGROUND

Allergic asthma is a common childhood disease. Although T-lymphocyte activation plays a critical role in allergic asthma, the environmental factors promoting lymphocyte activation in children are not well defined.

OBJECTIVE

In a cohort of children at risk for asthma (n = 114), we determined whether the levels of cockroach (Bla g 1 or 2), house dust mite (Der f 1), and cat allergen (Fel d 1) in the home during infancy was associated with subsequent allergen-specific lymphocyte proliferation in later life.

METHODS

Dust samples from multiple sites in the home were collected at 3 months of age and were measured for allergen levels. Serial questionnaires were applied. At a median age of 2 years, PBMCs were isolated and lymphocyte proliferation to the home allergens and PHA was determined.

RESULTS

Increased lymphocyte proliferative responses to Bla g 2 were associated with higher home levels of Bla g 1 or 2 (P for trend with kitchen Bla g levels =.011), in analyses adjusting for cold in the past week. Proliferative responses to Der f 1 were higher in homes with family room levels of Der f 1 > or =10 microg/g dust than in homes with Der f 1 <2 microg/g, but differences were not significant in analyses adjusting for cold (P =. 15). Repeated wheeze in the first 2 years of life was associated with increased allergen-specific and PHA proliferative responses.

CONCLUSION

Early-life cockroach allergen exposure at 3 months of age predicts allergen-specific lymphocyte proliferative responses at a median of 2 years of age.

The intestinal epithelial cell: processing and presentation of antigen to the mucosal immune system

The immunologic tone of the intestinal tract is one of suppressed or highly regulated responses. While there are several components (intrinsic and extrinsic to the gut-associated lymphoid tissue) responsible for this immunologically suppressed tone, the intestinal epithelial call (IEC) has been proposed as a key player in this process. IECs can take up and process antigen but distinct surface molecules and restriction elements allow them to present these antigens to unique regulatory T cells. These include the expression of the class Ib molecule CD1d as well as a novel CD8 ligand, gp180. These molecules come together to activate a subpopulation of CD8+ regulatory cells whose function is to suppress immune responses in an antigen non-specific fashion most likely through cognate interactions. This form of regulation may be unique to the gut-associated lymphoid tissue which is consistent with the unusual demands upon this part of the immune system.

Induction of donor-specific hyporesponsiveness and prolongation of cardiac allograft survival by jejunal administration of donor splenocytes

BACKGROUND

Donor-specific immunosuppression is important in transplantation surgery. We examined the immunosuppressive effects of donor splenocytes administered postoperatively into the jejunum and the effect of such treatment on the survival of heterotopic vascularized cardiac allograft in rats.

METHODS

Lewis (LEW, RT-1l) recipient rats were treated with 5x10(7) Brown Norway (BN, RT-1n) donor splenocytes for 5 days orally, intrajejunally, or subcutaneously. The immune responses of LEW treated with either donor BN or irrelevant Wistar King A (WKA, RT-1k) were examined by mixed lymphocyte reaction (MLR) and delayed type hypersensitivity (DTH). The effect of postoperative enteral treatment for 6 days with suboptimal dose of cyclosporine (CsA) on heterotopic cardiac allotransplantation was investigated. We measured the production of cytokines (interleukin [IL]-2, IL-4, IL-10, and interferon-gamma [IFN-gamma]) in the supernatant of MLR by ELISA. The effect of intravenous dose of GdCls to block Kupffer cell function was also investigated before the administration of splenocytes.

RESULTS

MLR and DTH responses were strongly inhibited in a BN-restricted manner after jejunal or oral feeding of donor BN splenocytes but not by subcutaneous injection or injections by any routs of WKA splenocytes. The effect was more prominent in jejunal than oral feeding. Immunosuppression was associated with a significant inhibition of IL-2 and IFN-gamma production and increased concentrations of IL-4 and IL-10 in MLR supernatants. Immunosuppression was abrogated by pretreatment with GdCl3. Postoperative intrajejunal feeding of donor splenocytes with CsA significantly prolonged cardiac allograft survival time (18.7+/-7.3 vs. 9.9+/-1.7 days for control animals).

