Gastrointestinal stability of baker's yeast allergens: an in vitro study

Digestibility of allergens extracted from natural rubber latex and vegetable foods

BACKGROUND

Several cross-reactive allergens are now known to be involved in the defense responses of higher plants. Such proteins are drawing the attention of plant breeders because of their antimicrobial or stress-alleviating activities. Plants genetically modified to express defense-related proteins are being developed. The current concern is focused on the allergenicity of these intentionally expressed proteins.

OBJECTIVE

It is believed that food allergens are proteins resistant to digestion. Digestibility tests have been accepted as an appropriate method for evaluating the allergenicity of newly introduced proteins. In this study we investigated the usefulness of this method for detecting allergens from natural rubber latex and vegetable foods.

METHODS

Proteins were extracted from rubber latex, potato, and 5 kinds of fruits. Simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) were used for the digestibility test. An aliquot of each digest was periodically withdrawn and analyzed. Allergens were detected with pooled sera from individuals with latex allergy or patients given a diagnosis of oral allergy syndrome.

RESULTS

Most latex and vegetable food proteins were digested by the SGF within 4 minutes. Numerous allergens were also decomposed by the SGF within 8 minutes. Although vegetable food allergens were relatively stable in the SIF, kiwi allergens were substantially degraded by the SIF within 16 hours.

CONCLUSION

The pronounced lability of the plant-derived allergens was thought to reflect the discrete sensitization and elicitation processes of patients with latex-fruit syndrome or oral allergy syndrome. These results indicate that the allergenicity of a newly expressed protein should be carefully evaluated according to not only its digestibility but also other important properties.

Class I endochitinase containing a hevein domain is the causative allergen in latex-associated avocado allergy

BACKGROUND

In the medical literature immunoglobulin (Ig)E-mediated sensitization to avocado is rarely reported. On the other hand, more than 50% of subjects having IgE-mediated natural rubber latex allergy are sensitized to avocado fruit as demonstrated by skin-prick testing and/or specific IgE measurements and about 10-20% report hypersensitivity reactions after ingesting avocado.

OBJECTIVE

The underlying pathomechanism of latex-associated avocado allergy is still unknown. The conserved hevein domain of the major latex allergen prohevein (Hev b 6.01) is a ubiquitous chitin-binding protein structure that can be found in several plant proteins and may be responsible for the observed cross-reactivity between latex and avocado fruit.

METHODS

Chitin-binding avocado proteins (CBAPs) were isolated by affinity-chromatography and their IgE-binding characteristics were studied by immunoblotting using the sera from 15 avocado-sensitized latex patients. Inhibition experiments using isolated hevein and CBAPs as inhibitor solutions were performed to study the immunological cross-reactivity between both protein species and to assess the role of the CBAPs as mediators in latex-associated avocado allergy.

RESULTS

In 80% of avocado-sensitized subjects (n = 15), IgE antibodies directed against a 31-kDa allergen were detected by immunoblotting. This IgE-binding protein was identified by protein sequencing to be a class I endochitinase containing a hevein domain at the N-terminus. Purified native and digested (using simulated gastric fluid) endochitinase were able to completely block all avocado-specific IgE antibodies in six out of seven avocado patients.

CONCLUSIONS

Sensitization to endochitinase class I containing a hevein domain is the main underlying pathomechanism in latex-mediated avocado allergy.

Characterization of oligosaccharides from an antigenic mannan of Saccharomyces cerevisiae

Mannans of the yeast Saccharomyces cerevisiae have been implicated as containing the allergens to which bakers and brewers are sensitive and also the antigen recognized by patients with Crohn's disease. A fraction of S. cerevisiae mannan, Sc500, having high affinity for antibodies in Crohn's patients has been characterized by NMR spectroscopy followed by fragmentation using alkaline elimination, partial acid hydrolysis and acetolysis. The released oligosaccharides were separated by gel filtration on a Biogel P4 column and analyzed by fluorescence labeling, HPLC and methylation analysis. The relationship between structure and antigen activity was measured by competitive ELISA. The antigenic activity of the original high molecular weight mannan could be ascribed to terminal Manalpha1-->3Manalpha1-->2 sequences which are rarely found in human glycoproteins but were over-represented in Sc500 compared to other yeast mannans.

