Assessment [correction of Asessment] of the brown Norway rat as a suitable model for the investigation of food allergy

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.

Peptide array-based inhibition ELISA for evaluating antigenicity in infant formulas

With increased awareness among consumers regarding food safety and security, food allergen control has become an indispensable requirement in the food industry. Although several methods for detecting allergens in food products are available, highly sensitive techniques are required. In this study, we developed a technique named as peptide array-based inhibition enzyme-linked immunosorbent assay (ELISA), Pep-iEIA, for evaluating antigenicity and detecting cow's milk antigen in infant formula products, using a peptide array consisting of a series of overlapping peptides found in allergenic milk proteins. Pep-iEIA was used to examine five cow's milk-based infant formulas with different degrees of hydrolyzation, and the assay offered both more sensitive detection and detailed analysis of remaining antigenic peptides in allergen compared to conventional ELISA. The antigenicity level of the allergenic peptides identified using Pep-iEIA was confirmed by surface plasmon resonance assay. We believe that Pep-iEIA will be highly useful for antigenicity evaluation of dairy products consumed by infants and patients with cow's milk allergy.

Design, quality, safety and efficacy of extensively hydrolyzed formula for management of cow's milk protein allergy: What are the challenges?

Cow's milk protein allergy (CMPA) is one of the most common food allergies in infancy. Clinical food allergy guidelines recommend an extensively hydrolyzed formula (EHF) as the first-line treatment in nonbreastfed infants with CMPA. Designing and commercializing EHF poses both technical and regulatory challenges. Each manufacturing step, from sourcing of raw materials to release of the final product, needs to be managed in accordance with comprehensive quality systems. To avoid cross-contamination via externally sourced ingredients, suppliers should be carefully selected based on quality requirements. Strict zoning of the manufacturing areas according to contamination risk and air flow control are effective strategies to prevent accidental allergen contamination. Furthermore, dedicated manufacturing lines for hypoallergenic products are used to prevent potential cross-contamination from other products produced on the same line. The enzymatic hydrolysis, heat treatment and ultrafiltration used are specific to each manufacturer. Consequently, EHF are a heterogenous group of products with differences in the molecular weight profile of peptides, content of residual immunogenic cow's milk allergens, and residual in-vitro allergenicity. These differences are likely to affect clinical efficacy and safety. As not all commercialized EHF products have undergone formal testing in the laboratory and clinical trials, there is a need to develop guidelines for minimum technical and regulatory requirements for EHF products, including validated assays for ongoing quality control. Clinical trials assessing new EHF products for their hypoallergenicity and ability to support normal growth remain the definitive proof of efficacy and safety in infants and young children with CMPA.

Investigations of immunogenic, allergenic and adjuvant properties of Cry1Ab protein after intragastric exposure in a food allergy model in mice

Background

In genetically modified (GM) crops there is a risk that the inserted genes may introduce new allergens and/or adjuvants into the food and feed chain. The MON810 maize, expressing the insecticidal Cry1Ab toxin, is grown in many countries worldwide. In animal models, intranasal and intraperitoneal immunisations with the purified Cry1Ab proteins have induced immune responses, and feeding trials with Cry1Ab-containing feed have revealed some altered immune responses. Previous investigations have primarily measured antibody responses to the protein, while investigations of clinical food allergy symptoms, or allergy promotion (adjuvant effect) associated with the Cry1Ab protein are largely missing. We aimed to investigate immunogenic, allergenic and adjuvant properties of purified Cry1Ab toxin (trypCry1Ab, i.e., trypsin activated Cry1Ab) in a mouse model of food allergy.

Method

Female C3H/HeJ mice were immunized by intragastric gavage of 10 μg purified, trypsin activated Cry1Ab toxin (trypCry1Ab) alone or together with the food allergen lupin. Cholera toxin was added as a positive control for adjuvant effect to break oral tolerance. Clinical symptoms (anaphylaxis) as well as humoral and cellular responses were assessed.

Results

In contrast to results from previous airway investigations, we observed no indication of immunogenic properties of trypCry1Ab protein after repeated intragastric exposures to one dose, with or without CT as adjuvant. Moreover, the results indicated that trypCry1Ab given by the intragastric route was not able to promote allergic responses or anaphylactic reactions against the co-administered allergen lupin at the given dose.

