Identification of the soybean hull allergens responsible for the Barcelona asthma outbreaks

EAACI Molecular Allergology User's Guide 2.0

Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE-mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE-mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well-defined, highly pure molecules for component-resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the "EAACI Molecular Allergology User's Guide" (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state-of-the-art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

Anti-allergic activity of mung bean (Vigna radiata (L.) Wilczek) protein hydrolysates produced by enzymatic hydrolysis using non-gastrointestinal and gastrointestinal enzymes

Mung bean seed is a well-known plant protein consumed in Asian countries but the protein is usually retrieved as a waste product during starch production. This study investigated the anti-allergic property of mung bean protein hydrolysates (MBPH) produced by enzymatic hydrolysis using non-gastrointestinal (non-GI), GI and a combination of non-GI+GI enzymes. The hydrolysates were investigated for any anti-allergic property by detecting the amount of β-hexosaminidase released in RBL-2H3 cells, and complemented with the MTT assay to show cell viability. It was found that MBPH hydrolyzed by a combination of flavourzyme (non-GI enzyme) and pancreatin (GI enzyme) exhibited the highest anti-allergic activity (135.61%), followed by those produced with alcalase, a non-GI enzyme (121.74%) and 80.32% for pancreatin (GI enzyme). Minimal toxicity (<30%) of all hydrolysates on RBL-2H3 cells line was observed. The results suggest that MBPH can potentially serve as a hypoallergenic food ingredient or supplement. PRACTICAL APPLICATIONS: Mung bean (Vigna radiata L. (Wilczek)) is also known as "green gram" and it is an excellent source of protein. The major mung bean storage proteins are the globulin, albumin and legumin, which are also referred to as legume allergens. Our study showed that mung bean peptides obtained after enzymatic hydrolysis influenced β-hexosaminidase inhibition without any toxic effect on RBL-2H3 cells. This indicates that mung bean allergenicity can be reduced after enzymatic hydrolysis and the protein hydrolysates could be as a hypoallergic food, ingredient, supplement and/or protein substitute in the formulation of food products.

EAACI Molecular Allergology User's Guide

The availability of allergen molecules ('components') from several protein families has advanced our understanding of immunoglobulin E (IgE)-mediated responses and enabled 'component-resolved diagnosis' (CRD). The European Academy of Allergy and Clinical Immunology (EAACI) Molecular Allergology User's Guide (MAUG) provides comprehensive information on important allergens and describes the diagnostic options using CRD. Part A of the EAACI MAUG introduces allergen molecules, families, composition of extracts, databases, and diagnostic IgE, skin, and basophil tests. Singleplex and multiplex IgE assays with components improve both sensitivity for low-abundance allergens and analytical specificity; IgE to individual allergens can yield information on clinical risks and distinguish cross-reactivity from true primary sensitization. Part B discusses the clinical and molecular aspects of IgE-mediated allergies to foods (including nuts, seeds, legumes, fruits, vegetables, cereal grains, milk, egg, meat, fish, and shellfish), inhalants (pollen, mold spores, mites, and animal dander), and Hymenoptera venom. Diagnostic algorithms and short case histories provide useful information for the clinical workup of allergic individuals targeted for CRD. Part C covers protein families containing ubiquitous, highly cross-reactive panallergens from plant (lipid transfer proteins, polcalcins, PR-10, profilins) and animal sources (lipocalins, parvalbumins, serum albumins, tropomyosins) and explains their diagnostic and clinical utility. Part D lists 100 important allergen molecules. In conclusion, IgE-mediated reactions and allergic diseases, including allergic rhinoconjunctivitis, asthma, food reactions, and insect sting reactions, are discussed from a novel molecular perspective. The EAACI MAUG documents the rapid progression of molecular allergology from basic research to its integration into clinical practice, a quantum leap in the management of allergic patients.

An update on hypoallergenicity of peanut and soybean: where are we now?

