Apple allergy: the IgE-binding potency of apple strains is related to the occurrence of the 18-kDa allergen

Characterization and Quantification of Mal d 1 Isoallergen Profiles and Contents in Traditional and Commercial Apple Varieties by Mass Spectrometry

The apple allergy in Northern Europe is a cross-reaction to the birch pollen allergy. No correlation between the allergenicity of an apple variety and the content of the major apple allergen Mal d 1, a homologue to the Bet v 1 allergen in birch, could be found using ELISA, so far. Therefore, an impact of polyphenols and/or differences in the isoallergen profile are discussed. To allow a more detailed analysis of the Mal d 1 content and the isoallergen profile, a mass spectrometric method was applied to investigate differences in the flesh and peel of 10 traditional varieties and 10 commercial breeds. The data revealed often, but not always, lower Mal d 1 contents in traditional varieties grown in orchard meadows, which was more obvious in the flesh. Differences among the peels were less pronounced. A closer look at the individual isoallergens 1.01, 1.02, 1.03, and 1.06 reveals an increased impact of the minor isoallergens 1.03 and 1.06 on the allergenic potential, since commercial breeds like Braeburn, Santana, and Holstein Cox, which are considered to have reduced allergenic potentials, were characterized by low levels of these isoallergens.

BSACI guideline for the diagnosis and management of pollen food syndrome in the UK

Pollen food syndrome (PFS) is a highly prevalent food allergy affecting pollen-sensitized children and adults. Sufferers experience allergic symptoms when consuming raw plant foods, due to the homology between the pollen allergens and unstable proteins in these foods. The triggers involved can vary depending on the pollen sensitization, which in turn is affected by geographical location. The British Society of Allergy and Clinical Immunology (BSACI) Standards of Care Committee (SOCC) identified a need to develop a guideline for the diagnosis and management of PFS in the United Kingdom (UK). Guidelines produced by the BSACI use either the GRADE or SIGN methodology; due to a lack of high-quality evidence these recommendations were formulated using the SIGN guidelines, which is acknowledged to be less robust than the GRADE approach. The correct diagnosis of PFS ensures the avoidance of a misdiagnosis of a primary peanut or tree nut allergy or confusion with another plant food allergy to non-specific lipid transfer proteins. The characteristic foods involved, and rapid-onset oropharyngeal symptoms, mean PFS can often be diagnosed from the clinical history alone. However, reactions involving tree nuts, peanuts and soya milk or severe/atypical reactions to fruits and vegetables may require additional diagnostic tests. Management is through the exclusion of known trigger foods, which may appear to be simple, but is highly problematic if coupled with a pre-existing food allergy or for individuals following a vegetarian/vegan diet. Immunotherapy to pollens is not an effective treatment for PFS, and although oral or sublingual immunotherapy to foods seems more promising, large, controlled studies are needed. The typically mild symptoms of PFS can lead to an erroneous perception that this condition is always easily managed, but severe reactions can occur, and anxiety about the onset of symptoms to new foods can have a profound effect on quality of life.

Apple allergy: Causes and factors influencing fruits allergenic properties-Review

BACKGROUND

Apple tree fruits (Malus × domestica Borkh.) are a rich source of nutrients and nutraceuticals and are recommended as a part of the healthy, staple diet. However, apples could be also the cause of allergies including severe reactions. Allergies to fruits like apples are predominantly associated with pollinosis. In North and Central Europe, sensitisation to apples is caused mainly by cross-reactive birch pollen aeroallergen, whereas in the Mediterranean area of Europe, apple allergy is mostly associated with allergies to peach. The allergenicity of apples differ across cultivars but only a few varieties were studied. Some factors changing apples allergenicity were identified, including unmodifiable and potentially modifiable factors for example cultivation method, ripening stage and storage conditions.

AIM

This review presents current knowledge about the molecular basis of apple allergenicity and factors influencing its level.

CONCLUSIONS

Selecting cultivars with low potential of allergenicity, removing apple peel and heat treatment could reduce the risk of severe allergy reaction incidence and presumably can be used in birch pollen immunotherapy.

Molecular and Immunological Identification of Low Allergenic Fruits among Old and New Apple Varieties

About 50–70% of patients allergic to birch pollen suffer from sensitization after apple ingestion. Apple allergenicity was established in only few varieties. Studies were performed on apple fruits of 21 traditional and nine modern varieties organically, intensively, or integratively produced. The aim of the study was to assess whether the factors like cultivation method, maturity stage, genotype, or type of tissue place an impact on the allergenic potential of apples. To answer these questions, we used semiquantitative real-time PCR, ELISA, and immunoblotting. Apple allergen genes present divergent expression across apple cultivars. Expression of the Mal d 1.06A correlates with the Mal d 1 level and is affected by the cultivation method and maturity of the fruit. The content of the main allergen Mal d 1 varied widely across cultivars. Interestingly, in our study, the Gala variety presented a low Mal d 1 concentration regardless of the cultivation method. Based on the Mal d 1.06A expression, the Mal d 1 protein content, and the immunoreactivity assay, the Kandil Sinap, Kosztela, Rumianka from Alma-Ata, Kantówka Gdańska, Reinette Coulon, and Gala cultivars emerged as potentially hypoallergenic apple cultivars. Our study allowed distinguishing between potentially low, medium, and highly allergenic varieties.

