Immune-mediated effects upon oral challenge of ovalbumin-sensitized Brown Norway rats: further characterization of a rat food allergy model

Integrating Widely Targeted Lipidomics and Transcriptomics Unravels Aberrant Lipid Metabolism and Identifies Potential Biomarkers of Food Allergies in Rats

SCOPE

Oral food challenges (OFCs) are currently the gold standard for determining the clinical reactivity of food allergy (FA) but are time-consuming, expensive, and risky. To screen novel peripheral biomarkers of FA and characterize the aberrant lipid metabolism in serum, 24 rats are divided into four groups: peanut, milk, and shrimp allergy (PA, MA, and SA, respectively) and control groups, with six rats in each group, and used for widely targeted lipidomics and transcriptomics analysis.

METHODS AND RESULTS

Widely targeted lipidomics reveal 144, 162, and 206 differentially accumulated lipids in PA, MA, and SA groups, respectively. The study integrates widely targeted lipidomics and transcriptomics and identifies abnormal lipid metabolism correlated with widespread differential accumulation of diverse lipids (including triacylglycerol, diacylglycerol, sphingolipid, and glycerophospholipid) in PA, MA, and SA. Simplified random forest classifier is constructed through five repetitions of 10-fold cross-validation to distinguish allergy from control. A subset of 15 lipids as potential biomarkers allows for more reliable and more accurate prediction of FA. Independent replication validates the reproducibility of potential biomarkers.

CONCLUSION

The results reveal the major abnormalities in lipid metabolism and suggest the potential role of lipids as novel molecular signatures for FA.

Assessment of the potential allergenicity of genetically-engineered food crops

An extensive safety assessment process exists for genetically-engineered (GE) crops. The assessment includes an evaluation of the introduced protein as well as the crop containing the protein with the goal of demonstrating the GE crop is "as-safe-as" non-GE crops in the food supply. One of the evaluations for GE crops is to assess the expressed protein for allergenic potential. Currently, no single factor is recognized as a predictor for protein allergenicity. Therefore, a weight-of-the-evidence approach, which accounts for a variety of factors and approaches for an overall assessment of allergenic potential, is conducted. This assessment includes an evaluation of the history of exposure and safety of the gene(s) source; protein structure (e.g. amino acid sequence identity to human allergens); stability of the protein to pepsin digestion in vitro; heat stability of the protein; glycosylation status; and when appropriate, specific IgE binding studies with sera from relevant clinically allergic subjects. Since GE crops were first commercialized over 20 years ago, there is no proof that the introduced novel protein(s) in any commercialized GE food crop has caused food allergy.

IgG Expression upon Oral Sensitization in Association with Maternal Exposure to Ovalbumin

The role of maternal allergen exposure in the allergenicity of the offspring remains controversial. Some studies have shown that maternal exposure is a risk factor for allergy in the offspring, whereas other studies have shown that maternal exposure induces immune tolerance and protects offspring from allergy disease. Therefore, we utilized maternal rat allergen exposure model to evaluate the offspring immune reactions to ovalbumin protein and to determine whether the Brown Norway (BN) rat model is a suitable animal model for studying the allergenicity of food proteins. For three generations, rats received an allergens or non-allergens by gavage during the pregnancy and lactation periods. After weaning, the offspring rats were used for oral sensitization experiment. In the sensitization experiment, the control rat, which had maternal exposure to phosphate-buffered saline (PBS), exhibited full response of IgG to oral exposure to OVA. The IgG level was significantly lower in F1 rats that were sensitized by maternal exposure to ovalbumin(OVA). Moreover, the lowest IgG level was found for the F3b sensitized by maternal rats exposed to OVA allergen for three continuous generations. Compared with maternal OVA exposure prior to postnatal sensitization, the sensitization via maternal PBS led to a higher serum level of OVA-specific IgG. However, the OVA-specific IgG levels for the two generations of maternal PBS exposure prior to postnatal sensitization was not higher than that for the one generation of maternal rats exposed to PBS prior to postnatal sensitization. Our studies demonstrate that maternal OVA exposure during the pregnancy and lactation can affect the results of oral sensitization studies using ovalbumin protein. BN rats must be bred in non-allergen conditions for at least one generation to avoid problems in rat models for studying the allergenicity of food proteins.

Effect of a cocoa-enriched diet on immune response and anaphylaxis in a food allergy model in Brown Norway rats

Previous studies have demonstrated that cocoa intake decreased Th2 immune-related antibodies in rats. In consequence, we aimed to study in depth this cocoa action, particularly assessing its effect on a rat model of food allergy (FA) and also on an anaphylactic response. The involvement of the intestinal immune system was analyzed to allow the action mechanisms to be investigated. The role of cocoa flavonoids in the antiallergic properties of cocoa was also established. Brown Norway rats were fed either a reference diet or diets containing conventional cocoa (CC) or nonfermented cocoa (NFC). FA to ovalbumin (OVA) was induced and, later, an anaphylactic response was provoked. As expected, the synthesis of anti-OVA IgE and other Th2-related antibodies was inhibited by CC diet. In addition, the release of mast cell protease II after anaphylaxis was partially prevented by CC, although other variables were not modified. The CC diet also attenuated the increase of some Th2-related cytokines released from mesenteric lymph node and spleen cells, and modulated the intestinal gene expression of molecules involved in allergic response. These results demonstrated the local and systemic influence of CC diet. The effects of the NFC diet were weaker than those of CC, suggesting that cocoa components other than flavonoids play a role in cocoa's action. In conclusion, by acting on intestinal and systemic immune functions, a cocoa-enriched diet in rats exhibited a protective effect against FA and partially against anaphylaxis, making this a food of high interest to the fields of health and immunonutrition.