Conclusion

The study suggests no immunogenic, allergenic or adjuvant capacity of the given dose of trypCry1Ab protein after intragastric exposure of prime aged mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-016-0148-x) contains supplementary material, which is available to authorized users.

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.

Evaluation of the antigenicity of hydrolyzed cow's milk protein formulas using the mouse basophil activation test

Hypoallergenic infant formulas are widely used for infants with cow's milk allergy. The aim of this study was to assess the utility of the mouse basophil activation test (BAT) in the evaluation of residual antigenicity in these formulas. Whole blood samples derived from β-lactoglobulin- or casein-immunized mice were incubated with one of the following formulas: conventional, partially hydrolyzed, or extensively hydrolyzed. Basophilic activation was analyzed by flow cytometry using an IgE-dependent activation marker CD200R1 and an IgG-dependent activation marker CD200R3. Systemic anaphylaxis was induced by i.v. injection of milk formula and results were compared. Conventional formula induced pronounced changes in CD200R1 and CD200R3 expression on basophils, whereas extensively hydrolyzed formulas did not elicit any changes in these markers. Similarly, challenge with conventional formula induced anaphylaxis, whereas extensively hydrolyzed formulas did not induce anaphylaxis. Although the partially hydrolyzed formula also induced basophilic activation and systemic anaphylaxis, the magnitude of these effects was smaller than that observed with the conventional formula. Compared to CD200R1, the observed trend in CD200R3 expression resembled the results obtained from systemic anaphylaxis test more closely. These findings show that mouse BAT, in particular using CD200R3, is highly useful for the evaluation of antigenicity of milk formulas.

The impact of structural integrity and route of administration on the antibody specificity against three cow's milk allergens - a study in Brown Norway rats

Background

Characterisation of the specific antibody response, including the epitope binding pattern, is an essential task for understanding the molecular mechanisms of food allergy. Examination of antibody formation in a controlled environment requires animal models. The purpose of this study was to examine the amount and types of antibodies raised against three cow’s milk allergens; β-lactoglobulin (BLG), α-lactalbumin (ALA) and β-casein upon oral or intraperitoneal (i.p.) administration. A special focus was given to the relative amount of antibodies raised against linear versus conformational epitopes.

Methods

Specific antibodies were raised in Brown Norway (BN) rats. BN rats were dosed either (1) i.p. with the purified native cow’s milk allergens or (2) orally with skimmed milk powder (SMP) alone or together with gluten, without the use of adjuvants. The allergens were denatured by reduction and alkylation, resulting in unfolding of the primary structure and a consequential loss of conformational epitopes. The specific IgG1 and IgE responses were analysed against both the native and denatured form of the three cow’s milk allergens, thus allowing examination of the relative amount of linear versus conformational epitopes.

Results

The inherent capacity to induce specific IgG1 and IgE antibodies were rather similar upon i.p. administration for the three cow’s milk allergens, with BLG = ALA > β-casein. Larger differences were found between the allergens upon oral administration, with BLG > ALA > β-casein. Co-administration of SMP and gluten had a great impact on the specific antibody response, resulting in a significant reduced amount of antibodies. Together results indicated that most antibodies were raised against conformational epitopes irrespectively of the administration route, though the relative proportions between linear and conformational epitopes differed remarkably between the allergens.

Conclusions

This study showed that the three-dimensional (3D) structure has a significant impact on the antibodies raised for both systemic and orally administered allergens. A remarkable difference in the antibody binding patterns against linear and conformational epitope was seen between the allergens, indicating that the structural characteristics of proteins may heavily affect the induced antibody response.

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.

A mouse model for food allergy using intraperitoneal sensitization

Food allergy is an important health issue. With the increasing interest in novel foods derived from transgenic crop plants, there is a growing need for the development of approaches for the characterization of the allergenic potential of proteins. Although most foreign proteins are immunogenic (able to induce IgG antibody responses), relatively few are important food allergens with the capacity to provoke IgE antibody production. There is currently no validated animal model for the determination of allergenic potential of food proteins. One approach that appears to show some promise is outlined in the current chapter. BALB/c strain mice are immunized by intraperitoneal injection and the potential to cause allergenicity assessed as a function of the induction of specific IgE antibody, measured by homologous passive cutaneous anaphylaxis. Progress to date with this method is summarized, and comparisons are made with other experimental models, including considerations of route of exposure, use of adjuvants and selection of appropriate end points.

