Potential, pitfalls, and prospects of food allergy diagnostics with recombinant allergens or synthetic sequential epitopes

Allergenicity of peanut allergens and its dependence on the structure

Food allergies are a global food safety problem. Peanut allergies are common due, in part, to their popular utilization in the food industry. Peanut allergy is typically an immunoglobulin E-mediated reaction, and peanuts contain 17 allergens belonging to different families in peanut. In this review, we first introduce the mechanisms and management of peanut allergy, followed by the basic structures of associated allergens. Subsequently, we summarize methods of epitope localization for peanut allergens. These methods can be instrumental in speeding up the discovery of allergenicity-dependent structures. Many attempts have been made to decrease the allergenicity of peanuts. The structures of hypoallergens, which are manufactured during processing, were analyzed to strengthen the desensitization process and allergen immunotherapy. The identification of conformational epitopes is the bottleneck in both peanut and food allergies. Further, the identification and modification of such epitopes will lead to improved strategies for managing and preventing peanut allergy. Combining traditional wet chemistry research with structure simulation studies will help in the epitopes' localization.

Physicochemical characterization and identification of major linear epitopes of sarcoplasmic calcium-binding protein (SCP) allergen from Pacific oyster (Crassostrea gigas)

BACKGROUND

Food allergy is a serious public nutritional health problem that has attracted extensive worldwide attention. Shellfish allergy is a long-lasting disorder that has a lifelong impact on health. Sarcoplasmic calcium-binding protein (SCP) plays a vital role in cell and muscle functions and has been identified as an allergen in oyster.

RESULTS

In this study, recombinant SCP (rSCP) with a molecular mass of 21 kDa was produced and identified based on SCP amino acid sequencing of Pacific oyster (Crassostrea gigas), and was used as a follow-up experimental material. Its physicochemical characterization showed that purified rSCP is highly stable to heat and acid-alkali and trypsin digestion but less resistant to pepsin digestion. We established an animal sensitization model and rSCP displayed stronger Immunoglobulin E (IgE)-binding activity with rat serum in the rSCP + cholera toxin (CT) group compared with the CT group and a control group. Five epitope peptides were identified as linear immunodominant epitopes by indirect competitive enzyme-linked immunosorbent assay (icELISA) for the first time. We also found that conformational epitopes may play a major role in the immunoreactivity of SCP.

CONCLUSION

These results are significant for understanding hypersensitization of humans to oyster and offer available preventive measures and treatment programs in further research. © 2021 Society of Chemical Industry.

Update of the S2k guideline on the management of IgE-mediated food allergies

Not available.

IgE and IgG4 responses to shrimp allergen tropomyosin and its epitopes in patients from coastal areas of northern China

Sensitization to allergens and their peptides varies among patients due to geographical or ethnic differences. The present study aimed to investigate immunoglobulin (Ig)E and IgG₄ responses to tropomyosin and its peptides in shrimp allergic patients from northern China. A total of 92 subjects were studied, including 35 shrimp allergic patients, 29 patients with house dust mite (HDM) and/or cockroach allergic patients and 28 healthy volunteers. Serum IgE and IgG₄ antibodies to recombinant shrimp tropomyosin (rPen a 1) and its peptides were measured by means of a light-initiated chemiluminescent assay. A total of 9 major sequential epitopes of Pen a 1 reported in the literature were synthesized. Of 35 shrimp allergic patients, 25 (71.4%) had positive Pen 1-specific IgE (sIgE) antibodies and 22 (62.9%) contained measurable rPen a 1-specific IgG₄ (sIgG₄) antibodies. A strong IgG₄ response accompanied the presence of IgE to Pen a 1. None of the patients with HDM and/or cockroach allergy demonstrated IgE reactivity to rPen a 1. The reaction frequency of IgE binding epitope was 20–48%, while that of IgG₄ binding epitope was 63.6–3.9%. The IgE and IgG₄ recognition patterns of the tropomyosin peptides demonstrated high interpatient heterogeneity. Diversity of IgE binding epitopes was positively correlated with Pen a 1 sIgE levels. In the study population, tropomyosin was a major allergen recognized by the majority of shrimp allergic patients, which is consistent with previous reports. However, none of the 9 epitopes are major (reaction frequency >50%) IgE-binding regions, indicating the epitopes profile may be different in other regions.