Development and characterization of an effective food allergy model in Brown Norway rats

BACKGROUND

Food allergy (FA) is an adverse health effect produced by the exposure to a given food. Currently, there is no optimal animal model of FA for the screening of immunotherapies or for testing the allergenicity of new foods.

OBJECTIVE

The aim of the present study was to develop an effective and rapid model of FA in Brown Norway rats. In order to establish biomarkers of FA in rat, we compared the immune response and the anaphylactic shock obtained in this model with those achieved with only intraperitoneal immunization.

METHODS

Rats received an intraperitoneal injection of ovalbumin (OVA) with alum and toxin from Bordetella pertussis, and 14 days later, OVA by oral route daily for three weeks (FA group). A group of rats receiving only the i.p. injection (IP group) were also tested. Serum anti-OVA IgE, IgG1, IgG2a, IgG2b and IgA antibodies were quantified throughout the study. After an oral challenge, body temperature, intestinal permeability, motor activity, and mast cell protease II (RMCP-II) levels were determined. At the end of the study, anti-OVA intestinal IgA, spleen cytokine production, lymphocyte composition of Peyer's patches and mesenteric lymph nodes, and gene expression in the small intestine were quantified.

RESULTS

Serum OVA-specific IgG1, IgG2a and IgG2b concentrations rose with the i.p. immunization but were highly augmented after the oral OVA administration. Anti-OVA IgE increased twofold during the first week of oral OVA gavage. The anaphylaxis in both IP and FA groups decreased body temperature and motor activity, whereas intestinal permeability increased. Interestingly, the FA group showed a much higher RMCP II serum protein and intestinal mRNA expression.

CONCLUSIONS

These results show both an effective and relatively rapid model of FA assessed by means of specific antibody titres and the high production of RMCP-II and its intestinal gene expression.

Development of an animal model to evaluate the allergenicity of food allergens

SCOPE

Considering the increasing numbers of patients suffering from food allergy (FA) as well as the great variety of novel foods and food compositions, an unmet need exists for the development of preclinical approaches to characterize the allergenic potential of proteins. The aim of our study was to evaluate the allergenicity of different food allergens in a rat model.

METHODS

Brown Norway rats were sensitized to protein extracts (RuBisCO, apple, soy, peanut, garden pea) or ovalbumin (OVA) combined with Bordetella pertussis and aluminium hydroxide, followed by oral allergen challenges.

RESULTS

Allergen-specific serum immunoglobulin production and the proliferation of mononuclear cells from spleen confirmed sensitization. To assess functional alterations in the gut, intestinal permeability was measured, which increased in sensitized and challenged animals compared to non-sensitized controls. Allergens with high allergenic potential (peanut, OVA, soy) caused a stronger immunological response than allergens with low allergenic potential, such as RuBisCO and apple. Moreover, the immunological responses were reduced when using boiled instead of raw soy and pea proteins.

CONCLUSION

This model mimics key features of FA and facilitates investigating the allergenicity of allergens in novel food or food compositions in vivo.

Allergic sensitization: screening methods

Experimental in silico, in vitro, and rodent models for screening and predicting protein sensitizing potential are discussed, including whether there is evidence of new sensitizations and allergies since the introduction of genetically modified crops in 1996, the importance of linear versus conformational epitopes, and protein families that become allergens. Some common challenges for predicting protein sensitization are addressed: (a) exposure routes; (b) frequency and dose of exposure; (c) dose-response relationships; (d) role of digestion, food processing, and the food matrix; (e) role of infection; (f) role of the gut microbiota; (g) influence of the structure and physicochemical properties of the protein; and (h) the genetic background and physiology of consumers. The consensus view is that sensitization screening models are not yet validated to definitively predict the de novo sensitizing potential of a novel protein. However, they would be extremely useful in the discovery and research phases of understanding the mechanisms of food allergy development, and may prove fruitful to provide information regarding potential allergenicity risk assessment of future products on a case by case basis. These data and findings were presented at a 2012 international symposium in Prague organized by the Protein Allergenicity Technical Committee of the International Life Sciences Institute's Health and Environmental Sciences Institute.

Systemic sensitization with the protein allergen ovalbumin augments local sensitization in atopic dermatitis

Mouse models of atopic dermatitis based on epicutaneous sensitization have shed light on the role of epicutaneous allergen entry in the development of respiratory and gastrointestinal allergy. However, the contribution of non-cutaneous modes of sensitization to skin diseases has not been evaluated. We assessed if systemic ovalbumin administration, in conjunction with local sensitization, could prime for a robust inflammatory response. Furthermore, we attempted to elucidate important aspects of disease pathogenesis previously unaddressed in mouse models. Mice that underwent intraperitoneal ovalbumin sensitization prior to epicutaneous challenge demonstrated an acute (Th2-polarized) atopic dermatitis-like phenotype upon local challenge. The inflammatory response was strikingly more robust than in mice that underwent epicutaneous sensitization alone. The lesional infiltrate contained a dendritic cell population that corresponded phenotypically with inflammatory dendritic epidermal cells of significance in human disease. Finally, in accordance with observations in human atopic dermatitis, there was an increase in cluster of differentiation (CD) 103 (α_E subunit)-expressing CD4⁺ T lymphocytes. However, the absence of CD103 on approximately 50% of infiltrating cells argues against a primary role for the α_Eβ₇ integrin in tissue homing. In conclusion, we present a mouse model of atopic dermatitis that reveals novel insights into the pathogenesis of this complex disease.