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 immune responses to food allergens in mice

There is considerable interest in the development and evaluation of approaches for the safety assessment of novel foods, and in particular in methods for characterisation of allergenic potential. One strategy that has found favour is a tiered approach in which the potential of novel proteins to induce allergic sensitisation is assessed based on considerations of stability of the protein in a simulated gastric juice and homology with, or structural similarity to, known allergens. Linked to such an approach may be evaluation of serological identity with proteins known to cause allergic disease. With the aim of supplementing such approaches with a more direct measurement of potential allergenic activity, attempts have been made to characterise the quality of immune responses elicited in BALB/c strain mice. Such evaluations comprise measurement of IgG and IgE antibody production and (to a lesser extent) of induced cytokine expression patterns. Investigations to date suggest that in mice proteins provoke variable immune responses, those with the potential to cause allergic sensitisation stimulating IgE (and IgG) antibody production. In contrast, non-allergenic, but nevertheless immunogenic, proteins are associated with IgG antibody responses in the absence of marked IgE production. Consistent with the selective activation of selective type 2 T lymphocyte responses, exposure of mice to allergenic protein is associated with preferential expression of IL-4, -5, -10 and -13. Collectively these data suggest that characterisation of the nature of immune response induced in mice by proteins may provide a useful adjunct or alternative to current strategies for the assessment of allergenic potential.

Peanut- and cow's milk-specific IgE, Th2 cells and local anaphylactic reaction are induced in Balb/c mice orally sensitized with cholera toxin

BACKGROUND

The development of animal models developing specific immunoglobulin (Ig)E presenting the same specificity as human IgE and similar clinical symptoms as those observed in allergic patients are of great interest for the understanding of mechanisms involved in the induction and regulation of food allergy.

METHODS

Balb/c female mice were sensitized with whole peanut protein extract (WPPE) by means of intraperitoneal (i.p.) injections with alum or gavages with cholera toxin (CT). The WPPE specific IgE, IgG1 and IgG2a were monitored. Th2 cells activation was analysed assaying interleukin (IL)-4 and IL-5 vs IFNgamma on reactivated splenocytes. Local anaphylactic reaction was evaluated by assaying histamine in faecal samples. The oral sensitization protocol was further extended to cow's milk proteins (CMP).

RESULTS

Balb/c mice developed high peanut-specific IgE and IgG1 responses either after i.p. or oral sensitizations. In both cases, antibodies were specific to polymer of glycinin fragments, containing polypeptides from Ara h3/4, and to a lesser extent to Ara h1 and Ara h2. Interleukin-4 and IL-5 production were evidenced. Balb/c mice could also be sensitized to CMP, as demonstrated by CMP-specific IL-4 and IL-5 secretions and induction of IgE specific for whole caseins, beta-lactoglobulin, serum bovine albumin and lactoferrin. Of interest was the occurrence of a local anaphylactic reaction in the peanut and CM models.

CONCLUSIONS

In contrast with previous authors, Balb/c mice were sensitized and evidenced an allergic reaction after oral administrations of peanut or CMP plus CT, providing an interesting model for further studies on immunopathogenic mechanisms.

RETRACTED: Promising treatments in development for food allergies

Up to 6% of young children and 2% of adults suffer from food allergy. Among them many have IgE-mediated food allergy, a condition with potentially fatal allergic reactions. The only proven treatment is avoidance of the offending food, which can be identified using standardised allergic tests. However, several studies have addressed possible definite treatment options for food allergy. Immunotherapy, administered orally or by systemic injections, shows promising preliminary results, but these therapeutics are based on studies with insufficient scientific support, or are associated with a high risk of severe side effects. At present, no studies can support pharmacotherapy. However, promising results were recently published with anti-IgE antibodies in a human trial, and various approaches in a mouse model of food allergy (chinese herbal medicine, specific modulation of the T-cell response). Rapidly evolving findings might provide hope for a cure for food allergy in the near future.