Mass spectrometry to complement standardization of house dust mite and other complex allergenic extracts

In the United States, the Center for Biologics Evaluation and Research of the US Food and Drug Administration regulates biologics used for diagnosis and treatment of allergic diseases. The Code of Federal Regulations 21CFR680.3(e) states that when measured, the potency of an allergenic extract is assessed according to its allergenic activity. As of 2016, 19 allergenic extracts are standardized for potency in the United States. While these standardized extracts constitute a minority of those available, they treat the most prevalent allergies (e.g. grass and ragweed pollens, dust mites, and cat) and those that induce life-threatening anaphylaxis (e.g. Hymenoptera venom). Standardization for potency enhances safety and efficacy of immunotherapy by minimizing the risks of variations in allergen dosing when switching from one lot of manufactured extract to another, and by providing an objective measure of stability of each lot of allergenic extract over time. Allergenic extracts that have multiple immunodominant allergenic proteins are standardized with little or no information about compositional differences among extracts. Here, we propose application of mass spectrometry towards measurement of compositional differences among extracts that may affect the efficacy and safety of allergen immunotherapy. In addition, we discuss of house dust mite allergen extracts as a prototypical complex extract that may be standardized by mass spectrometry.

Additional indications for the low allergenic properties of the apple cultivars Santana and Elise

Patients with Oral Allergy Syndrome (OAS) to fresh apple may tolerate low allergenic apple cultivars. We aimed to investigate if the low allergenic properties of Elise and Santana, as previously identified in a Dutch population, could be generalised within North West Europe within the birch pollen region with regard to both the prevalence and degree of sensitization. Prick-to-prick tests (PTP) were performed in eighty-five adult patients with OAS to fresh apple in Great Britain, Switzerland and Northern Italy, before the birch pollen season, using the putatively low allergenic apple cultivars Elise, Santana, Granny Smith, Modi and Mcintosh, as well as the putatively high allergenic apple cultivars Golden Delicious and Kanzi. No significant differences in percentages of negative responses of PTPs were found between the three countries. Negative responses did not differ from negative responses to the different apple cultivars we previously found in 2006/2007 in the Netherlands. The size of the PTPs of all apple cultivars tested were correlated to the size of the skin prick tests with birch pollen. These results add to the indications for the low allergenic properties of the low allergenic apple cultivars Santana and Elise, as the number of negative responses were reproducible in three countries within the birch pollen region and were similar to previous results in the Netherlands. These results justify oral challenge studies with Elise and Santana within the birch pollen region, to establish the low allergenic properties for the benefit for apple allergic consumers for definite conclusions.

Oral challenges with four apple cultivars result in significant differences in oral allergy symptoms

BACKGROUND

We analyzed the hypoallergenic potential of a recently bred apple selection with unusually low content of Mal d 1, using an oral challenge model with three additional apple cultivars for comparison.

METHODS

Sixty-six birch pollen-allergic individuals with a history of oral allergy syndrome after apple intake were subjected to a double-blind oral provocation with two apple cultivars (B:0654 and 'Discovery'). Thirteen also tested two other apple cultivars ('Ingrid Marie' and 'Gloster'). Three doses were given consecutively, 30 min apart: 10 g without peel, and 10 and 50 g with peel. A final assessment was conducted 30 min after the last intake. Oral symptoms were graded from 0 to 5. Total oral symptom score (TOS) included all scores for each cultivar at all time points.

RESULTS

B:0654 induced significantly higher TOS than 'Discovery' when tested by 66 individuals, in spite of its lower Mal d 1 content. TOS values were higher in females and increased with increasing age of the individuals when challenged with 'Discovery'. Among the 13 individuals who tested all four cultivars, B:0654 produced a higher score after the second dose compared to 'Ingrid Marie'. This was also the case after the third dose compared to 'Ingrid Marie' and 'Gloster', and again 30 min after the last intake compared to each of the other three cultivars, as well as a higher TOS compared to each of the other three cultivars (all p < 0.01).

CONCLUSIONS

Our test was safe and well tolerated, and produced significant differences among the apple cultivars. Contrary to expectations, B:0654 was less well tolerated than the other three cultivars.

Apple hypanthium firmness: new insights from comparative proteomics

Fruit firmness constitutes an important textural property and is one of the key parameters for estimating ripening and shelf life, which has a major impact on commercialization. In order to decipher the mechanisms related to firmness of apples (Malus × domestica Borkh.), two-dimensional gel electrophoresis (2-DE) was used to compare the total proteome of high and low firmness phenotypes from apple hypanthia of a 'Golden Delicious' × 'Dietrich' population. A total of 36 differentially regulated protein spots were positively identified by matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS) and then validated against the Malus expressed sequence tags (EST) database. The findings of this study indicated a lower expression of ethylene biosynthesis related proteins in the high firmness phenotype, which could be linked to the slowing down of the ripening and softening processes. The reduced accumulation of proteins involved in ethylene biosynthesis juxtaposed to the upregulation of a transposase and a GTP-binding protein in the high firmness phenotype. The results also showed higher expression of cytoskeleton proteins in the high firmness phenotype compared to the low firmness phenotype, which play a role in maintaining cell structure and possibly fruit integrity. Finally, a number of proteins involved in detoxification and defense were expressed in fruit hypanthium. This proteomic study provides a contribution towards a better understanding of regulatory networks involved in fruit hypanthium firmness and/or softening, which could be instrumental in the development of improved fruit quality.

Continuous apple consumption induces oral tolerance in birch-pollen-associated apple allergy

BACKGROUND

Patients with birch pollen allergy (major allergen: Bet v 1) have often an associated oral allergy syndrome (OAS) to apple, which contains the cross-reactive allergen Mal d 1. As successful birch pollen immunotherapy does not consistently improve apple related OAS symptoms, we evaluated whether regular apple consumption has an effect on OAS and immune parameters of Mal d 1 or Bet v 1 allergy.