Progress in the Analysis of Food Allergens through Molecular Biology Approaches

Food allergies associated with class E immunoglobulins (IgE) are a serious health problem that affects between 1% and 10% of the population of developing countries, with a variability that depends on the geographical area and age range considered. These allergies are caused by a cross-link reaction between a specific food protein (the allergen) and the host IgE. Allergic reactions can range from mild itching to anaphylactic shock and there are no clues to predict the effects of an allergen. Strict avoidance of allergenic food is the only way to avoid possible serious allergic reactions. In the last 30 years a growing number of molecular studies have been conducted to obtain information on the diffusion of food allergens and to establish the structural basis of their allergenicity. At the same time, these studies have also allowed the development of molecular tools (mainly based on synthetic peptides and recombinant allergens) that can be of great help for diagnostic and therapeutic approaches of food allergies. Accordingly, this review focuses on advances in the study of food allergens made possible by molecular technologies and how results and technologies can be integrated for the development of a systematic food molecular allergology. The review may be of interest both to scientists approaching this field of investigation and to physicians who wish to have an update on the progress of research in diagnosis and therapy of food allergies.

Allergen-specific IgE and IgG4 patterns among patients with different allergic diseases

Background

In addition to allergen-specific IgE (sIgE), allergen-specific IgG4 (sIgG4) antibodies are also involved in the immune response resulting from an allergen exposure. The aim of our study was to analyze sIgE and sIgG4 patterns in the most common allergic disorders: bronchial asthma, upper airway disorders and atopic dermatitis.

Methods

In this study a screening analysis of blood serum samples from 673 patients aged from 6 months to 17 years with different allergic entities was performed on microarrays. sIgE and sIgG4 levels to the most common allergens were estimated.

Results

sIgE response to most pollen allergens is more strongly associated with respiratory diseases than with atopic dermatitis, while sIgE responses to cat and dog dander are more strongly associated with bronchial asthma than with atopic dermatitis and upper airway disorders such as rhinosinusitis and allergic rhinitis. A lower prevalence of sIgG4 to pollen allergens in cases of atopic dermatitis is observed compared with that in cases of asthma and upper airway disorders. Analyzing all the allergic disorders, one can see that sIgG4 response to inhalant allergens is strongly associated with sensitization to the corresponding allergen.

Conclusion

Allergen-specific IgE and IgG4 patterns that are relevant to concrete allergic diseases differ by sIgE and sIgG4 prevalences to defined allergens.

Electronic supplementary material

The online version of this article (10.1186/s40413-018-0220-5) contains supplementary material, which is available to authorized users.

Patterns of sensitization to inhalant and food allergens among pediatric patients from the Moscow region (Russian Federation)

The immunological profiles of human specific IgE (sIgE) and specific IgG4 (sIgG4) vary by genetic predisposition, living conditions in different geographical locations and patient’s age. The aim of our study was to analyze sIgE and sIgG4 patterns and their age-dependent changes in patients from the Moscow region. For identifying sIgE and sIgG4 profiles the blood samples from 513 patients aged 6 months to 17 years who were showing symptoms of allergic diseases were analyzed using microarrays containing 31 allergens. The highest sIgE prevalence was observed for birch pollen (32%) among pollen allergens, cat dander (24%) among indoor allergens, and egg whites (21%) among food allergens. The most common sIgG4 response was developed toward egg whites (80% of patients). Age-related elevation was identified for patients with increased sIgE to pollen allergens and indoor allergens (cat or dog dander and house dust mites). For each allergen, the proportion of cases with significant levels of sIgG4 appeared to increase with patients’ age. The data on allergen-specific sIgE and sIgG4 prevalence show both general trends and some local special aspects that are indicative for the Moscow region. This information should be useful in terms of epidemiology of allergic diseases.

Spontaneous food allergy in Was-/- mice occurs independent of FcεRI-mediated mast cell activation

BACKGROUND

Food allergies are a growing health problem, and the development of therapies that prevent disease onset is limited by the lack of adjuvant-free experimental animal models. We compared allergic sensitization in patients with food allergy or Wiskott-Aldrich syndrome (WAS) and defined whether spontaneous disease in Was^-/- mice recapitulates the pathology of a conventional disease model and/or human food allergy.

METHODS

Comparative ImmunoCAP ISAC microarray was performed in patients with food allergy or WAS. Spontaneous food allergy in Was^-/- mice was compared to an adjuvant-based model in wild-type mice (WT-OVA/alum). Intestinal and systemic anaphylaxis was assessed, and the role of the high-affinity IgE Fc receptor (FcεRI) in allergic sensitization was evaluated using Was^-/- Fcer1a^-/- mice.