Effect of maternal dietary cow's milk on the immune response to beta-lactoglobulin in the offspring: a four-generation study in mice

BACKGROUND

Evaluation of immune responses to food proteins in animal models requires that the animals are not already sensitized or orally tolerized against the proteins in question. Since maternal transfer of specific immune responses has been observed, breeding of animals on an antigen-free diet for several generations may be necessary to obtain immunologically naive animals.

METHODS

To determine the most appropriate breeding conditions of mice to be used in immunological studies on food proteins, we examined immune responses towards beta-lactoglobulin (BLG) in mice bred on a milk-containing diet (F0) and then for three generations (F1-F3) on a commercially available milk-free diet. The specific antibody and cell-proliferative response to BLG was compared in non-immunized and immunized BALB/c mice, and in mice orally tolerized to BLG prior to immunization.

RESULTS

The immune response to BLG in the F1 generation deviated from the response observed in the F0 and F2/F3 generations. Importantly, trace amounts of BLG detected in the commercial milk-free diet did not induce oral tolerance.

CONCLUSIONS

The study showed that breeding mice on an antigen-free diet for at least two generations is required to attain animals appropriate for immunological studies of food proteins. Although the small quantity of BLG in the milk-free diet did not induce detectable oral tolerance in the present study, it is strongly recommended that the potential effect of contaminating dietary antigen is considered in future studies on food proteins.

Safety determination for the use of bovine milk-derived lactoferrin as a component of an antimicrobial beef carcass spray

Bovine milk-derived lactoferrin (BMDL), an iron-binding glycoprotein, is known to be an effective natural antimicrobial. It is used as a spray, applied electrostatically, to raw beef carcasses to detach bacteria adhering to the surface in order to reduce microbial contamination. The use of BMDL as a component (at not more than 2% by weight) of an antimicrobial spray was determined Generally Recognized As Safe (GRAS) (GRN 67) for three proposed uses (i.e., beef carcasses, subprimals, and finished cuts), provided that the ingredient statement of food products that contain milk-derived lactoferrin identifies the source of the protein. The use of BMDL spray on only beef carcasses (not subprimals or finished cuts) at a level not to exceed 0.20 ml of formulation per kg of beef was determined safe without the requirement of labeling of food products so treated. The two key components of the assessment are: (1) a determination that exogenous lactoferrin exposure (resulting from its application to beef carcasses) is in the range of existing background exposures of lactoferrin as a result of lactoferrin found naturally in beef, and (2) a determination that this potentially small incremental increase in lactoferrin is safe (i.e., there is no reasonable expectation that BMDL will become an allergen under the conditions of its intended use).

Future therapeutic options in food allergy

Up to 5% of young children and 2% of adults suffer from food allergy. Among them many have immunoglobulin E (IgE)-mediated food allergy, a condition with potentially fatal allergic reactions. Several studies have addressed possible definite treatment options for food allergy. Immunotherapy, by the oral route or by systemic injections shows promising preliminary results, but current interpretation of these therapeutic options are mostly handicapped by studies with insufficient scientific support, or by severe side-effects. Currently, no studies can support pharmacotherapy. Finally, most promising results were recently published with anti-IgE antibodies in a human trial, or various approaches in a mouse model of food allergy (chinese herbal medicine, specific modulation of the T cell response). Rapidly evolving findings might provide hope for a cure of food allergy in the near future.

Evaluation of protein allergenic potential in mice: dose-response analyses

BACKGROUND

With the increasing interest in novel foods derived from transgenic crop plants, there is a growing need for the development of approaches for the characterization of the allergenic potential of proteins. Whereas immunogenicity is a common property of foreign proteins, including food proteins, relatively few are significant dietary allergens with the inherent capacity to provoke IgE antibody production and immediate-type hypersensitivity responses.

OBJECTIVE

In order to evaluate an approach for the measurement of the allergenic potential of proteins, detailed dose-response analyses of humoral immune responses induced following systemic exposure of BALB/c strain mice to proteins known to differ in terms of sensitizing activity have been conducted.