Use of animal models to investigate major allergens associated with food allergy

Food allergy is an emerging epidemic that affects all age groups, with the highest prevalence rates being reported amongst Western countries such as the United States (US), United Kingdom (UK), and Australia. The development of animal models to test various food allergies has been beneficial in allowing more rapid and extensive investigations into the mechanisms involved in the allergic pathway, such as predicting possible triggers as well as the testing of novel treatments for food allergy. Traditionally, small animal models have been used to characterise immunological pathways, providing the foundation for the development of numerous allergy models. Larger animals also merit consideration as models for food allergy as they are thought to more closely reflect the human allergic state due to their physiology and outbred nature. This paper will discuss the use of animal models for the investigation of the major food allergens; cow's milk, hen's egg, and peanut/other tree nuts, highlight the distinguishing features of each of these models, and provide an overview of how the results from these trials have improved our understanding of these specific allergens and food allergy in general.

Allergic reactions compared between BN and Wistar rats after oral exposure to ovalbumin

There is currently no validated animal model for evaluating the potential allergenicity of food proteins. This study aimed to compare the allergic reactions between BN and Wistar rats after oral exposure to ovalbumin (OVA) by studying immune responses and clinical manifestations. Female BN and Wistar rats were orally exposed to OVA on days 1 and 14, and thereafter daily from day 15 to day 42. Sera and plasma were screened for OVA-specific antibodies and histamine. On day 49, all the OVA-sensitized animals were orally challenged with OVA before blood pressure was measured. One day later (on day 50), histopathology and differential cell counts were performed. The results indicate that oral exposure of BN rats to OVA yielded IgE, IgG, and IgG(2a) antibody responses that were generally of higher levels than those observed in Wistar rats (p < 0.05). However, the Wistar rats presented with more serious clinical manifestations and histopathologic changes that could have serious implications for any OVA-induced anaphylaxis. The studies here proved that OVA-sensitized BN and Wistar rats evinced different immune responses and clinical manifestations; these outcomes suggested that the two rat strains might differ in their immunologic mechanisms of allergy and that there was no correlation between immune responses and the severity of clinical symptoms. To be clear, the data from these studies should be viewed as 'preliminary', as only a single protein allergen was examined. Accordingly, further studies are needed to compare the allergic reactions between BN and Wistar rats by using purified strong-, weak-, and non-allergenic proteins based on the experiments reported here.

Evaluation of biotechnology-derived novel proteins for the risk of food-allergic potential: advances in the development of animal models and future challenges

Increasing concern from the public about the safety of genetically modified food has made critical to have suitable methods for recognizing associated potential hazards. Hierarchical approaches to allergenicity determination were proposed, and these include evaluation of the structural and sequence homology and serological identity of novel proteins with existing allergens, measuring the resistance to proteolytic digestion and assessment of sensitizing potential using animal models. Allergic individuals have a predisposed (i.e. atopic) genetic background, and a close resemblance to this setup is therefore desirable in animal models, which is possible by using a strain of an animal species that is prone for allergic disorders. So far, none of the animal model has been validated for the purpose of hazard identification in the context of safety assessment. However, the available knowledge suggests that the judicious use of an appropriate animal model could provide important information about the allergic potential of novel proteins. This paper provides an up-to-date review of the progress made in the field of development of in vivo models in this direction and the further goals that have to be achieved.

Mucosal mast cells mediate motor response induced by chronic oral exposure to ovalbumin in the rat gastrointestinal tract

We previously demonstrated that oral chronic exposure to ovalbumin (OVA) causes intestinal hypermotility in Sprague-Dawley rats. In this study, the objective was to determine the mechanism of action of OVA and the role of mucosal mast cells in the regulation of motor activity in this model. Rats were orally exposed to OVA during 6 weeks. Intestinal mucosal mast cells (IMMCs) were counted and rat mast cell protease II (RMCPII) measured in duodenum, jejunum, ileum and colon. Anti-OVA IgE, IgG, and IL-4 were measured in serum. Eosinophils and IgE(+) cells were counted in jejunum. In an additional study rats were treated with the mast cell stabilizer ketotifen and mast cell number, RMCPII concentration and motor activity in vitro were evaluated. OVA exposed rats showed an increase in mucosal mast cell number and in RMCPII content in small intestine and colon. However, variables of a Th(2) type response were not affected by exposure to OVA: (i) neither OVA specific IgE nor IgG were found; (ii) IL-4 did not increase and, (iii) the number of eosinophils and IgE(+) cells was identical in the exposed and unexposed groups. These results brought us to hypothesize a possible non-Ig-mediated action of OVA on mast cells. Ketotifen significantly diminished the response to OVA: Ketotifen reduced the number of mast cells and the RMCPII content and blocked increased intestinal contractility. In addition ketotifen modified motor response in both OVA exposed and unexposed animals giving evidence of the importance of mast cells in intestine motor activity driving.