CONCLUSION

Jejunal administration of splenocytes produces donor-specific immunosuppression and prolongs cardiac allograft survival. Our results suggest the involvement of T helper (Th) 2 cytokines and Kupffer cells in the induction of immune hyporesponsiveness, and indicate that this method represents a unique approach for induction of donor-specific immunosuppression.

Prolongation of survival of primary renal allografts by feeding of donor spleen cells

We have found that feeding Brown Norway (BN) rat spleen cells to Lewis rats prior to transplanting BN kidneys prolongs allograft survival (mean: 8.8 days in unfed rats, 21 days in the BN cell-fed rats; longest survival: 11 days without allo-feeding vs. 37 days with feeding). We have also found that feeding BN cells both before and after transplantation further extends survival (mean: 38 days; longest survival: 105 days). We also examined the cells infiltrating the grafts during the early stages of the allograft response (day 5). Using flow cytometry, we found a significant decrease in the number of leukocytes infiltrating the transplanted kidneys of fed animals. This decrease was mainly due to a drop in the number of infiltrating T cells. We also found that cytokine mRNA production by the graft-infiltrating lymphocytes, assessed by reverse transcription polymerase chain reaction, showed a significant increase in interleukin-4 and transforming-growth factor-beta mRNA in the graft-infiltrating lymphocytes of fed animals compared with the controls.

Immune responses to dietary antigens: oral tolerance

The concept of immunologically mediated tolerance to food antigens through exposure to mucosal antigen has been the subject of continuous scientific debate. After a decline in interest in the mid-1980s, oral tolerance has again attracted the attention of immunologists. Here, Stephan Strobel and Allan Mowat discuss how this central immunological principle has potential new therapeutic applications for the treatment of autoimmune, inflammatory and possibly food-allergic diseases.

Food allergy: predictive testing of food products

Food allergy is a substantial cause of distress in humans. Several biotechnological techniques can be applied to reduce the antigenicity of food proteins to produce for instance hypoallergenic infant formulas. Biotechnological techniques synthesizing new proteins or new biological varieties for applications in food are also available. For such biotechnologically for derived protein products (novel foods), allergenicity may also pose a major concern. For safety reasons, it is of importance to evaluate the residual antigenicity of modified protein products, to screen for possible cross-reactivity to prevent reactions in previously sensitized individuals, and to test for sensitizing properties of new and/or modified protein products. Besides physico-chemical and immunochemical analyses, several in vitro and in vivo bioassays may be applied in studying the antigenic or allergenic properties of (new or modified) food proteins. In this paper, an overview of several available assays and new developments for determining the antigenic or allergenic properties of dietary proteins, as well as their possible applications and limitations is presented. Special attention is paid to the role of the gastro-intestinal tract physiology in food allergy and in the evaluation of the allergenic potential of food proteins and to the possible applications of animal models in food allergy research and in the evaluation of the allergenicity of food proteins.