RESULTS

Mice were exposed to a range of concentrations of ovalbumin, a major allergenic constituent of hen's egg, a purified peanut allergen, Arachis hypogea agglutinin, or to the milk allergen bovine serum albumin, and to materials considered to lack significant allergenicity: a crude potato protein extract and a purified potato protein, potato agglutinin. The specific IgE antibody was measured by homologous passive cutaneous anaphylaxis assay, and the specific IgG antibody was measured by enzyme-linked immunosorbent assay. Each of the five proteins was immunogenic in mice, inducing IgG antibody responses at all doses tested, although there was some variation with respect to the vigour of IgG responses. Marked differences in the capacity of these proteins to induce IgE responses were observed, however, with relatively high-titre IgE antibody provoked by all three allergens over the dose ranges examined, whereas the potato proteins stimulated low-titre IgE antibody at the highest dose (10%) only. Importantly, differences in IgE antibody production have been observed against a background of equivalent immunogenicity (IgG antibody responses).

CONCLUSION

The data presented here suggest that the measurement of antibody (IgE) responses in BALB/c mice appears to identify allergens accurately and to distinguish them from those materials that apparently lack allergenicity.

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.

Effect of subchronic feeding of genetically modified corn (CBH351) on immune system in BN rats and B10A mice

Subchronic animal feeding studies to examine the effect on the immune system of genetically modified corn CBH351, which contains the Cry9C protein derived from Bacillus thuringiensis subspecies tolworthi, were conducted in female BN rats and B10A mice. The studies were designed to compare the effect of a line of genetically modified corn CBH351 (GM corn) with that of isoline corn (non-GM corn). Heat-treated corn meal was incorporated into the diets of the rats and mice at a concentration of 50%. The study duration was 13 weeks. Growth, food intake, and organ weights of the thymus, spleen, and liver were compared between animals fed the non-GM and GM lines. The histological findings in thymus, spleen, mesenteric lymph nodes, Peyer's patches, small intestines, liver, kidney, and bone marrow, and the presence of Cry9C-specific IgE, IgG, IgG1 and IgA antibodies in serum were also compared. The results showed no significant differences in growth, feeding value, or the histological findings in immunity-related organs between the animals fed the GM and non-GM lines. Production of Cry9 C-specific IgE and IgA was not detected in the serum of either group. Production of Cry9C-specific IgG and IgG1 was slightly increased in the 50% GM groups of BN rats. No Cry9C-specific IgG or IgG1 was detected in the serum of BN rats fed the diet containing 5% GM-corn In conclusion, no immunotoxic activity was detected in the GM-corn-fed rats and mice in this subchronic dietary study.

Immunogenic properties of rapidly digested food proteins following gavage exposure of mice: a comparison of ovalbumin with a potato acid phosphatase preparation

The ability of food proteins to resist digestion in simulated gastric fluid (SGF) correlates with allergenic potential. The purpose of the current investigations was to determine whether this association is due solely to the failure of unstable proteins to elicit an immune response when administered orally. We have examined immune responses induced in BALB/c mice by gavage administration of ovalbumin (OVA) and a crude potato protein extract (PPE) containing acid phosphatase activity. The stability of OVA and PPE in SGF was measured using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The ability of these proteins to stimulate specific IgG and IgE antibody production in mice following parenteral (intraperitoneal; ip) or oral (gavage) exposure was compared using enzyme-linked immunosorbent and homologous passive cutaneous anaphylaxis assays, respectively. Both OVA and PPE induced specific IgG antibody responses when administered either by gavage or by ip injection. Parenteral, but not gavage, exposure to OVA was associated with robust IgE antibody responses. Administration of PPE failed to stimulate strong IgE production via either route of exposure. Differential stability in SGF was observed, with PPE being digested extremely rapidly (within 1 min), whereas OVA was more resistant. The strong association reported by others between stability in SGF and allergenic potential is unlikely to be solely due to orally-ingested labile proteins failing to provoke immune responses due to degradation in the stomach.