The importance of dietary control in the development of a peanut allergy model in Brown Norway rats

This report describes the further development of a peanut allergy model in Brown Norway (BN) rats and in particular the importance of allergen-free breeding of the laboratory animals for the allergen to be used. For this purpose BN rats were bred for 3 generations on soy- and peanut-free feed since it is known that the legumes peanut and soy are cross-reactive. In addition, the effect of cholera toxin (CT), an oral adjuvant often used to increase the sensitivity of food allergy models, was investigated in the BN rat model. BN rats that were bred on both soy- and peanut-free feed could be sensitized orally to peanut (all exposed rats developed peanut-specific IgE, IgG2a and IgG1) and the adjuvant CT could only enhance this sensitization to a limited extent. We also found different protein recognition patterns against purified peanut allergens (Ara h1, Ara h2 and Ara h3) between intraperitoneally (i.p.) and orally sensitized BN rats. Orally sensitized rats recognized all tested allergens whereas i.p. sensitized rats only recognized Ara h1 and Ara h2. Our conclusion is that a model for food allergy should preferably be (A) oral and (B) if possible without the use of adjuvantia. Our model in BN rats unites these preferred characteristics. In addition, we show the importance of dietary control when conducting oral sensitization studies. Special attention must be paid to unscheduled dietary pre-exposure of the animals to the protein under investigation to obtain optimal oral sensitization.

Characterisation of the oral adjuvant effect of lemnan, a pectic polysaccharide of Lemna minor L

Lemnan LM, apiogalacturonanic pectin of duckweed Lemna minor L. was tested for adjuvant properties following oral administration with protein antigen. Male Swiss mice were orally immunized thrice with weekly intervals with free OVA or OVA with lemnan (LM). Lemnan LM was shown to increase delayed type hypersensitivity (DTH) and serum anti OVA IgG responses. LM was established to increase levels of both serum IgG1 and IgG2a subclasses, intestinal IgA and failed to elevate levels of serum IgE. Lemnan was found to increase the adhesion of macrophages and to enhance the generation of oxygen radicals by macrophages in response to phorbol 12-myristate 13-acetate. Serum OVA levels were four-fold higher in mice immunized with the mixture of OVA and LM in comparison with those in mice immunized with OVA only. Thus, substantial systemic and local mucosal immune responses were attained by oral immunization with the mixture of OVA and lemnan. Lemnan appeared to elicit adjuvant activity via induction of both Th1- and Th2-type responses. The immunopotentiating effect of lemnan may result from enhanced antigen ingestion and stimulation of macrophage activity.

Studies on BN rats model to determine the potential allergenicity of proteins from genetically modified foods

AIM: To develop a Brown Norway (BN) rat model to determine the potential allergenicity of novel proteins in genetically modified food.

METHODS: The allergenicity of different proteins were compared, including ovalbumin (OVA), a potent respiratory and food allergen, bovine serum albumin (BSA), a protein that is considered to have a lesser allergenic potential, and potato acid phosphatase (PAP), a non-allergenic protein when administered to BN rats via different routes of exposure (intraperitoneally or by gavage). IgG and IgE antibody responses were determined by ELISA and PCA, respectively. An immunoassay kit was used to determine the plasma histamine level. In addition, possible systemic effect of allergens was investigated by monitoring blood pressure.

RESULTS: OVA provoked very vigorous protein-specific IgG and IgE responses, low grade protein-specific IgG and IgE responses were elicited by BSA, while by neither route did PAP elicit anything. In either routes of exposure, plasma histamine level in BN rats sensitized with OVA was higher than that of BSA or PAP. In addition, an oral challenge with BSA and PAP did not induce any effect on blood pressure, while a temporary drop in systolic blood pressure in few animals of each routes of exposure was found by an oral challenge with OVA.

CONCLUSION: BN rat model might be a useful and predictive animal model to study the potential allergenicity of novel food proteins.

Dietary fat and an exogenous emulsifier increase the gastrointestinal absorption of a major soybean allergen, Gly m Bd 30K, in mice

The mechanisms by which food allergens are absorbed and sensitized via the gastrointestinal tract have not been well characterized. In this study, the gastrointestinal absorption of a major soybean allergen, Gly m Bd 30K, in young and older mice, and the effects of dietary fat and exogenous emulsifier were investigated. In Expt. 1, Gly m Bd 30K [0, 500 or 2000 mg/kg body weight (BW)] was administered orally to 24-d-old mice, and blood was sampled at various time points over a 120-min period. Plasma Gly m Bd 30K was measured by sandwich ELISA and immunoblotting. Its concentration peaked at 30 min and was dose dependent. Intact Gly m Bd 30K and its 20-kDa fragments were identified in plasma after absorption. In Expt. 2, 24-d-old mice administered soy milk containing 1 mg Gly m Bd 30K showed a steady increase in plasma Gly m Bd 30K from 60 to 120 min that was significantly higher than that in 10-wk-old mice. In Expt. 3, when corn oil (5 or 30%) was coadministered with Gly m Bd 30K (2000 mg/kg BW) to 24-d-old mice, the plasma concentration increased significantly and generally reached a plateau after 30 min. The absorption after the coadministration of 30% corn oil and 3% sucrose fatty acid ester was higher than after the administration of 30% corn oil alone. Intact Gly m Bd 30K and its fragments that were < 20 kDa survived digestion and were absorbed into the blood. We propose that absorption was enhanced by fat carrier-mediated transport.