METHODS

A total of 40 patients with a clear history of birch pollen rhinoconjunctivitis and associated OAS to apple were included in an open, randomized, controlled clinical trial: 27 patients consumed daily defined amount of apple (1-128 g), doubling the amount every two to three weeks, while 13 patients remained untreated. Primary endpoint was the proportion of patients that achieved tolerance to at least 128 g of apple at the end of the study after 8 months. Exploratory endpoints were questionnaire about cross-reactive food and pollen allergy symptoms, conjunctival provocation test with birch pollen and Bet v 1, and in vitro tests (tIgE, sIgE, and IgG4 to Mal d 1 and Bet v 1; basophil activation test with both allergens).

RESULTS

Seventeen of 27 patients in active group and none of 13 patients in control group (P = 0.0001) could tolerate a whole apple after the intervention. However, differences in endpoints reflecting systemic immune reactivity did not reach statistical significance.

CONCLUSION

In patients with OAS to apple, tolerance can be safely induced with slowly, gradually increasing consumption of apple. However, the observation of a relapse after discounting of apple consumption and absence of immunologic changes suggest that induced tolerance is only transient.

Identification of low allergenic apple cultivars using skin prick tests and oral food challenges

BACKGROUND

As oral allergy syndrome (OAS) symptoms to apple are frequent, we aimed to identify low allergenic apple cultivars and to validate the prick-to-prick skin prick test (SPT) as a suitable screening method.

METHODS

Sixty-eight apple cultivars were tested by SPTs in 33 Dutch adults with OAS, before and during the birch pollen season in 2006 and 2007, respectively. Three cultivars yielding the largest number of negative SPTs (Elise, Santana and Pink Lady®) and one reference cultivar (Golden Delicious) were subsequently tested by single-blind oral food challenges (SBFC) just after picking in fall 2007 (fresh) and in spring 2008 (stored), outside the birch pollen season and preceded by SPTs. In spring, Santana was replaced by Modi®.

RESULTS

In fresh apples, OAS symptoms of Elise, as measured by cumulative scores on a Visual Analogue Scale VASt, were significantly lower than those of Santana, Pink Lady and Golden Delicious (P = 0.021; 0.040 and 0.005, respectively). VASt scores of Santana were significantly lower than those of Golden Delicious (P = 0.049). In stored apples, VASt scores of Elise were significantly lower than that of Golden Delicious (P = 0.038). VASt scores of fresh apples did not differ significantly from stored apples, except in Golden Delicious (spring < fall: P = 0.021). The SPTs did not predict the severity of OAS.

CONCLUSION

SPTs are not useful to assess the allergenicity of apple cultivars. By using SBFC, Elise and Santana were identified as low allergenic apple cultivars in patient with OAS. Our data on the effect of storage are inconclusive.

Screening of Ole e 1 polymorphism among olive cultivars by peptide mapping and N-glycopeptide analysis

In the present paper, we have used 2-DE coupled to MS analysis to examine the molecular variability of the Ole e 1 allergen in three olive cultivars (cvs). Our results confirmed that the predicted polymorphism of Ole e 1 at cDNA level is extended to the expressed protein. The profiles of both the Ole e 1 peptides and the N-glycan variants significantly changed among cvs. We observed that Picual and Arbequina cvs presented the highest and lowest degree of Ole e 1 polymorphism, respectively. Some of these peptides and N-glycans were distributed in a cv-specific manner. The putative implications of this molecular polymorphism in the development of the allergy symptoms are discussed.

Apple (Malus domestica L. Borkh.) allergen Mal d 1: effect of cultivar, cultivation system, and storage conditions

It has been reported on the basis of skin prick tests and gene expression studies that apple cultivars differ in their allergenic potential. Only a few studies have tried to measure the amount of the major apple allergen Mal d 1 so far. Mal d 1 belongs to the pathogenesis-related proteins, a family of proteins that are induced by pathogens and environmental stress. Due to cross-reactivity between Bet v 1 and proteins present in several plant-derived foods, birch pollen allergic patients develop food allergies, most frequently to apples. Mal d 1 content was quantified in different apple cultivars, cultivated at the research stations Klein-Altendorf and Bavendorf, dependent on cultivation method and storage conditions by sandwich-ELISA. Apple cultivars differ considerably in their Mal d 1 content. A high variability in Mal d 1 content was determined within one cultivar and between the two locations for the same apple cultivar. In most cases organically cultivated fruit showed lower Mal d 1 content in comparison to fruit from integrated production. At harvest the detected concentration of Mal d 1 was low, but during storage the Mal d 1 content increased significantly.

Assessment of allelic diversity in intron-containing Mal d 1 genes and their association to apple allergenicity

BACKGROUND

Mal d 1 is a major apple allergen causing food allergic symptoms of the oral allergy syndrome (OAS) in birch-pollen sensitised patients. The Mal d 1 gene family is known to have at least 7 intron-containing and 11 intronless members that have been mapped in clusters on three linkage groups. In this study, the allelic diversity of the seven intron-containing Mal d 1 genes was assessed among a set of apple cultivars by sequencing or indirectly through pedigree genotyping. Protein variant constitutions were subsequently compared with Skin Prick Test (SPT) responses to study the association of deduced protein variants with allergenicity in a set of 14 cultivars.