Sensitizing capacity and residual allergenicity of hydrolyzed cow's milk formulae: results from a murine model

BACKGROUND

Cow's milk allergy is the most common cause of clinically relevant adverse reactions to food in infants and children. Partially and extensively hydrolyzed formulae are used for the therapy and prevention of cow's milk allergy. However, the immunogenic potency of hydrolyzed cow's milk formulae to induce and/or enhance the allergic phenotype in vivo is still under debate. The aim of this study was to assess the sensitizing capacity and residual allergenicity of various partially and extensively hydrolyzed cow's milk formulae in a murine model of cow's milk allergy.

METHODS

BALB/c mice were immunized with either a cow's milk formula or various partially and extensively hydrolyzed formulae. Immediate cutaneous hypersensitivity reactions and allergen-specific antibody production were assessed.

RESULTS

Although immunization with cow's milk resulted in 12/13 cases in a positive skin test response to intradermal injection of cow's milk formulae, only 1 mouse showed a positive skin test to one of the partially hydrolyzed formulae, and none showed positive reactions to other partially hydrolyzed formulae, any of the extensively hydrolyzed formulae, phosphate-buffered saline or the amino acid formula. However, 6 of 8 mice showed positive skin tests when immunized with partially hydrolyzed formulae and with one of the extensively hydrolyzed formulae.

CONCLUSIONS

The residual allergenic potential is markedly reduced in many hydrolyzed formulae, but most of the formulae investigated could induce an allergic immune response in BALB/c mice. Our murine model seems to be suitable to investigate the sensitizing capacity of hydrolyzed formulae and to differentiate even between extensively hydrolyzed formulae.

Determination of protein allergenicity: studies in mice

There is a need to identify and characterize the allergenic potential of novel proteins introduced into genetically-modified crop plants. Although several approaches have already been described, none of these measures directly the ability of proteins to cause allergic sensitization. For this reason there has been a growing interest in the development of suitable animal models. This article describes experience to date with a method based upon assessment of serological (IgG and IgE antibody) responses induced in BALB/c strain mice by proteins. Comparisons have been made between intraperitoneal (i.p.) administration and exposure by gavage using both allergenic and non-allergenic proteins. The available data indicate that responses provoked by i.p. exposure permit the identification of proteins that have the inherent potential to induce IgE antibody production and allergic sensitization. Moreover, this approach also provides a rank order of proteins with respect to allergenic potency that apparently reflects what is known of their relative sensitizing activity in humans. By comparison, oral exposure of mice by gavage is somewhat less sensitive. On this basis it is proposed that the inherent sensitizing potential of novel proteins can be evaluated as a function of IgE antibody responses stimulated by parenteral (i.p.) exposure of BALB/c mice.

Food allergy: what are the issues?

With a growing interest in the development of genetically modified crop plants there is a need for appropriate approaches to safety assessment. Among the issues that have to be addressed is consideration of whether the products of novel genes have the potential to cause allergic sensitization. Resulting from a collaboration between the International Food Biotechnology Council and the International Life Sciences Institute recommendations have been made for a step-wise approach to the assessment of allergenic potential based upon considerations of serological identity, and sequence or structural homology, with known allergens and examination of the stability of the test protein in a simulated gastric fluid. In parallel there has been interest in the development of animal models, which would permit a more direct evaluation of potential allergenic activity. Progress in these areas is reviewed briefly in the context of what is known of food allergy and some of the important issues, which must be addressed in designing safety assessment strategies identified.

Divergent antibody isotype responses induced in mice by systemic exposure to proteins: a comparison of ovalbumin with bovine serum albumin