Hypersensitivity to ovalbumin induces chronic intestinal dysmotility and increases the number of intestinal mast cells

Undiagnosed food allergies have been proposed as possible causes of promoting and perpetuating irritable bowel syndrome . Our aim was to find out if sensitization could induce chronic functional motor disturbances in the intestine and the mechanisms implicated. Rats were sensitized to ovalbumin (OVA) following three hypersensitivity induction protocols, two parenteral and one oral. Rat mast cell protease II (RMCP II) release in response to OVA challenge and immunoglobulin E (IgE) concentration were measured in serum. At least 1 week after challenge, small intestinal motility was evaluated using strain gauges. Intestinal tissue samples from orally sensitized rats were checked for in vitro stimulation with OVA. Mucosal mast cells were counted from duodenum sections. All sensitized rats showed intestinal hypermotility. Only rats sensitized by parenteral procedure showed an increase in RMCP II after OVA challenge in serum. IgEs increased only in the Bordetella pertussis sensitized group. Small intestine sections from orally sensitized rats released more RMCP II than sections from control rats. All sensitized rats showed an increase in the number of mucosal mast cells in duodenum. In conclusion, hypersensitivity to food proteins induces chronic motor alteration that persists long after antigen challenge and an excited/activated state of sensitized mucosal mast cells.

The Hyperresponsiveness of W/Wv Mice to Oral Sensitization Is Associated with a Decrease in TCR.GAMMA..DELTA.-T Cells

We have already reported that WBB6F1-W/W(v) (W/W(v)) mice, which have mutations in the c-kit gene, are highly susceptible to oral sensitization, and that the proportion of TCRgammadelta-T cells among the intraepithelial lymphocytes (IELs) (gammadelta-IELs) of W/W(v) is much lower than in congenic wild-type (+/+) mice. In this study we examined an inhibitory role of gammadelta-IELs in oral sensitization using two different methods. First, wild-type (+/+) mice were sensitized by oral administration of 1.0 mg ovalbumin (OVA) by gavage every day for 9 weeks after anti-TCRgammadelta antibody treatment 4 times. The treatment resulted in an enhanced OVA-specific IgG1 antibody production, active systemic anaphylaxis (ASA), and Th2-dominant cytokine production. Next, W/W(v) mice whose bone marrow cells were reconstituted from C57BL/6J mice for 5 months were sensitized by oral administration of OVA. The OVA-specific IgG1 antibody titer in the bone marrow-reconstituted W/W(v) mice was neither significantly enhanced, nor ASA was induced. The proportion of gammadelta-IELs in the reconstituted mice was much higher than that in the untreated W/W(v) mice. The above findings suggest that the decrease or increase in number of gammadelta-IELs enhances or decreases oral sensitization respectively. These results show that gammadelta-IELs have an important role in the oral tolerance to food antigens.

Relevance of Ara h1, Ara h2 and Ara h3 in peanut-allergic patients, as determined by immunoglobulin E Western blotting, basophil-histamine release and intracutaneous testing: Ara h2 is the most important peanut allergen

BACKGROUND

A number of allergenic proteins in peanut has been described and the relative importance of these allergens is yet to be determined.

OBJECTIVES

We have investigated the relevance of previously identified peanut allergens in well-characterized peanut-allergic patients by in vitro, ex vivo and in vivo assays.

METHODS

Thirty-two adult peanut-allergic patients were included based on careful and standardized patient history and the presence of peanut-specific IgE. The diagnosis peanut allergy was confirmed using double-blind placebo-controlled food challenges in 23 patients. Major peanut allergens Ara h1, Ara h2 and Ara h3 were purified from peanuts using ion-exchange chromatography. IgE immunoblotting was performed and IgE-cross-linking capacity was examined by measuring histamine release (HR) after incubating patient basophils as well as passively sensitized basophils with several dilutions of the allergens. Intracutaneous tests (ICTs) using 10-fold dilution steps of the purified allergens and crude peanut extract were performed.

RESULTS

Ara h2 was recognized most frequently (26 out of 32) in all tests and induced both positive skin tests and basophil degranulation at low concentrations, whereas Ara h1 and Ara h3 were recognized less frequently and reacted only at 100-fold higher concentrations as analysed with HR and intracutaneous testing (ICT). Next to the three tested allergens, proteins with molecular weights of somewhat smaller than 15 kDa were identified as a IgE-binding proteins on immunoblot in the majority of the patients (20 out of 32).

CONCLUSION

We conclude that Ara h2 is, for our patient group, the most important peanut allergen, and that previously unidentified peanut proteins with molecular weights of somewhat smaller than 15 kDa may be important allergens as well. ICT in combination with basophil-HR and IgE immunoblotting provides insight in the patient specificity towards the individual peanut allergens.

Food allergy: what do we learn from animal models?

PURPOSE OF REVIEW

This review summarizes selected articles on animal models of food allergy published in 2003. The research areas that are covered include mechanistic studies, the search for new therapies, as well as screening models for hazard identification of potential allergens.

RECENT FINDINGS

Novel treatment options of both prevention and therapeutic strategies have been reported with promising results. The induction of de-sensitization to food proteins was achieved by exposure to a mixture of recombinant food allergens and T helper 1 (Th1)-skewing bacterial components. Furthermore, research in animal models has provided new insights into the role of protein structure, digestion, and gut permeability in sensitization and tolerance induction to food proteins. The Th2 hypothesis of food allergy was tested in mouse strains, linking genetic susceptibility to sensitization with differential Th1-Th2 responses. In this context, the role of the liver in development of food antigen-specific Th2 cells, and the importance of costimulatory molecules in Th2 skewing were demonstrated. Finally, rodent models to predict potential allergenicity of novel foods have been further developed using different routes of sensitization.