RESULTS

From the seven intron-containing Mal d 1 genes investigated, Mal d 1.01 and Mal d 1.02 were highly conserved, as nine out of ten cultivars coded for the same protein variant, while only one cultivar coded for a second variant. Mal d 1.04, Mal d 1.05 and Mal d 1.06 A, B and C were more variable, coding for three to six different protein variants. Comparison of Mal d 1 allelic composition between the high-allergenic cultivar Golden Delicious and the low-allergenic cultivars Santana and Priscilla, which are linked in pedigree, showed an association between the protein variants coded by the Mal d 1.04 and -1.06A genes (both located on linkage group 16) with allergenicity. This association was confirmed in 10 other cultivars. In addition, Mal d 1.06A allele dosage effects associated with the degree of allergenicity based on prick to prick testing. Conversely, no associations were observed for the protein variants coded by the Mal d 1.01 (on linkage group 13), -1.02, -1.06B, -1.06C genes (all on linkage group 16), nor by the Mal d 1.05 gene (on linkage group 6).

CONCLUSION

Protein variant compositions of Mal d 1.04 and -1.06A and, in case of Mal d 1.06A, allele doses are associated with the differences in allergenicity among fourteen apple cultivars. This information indicates the involvement of qualitative as well as quantitative factors in allergenicity and warrants further research in the relative importance of quantitative and qualitative aspects of Mal d 1 gene expression on allergenicity. Results from this study have implications for medical diagnostics, immunotherapy, clinical research and breeding schemes for new hypo-allergenic cultivars.

Thresholds for food allergens and their value to different stakeholders

Thresholds constitute a critical piece of information in assessing the risk from allergenic foods at both the individual and population levels. Knowledge of the minimum dose that can elicit a reaction is of great interest to all food allergy stakeholders. For allergic individuals and health professionals, individual threshold data can inform allergy management. Population thresholds can help both the food industry and regulatory authorities assess the public health risk and design appropriate food safety objectives to guide risk management. Considerable experience has been gained with the double-blind placebo-controlled food challenge (DBPCFC), but only recently has the technique been adapted to provide data on thresholds. Available data thus vary greatly in quality, with relatively few studies providing the best quality individual data, using the low-dose DBPCFC. Such high quality individual data also form the foundation for population thresholds, but these also require, in addition to an adequate sample size, a good characterization of the tested population in relation to the whole allergic population. Determination of thresholds at both an individual level and at a population level is influenced by many factors. This review describes a low-dose challenge protocol developed as part of the European Community-funded Integrated Project Europrevall, and strongly recommends its wider use so that data are generated that can readily increase the power of existing studies.

Screening and identification of putative allergens in berry fruits of the Rosaceae family: technical challenges

Cross-reactive proteins in small fruits of the Rosaceae family like strawberry, raspberry and blackberry revealed an unexpected complex IgE-reactivity pattern. Several copies of PR-10 and PR-14 proteins were detected by Southern blots in strawberry, raspberry and blackberry. In raspberry, the highest similarity at the DNA level for PR-10 and PR-14 (Rub i 1 and Rub i 3) was detected to strawberry sequences of Fra a 1 and Fra a 3. At the protein level, Rub i 1 and Rub i 3 showed more than 70% identity with homologous proteins of rosaceous fruits. Furthermore, raspberries contained additional putative allergens, e.g. class III acidic chitinases and cyclophilins. Blackberries were shown to share at least two well-known major fruit allergens with other rosaceous fruits, namely PR-10s and PR-14s homologous proteins. However the IgE-reactive proteins of small fruits are still not extensively investigated. The main challenges in studying small fruit allergens are the complexity of the fruit matrix, the diversity of physico-chemical properties of fruit proteins, the lack of appropriate protein extraction procedures and the missing information about the influence of processing treatments on food components.

Assessing allergen levels in peach and nectarine cultivars

BACKGROUND

The lipid transfer protein Pru p 3 has been identified as a major peach fruit allergen. However, the putative peach member of the Bet v 1 family, Pru p 1, has been neither identified nor characterized.

OBJECTIVES

To determine the distribution and solubility properties of the main peach allergens and to quantify Pru p 3 and Pru p 1 levels in peach and nectarine cultivars.

METHODS

Peach peel and pulp were extracted using different buffers, and extracts were analyzed by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunodetection using polyclonal antibodies against lipid transfer proteins, profilins, and Bet v 1 homologues. Pru p 3 was quantified in peach and nectarine cultivars using a sandwich enzyme-linked immunosorbent assay method. A similar method was developed to quantify Pru p 1.

RESULTS

A differential distribution between peel and pulp and different solubility properties were found for Pru p 3, Pru p 1, and peach profilin. Mean Pru p 3 levels were 132.86, 0.61, and 16.92 microg/g of fresh weight of peels, pulps, and whole fruits, respectively. The corresponding mean Pru p 1 levels were 0.62, 0.26, and 0.09 microg/g of fresh weight. Most US cultivars showed higher levels of both allergens than Spanish cultivars.

CONCLUSIONS

The different distribution and solubility properties of the main peach allergens can determine the quality of fruit extracts used as diagnostic tools. These differences, together with the natural variation of Pru p 3 and Pru p 1 levels among peach and nectarine cultivars, can be exploited to reduce peach allergenicity by means of industrial processing and plant breeding.

Enhancement of hazelnut extract for IgE testing by recombinant allergen spiking

BACKGROUND

Hazelnuts are a common cause of food allergic reactions. Most hazelnut allergic individuals in central and northern Europe are sensitized to Cor a 1, a member of the PR-10 protein family, while the lipid transfer protein Cor a 8 acts as a major allergen in the south of Europe. Other allergens, including profilin and seed storage proteins, may be important in subgroups of patients. Reliable detection of specific IgE in the clinical diagnosis of food allergy requires allergen reagents with a sufficient representation of all relevant allergen components. Some reported observations suggest that natural hazelnut extract may not be fully adequate in this respect.