Legumes are one of the major sources of proteins and positively correlate with the development of modern society. At the same time, unfortunately, they significantly contribute to the rising prevalence of food allergy.

A Novel Pathogenesis-Related Class 10 Protein Gly m 4l, Increases Resistance upon Phytophthora sojae Infection in Soybean (Glycine max [L.] Merr.)

Phytophthora root and stem rot of soybean, caused by Phytophthora sojae (P. sojae), is a destructive disease in many soybean planting regions worldwide. In a previous study, an expressed sequence tag (EST) homolog of the major allergen Pru ar 1 in apricot (Prunus armeniaca) was identified up-regulated in the highly resistant soybean 'Suinong 10' infected with P. sojae. Here, the full length of the EST was isolated using rapid amplification of cDNA ends (RACE). It showed the highest homology of 53.46% with Gly m 4 after comparison with the eight soybean allergen families reported and was named Gly m 4-like (Gly m 4l, GenBank accession no. HQ913577.1). The cDNA full length of Gly m 4l was 707 bp containing a 474 bp open reading frame encoding a polypeptide of 157 amino acids. Sequence analysis suggests that Gly m 4l contains a conserved 'P-loop' (phosphate-binding loop) motif at residues 47-55 aa and a Bet v 1 domain at residues 87-120 aa. The transcript abundance of Gly m 4l was significantly induced by P. sojae, salicylic acid (SA), NaCl, and also responded to methyl jasmonic acid (MeJA) and ethylene (ET). The recombinant Gly m 4l protein showed RNase activity and displayed directly antimicrobial activity that inhibited hyphal growth and reduced zoospore release in P. sojae. Further analyses showed that the RNase activity of the recombinant protein to degrading tRNA was significantly affected in the presence of zeatin. Over-expression of Gly m 4l in susceptible 'Dongnong 50' soybean showed enhanced resistance to P. sojae. These results indicated that Gly m 4l protein played an important role in the defense of soybean against P. sojae infection.

Measurement of endogenous allergens in genetically modified soybeans--short communication

The measurement of endogenous allergens is required by the European Commission (EC) as part of the compositional analysis for GM products from host plants that are common causes of food allergy, such as soybean (EC Implementing Regulation No. 503/2013). In each case, the EC Implementing Regulation indicates that analysis be conducted on identified allergens as specified in the Organization of Economic Cooperation and Development (OECD) consensus documents on compositional considerations for new plant varieties. This communication discusses the methods available to measure endogenous allergens as well as the endogenous soybean allergens that should be analyzed. It is suggested herein that in conjunction with the 2012 OECD consensus document on soybean, any list of soybean allergens should be based on clinically relevant data among publicly available allergen databases and peer-reviewed scientific publications, and the ability to measure the identified allergen. Based on a detailed analysis of the scientific literature, the following key points are recommended: (1) the acceptance of serum-free, quantitative analytical method data as an alternative to traditional IgE reactivity qualitative or semi-quantitative data for evaluation of endogenous soybean allergen content; (2) eight of the 15 potential allergens listed in the OECD soybean consensus document (Gly m 3, Gly m 4, Gly m Bd28K, Gly m Bd30K, Gly m 5, Gly m 6, Gly m 8, and Kunitz trypsin inhibitor) have both appropriate supporting clinical data and sufficient sequence information to be evaluated in comparative endogenous soybean allergen studies; and (3) the remaining seven proteins (Gly m 1, Gly m 2, unknown 50kDa protein, unknown 39kDa protein, P-22-25, lipoxygenase and lectin) lack sufficient data for clear classification as confirmed allergens and/or available sequence information and should not be currently included in the measurement of endogenous soybean allergens in the compositional analysis for the EU.

Sensitization and symptoms associated with soybean exposure in processing plants in South Africa

BACKGROUND

Following the results of a previous study that highlighted the potential for significant levels of dust exposure in South African soybean processing plants, a clinical investigation was undertaken to study the respiratory health of workers in this industry.