SUMMARY

Currently, several animal models of food allergy are used, including mouse, rat, swine, and dog. Continuing research in these models may elucidate the immunological mechanisms that underlie the sensitization and challenge phase of food allergy and may result in improved therapeutic options. Furthermore, the development of animal models to predict relative allergenicity of novel foods remains an important topic.

Chronic allergy to dietary ovalbumin induces lymphocyte migration to rat small intestinal mucosa that is inhibited by MAdCAM-1

Few models have described a chronic food allergy with morphological changes in the intestinal mucosa. Here we established an ovalbumin (OVA)-induced, cell-mediated, allergic rat model and examined lymphocyte migration in the gut. Brown Norway rats were intraperitoneally sensitized to OVA and then given 10 mg OVA/day by gastric intubation for 6 wk. Lymphocyte subsets and adhesion molecules were examined immunohistochemically, and the migration of T lymphocytes to microvessels of Peyer's patches and villus mucosa was observed by using an intravital microscope. Serum OVA-specific IgG and IgE levels were increased in animals repeatedly exposed to OVA. Significant villus atrophy and increased crypt depth was accompanied by increased infiltration of T lymphocytes in the small intestinal mucosa of the group given OVA. Expression of rat mast cell protease II and of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) was also increased in these groups. The administration of anti-MAdCAM-1 antibody significantly attenuated the OVA-induced changes in the mucosal architecture and in CD4 T lymphocyte infiltration. Intravital observation demonstrated that in rats with a chronic allergy, T lymphocytes significantly accumulated in villus microvessels as well as in Peyer's patches via a MAdCAM-1-dependent process. Our model of chronic food allergy revealed that lymphocyte migration was increased with MAdCAM-1 upregulation.

An oral Brown Norway rat model for food allergy: comparison of age, sex, dosing volume, and allergen preparation

The purpose of the presented experiments was to study the possibility of using the Brown Norway rat as a model for food allergy in our laboratory. Specific serum IgE against ovalbumin (OVA) was induced after dosing male and female Brown Norway rats daily by gavage for 35 days. The influence of various preparations of allergen: OVA grade II, OVA grade V, and fresh egg white, age (4 versus 8 weeks), dosing volumes, and animal suppliers was studied. A general finding was that females had statistically significantly higher specific IgE and IgG titres and number of responders than males. Egg white preparation, age, dosing volume, and animal supplier did not statistically significantly influence the median IgE and IgG titres and number of responders. The difference between immune responses in males and females could not be attributed to variations in daily intake of OVA or exposure via the lung. In our hands, the oral Brown rat food allergy model gives rise to a moderate number of IgE responders, 13-38 and 38-75% in males and females, respectively. For further experiments with this model in our laboratory, females seem the sex of choice.

Oral sensitization of W/W(v) mice with ovalbumin and possible involvement of the decrease in gammadelta-T cells

Mast-cell-deficient WBB6F1-W/W(v) mice (W/W(v)) and congenic wild-type (+/+) mice were sensitized by oral administration of 0.1 or 1.0 mg ovalbumin (OVA) in the form of gavage every day for 9 weeks, and active systemic anaphylaxis (ASA) was induced by intraperitoneal injection of OVA. Production of OVA-specific IgG1 in response to oral sensitization of the W/W(v) mice was very high, and the production of IL-4, IL-5 and IL-10 by splenocytes re-stimulated with OVA in vitro was increased. These findings suggest that Th2-dominant helper T-cell activation had occurred. By contrast, production of OVA-specific IgG1 was low in +/+ mice, and no significant increase in production of Th2-type cytokines by the splenocytes of +/+ mice was observed. Population analysis in Peyer's patches by flow cytometry revealed that the proportion of the CD11c(+) cell in the W/W(v) mice was slightly increased after antigen stimulation. Analysis of the cell surface markers of intraepithelial lymphocytes (IELs) by flow cytometry showed that the proportion of TCRgammadelta-T cells was extremely lower in the W/W(v) mice, especially in the antigen sensitized group. The proportion of TCRgammadelta-T cells in the splenocytes of W/W(v) mice was also lower than in +/+ mice. Taken together, the above findings indicate that W/W(v) mice seems to be a good model not only for studying the induction mechanism of food allergy but for examining the role of TCRgammadelta-T cells in food-induced hypersensitivity.