METHODS

The capacity of immobilized natural hazelnut extract to bind Cor a 1-, Cor a 2- and Cor a 8-specific IgE and IgG antibodies was investigated by serum adsorption and extract dilution experiments and by the use of allergen specific rabbit antisera. All measurements were performed with the ImmunoCAP assay platform.

RESULTS

The experimental results revealed an incomplete capacity of immobilized hazelnut extract to capture IgE antibodies directed to the major allergen Cor a 1. Spiking of hazelnut extract with recombinant Cor a 1.04 prior to solid phase coupling gave rise to significantly enhanced IgE antibody binding from Cor a 1 reactive sera. The spiking did not negatively affect the measurement of IgE to extract components other than Cor a 1.

CONCLUSION

A hazelnut allergen reagent with enhanced IgE detection capacity can be generated by supplementing the natural food extract with recombinant Cor a 1.04.

Currant allergy and the Rosaceae-grass pollen allergy syndrome: a case report

BACKGROUND

Despite the increasing use of currants in culinary recipes, currant allergy has rarely been reported.

OBJECTIVES

To study a case of currant allergy and to explore cross-reactivity between grass pollen and Rosaceae family fruit allergens.

METHODS

Skin prick tests to pollen and skin prick-to-prick tests with currants and peach were performed. Specific IgE levels were determined using the CAP method. We prepared a protein extract of 0.1 mg/mL in phosphate-buffered saline using red currant in the presence of protease inhibitors. Immunoblot inhibition studies were performed to explore cross-reactivity between grass pollen and currant allergens.

RESULTS

Skin prick test results were positive to Dactylis, arizonic, and olive pollens. Results of skin prick-to-prick tests with fresh red and black currants were negative and positive, respectively, to peach. The specific IgE level was 5.7 KU/L to red currant and 2.92 KU/L to peach (CAP). Western blot analysis with red currant extract revealed specific IgE protein bands of 37 and 26 kDa. Preincubation of sera with extracts from red currant and peach inhibited both IgE bands, and preincubation with Dactylis pollen inhibited the 37-kDa band only.

CONCLUSIONS

We report a case of allergy to grass pollen with an oral allergy syndrome involving several fruits from 2 different families of the Rosidae subclass confirmed by in vitro tests. Inhibition studies demonstrated cross-reactivity between different fruits (currant and raspberry) from the Rosidae subclass and were incomplete with grass pollen allergens.

Influence of cultivar and processing on cherry (Prunus avium) allergenicity

Oral allergy syndrome is an immediate food allergic event that affects lips, mouth, and pharynx, is often triggered by fruits and vegetables, and may be associated with pollinosis. Here, we report on the allergenic pattern of different varieties of cherry (Prunus avium) and results obtained by applying several technological processes to the selected varieties. Whole cherries were submitted to chemical peeling, thermal treatment, and syruping processes, and the relative protein extracts were analyzed by in vitro (sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting analysis) and in vivo tests (skin prick test). Electrophoretic analyses demonstrated that there was no marked difference among cherry cultivars. Chemical peeling successfully removed Pru av 3, a lipid transfer protein (LTP) responsible for oral allergy syndrome in patients without pollinosis, leading to the industrial production of cherry hypoallergenic derivatives. Furthermore, the syruping process removed almost all allergenic proteins to whom patients with pollinosis are responsive. In vivo tests confirmed electrophoretic results.

Allergenicity assessment of apple cultivars: hurdles in quantifying labile fruit allergens

BACKGROUND

Assessment of allergenicity of foods is important for allergic consumers and regulators. Immunoassays to measure major food allergens are widely applied, often giving variable results. Using the major apple allergen Mal d 1 as a model, we aimed to establish at the molecular level why different immunoassays for assessing allergenicity of apple cultivars produce conflicting outcomes.

METHODS

Mal d 1 was measured in 53 cultivars from Italy and 35 from The Netherlands, using four different immunoassays. Purified Mal d 1 standards were molecularly characterized by size-exclusion chromatography (SEC) and mass spectrometry (MS).

RESULTS

Three immunoassays using an identical standard gave similar results. Minor differences in sample preparation already resulted in significant loss of allergenicity. The fourth assay, using a different Mal d 1 standard, gave 10- to 100-fold lower outcomes. By SEC, this standard was shown to be almost fully aggregated. This aggregation was accompanied by a decrease of the mass of the Mal d 1 molecule by approximately 1 kDa as analyzed by MS. The deviating immunoassay was shown to selectively recognize this aggregated form of Mal d 1, whereas the other three assays, including the one based on IgE antibody recognition, preferentially bound non-aggregated allergen.

CONCLUSIONS

Variable and poorly controllable major allergen modification in both extracts and standards hamper accurate allergenicity assessments of fruits.

Effect of postharvest storage on the expression of the apple allergen Mal d 1

Consumption of fresh apples can cause allergy in susceptible individuals. A competitive enzyme-linked immunosorbent assay (ELISA) has been developed to determine Mal d 1 levels in apple pulp using a monoclonal antibody (BIP-1). The ELISA was able to rank ten cultivars according to their Mal d 1 content (between 3.8 and 72.5 mug/g pulp). For the first time, it has been demonstrated that growing conditions and postharvest storage, using three different treatments over a 5 month period in 2 consecutive years, increase Mal d 1 expression at a translational and transcriptional level (3.5- and 8.5-fold under controlled atmosphere storage). Expression of three major Mal d 1 isoforms was observed by real-time polymerase chain reaction over the 5 month storage period, and Mal d 1.02 was the most highly expressed isoform. In conclusion, Mal d 1 gene expression was significantly increased during modified atmosphere storage. Individuals suffering from birch pollen-apple allergy syndrome might experience fewer problems consuming freshly picked apples.