Inductive events in oral tolerance in the TCR transgenic adoptive transfer model

Oral administration of antigen induces a systemic hyporesponsiveness termed oral tolerance. High doses of oral antigen lead to deletion or anergy of T-cells whereas low doses induce regulatory T-cells that secrete Th2 cytokines (IL-4/IL-10) and TGF-beta. The initiating events associated with oral tolerance have not been well characterized. We investigated the induction phase of oral tolerance by adoptively transferring ovalbulumin (OVA) p (323-339) TcR specific transgenic (Tg+) T-cells into BALB/c recipients that were then fed either a high (5 mg x 5) or a low (0.1 mg x 5) dose of OVA 323-329 peptide. The frequency of Tg+ T-cells in lymphoid tissues was determined by flow cytometry using an anti-clonotypic monoclonal antibody. In high-dose-fed animals, Tg+ cells increased six- to eightfold in Peyer's patches after one feeding and then progressively decreased to 44% of those in the control by Day 20. In contrast, a biphasic-type response was observed in lymph node and spleen where Tg+ cells decreased after the first feeding, returned to the control level, and then decreased to 36-63% of the control level by Day 20. In low-dose-fed animals, changes in Tg+ T cells were only observed in Peyer's patches after five feedings, where cells increased approximately twofold. T-cell activation as measured by proliferation and IFN-gamma secretion occurred in both low- and high-dose-fed animals after only one feeding and then declined whereas secretion of Th2 cytokines and TGF-beta remained high even 10 days after the last feeding in low-dose-fed animals. Immunization with OVA/CFA demonstrated peripheral tolerance as measured by decreased proliferation and IFN-gamma secretion and was associated with increased production of TGF-beta and IL-10. These results suggest that the inductive phase of oral tolerance is characterized by an activation of antigen-specific T-cells that involves the initial secretion of IFN-gamma followed by prolonged secretion of Th2 cytokines and TGF-beta.

Experimental autoimmune uveitis: molecular mimicry and oral tolerance

Intraocular inflammatory disease or uveitis, which affects the uveal tract and the retina of the eyes in human, is the major cause of visual impairment. Experimental autoimmune uveitis (EAU) is a T-cell-mediated autoimmune disease directed against retinal proteins and has been studied in several mammalian species including subhuman primates as a model for human posterior uveitis. Autoimmune responses provoked by molecular mimicry occur when the nonself and host determinants are similar enough to cross-react yet different enough to break immunological tolerance, and is one of the proposed mechanisms for induction of autoimmune diseases. Therapeutic immunomodulatory strategies have been used to induce antigen-specific peripheral immune tolerance in animal models of T-cell-mediated autoimmune diseases by oral administration of autoantigens. Oral tolerance leads to unique mechanisms of tissue and disease-specific immunosuppression, which would circumvent the immunotherapeutic problem of multiple target tissue autoreactivity. Several groups have investigated the effects of delivering autoantigens across gastric mucosal surfaces. This review briefly discusses molecular mimicry and the mechanism of induction of oral tolerance with respect to immunopathogenesis of T-cell-mediated autoimmune disease in general and EAU in particular.

Environmental pollutants as co-factors in IgE production

While there is a general perception that 'pollutants' present in the natural environment may act in concert with genetic factors in the host to precipitate primary allergic sensitization, there is a clear need for more hard data to establish the degree to which this actually occurs in different environmental settings, and to elucidate the underlying mechanism. It is evident that animal model systems provide viable avenues for studies on mechanisms, and several laboratories are actively engaged in this work. However, questions relating to the magnitude of these environmental effects on human allergic disease present more substantial problems, which can only be addressed by large-scale epidemiological studies on well-defined populations, backed up by comprehensive environmental monitorings. At present, the best defined area of the human literature is clearly the early postnatal data, which establishes that the first 1-2 months of life are a major risk period for life-long allergic sensitization to seasonal antigens. Broadening of these studies to encompass environmental monitoring, aimed at the identification of environmental cofactors which may synergize with early allergen exposure, is therefore a logical step for the future research.

Mucosal IgA elaboration

Secretory IgA is the main immunoglobulin present along mucosal surfaces. It is elicited best by oral rather than parenteral administration of specific antigens. The role of antigen form on the development of a secretory IgA response is still unclear. IgA protects by preventing attachment of microorganisms or their toxic products to the surface epithelium. A wide variety of regulatory T cells are now known to be of considerable importance in optimizing the secretory IgA response. This regulation is at least partly due to the elaboration of small polypeptide products (lymphokines). These lymphokines have been shown to be key signals during the maturation of IgA precursor B cells to IgA-secreting plasma cells. By studying models of the mucosal immune system which closely approximate the natural mucosal immune response, it should be possible to develop vaccines against many pathogenic microorganisms, their toxic products, and to toxicants and carcinogens within the environment.