Brown Norway rat ovalbumin-specific immunoglobulin E antibodies increase the human basophil expression of CD63 marker

Anaphylactic shock is an immunoglobulin E (IgE)-dependent hypersensitivity. Biological tests like leucocyte histamine release (LHR) and human basophil activation (HBA), frequently used in human allergy, reflect both the amount of IgE fixed on cells and the cellular reactivity. To assess whether serum-specific IgE from Brown Norway (BN) rats prepared for ovalbumin (OVA)-induced anaphylactic shocks can activate human basophils which has a potential interest in experimental allergy: such a test could rapidly assert an IgE sensitization in laboratory animals genetically T-helper 2 (Th2)-predisposed. Rats (n = 39) were immunized three times (day 0, day 5 and day 21) with OVA injected subcutaneously. One week after the third immunization, a shock was induced with an intravenous (i.v.) bolus of OVA. Sensitization was assessed by passive cutaneous anaphylaxis (PCA) test and dosages of serum IgE antibodies anti-OVA by enzyme-linked immunosorbent assay. Blood basophils were counted before and during the shock. Before the shock induction (at day 21), an LHR test was performed on rat blood, and human basophils were sensitized with rat sera. HBA was demonstrated by the increase in the percentage of cells expressing CD63 antigen membrane, measured by flow cytometry. Twenty-one days after the first subcutaneous (s.c.) immunization, the rat serum induced a significant HBA. HBA was observed neither with the same serum previously heated nor with the serum from nonimmunized rats (NIRs). OVA-specific IgEs were significantly increased in immunized rat (IR) serum. The PCA test was negative when the serum was previously heated (56 degrees C). We never observed any circulating basophils, and LHR test was negative. After OVA i.v. administration, all IRs died rapidly. HBA testing strongly suggests a mediation by specific IgE in the increase of CD63 in BN rats. Thus, HBA test seems useful in assessing whether an experimental allergy was induced in animals genetically predisposed to an immune response, Th2-mediated, like BN rat. We also conclude that rat basophil activation does not participate in the histamine release during anaphylactic shock in sensitized BN rats.

Constitutive nitric oxide synthase inhibition combined with histamine and serotonin receptor blockade improves the initial ovalbumin-induced arterial hypotension but decreases the survival time in brown norway rats anaphylactic shock

Anaphylactic shock accidents after allergen exposure are frequent. After immunization with ovalbumin (OVA), a common dietary constituent, we evaluated the efficacy of pretreatment with histamine-receptor or serotonin-receptor blockers administered alone or in combination with a nitric oxide synthase inhibitor (L-NAME) on OVA-induced anaphylactic shock in Brown Norway rats. Animals were allocated to the following groups (n = 6 each): control (0.9% saline); diphenydramine (15 mg kg(-1)); cimetidine (20 mg kg(-1)); diphenydramine + cimetidine; dihydroergotamine (50 microg kg(-1)); diphenydramine + cimetidine + dihydroergotamine; L-NAME (100 mg/kg) alone or associated with diphenydramine, cimetidine, diphenydramine + cimetidine, dihydroergotamine, or diphenydramine + cimetidine + dihydroergotamine. Mean arterial blood pressure (MABP), heart rate (HR), and survival time were monitored for 60 min following treatment. The shock was initiated with i.v. OVA. The MABP drop after i.v. OVA was worsened by diphenydramine and was modestly attenuated by cimetidine, dihydroergotamine, or both together. L-NAME potentiated slightly the effects of cimetidine and dihydroergotamine by lessening the initial MABP decrease, but this transient effect was not sufficient to prevent the final collapse or to improve survival time. Decreased vasodilatory (prostaglandins E2), increased vasoconstrictory (thromboxane B2) prostaglandins, and unchanged leukotriene C4 concentrations were contributory to the overall hemodynamic changes. Thus, the combined blockade of vasodilator mediators (histamine, serotonin, and nitric oxide) slowed the MABP drop in anaphylactic shock, but did not improve survival. More studies are needed to understand these discordant effects.

A search for an animal model of the Spanish toxic oil syndrome

To date, pathology characteristics of toxic oil syndrome (TOS), a disease associated with consumption of a contaminated cooking oil in Spain in 1981, have not been reproduced in an animal model. As vasculitis, eosinophilia, and a rise in circulating IgE levels were features of the acute phase of TOS, leading to an autoimmune outcome, a review of predisposition to these aspects across species was conducted. The intent was to determine predisposed strains or species that potentially might be effective in testing the toxic oils and thus defining the precise identity of the toxic contaminant(s). A number of potential candidates emerge from this review. Among mice, these include the NZB mouse hybrids, the MRL/lpr and SJL/J strains, and a transgenic mouse model of eosinophilia. The Brown Norway may be the most appropriate rat strain, while beagle dogs inbred to be genetically predisposed to immune complex disease and vasculitis are also a candidate species. Of the more exotic species, the mink and ferret have characteristics that might make them suitable candidates for testing oil samples.

Examination of oral sensitization with ovalbumin in Brown Norway rats and three strains of mice

We studied the conditions needed to sensitize animals to the oral feeding of food allergens, without induction of tolerance, in order to investigate the allergenicity of orally ingested food proteins. Brown Norway (BN) rats were sensitized by daily OVA (ovalbumin)-gavage or by drinking OVA containing water ad libitum and the ASA (active systemic anaphylaxis) response, as the immediate hypersensitivity response to antigen stimulation after oral sensitization, was examined. The oral administration of OVA by gavage produced a higher OVA-specific IgE response and an increase in serum histamine after antigen challenge, as compared to those produced by drinking water. Next, we examined the effect of murine age, the oral feeding technique and the oral feeding dose on sensitization using BALB/c, B10A and ASK mice. Twenty-week-old mice showed the strongest OVA-specific IgE and IgG1 responses and ASA-associated serum histamine contents increased with gavage in the three different age groups of BALB/c mice. Administering 0.1 mg of OVA by gavage daily for 9 weeks appeared to induce a higher response than administering 1 mg of OVA, in terms of OVA-specific IgE and IgG1 antibody responses and ASA responses. Among the three strains of mice, B10A mice exhibited the highest response in terms of OVA-specific IgE and IgG1 antibody and ASA responses. These findings suggested BN rats and B10A mice were suitable models for oral sensitization with antigen protein and that oral sensitization in mice requires low dose, intermittent antigen intakes.