Maturity and storage influence on the apple (Malus domestica) allergen Mal d 3, a nonspecific lipid transfer protein

Consumption of apples can provoke severe allergic reactions, in susceptible individuals, due to the presence of the allergen Mal d 3, a nonspecific lipid transfer protein, found largely in the fruit skin. Levels of Mal d 3 were determined in peel as a function of apple cultivar, position of the fruit growing on the tree, apple maturity, and postharvest storage by ELISA. As the apples mature, Mal d 3 levels increased, although the rate was dependent on cultivar and tree position. During storage, levels of Mal d 3 decreased in all cultivars (cvs. Cox, Jonagored, and Gala), the rate of overall decrease being greatest under controlled atmosphere conditions. There was no correlation between Mal d 3 levels and total apple peel protein, indicating specific alterations in Mal d 3 expression. Thus pre- and postharvest treatments (i.e., storage) can modify the allergen load in apple peel, the highest levels being found in overly mature and freshly harvested fruits.

Allergenicity of 10 different apple varieties

BACKGROUND

More than 100 apple varieties are consumed worldwide. However, the allergenic composition of most apple varieties has not been fully characterized.

OBJECTIVE

To analyze the antigenic and allergenic profiles of 10 different commercially available apple varieties.

METHODS

Golden, Golden Perlim, Reineta, Reineta Parda, Fuji, Verdedoncella, Granny-Smith, Pink Lady, Royal Gala, and Starking apple varieties were carefully peeled. Peels were individually extracted and centrifuged, and the supernatants were collected, dialyzed, filtered, frozen, and freeze-dried. The extracts were characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblots. Protein content was measured using the Lowry-Biuret method. Twenty-two Spanish patients with oral allergy syndrome after apple ingestion were included in the study. Specific IgE to all apple varieties and birch pollen was evaluated. Eleven patients underwent skin prick testing using extracts of Golden, Starking, and Reineta Parda varieties to determine differences in their in vivo allergenicity.

RESULTS

The antigenic profile of the 10 varieties showed differences using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A 9-kDa band, which could correspond to Mal d 3, was visualized in all the extracts. The Starking variety had the highest protein content. Higher specific IgE values were also obtained for the Starking variety, and the lowest values were for Reineta Parda and Royal Gala. The largest wheals were obtained in all patients with the Starking variety, and the smallest with Reineta Parda. Fourteen patients (64%) recognized Mal d 3 in the Golden variety using immunoblots; 6 patients (27%), who also had specific IgE to Betula, recognized bands with higher molecular weights.

CONCLUSIONS

We demonstrated differences in the antigenic and allergenic profiles of the analyzed varieties and a significant variation in Mal d 3 content.

Comparison of the allergenicity of Actinidia deliciosa (kiwi fruit) and Actinidia chinensis (gold kiwi)

Actinidia chinensis (gold kiwi) is a newly available fruit which has been shown to have in vitro immunoglobulin E (IgE) cross-reactivity with green kiwi. This is the first study to investigate clinical reactivity of gold kiwi. Five patients clinically allergic to green kiwi were investigated by skin test and double-blind placebo controlled food challenge (DBPCFC) with gold kiwi fruit. IgE-binding patterns of individual sera from the five challenged patients and a pool of sera from a further nine patients with kiwi allergy were compared in the two fruits by Western blotting. Cross reactivity of proteins in the two fruits was assessed by inhibition of immunoblots and by IgE enzyme-linked immunosorbent assay (ELISA) inhibition. Four of the five patients had a positive DBPCFC to gold kiwi. Western blotting showed marked differences in the allergen patterns of green and gold kiwi. However, inhibition of the immunoblots and ELISA assay reveals extensive inhibition of IgE binding to proteins in each fruit by the alternative species. Gold kiwi fruit is allergenic and patients allergic to green kiwi are at risk of reacting to the gold kiwi fruit. Despite having different protein profiles and IgE-binding patterns, the two species have proteins that extensively cross-inhibit the binding to IgE.

Genomic characterization and linkage mapping of the apple allergen genes Mal d 2 (thaumatin-like protein) and Mal d 4 (profilin)

Four classes of apple allergens (Mal d 1, -2, -3 and -4) have been reported. By using PCR cloning and sequencing approaches, we obtained genomic sequences of Mal d 2 (thaumatin-like protein) and Mal d 4 (profilin) from the cvs Prima and Fiesta, the two parents of a European reference mapping population. Two copies of the Mal d 2 gene (Mal d 2.01 A and Mal d 2.01 B) were identified, which primarily differed in the length of a single intron (378 or 380 nt) and in one amino acid in the signal peptide. Both Mal d 2.01 A and Mal d 2.01 B were mapped at identical position on linkage group 9. Genomic characterization of four Mal d 4 genes (Mal d 4.01 A and B, Mal d 4.02 A and Mal d 4.03 A) revealed their complete gDNA sequences which varied among genes in length from 862 to 2,017 nt. They all contained three exons of conserved length: 123, 138, and 135 nt. Mal d 4.01 appeared to be duplicated in two copies and located on linkage group 9. Mal d 4.02 A and Mal d 4.03 A were single copy genes located on linkage group 2 and 8, respectively.