METHODS

Workers from three soybean-processing plants were studied with a respiratory questionnaire and estimation of atopy and specific soybean IgE.

RESULTS

A total of 144 of the 181 (79.6% participation rate) plant employees completed the questionnaire and 136 (75.1%) gave blood samples for analysis of specific IgE. There was a significant association between work-related chest tightness (OR 4.0 [95% CI 1.3-12.6]), work-related nasal symptoms (OR 4.3 [95% CI 1.3-14.6]) and cough or chest tightness after handling soybean (OR 3.6 [95% CI 1.1-11.6]) and soybean sensitization. There was a significant association between current exposure to dust during soybean off-loading and "flu-like" illness (OR 2.7 [95% CI 1.0-7.2]), and cough or chest tightness after such work (OR 7.4 [95% CI 2.4-23.6]). The strongest predictor of work related nasal symptoms was sensitization to soybean, the latter strongly predicted by the presence of atopy (OR 34.7 [95% CI 6.6-182.5]).

CONCLUSIONS

Exposure and sensitization to soybean were associated with the presence of work related symptoms, including flu-like symptoms, cough, chest tightness, and nasal symptoms. The aetiology of these symptoms and more particularly the best intervention strategies require more detailed investigation.

All three subunits of soybean beta-conglycinin are potential food allergens

Soybeans are recognized as one of the "big 8" food allergens. IgE antibodies from soybean-sensitive patients recognize more than 15 soybean proteins. Among these proteins only the alpha-subunit of beta-conglycinin, but not the highly homologous alpha'- and beta-subunits, has been shown to be a major allergenic protein. The objective of this study was to examine if the alpha'- and beta-subunits of beta-conglycinin can also serve as potential allergens. Immunoblot analysis using sera collected from soybean-allergic patients revealed the presence of IgE antibodies that recognized several soy proteins including 72, 70, 52, 34, and 21 kDa proteins. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF) analysis of trypsin-digested 72, 70, and 52 kDa proteins indicated that these proteins were the alpha'-, alpha-, and beta-subunits of beta-conglycinin, respectively. Additionally, purified alpha'-, alpha-, and beta-subunits of beta-conglycinin were recognized by IgE antibodies present in the soybean-allergic patients. The IgE reactivity to the beta-subunit of beta-conglycinin was not abolished when this glycoprotein was either deglycosylated using glycosidases or expressed as a recombinant protein in Escherichia coli . The results suggest that in addition to the previously recognized alpha-subunit of beta-conglycinin, the alpha'- and beta-subunits of beta-conglycinin also are potential food allergens.

Allergenicity of soybean: new developments in identification of allergenic proteins, cross-reactivities and hypoallergenization technologies

Soybean is considered one of the "big eight" foods that are believed to be responsible for 90% of all allergenic reactions. Soy allergy is of particular importance, because soybeans are widely used in processed foods and, therefore, represent a particularly insidious source of hidden allergens. Although significant advances have been made in the identification and characterization of soybean allergens, scientists are not completely certain about which proteins in soy cause allergic reactions. At least 16 allergens have been identified. Most of them, as with other plant food allergens, have a metabolic, storage, or protective function. These allergens belong to protein families which have conserved structural features in relation with their biological activity, which explains the wide immunochemical cross-recognition observed among members of the legume family. Detailed analysis of the structure-allergenicity relationships has been hampered by the complexity and heterogeneity of soybean proteins. A variety of technological approaches have been attempted to decrease soybean allergenicity. This paper provides a comprehensive review of the current body of knowledge on the identification and characterization of soybean allergens, as well as an update on current hypoallergenization techniques.