Determination of protein allergenicity: studies in rats

For the safety evaluation of genetically engineered crops the potential allergenicity of the newly introduced protein(s) has become an important issue. There is, however, no universal and reliable test system for the evaluation of the allergenic potency of food products. The best known allergy assessment proposal is the careful stepwise process using the IFBC/ILSI decision tree. Unfortunately, the described tests are not always conclusive, especially if the gene source coding for the protein has no history of dietary use and/or an unknown history in terms of allergenicity. The further testing warranted should in particular be focused on the prediction of the sensitizing potential of the novel protein, for which animal models are considered to be needed. In this paper the results are summarized of a promising food allergy model developed in Brown Norway (BN) rats. The results demonstrate that BN rats can be sensitized orally to the various allergenic food proteins tested, resulting in significant antigen-specific IgE responses, without the use of adjuvants. Upon oral challenge of previously sensitized animals, local and systemic immune-mediated effects, such as increased gastrointestinal permeability and decreased breathing frequency and blood pressure, could also be observed.

Induction of active systemic anaphylaxis by oral sensitization with ovalbumin in mast-cell-deficient mice

Mast-cell-deficient W/W(v) mice were sensitized by oral administration of 0.1 and 1.0 mg ovalbumin (OVA) by gavage every day for 9 weeks, and active systemic anaphylaxis (ASA) was induced by intraperitoneal injection of OVA. The production of OVA-specific IgE and IgG1 by oral immunization of the W/W(v) mice was high, and the production of IL-4 by splenocytes re-stimulated with OVA in vitro was increased. In contrast, production of OVA-specific IgG2a and IgG2b was low, and production of IFN-gamma by splenocytes after re-stimulation with OVA in vitro was rather decreased. These findings suggest that Th2-dominant helper T-cell activation had occurred. No increase in serum histamine level was observed following ASA induction. However, the plasma platelet-activating factor (PAF) levels of the mice sensitized with 0.1 and 1.0 mg OVA by gavage increased significantly. The increases in plasma PAF correlated well with the ASA-associated decreases in body temperature, suggesting that PAF plays an important role in ASA in W/W(v) mice. Taken together the above findings indicate that W/W(v) mice are a good model not only for studying induction of food allergy but also for examining the role of PAF in food-induced hypersensitivity.

Comparison of antibody responses to hen's egg and cow's milk proteins in orally sensitized rats and food-allergic patients

BACKGROUND

No adequate enteral sensitization models are available to study food allergy and the allergenicity of food proteins. To further validate an enteral brown Norway (BN) rat sensitization model under development, we studied specific protein recognition to determine whether a comparable pattern of proteins is recognized by the rat immune system and the human immune system.

METHODS

The animals were exposed to either ovalbumin as a positive reference control, hen's egg-white-protein extract, or a cow's milk preparation by daily gavage dosing (0.5, 1, 2.5, 5, 10, or 15 mg protein per rat/day) for 9 weeks. No adjuvants were used during the sensitization studies. The specificities of antibodies against hen's egg-white proteins or cow's-milk proteins in sera from orally sensitized rats and food-allergic patients were studied and compared by immunoblotting.

RESULTS

The IgG and IgE antibodies to hen's egg-white proteins and cow's-milk proteins present in sera from orally sensitized rats and food-allergic patients showed a comparable pattern of protein recognition.

CONCLUSIONS

Upon daily intragastric exposure to food allergens, the specificities of the induced antibody responses in the BN rat resemble those found in food-allergic patients. These studies add further support to the hypothesis that the BN rat may provide a suitable animal model for food allergy research and research on the allergenicity of food proteins.

An oral sensitization model in Brown Norway rats to screen for potential allergenicity of food proteins

We developed an oral sensitization protocol for food proteins for the rat. Young Brown Norway (BN) rats were exposed to 1 mg ovalbumin (OVA) by daily gavage dosing for 42 days without the use of an adjuvant. OVA-specific IgE and IgG responses were determined by ELISA. On an oral challenge with OVA some clinical symptoms of food allergy-like effects on the respiratory system, blood pressure, and permeability of the gastrointestinal barrier were studied. In addition, BN rats were orally exposed to a total hen egg white protein (HEW) extract and cow's milk (CM) and the specificities of induced antibody responses were compared with the specificities of antibodies in sera from egg- and milk-allergic patients using immunoblotting. Animals orally exposed to the allergens developed specific IgE and IgG antibodies which recognized the same proteins compared with antibodies from egg- or CM-allergic patients. Among the various clinical symptoms of food allergy, gut permeability was increased after an oral challenge. In addition, some animals demonstrated a temporary decrease in breathing frequency or systolic blood pressure. The results obtained show that the Brown Norway rat is a suitable animal model for inducing specific IgG and IgE responses on daily intragastric dosing of OVA without the use of an adjuvant. Moreover, local immune-mediated effects on oral challenge are observed. The observation that enterally exposed BN rats and food-allergic patients demonstrate antibody responses to a comparable selection of proteins on exposure to different protein mixtures (HEW and CM) further supports the suitability of the BN rat as an animal model for food allergy research and for the study of the allergenicity of (novel) food proteins.