In vivo assessment with prick-to-prick testing and double-blind, placebo-controlled food challenge of allergenicity of apple cultivars

BACKGROUND

Apple cultivars have been reported to differ in allergenicity on the basis of in vitro and skin prick tests with apple extracts.

OBJECTIVES

We sought to evaluate the efficacy of the prick-to-prick method in assessing differences in allergenicity of apple cultivars and to confirm differences by means of double-blind, placebo-controlled food challenge (DBPCFC).

METHODS

Intra-assay and intracultivar variation of prick-to-prick test results were determined in 6 Dutch and 8 Spanish patients with apple allergy by using 5 apples of the cultivars Golden Delicious, Fuji, and Ecolette in duplicate. In addition, 21 cultivars were screened for allergenicity in 15 Dutch patients with birch pollen and apple allergy. Two selected cultivars (Golden Delicious and Santana) were tested with DBPCFCs. The influence of storage conditions on allergenicity was assessed in 5 cultivars.

RESULTS

Intra-assay variation of skin prick testing was 3.9%, and intracultivar variation was 4.1%. A ranking of 21 cultivars was made on the basis of prick-to-prick tests in 9 patients. Apple cultivars were classified as of low, intermediate, and high allergenicity, with a significant difference between low and high allergenicity (P < .001). A significant difference in allergenicity determined between Golden Delicious and Santana cultivars (P < .05) was confirmed by means of DBPCFC. With 5 cultivars, controlled atmosphere (2.5% oxygen/1% carbon dioxide) was shown to reduce allergenicity (P < .001) by 15% compared with storage at 2 degrees C.

CONCLUSIONS

Prick-to-prick testing with fresh apples is a reproducible method of assessing allergenicity. Apples can be classified as of low or high allergenicity for the majority of patients. This was confirmed by using DBPCFCs. Selection of cultivars and control of storage conditions are both viable strategies for reduction of symptoms in patients with apple allergy.

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.

Genomic cloning and linkage mapping of the Mal d 1 (PR-10) gene family in apple (Malus domestica)

Fresh apples can cause birch pollen-related food allergy in northern and central European populations, primarily because of the presence of Mal d 1, the major apple allergen that is cross-reactive to the homologous and sensitizing allergen Bet v 1 from birch. Apple cultivars differ significantly in their allergenicity. Knowledge of the genetic basis of these differences would direct breeding for hypoallergenic cultivars. The PCR genomic cloning and sequencing were performed on two cultivars, Prima and Fiesta, which resulted in 37 different Mal d 1 gDNA sequences. Based on the mapping of sequence-specific molecular markers, these sequences appeared to represent 18 Mal d 1 genes. Sixteen genes were located in two clusters, one cluster with seven genes on linkage group (LG) 13, and the other cluster with nine genes on the homoeologous LG 16. One gene was mapped on LG 6, and one remained unmapped. According to sequence identity, these 18 genes could be subdivided into four subfamilies. Subfamilies I-III had an intron of different size that was subfamily and gene-specific. Subfamily IV consisted of 11 intronless genes. The deduced amino acid sequence identity varied from 65% to 81% among subfamilies, from 82% to 100% among genes within a subfamily, and from 97.5% to 100% among alleles of one gene. This study provides a better understanding of the genetics of Mal d 1 and the basis for further research on the occurrence of allelic diversity among cultivars in relation to allergenicity and their biological functions.

Silencing the major apple allergen Mal d 1 by using the RNA interference approach

BACKGROUND

Apple allergy is dominated by IgE antibodies against Mal d 1 in areas where birch pollen is endemic. Apples with significantly decreased levels of Mal d 1 would allow most patients in these areas to eat apples without allergic reactions.

OBJECTIVE

The aim of this study was to inhibit the expression of Mal d 1 in apple plants by RNA interference.

METHODS

In vitro -grown apple plantlets were transformed with a construct coding for an intron-spliced hairpin RNA containing a Mal d 1-specific inverted repeat sequence separated by a Mal d 1-specific intron sequence. The presence of the construct in transformants was checked by PCR. Expression of Mal d 1 in leaves was monitored by prick-to-prick skin testing in 3 patients allergic to apples and by immunoblotting with a Mal d 1-reactive mAb and with IgE antibodies against Mal d 1.

RESULTS

After transformation, plantlets were selected on the basis of having a normal phenotype and growth rate. With PCR, in 6 of 9 selected plantlets, the presence of the gene-silencing construct was demonstrated. By skin prick test it was shown that a wild-type plantlet had significantly ( P < .05) higher allergenicity than 5 of the transformants. Reduction of expression of Mal d 1 was confirmed by immunoblotting. In wild-type and unsuccessful transformants, a strong band was detected with Mal d 1-reactive mAb 5H8 at the expected apparent M r of 17 kDa. This band was virtually absent in the transformants that carried the gene-silencing construct. With human IgE antibodies, the same observations were made.

CONCLUSIONS

Mal d 1 expression was successfully reduced by RNA interference. This translated into significantly reduced in vivo allergenicity. These observations support the feasibility of the production by gene silencing of apples hypoallergenic for Mal d 1.

Flow cytometric analysis of in vitro activated basophils, specific IgE and skin tests in the diagnosis of pollen-associated food allergy

BACKGROUND

Specific immunoglobulin E (IgE) and commercially available skin prick tests have been demonstrated to be unreliable methods to diagnose pollen-associated food allergy. To evaluate the predictive value of the basophil activation test (BAT) in pollen-associated food allergy, the apple-mediated oral allergy syndrome (OAS) in patients with birch pollinosis was chosen as a representative model.