RESULTS

Polysensitization to food was detected in both WAS and food-allergic patients which was recapitulated in the Was^-/- model. Oral administration of ovalbumin (OVA) in Was^-/- mice induced low titers of OVA-specific IgE compared to the WT-OVA/alum model. Irrespectively, 79% of Was^-/- mice developed allergic diarrhea following oral OVA challenge. Systemic anaphylaxis occurred in Was^-/- mice (95%) with a mortality rate >50%. Spontaneous sensitization and intestinal allergy occurred independent of FcεRI expression on mast cells (MCs) and basophils.

CONCLUSIONS

Was^-/- mice provide a model of food allergy with the advantage of mimicking polysensitization and low food-antigen IgE titers as observed in humans with clinical food allergy. This model will facilitate studies on aberrant immune responses during spontaneous disease development. Our results imply that therapeutic targeting of the IgE/FcεRI activation cascade will not affect sensitization to food.

Can we identify patients at risk of life-threatening allergic reactions to food?

Anaphylaxis has been defined as a 'severe, life-threatening generalized or systemic hypersensitivity reaction'. However, data indicate that the vast majority of food-triggered anaphylactic reactions are not life-threatening. Nonetheless, severe life-threatening reactions do occur and are unpredictable. We discuss the concepts surrounding perceptions of severe, life-threatening allergic reactions to food by different stakeholders, with particular reference to the inclusion of clinical severity as a factor in allergy and allergen risk management. We review the evidence regarding factors that might be used to identify those at most risk of severe allergic reactions to food, and the consequences of misinformation in this regard. For example, a significant proportion of food-allergic children also have asthma, yet almost none will experience a fatal food-allergic reaction; asthma is not, in itself, a strong predictor for fatal anaphylaxis. The relationship between dose of allergen exposure and symptom severity is unclear. While dose appears to be a risk factor in at least a subgroup of patients, studies report that individuals with prior anaphylaxis do not have a lower eliciting dose than those reporting previous mild reactions. It is therefore important to consider severity and sensitivity as separate factors, as a highly sensitive individual will not necessarily experience severe symptoms during an allergic reaction. We identify the knowledge gaps that need to be addressed to improve our ability to better identify those most at risk of severe food-induced allergic reactions.

Prevalence of sensitization to food allergens and challenge proven food allergy in patients visiting allergy centers in Rawalpindi and Islamabad, Pakistan

In this study, we estimated the prevalence of food allergy in the adult allergic patients of Rawalpindi and Islamabad , Pakistan, based on self-report, skin prick test (SPT) and oral food challenge test (OFC). SPT was used for the estimation of sensitization to wheat, egg, milk, beef, chicken, mutton, fish, corn, lentils, rice, soya, peanut and banana. Among 689 patients, 39.19 % showed sensitivity to one or more foods, where, sensitization to wheat (156; 22.6 %) was highest, followed by egg (148; 21.48 %) and milk (138; 20.03 %). Sensitization to various proteins ranged between 15.53–15.97 %, while lentils, corn, rice, soya and peanut sensitization was 15.4, 16, 12.5, 12 and 11.5 % respectively. Only 7.1 % patients were SPT positive for banana allergen. SPT was performed in patients with self-reported food allergy (341/689) and also with no self-reported history of food allergy (348/689). SPT results were positive in 69.8 % of the self-report group, whereas, in the patients with no self-reported food allergy 9.2 % were found sensitized to one or more tested food allergens. 101 patients were recruited for OFC, 61 % of these were confirmed of food allergy. The prevalence of food allergy in the study population was 9 %. Food specific OFC results show that wheat allergy is affecting 1.6 % (95 % CI 0.9–2.84 %) of the total allergy patients, followed by egg allergy 1.31 % (95 % CI 0.70–2.47 %). Furthermore, corn allergy, rice allergy and peanut allergy were 1.02, 0.87 and 0.73 %, respectively. In conclusion, wheat allergy is the most prevalent, followed by egg, chicken, beef and fish allergy, respectively.

Comparison and clinical utility evaluation of four multiple allergen simultaneous tests including two newly introduced fully automated analyzers

Background

We compared the diagnostic performances of two newly introduced fully automated multiple allergen simultaneous tests (MAST) analyzers with two conventional MAST assays.

Methods

The serum samples from a total of 53 and 104 patients were tested for food panels and inhalant panels, respectively, in four analyzers including AdvanSure AlloScreen (LG Life Science, Korea), AdvanSure Allostation Smart II (LG Life Science), PROTIA Allergy-Q (ProteomeTech, Korea), and RIDA Allergy Screen (R-Biopharm, Germany). We compared not only the total agreement percentages but also positive propensities among four analyzers.