Suggestions for the Assessment of the Allergenic Potential of Genetically Modified Organisms

The prevalence of allergic diseases has been increasing continuously and, accordingly, there is a great desire to evaluate the allergenic potential of components in our daily environment (e.g., food). Although there is almost no scientific evidence that genetically modified organisms (GMOs) exhibit increased allergenicity compared with the corresponding wild type significant concerns have been raised regarding this matter. In principle, it is possible that the allergenic potential of GMOs may be increased due to the introduction of potential foreign allergens, to potentially upregulated expression of allergenic components caused by the modification of the wild type organism or to different means of exposure. According to the current practice, the proteins to be introduced into a GMO are evaluated for their physiochemical properties, sequence homology with known allergens and occasionally regarding their allergenic activity. We discuss why these current rules and procedures cannot predict or exclude the allergenicity of a given GMO with certainty. As an alternative we suggest to improve the current evaluation by an experimental comparison of the wild-type organism with the whole GMO regarding their potential to elicit reactions in allergic individuals and to induce de novo sensitizations. We also recommend that the suggested assessment procedures be equally applied to GMOs as well as to natural cultivars in order to establish effective measures for allergy prevention.

Severe oral allergy syndrome and anaphylactic reactions caused by a Bet v 1- related PR-10 protein in soybean, SAM22

BACKGROUND

Anaphylactic reactions to soy products have been attributed to stable class 1 food allergens.

OBJECTIVE

IgE- mediated reactions to a soy-containing dietary food product in patients allergic to birch pollen were investigated.

METHODS

Detailed case histories were taken from 20 patients. Their sera were analyzed for IgE (UniCAP) specific for birch, grass, mugwort, the recombinant birch allergens rBet v 1 and rBet v2, and soy protein. Extracts from birch pollen, soy isolate, rBet v 1, and the recombinant PR-10 soy protein rSAM22 were coupled to paper disks or nitrocellulose for IgE measurements (enzyme allergosorbent test) or Western blot analysis. Enzyme allergosorbent testing, Western blot inhibition, and histamine release studies were performed with the same allergens.

RESULTS

Most patients (17/20) experienced facial, oropharyngeal, and/or systemic allergic symptoms within 20 minutes after ingesting the soy product for the first time. Birch pollen allergy (16/20) was common, along with oral allergy syndrome to apple (12/20) or hazelnut (11/20). IgE levels to birch and Bet v 1 but not to other inhalants were high in 18 of 20 patients. Significant IgE binding to rSAM22 occurred in 17 of 20 patients. Blot experiments with the soy isolate revealed IgE-binding bands at 17 kd (15/20), 22 kd (1/20), and 35 to 38 kd (2/20); the former was inhibited by preincubation of the sera with rBet v 1 or rSAM22. Birch extract and soy isolate, rBet v 1, and rSAM22 induced dose-dependent histamine release in the nanomolar range.

CONCLUSION

Immediate-type allergic symptoms in patients with birch pollen allergy after ingestion of soy protein-containing food items can result from cross-reactivity of Bet v 1 -specific IgE to homologous pathogenesis-related proteins, particularly the PR-10 protein SAM22.

Identification of the soybean hull allergens involved in sensitization to soybean dust in a rural population from Argentina and N-terminal sequence of a major 50 KD allergen

BACKGROUND

Sensitization to soybean hull (SH) allergens occurs in subjects from Argentina, a soybean producer country. However, the causative allergens have not been identified. The purposes of this study are to: (i) identify the SH allergens using sera of 29 subjects with asthma and/or allergic rhinitis from Argentina exposed to soybean dust who have a positive (weal with SH/weal with histamine > or = 0.5) skin prick test to SH; and (ii) determine the N-terminal amino acid sequence of a major 50 K SH allergen that sensitizes this population.

METHODS

All sera were assayed for specific IgE (RIA), IgG4 (ELISA), and IgE and IgG4-Western blots. A sera pool from 10 healthy subjects was a negative control. N-terminal amino acid sequencing was performed by the Edman degradation method.

