Purification of egg-white allergens

Functional properties of ovotransferrin from chicken egg white and its derived peptides: a review

With emerging trends in the food and pharmaceutical industries, potential applications of egg-derived bioactive compounds were recognized. Ovotransferrin is a major egg white functional protein responsible for multiple bioactivities. The objectives of this review are to provide scientific evidence of the functional properties of chicken ovotransferrin and its derived peptides and to identify future research approaches and applications. Various easy, economical, and non-toxic methods have been reported to produce ovotransferrin with high yield and purity, and chemical and enzymatic approaches have been employed to release bioactive peptides. The native ovotransferrin is known to have antimicrobial, antioxidant, anticancer, and immunomodulatory activities. The peptides produced from ovotransferrin also are reported to have antioxidant, antimicrobial, antihypertensive, and anticancer properties. However, little or no application of these compounds in the food and pharmaceutical areas is available yet. Therefore, the practical application of OTF in nutraceutical and pharmaceutical areas are among the emerging areas of research.

Selection and characterization of DNA aptamers for egg white lysozyme

We have selected aptamers binding to lysozyme from a DNA library using capillary electrophoresis-systematic evolution of ligands by exponential enrichment. During the selection process the dissociation constant of the ssDNA pool decreased from the micromolar to the low nanomolar range within five rounds of selection. The final aptamer had a dissociation constant of 2.8 ± 0.3 nM, 6.1 ± 0.5 nM, and 52.9 ± 9.1 nM as determined by fluorescence anisotropy, surface plasmon resonance and affinity capillary electrophoresis respectively. The aptamers were successfully challenged for specificity against other egg white proteins. The high affinity aptamers open up possibilities for the development of aptamer based food and medical diagnostics.

The panel of egg allergens, Gal d 1-Gal d 5: Their improved purification and characterization

Egg proteins represent one of the most important sources evoking food allergic reactions. In order to improve allergy diagnosis, purified and well-characterized proteins are needed. Although the egg white allergens Gal d 1, 2, 3 and 4 (ovomucoid, ovalbumin, ovotransferrin, and lysozyme) are commercially available, these preparations contain impurities, which affect exact in vitro diagnosis. The aim of the present study was to set up further purification protocols and to extend the characterization of the physicochemical and immunological properties of the final batches. The egg white allergens Gal d 1-4 were purified from commercial preparations, whereas Gal d 5 (alpha-livetin) was purified from egg yolk. The final batches of Gal d 1-5 consisted of a range of isoforms with defined tertiary structure. In addition, the IgE binding capacity of the purified egg allergens was tested using allergic patients' sera. The allergen batches will be further used to set up allergen specific diagnostic assays and to screen a larger collection of patients' sera.

Modulation of ovomucoid-specific oral tolerance in mice fed plant extracts containing lectins

We investigated the effect of feeding extracts of four different legumes (red kidney bean (Phaseolus vulgaris), peanut (Arachis hypogaea), soyabean (Glycine max) and pea (Pisum sativum) on the specific immune response against a food protein. Mice were fed ovomucoid and the specific immune response was evaluated. Ovomucoid fed alone resulted in oral tolerance induction measured as both a reduced ovomucoid-specific spleen cell proliferation and antibody response. Feeding kidney-bean extract prevented induction of oral tolerance to ovomucoid measured as spleen cell proliferation in vitro. Pure kidney-bean lectin also prevented oral tolerance induction, suggesting that lectin in the kidney-bean extract caused inhibition of oral tolerance. Parenteral administration (intravenous and intraperitoneal) of pure kidney-bean lectin had no significant influence on oral tolerance induction. Soyabean extract also influenced the immune response against ovomucoid; however, this was not as pronounced as for kidney bean and was only significant (P<0.001) for the antibody response. No effect was observed when pea extract was fed and peanut extract had a non-significant effect on induction of oral tolerance and on the general immune response. Plasma antibodies against kidney-bean lectin, but not against the three other legume lectins, were detected. Our current findings show that other dietary components can influence the specific immune response against food proteins. Various dietary components may thus contribute to the onset of adverse immunological responses.

Isolation of food allergens

The identification of food allergens is a priority in the management of food allergy, because of the need to obtain standardized extracts and pure allergens for diagnosis and therapy. It is thus important to develop methods for purification of allergenic molecules in order to study their biological and immunological characteristics. Protocols for protein extraction from foods and for allergen purification are reviewed in this paper. We report published methods for extraction of allergens from either animal and vegetable foods and detailed purification methodologies including ion-exchange, gel filtration and reversed-phase chromatography of well known allergens.

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.

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.

Immunochemical detection of egg-white antigens and allergens in meat products

BACKGROUND

The purpose of this study was to detect antigens and allergens in egg-white byproduct ingredients and after their incorporation in processed pork meat pastes. Commercially prepared foods may have potentially allergenic ingredients (egg, milk, soybean, wheat, and peanut) added in processing. Since allergic patients may react to unidentified ingredients, it is important to assess the allergenic potency of these food proteins added during processing. Egg white was chosen as an experimental model, since egg is one of the most prevalent allergens in food hypersensitivity.

METHODS

Experimental pork meat pastes containing egg white underwent pasteurization and sterilization. Ingredients derived from egg-white or paste extracts were isoelectrofocused and then blotted onto cyanogen bromide-activated nitrocellulose membranes. Egg-white antigens were identified in ingredients and in meat products with rabbit anti-egg-white antiserum by isoelectric focusing immunoblotting. Allergens were identified with sera from sensitized patients. A sensitive ELISA test was developed to detect egg-white proteins in raw, pasteurized, and sterilized meat products.

RESULTS

Antigens and allergens in four egg-white byproducts were detected. Egg-white antigens were detectable in all ingredients and meat pastes by ELISA. Allergens were detected in ingredients and in raw and pasteurized products by immunoprint techniques and ELISA.

CONCLUSIONS

Masked egg-white allergens are recognized by human serum IgE after pasteurization. Egg-white antigens are detectable in sterilized meat by ELISA techniques. Ingestion of processed foods could entail a risk of allergic reactions for sensitized consumers.

Inhalant allergy to egg yolk and egg white proteins

BACKGROUND

Several egg white and egg yolk and avian proteins have been described as a cause of inhalant allergy. Sometimes inhalational type I hypersensitivity to these proteins is associated with food allergy to egg.

OBJECTIVE

We studied two patients who experienced respiratory and food allergic symptoms upon exposure to egg or avian antigens through the inhalative or digestive routes. Clinical and immunological studies were carried out in order to identify individual allergens from these sources that could be responsible for crossreactivity reactions.

RESULTS

Patient 1 showed IgE sensitization to egg yolk livetins, feathers, and chicken serum. Specific bronchial challenge with chicken albumin and livetin extracts elicited a positive early asthmatic response and an increase in serum eosinophil cationic protein. Immunoblot and CAP-inhibition studies in this patient supported that chicken albumin (alpha-livetin) was the crossreactive antigen present in egg yolk and chicken serum and feathers. Patient 2 showed sensitization to egg white, ovomucoid and lysozyme. However, SDS-PAGE and immunoblot studies demonstrated contaminating lysozyme in the ovomucoid extract and identified lysozyme as the main allergen causing egg sensitization in this patient. Conjunctival challenge test confirmed allergy to lysozyme.

CONCLUSION

Egg yolk and egg white proteins may act not only as ingested allergens but also as aeroallergens. Immunological studies using highly purified preparations of egg proteins are useful for the accurate diagnosis of allergic reactions to egg proteins and to identify individual allergens that may be responsible for crossreactivity reactions.