Results

Evaluation of AdvanSure Allostation Smart II as upgraded version of AdvanSure AlloScreen revealed good concordance with total agreement percentages of 93.0% and 92.2% in food and inhalant panel, respectively. Comparisons of AdvanSure Allostation Smart II or PROTIA Allergy-Q with RIDA Allergy Screen also showed good concordance performance with positive propensities of two new analyzers for common allergens (Dermatophagoides farina and Dermatophagoides pteronyssinus). The changes of cut-off level resulted in various total agreement percentage fluctuations among allergens by different analyzers, although current cut-off level of class 2 appeared to be generally suitable.

Conclusions

AdvanSure Allostation Smart II and PROTIA Allergy-Q presented favorable agreement performances with RIDA Allergy Screen, although positive propensities were noticed in common allergens.

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Two new multiple allergen simultaneous tests (MAST) analyzers are evaluated.

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AdvanSure Smart II and PROTIA presented favorable agreement performance with RIDA.

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Positive propensity of new assays for D. farina and D. pteronyssinus was noticed.

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The changes of cut-off level resulted in total agreement percentage fluctuations.

Applications of Molecular Diagnostic Testing in Food Allergy

IgE-mediated food allergy is a relevant health problem inducing symptoms ranging from mild local reactions up to severe life-threatening situations. Currently, no immunotherapy is available and avoidance of the incriminating food is the method of choice. Therefore, reliable diagnostic tools to formulate dietary recommendations and to avoid unnecessary exclusion diets for the individual patient are urgently needed. This review provides an update on the current knowledge on food allergens and their application in various diagnostic approaches such as skin prick test, basophil activation test, and serum IgE testing. Furthermore, these new approaches are discussed and compared to conventional extract-based assays and correlated to the gold standard of food allergy diagnosis, the double-blind placebo-controlled food challenge. Finally, the application of food allergens for preventive measurements such as allergen detection assays and the determination of threshold levels for allergen levels are discussed.

Interfaces between allergen structure and diagnosis: know your epitopes

Allergy diagnosis is based on the patient's clinical history and can be strengthened by tests that confirm the origin of sensitization. In the past 25 years, these tests have evolved from the exclusive in vivo or in vitro use of allergen extracts, to complementary molecular-based diagnostics that rely on in vitro measurements of IgE reactivity to individual allergens. For this to occur, an increase in our understanding of the molecular structure of allergens, largely due to the development of technologies such as molecular cloning and expression of recombinant allergens, X-ray crystallography, or nuclear magnetic resonance (NMR), has been essential. New in vitro microarray or multiplex systems are now available to measure IgE against a selected panel of purified natural or recombinant allergens. The determination of the three-dimensional structure of allergens has facilitated detailed molecular studies, including the analysis of antigenic determinants for diagnostic purposes.

Identification of two metallothioneins as novel inhalative coffee allergens cof a 2 and cof a 3

Background

Dust of green coffee beans is known to be a relevant cause for occupational allergic disorders in coffee industry workers. Recently, we described the first coffee allergen (Cof a 1) establishing an allergenic potential of green coffee dust.

Objective

Our aim was to identify allergenic components of green coffee in order to enhance inhalative coffee allergy diagnosis.

Methods

A Coffea arabica pJuFo cDNA phage display library was created and screened for IgE binding with sera from allergic coffee workers. Two further coffee allergens were identified by sequence analysis, expressed in E. coli, and evaluated by Western blots. The prevalence of sensitization to recombinant Cof a 1, Cof a 2, and Cof a 3 and to commercially available extract was investigated by ELISA (enzyme-linked immunosorbent assay) respectively CAP (capacity test) screening in 18 sera of symptomatic coffee workers.

Results

In addition to the previously described chitinase Cof a 1, two Coffea arabica cysteine-rich metallothioneins of 9 and 7 kDa were identified and included in the IUIS Allergen Nomenclature as Cof a 2 and Cof a 3. Serum IgE antibodies to at least one of the recombinant allergens were found in 8 out of 18 symptomatic coffee workers (44%). Only 2 of the analysed sera (11%) had reacted previously to the commercial allergy test.

Conclusions

In addition to the previously described Cof a 1 we have identified two further coffee proteins to be type I coffee allergens (Cof a 2 and Cof a 3) which may have a relevant potential for the specific diagnosis and/or therapy of coffee allergy.