RESULTS

Positive specific IgE only was found in 12/29 (41.4%), IgG4 in 3/29 (10.3%), and both IgE and IgG4 in 14/29 (48.3%) sera. IgE-Western blot demonstrates: (i) an allergen, MW 50 K (51.7% binding); (ii) one or two distinct allergens, MW < 20.2 K (72.4% binding), depending on the sera; and (iii) 1-5 additional IgE binding proteins, MW > 20.2 to < 46.9 K (41.4% binding), depending on the sera. IgG4-Western blot demonstrates: (i) a band, MW 70K (31% binding); (ii) a band, MW 50 K (17.2% binding); (iii) one or two additional bands, MW < 20.2 K (51.7% binding), depending on the sera; and (iv) a band, MW > 20.2 to < 28.5 K (20.7% binding). The 50 K allergen N-terminal amino acid sequence of the first 17 amino acids indicates a significant homology with chlorophyll A-B binding protein precursors from tomato, spinach, and petunia.

CONCLUSIONS

Specific IgE and IgG4 to SH are common in sera from allergic individuals living in rural areas in Argentina. SH contain an IgE binding protein, MW about 50 K, not previously described. Sensitization to this allergen is common in subjects who are repeatedly exposed to soybean dust inhalation.

A soybean G2 glycinin allergen. 1. Identification and characterization

BACKGROUND

Multiple allergens have been documented in soybean extracts. IgE from individuals allergic to soybeans, but not to peanut, was shown by immunoblot analysis to bind to proteins with a molecular weight of approximately 21 kD. These findings suggested that unique proteins in soybeans might be responsible for soybean allergic reactivity. The objective of the present study was to identify unique proteins in soybean extracts that bind to specific IgE from soybean-sensitive individuals, and to characterize the allergen using physicochemical methods and IgE binding.

METHODS

Two-dimensional and preparative SDS-PAGE/IgE immunoblot analysis was used to identify a 22-kD soybean-specific allergen from crude soybean extracts. N-terminal sequence analysis was used to determine the identification of the protein binding IgE from soybean-sensitive individuals.

RESULTS

IgE immunoblot and amino acid sequence analysis identified the 22-kD protein as a member of the G2 glycinin soybean protein family. Further investigation revealed that the IgEs reacted with basic chains from each member of the glycinin family of soybean storage proteins.

CONCLUSIONS

Each of the subunits from glycinin, the storage protein that is the most prevalent component of soybean, are major allergens.

Occupational asthma caused by soybean flour in bakers--differences with soybean-induced epidemic asthma

BACKGROUND

Soybean dust has been identified as the causative agent of occupational asthma and asthma epidemics. Two main soybean hull allergens responsible for asthma outbreaks, Gly m 1 and Gly m 2, have been identified and purified.

OBJECTIVE

The soybean allergens causing occupational asthma in exposed bakers were investigated and compared with those involved in epidemic asthma.

METHODS

We report four bakers or confectioners with work-related respiratory symptoms who were exposed to soybean flour used as a baking additive. The causative role of soybean flour was investigated by immunological tests and specific inhalation challenge tests. Soybean flour allergens causing occupational asthma were characterized by immunoblotting. Immunoglobulin (Ig) E-reactivity to Gly m 1 and Gly m 2 was assessed using enzyme-linked immunosorbent assay.

RESULTS

Sensitization to soybean flour was demonstrated by skin and serological tests and was confirmed by positive inhalation tests. Bronchial challenge test to soybean flour extract elicited immediate or dual asthmatic responses. Immunoblotting with soybean flour and soybean hull extracts showed IgE-binding mainly to high molecular weight (MW) allergens. There was an important individually different allergic response to inhalant soybean components. None of the patients showed IgE-reactivity against Gly m 1 and only one patient showed IgE-reactivity to the soybean hull allergen Gly m 2.

CONCLUSION

These bakery workers had developed IgE-mediated occupational asthma to soybean flour. The allergens involved in occupational asthma caused by soybean flour are predominantly high MW proteins that are present both in soybean hull and flour, and they are different from the allergens causing asthma outbreaks, which are mainly low MW proteins concentrated in the hull.