METHODS

Patients with birch pollen allergy and a history of apple-mediated OAS (OAS(+), n = 29), patients with birch allergic without OAS (OAS(-), n = 22), and healthy controls (HC, n = 10) without birch pollen allergy and OAS were included. Apple IgE was quantified by the CAP FEIA method. Skin prick tests were performed with a Jonagold apple extract. Flow cytometric analysis of basophils activated with the same Jonagold extract was based on double staining with anti-IgE/anti-CD63 monoclonal antibodies.

RESULTS

Comparison between OAS(+) subjects and HC showed sensitivities and specificities of 96% and 100% for apple IgE and 88% and 100% for the apple skin prick test, respectively. For the BAT, sensitivity and specificity were 100%. In contrast, when nonresponders on the BAT were considered, sensitivity decreased to 90%. In a separate analysis between OAS(+) and OAS(-) subjects, specificities decreased to 30% for apple IgE and to 80% for the apple skin test, respectively. The BAT reached a sensitivity of 88% and a specificity of 75%.

CONCLUSION

Flow cytometry-assisted quantification of in vitro basophil activation seems to be a reliable instrument in the diagnosis of this model of pollen-associated food allergy. In addition, this study reemphasizes that the specificity of diagnostic allergy tests decreases considerably when, apart from HC, control individuals with cross-reactive antibodies are included.

Presence of allergenic proteins in different peach (Prunus persica) cultivars and dependence of their content on fruit ripening

It has been reported that various cultivars of fruits and vegetables may present a different pattern for the contained allergens. Here, we report on the different content in allergenic proteins for different peach (Prunus persica) cultivars, sampled during two consecutive harvest seasons. Fruits from six cultivars of peaches were harvested fully ripe, and the proteins extracted from whole or chemically peeled fruits were analyzed by SDS-PAGE and immunoblotting. All the protein extracts from whole fruit contained a 9 kDa protein. This protein proved to be absent in the extracts taken from chemically peeled fruit. In four cultivars, this protein corresponds to the allergen Pru p3, a lipid transfer protein that causes the oral allergy syndrome (OAS) in sensitized people. In the following year, fruits from four of the six cultivars of peaches studied previously were harvested at different times, at one and two weeks before the commercial ripening time and when fully ripe, to ascertain whether the presence of the 9 kDa allergen might be related to the ripening process. Two cultivars out of four produced an intense allergenic band corresponding to a 9 kDa protein already two weeks before the commercial ripening date, while the others showed a progressive increment of the 9 kDa allergen during ripening.

Effect of tree pollen specific, subcutaneous immunotherapy on the oral allergy syndrome to apple and hazelnut

BACKGROUND

The efficacy of specific immunotherapy (SIT) in pollen allergy is well established. However, its effect on pollen associated food allergy particularly the oral allergy syndrome (OAS) is not definitely ascertained.

OBJECTIVE

The purpose of this controlled prospective study was to investigate whether SIT with tree pollen, mainly birch, has an effect on OAS induced by apple or hazelnut in birch pollen-allergic individuals.

METHODS

Twenty-seven birch pollen-allergic subjects with OAS induced by apple or hazelnut underwent open oral provocation tests (OPT) with increasing doses (1 to 128 g) of fresh apple or ground hazelnut 1 year apart. Fifteen of 27 subjects were treated with SIT and 12 were not. Skin-prick test with birch pollen, apple and hazelnut, and specific serum IgE, IgG and IgG4 to rBet v 1, apple and hazelnut were determined.

RESULTS

Thirteen of 15 (87%) SIT-treated subjects could eat significantly (P <0.001) more of apple or hazelnut without any symptoms/signs. The average tolerated quantity increased from 12.6 to 32.6 g apple after 1 year in this group. In contrast, only one of 12 (8%) individuals without SIT was able to consume a higher amount without symptoms. On evaluating laboratory parameters, only IgG4 antibodies to rBet v 1 were found to be significantly (P <0.01) increased in the SIT-treated group after 1 year.

CONCLUSIONS

The study shows that SIT with extracts containing birch pollen has a positive impact on OAS to apple or hazelnut in birch pollen-allergic individuals. In spite of this outcome, the amount of apple/hazelnut tolerated is still small. Thus, the effect of SIT on the patients' management of OAS remains limited.

Bet v 1 homologues in strawberry identified as IgE-binding proteins and presumptive allergens

BACKGROUND

No strawberry allergen has so far been identified and characterized.

METHODS

Serum samples were collected from patients with a suggestive case history of adverse reactions to strawberry and other fruits. Extracts from fresh and frozen strawberries were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting and mass spectrometry. Patient blood samples were analysed for inhibition of IgE binding and basophil degranulation.

RESULTS

Several IgE-binding proteins could be detected. In more than half of the patient sera, a 20/18-kDa doublet band was observed in Western blotting. These two bands were excised and analysed by mass spectrometry showing the presence of proteins belonging to the Bet v 1 family of allergens. Inhibition of the IgE binding to the 20/18-kDa doublet was obtained by addition of two recombinantly expressed allergens belonging to the Bet v 1 family (Bet v 1 and Mal d 1) and strawberry protein extract. In a cell-based assay of patient blood samples, basophil degranulation could be induced by strawberry protein extract and by Bet v 1 and Mal d 1.

CONCLUSIONS

We conclude that strawberry homologues to Bet v 1 may be allergens of importance for adverse reactions to strawberry.