The utility of the ISAC allergen array in the investigation of idiopathic anaphylaxis

A diagnosis of idiopathic anaphylaxis following a detailed clinical assessment remains very challenging for patients and clinicians. Risk reduction strategies such as allergen avoidance are not possible. This study investigated whether the (ISAC) allergen array with 103 allergens would add diagnostic value in patients with idiopathic anaphylaxis. We extended the specific immunoglobulin (Ig)E testing in 110 patients with a diagnosis of idiopathic anaphylaxis from five UK specialist centres using ISAC arrays. These were divided into three groups: score I identified no new allergen sensitization beyond those known by previous assessment, score II identified new sensitizations which were not thought likely to explain the anaphylaxis and score III identified new sensitizations felt to have a high likelihood of being responsible for the anaphylaxis. A proportion (50%) of score III patients underwent clinical reassessment to substantiate the link to anaphylaxis in this group. The results show that 20% of the arrays were classified as score III with a high likelihood of identifying the cause of the anaphylaxis. A wide range of major allergens were identified, the most frequent being omega-5-gliadin and shrimp, together accounting for 45% of the previously unrecognized sensitizations. The ISAC array contributed to the diagnosis in 20% of patients with idiopathic anaphylaxis. It may offer additional information where a careful allergy history and follow-on testing have not revealed the cause of the anaphylaxis.

Overview of plant chitinases identified as food allergens

Food allergies are induced by proteins belonging to a limited number of families. Unfortunately, relationships between protein structure and capacity to induce the immune response have not been completely clarified yet, which precludes possible improvements in the diagnosis, prevention, and therapy of allergies. Plant chitinases constitute a good example of food allergenic proteins for which structural analysis of allergenicity has only been carried out partially. In plants, there are at least five structural classes of chitinases plus a number of chitinase-related polypeptides. Their allergenicity has been mostly investigated for chitinases of class I, due to both their higher prevalence among plant chitinases and by the high structural similarity between their substrate-binding domain and hevein, a well-known allergen present in the latex of rubber trees. Even if allergenic molecules have been identified for at least three other classes of plant chitinases, the involvement of the different structural motifs in the allergenicity of molecules has been disregarded so far. In this review, we provide a structurally based catalog of plant chitinases investigated for allergenicity, which could be a useful base for further studies aimed at better clarifying the structure-allergenicity relationships for this protein family.

[Personalised medicine for the diagnosis and treatment of allergic diseases]

Immunoglobulin E (IgE) mediated allergic diseases are characterised by heterogeneous clinical phenotypes and a large variety of different sensitisation patterns. Apart from genetic predisposition several environmental factors play a role in sensitisation and elicitation of symptoms. Since the majority of clinically relevant allergens are now available as purified recombinant allergens component-resolved in vitro diagnosis allows the sensitization profile of allergic patients to be determined at the molecular level. Such data may allow physicians to draw conclusions on the severity and persistence of a given allergic disease and to predict the outcome of allergen-specific immunotherapy (SIT) However, the potential of this approach needs to be demonstrated in controlled clinical trials. Moreover, in the context of atopic dermatitis, allergic rhinitis, allergic bronchial asthma as well as the atopic march several screening-biomarkers, diagnostic and prognostic biomarkers, biomarkers of severity and predictive biomarkers are presented and discussed in this article. Traditionally a relevant proportion of allergen-specific immunotherapies is performed in a personalised manner using named patient products manufactured on the basis of an individual prescription. Such named patient products are often mixtures containing several allergen extracts from different sources. However, there is no proven evidence for the safety and efficacy of this approach. In Germany the Therapy Allergen Ordinance ("Therapieallergene-Verordnung", TAV) regulates that in the future allergen products for SIT of insect venom allergies, allergies to pollen of early flowering trees and grass pollen and house dust mite allergies cannot be marketed as named patient products, but always require a marketing authorisation. Thus personalised SIT with named patient products is restricted to the treatment of less prevalent allergies, for which the generation of state-of-the-art clinical data is more difficult. Several recombinant allergens are currently evaluated in phase III clinical trials. In contrast to allergen extracts recombinant allergens offer the possibility to treat patients with a precisely adjusted mixture of the disease-eliciting allergen molecules. However, the implementation of this personalised approach to SIT within the given regulatory framework represents a challenge to regulators.