Whereas many foreign proteins are immunogenic, only a proportion is associated commonly with allergy, having the potential to induce the quality of immune response necessary for IgE antibody production and the development of immediate type hypersensitivity reactions in the gastrointestinal and/or respiratory tracts. In the context of toxicological evaluations there is a need to identify those properties that confer on proteins the ability to provoke allergic reactions. The characteristics of antibody responses induced in BALB/c strain mice following administration of ovalbumin (OVA), a significant human allergen, have been compared with those provoked by bovine serum albumin (BSA), a protein considered to have more limited allergenic potential. Intranasal or intraperitoneal (ip) administration of BSA or OVA elicited vigorous IgG and IgG1 antibody responses. Differential IgE antibody production was observed, however, with OVA stimulating relatively high IgE antibody titres at all doses tested whereas no or low titre IgE antibody was detected following exposure to BSA. Furthermore, a differential capacity for IgG2a antibody responses was observed, with only BSA provoking high titres of this IgG subclass. The relative quality of induced responses was equivalent following administration of these proteins via mucosal (in) tissue or via a non-mucosal (ip) route of exposure. IgG2a antibody production is promoted by the type 1 cytokine interferon gamma (IFN-gamma), whereas IFN-gamma and the type 2 cell product interleukin 4 exert reciprocal antagonistic effects on IgE antibody responses. Although cytokine expression patterns were not analysed in this series of experiments, the differential IgE and IgG subclass antibody responses induced by BSA and OVA are consistent with the preferential activation of T helper (Th) 1- and Th2-type cells, respectively. These data indicate that proteins can provoke in mice characteristic antibody (IgE and IgG) isotype profiles suggestive of discrete T lymphocyte responses and that such differences may be associated with variable allergenic activity.

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.

Allergy to bovine beta-lactoglobulin: specificity of immunoglobulin E generated in the Brown Norway rat to tryptic and synthetic peptides

BACKGROUND

Animal models which reflect the induction and development of food-allergic reactions are important in the identification of allergenic potential of food proteins and peptides. A number of rat strains, including PVG, Hooded Lister and Brown Norway have been shown to produce immunoglobulin (Ig) E antibodies to food proteins as well as to inhaled allergens. Previous work in our laboratory using the Brown Norway (BN) rat has shown that specific IgE is produced following administration of ovalbumin and milk products via both enteral and parenteral route; this has allowed us to rank ovalbumin, lactoferrin and bovine serum albumin in terms of their inherent allergenic potential and has enabled us to demonstrate that milk protein allergens recognized by the systemically-sensitized animal are consistent with those recognized by sera from cow's milk-allergic patients (the most common allergens recognized were beta-lactoglobulin and the alpha, beta and kappa-caseins).

OBJECTIVE

To demonstrate that the BN rat model can be used to identify the major IgE-binding peptides from beta-lactoglobulin, a known human food allergen, and that those IgE-binding peptides are similar to those recently identified using sera from cow's milk-allergic patients.

METHODS

BN rats were exposed to beta-lactoglobulin or to semiskimmed milk via the intraperitoneal route in the presence of the adjuvant carrageenan. Specific IgE raised against beta-lactoglobulin was determined by a direct enzyme immunoassay using acetyl-cholinesterase substrate; specific IgG responses were also monitored. Overlapping synthetic peptides and tryptic peptides were used within the ELISA to identify the major and minor IgE-binding immunoreactive sequences.

RESULTS

In terms of comparative immunogenicity, there appeared to be sequences that were predominantly IgE- or IgG-reactive. IgE-dominant regions were amino acid sequences 21-40, 41-60, 107-117 and 148-168 whereas sequences 1-24, 67-77, 82-92, 85-95 and 117-127 appeared more selective for IgG antibody recognition. An increased capacity to induce specific IgE was observed when the allergen was present in the context of whole food.

CONCLUSIONS

These studies provide evidence that the immune system of the BN rat and humans - at least in the case of milk allergens - is recognizing similar protein allergens and indeed, at the molecular level, similar peptide epitopes.

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

Although several in vivo antigenicity assays using parenteral immunization are operational, no full validated enteral models are available to study food allergy and allergenicity of food proteins. To further validate a developed enteral Brown Norway (BN) rat food allergy model, systemic and local immune-mediated reactions were studied upon oral challenges. The animals were exposed to ovalbumin (OVA) by daily gavage dosing (1 mg OVA/rat/day) for 6 weeks, without the use of an adjuvant, or by intraperitoneal injections with OVA together with AL(OH)3. Subsequently, effects on breathing frequency, blood pressure, and gastrointestinal permeability were investigated upon an oral challenge with 10 to 100 mg OVA in vivo. In both parenterally and orally sensitized rats, an increase in gut permeability (increased passage of beta-lactoglobulin as bystander protein) was determined between 0.5 and 1 h after an oral OVA challenge was given. An oral challenge with OVA did not induce a clear effect on the respiratory system or blood pressure in the majority of the animals. However, some animals demonstrated a temporary decrease in breathing frequency or systolic blood pressure. Upon oral challenge with OVA of orally and parenterally sensitized animals, local effects were observed in all animals whereas systemic effects were observed at a low frequency, which reflects the situation in food allergic patients after an oral challenge. These studies show that the BN rat provides a suitable animal model to study oral sensitization to food proteins as well as immune-mediated effects after oral challenge with food proteins.