IgE, IgA, and IgG responses to common yeasts in atopic patients

This study was undertaken to analyze the differences in exposure and sensitization to five common environmental yeasts. The responses of IgG, IgA, and IgE to Candida albicans, C. utilis, Cryptococcus albidus, Rhodotorula rubra, and Saccharomyces cerevisiae and purified S. cerevisiae enolase were analyzed by immunoblotting (IgE-IB), and the cross-reactivity of their IgE-binding components by IgE-IB inhibition. Twenty atopic subjects, with asthma, allergic rhinitis, or atopic dermatitis were included. In skin prick tests (SPT), 12 of the patients showed simultaneous reactivity to at least two of the five yeasts, four reacted to one of the yeasts, and four had no responses. Antigens run in SDS-PAGE and transferred to nitrocellulose were probed with enzyme-labeled IgA-, IgG-, and IgE-specific antibodies. The IgE immunoblotting revealed most IgE-binding bands in C. albicans (11 bands) followed by C. utilis (eight bands), S. cerevisiae (five bands), R. rubra (five bands), and Cr. albidus (four bands). Six of the IgE-binding bands of C. albicans and C. utilis shared molecular weight, and only two bands shared molecular weight with other yeasts. These were the 46-kDa band, shared by all five yeasts, and a 13-kDa band shared by four yeasts. Prominent IgE binding was seen to a 46-kDa band of C. albicans (seven patients), C. utilis (five patients), and S. cerevisiae (one patient) and to corresponding weak bands of Cr. albidus and R. rubra (one patient). The possible cross-reactivity of the 46-kDa band was analyzed by IgE-IB inhibition and densitometry, revealing clear C. albicans inhibition of C. utilis (80%) and enolase (98%) (autoinhibition 100%). The strongest IgG responses were seen against S. cerevisiae and C. albicans. The responses were mainly against mannans of C. albicans and S. cerevisiae, suggesting that most of the exposure is to these yeasts. Yeasts with different types of exposure, from saprophytic growth on human mucous membranes to exposure by air and food, were shown to cross-react at the allergenic level. Atopic patients primarily sensitized by C. albicans and S. cerevisiae may develop allergic symptoms by exposure to other environmental yeasts due to cross-reacting IgE antibodies.

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.

Assessment of the allergenic potential of foods derived from genetically engineered crop plants

This article provides a science-based, decision tree approach to assess the allergenic concerns associated with the introduction of gene products into new plant varieties. The assessment focuses on the source from which the transferred gene was derived. Sources fall into three general categories: common allergenic food proteins; less common allergenic foods or other known allergen sources; and sources with no history of allergenicity. Information concerning the amino acid sequence identity to known allergenic proteins, in vitro and/or in vivo immunologic assays, and assessment of key physiochemical properties are included in reaching a recommendation on whether food derived from the genetically modified plant variety should be labeled as to the source of the transferred gene. In the end, a balanced judgement of all the available data generated during allergenicity assessment will assure the safety of foods derived from genetically engineered crops. Using the approaches described here, new plant varieties generated by genetic modification should be introduced into the marketplace with the same confidence that new plant varieties developed by traditional breeding have been introduced for decades.

Immediate hypersensitivity to bakery, brewery and wine products in yeast-sensitive atopic dermatitis patients

Ultrafiltered (> 1000 Da) samples of beer, aged red wine, young white wine, sparkling wine and extracts of fresh wheat bread and dried rye bread were analysed by skin-prick test (SPT), radioallergosorbent test (RAST) inhibition, sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting to find out if they contain Saccharomyces cerevisiae (S. cerevisiae, baker's yeast) allergens. Serum pool consisting of S. cerevisiae positive sera was used in the assays. The results were compared with freeze-dried reference S. cerevisiae and cereal antigens. The beer, bread, red wine and sparkling wine extracts elicited immediate reactions. However, no evident correlation with suspected symptoms was observed. White wine extract caused reactions in four out of six atopic dermatitis (AD) patients with symptoms, and in five out of seven symptom-free AD patients and in two of the 24 controls. In SDS-PAGE, protein bands were found in wheat and rye bread extracts and beer. In IgE immunoblotting, however, no staining was seen with the S. cerevisiae positive sera suggesting that they were of cereal origin. In white wine and champagne extracts a non-specific staining was seen in the region 20 kDa representing, e.g. lectin-like activity. No baker's yeast antigen could be detected in brewery and bakery products with IgE-immunoblotting even in the excessively concentrated extracts. The IgE mediated allergy to baker's yeast alone should thus not lead to denial of bakery, brewery and wine products.

Thermal and storage stability of Saccharomyces cerevisiae (baker's yeast) allergens

The effect of storage and high temperatures on the stability of Saccharomyces cerevisiae allergens was studied by immunoblotting. Saccharomyces cerevisiae allergic serum pool and 125I- and galactosidase-labelled anti-IgE were used in the assays. Freeze-dried extracts were reconstituted with saline and with 50% glycerol and then stored at room (+20 degrees C) and refrigerator temperature (+6 degrees C) for different time periods. The stability was better in 50% glycerol at +6 degrees C than at room temperature without glycerol. However, after 1 month, two of the most important allergens of S. cerevisiae, the 48 and 32 kDa protein allergens, lost their IgE-binding capacity even in the extracts stored with 50% glycerol at +6 degrees C. The 45 kDa allergen was, on the other hand, quite stable after storage for 9 months at +6 degrees C. Although the beneficial effect of 50% glycerol was clear, storage at +6 degrees C, even with 50% glycerol should not exceed 1 month for S. cerevisiae extracts. Two commercially available S. cerevisiae extracts in solution with valid expiry dates were also analysed. They had only little allergenic potency, while a freeze-dried extract stored for 8 years showed good allergenic potency. Heating S. cerevisiae extracts resulted in precipitation, the precipitated fraction contained almost all the specific proteins as judged by electrophoresis and IgE detection. The supernatant fraction contained only a few allergens.