A murine model of IgE-mediated cow's milk hypersensitivity

BACKGROUND

Cow's milk allergy (CMA) is one of the leading causes of food allergy in children. Understanding the mechanisms involved in the development of CMA has been hampered by the lack of suitable animal models.

OBJECTIVE

We sought to develop a mouse model of IgE-mediated cow's milk hypersensitivity (CMH) that mimics the clinical features of immediate CMA in humans.

METHODS

Three-week-old C3H/HeJ mice were sensitized by intragastric administration of cow's milk (CM) plus cholera toxin and boosted 5 times at weekly intervals.

RESULTS

CM-specific IgE antibody levels were significantly increased at 3 weeks and peaked at 6 weeks after the initial feeding. Intragastric challenge with CM at week 6 elicited systemic anaphylaxis accompanied by vascular leakage, significantly increased plasma histamine, and increased intestinal permeability to casein. Histologic examination of intestinal tissue revealed marked vascular congestion, edema, and sloughing of enterocytes. The role of IgE in mediating CMH was confirmed by abrogation of passive cutaneous anaphylaxis reactions by heat inactivation of immune sera. Development of IgE-mediated CMH in this model is likely to be TH2 cell mediated because in vitro stimulation of spleen cells from mice allergic to CM induced significant increases in the levels of IL-4 and IL-5, but not IFN-gamma.

CONCLUSION

This model should provide a useful tool for evaluating the immunopathogenic mechanisms involved in CMA and for exploring new therapeutic approaches.

Solution structure of Der f 2, the major mite allergen for atopic diseases

House dust mites cause heavy atopic diseases such as asthma and dermatitis. Among allergens from Dermatophagoides farinae, Der f 2 shows the highest positive rate for atopic patients, but its biological function in mites has been perfectly unknown, as well as the functions of its homologs in human and other animals. We have determined the tertiary structure of Der f 2 by multidimensional nuclear magnetic resonance spectroscopy. Der f 2 was found to be a single-domain protein of immunoglobulin fold, and its structure was the most similar to those of the two regulatory domains of transglutaminase. This fact, binding to the bacterial surface, and other small pieces of information hinted that Der f 2 is related to the innate antibacterial defense system in mites. The immunoglobulin E epitopes are also discussed on the basis of the tertiary structure.

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.

Principles and characteristics of food allergens

Food allergens are typically proteins that are resistant to digestion, acid, and heat treatments. However, some notable exceptions exist. The amount of these proteins needed to elicit an allergic response in previously sensitized individuals is quite low (milligram amounts). The allergenicity of specific proteins derived from known allergenic sources can be determined, whereas the potential allergenicity of proteins derived from sources of unknown allergenicity is much harder to assess.

Brown Norway rat model of food allergy: effect of plant components on the development of oral sensitization

The Brown Norway (BN) rat was examined as a model for investigating factors that influence the development of food allergy. An antigen dose-response curve for the production of antigen-specific reaginic antibody (IgE) induced through the oral route was determined. Animals were dosed orally with 1.0, 2.5, 5.0, 7.5, 10.0 and 12.0 mg ovalbumin/ml (0.5 ml/100 g twice a week for 6 wk). To promote IgE production the adjuvant carrageenan was administered once a week by the i.p. route. The effect on oral sensitization of 1.5 mg Gypsophila sp. saponin/ml administered together with the antigen on oral sensitization was examined in animals treated with 2.5, 6.0 or 10.0 mg ovalbumin/ml. The number of animals producing antigen specific reaginic antibody in response to 2.5 mg ovalbumin/ml was significantly increased (P < 0.01) in the group that received saponin with 2.5 mg ovalbumin/ml. These studies indicate that the BN rat is a sensitive model for the investigation of allergic reactions to food and has the potential to determine the impact of other dietary factors on the development of oral sensitization.