Relationships between IgE/IgG4 epitopes, structure and function in Anisakis simplex Ani s 5, a member of the SXP/RAL-2 protein family

BACKGROUND

Anisakiasis is a re-emerging global disease caused by consumption of raw or lightly cooked fish contaminated with L3 Anisakis larvae. This zoonotic disease is characterized by severe gastrointestinal and/or allergic symptoms which may misdiagnosed as appendicitis, gastric ulcer or other food allergies. The Anisakis allergen Ani s 5 is a protein belonging to the SXP/RAL-2 family; it is detected exclusively in nematodes. Previous studies showed that SXP/RAL-2 proteins are active antigens; however, their structure and function remain unknown. The aim of this study was to elucidate the three-dimensional structure of Ani s 5 and its main IgE and IgG4 binding regions.

METHODOLOGY/PRINCIPAL FINDINGS

The tertiary structure of recombinant Ani s 5 in solution was solved by nuclear magnetic resonance. Mg2+, but not Ca2+, binding was determined by band shift using SDS-PAGE. IgE and IgG4 epitopes were elucidated by microarray immunoassay and SPOTs membranes using sera from nine Anisakis allergic patients. The tertiary structure of Ani s 5 is composed of six alpha helices (H), with a Calmodulin like fold. H3 is a long, central helix that organizes the structure, with H1 and H2 packing at its N-terminus and H4 and H5 packing at its C-terminus. The orientation of H6 is undefined. Regarding epitopes recognized by IgE and IgG4 immunoglobulins, the same eleven peptides derived from Ani s 5 were bound by both IgE and IgG4. Peptides 14 (L40-K59), 26 (A76-A95) and 35 (I103-D122) were recognized by three out of nine sera.

CONCLUSIONS/SIGNIFICANCE

This is the first reported 3D structure of an Anisakis allergen. Magnesium ion binding and structural resemblance to Calmodulin, suggest some putative functions for SXP/RAL-2 proteins. Furthermore, the IgE/IgG4 binding regions of Ani s 5 were identified as segments localized on its surface. These data will contribute towards a better understanding of the interactions that occur between immunoglobulins and allergens and, in turn, facilitate the design of novel diagnostic tests and immunotherapeutic strategies.

Diagnostic usefulness of component-resolved diagnosis by skin prick tests and specific IgE to single allergen components in children with allergy to fruits and vegetables

INTRODUCTION

The accurate identification of sensitizing proteins in patients allergic to plant-derived foods is extremely important, allowing a correct dietary advice. We aimed to evaluate the diagnostic usefulness of skin prick tests (SPT) and specific IgE (sIgE) with single molecular allergen components in children with allergy to fruits and vegetables.

METHODS

Twenty children underwent SPT with a palm profilin (Pho d 2, 50 μg/mL); a Mal d 1-enriched apple extract (2 μg/mL) (PR-10 allergen); and a peach Lipid Transfer Protein (LTP) (Pru p 3, 30 μg/mL). Detection of sIgE to rBet v 1, rBet v 2, Phl p 12 and Pru p 3 was also measured.

RESULTS

Allergy to multiple fruits and vegetables was observed in 11 (55%) children. Sensitization by SPT to Pho d 2, Mal d 1, and Pru p 3 occurred in 5, 7, and 8 cases, respectively. LTP sensitization appeared to be associated with peach allergy but not with severe reactions, and profilins sensitization to melon and tomato allergy. Kiwi sensitization (12 cases), the plant-derived food that caused more allergic reactions, seemed mostly species-specific. The concordance of SPT extracts and sIgE to the corresponding pan-allergens was high for profilins (k=0.857) and LTP (k=0.706), while for PR-10 allergens it was absent (k=0.079).

CONCLUSIONS

Pan-allergen sensitization in children with allergy to fruits and vegetables was common and often multiple. There was no association of severe reactions to LTP sensitization. The introduction of routine SPT to pan-allergens can be a simple and feasible way of improving diagnostic and therapeutic efficacy.

Recombinant allergen-based provocation testing

Over the last 25 years, recombinant allergens from all important allergen sources have been cloned and are now available as recombinant proteins. These molecules can be produced in practically unlimited amounts without biological or batch-to-batch variability. It has been shown in provocation tests that recombinant allergens have similar clinical effects as their natural counterparts. With the help of these tools it is possible to reveal the precise reactivity profiles of patients and to uncover and differentiate cross-reactivity from genuine sensitization to an allergen source. Although it has been shown some time ago that it would be possible to replace crude allergen extracts with recombinant allergens for skin prick testing, and even though the use of allergen components can improve routine diagnosis, these tools are still not available for clinical routine applications. The use of provocation tests is a crucial step in the development of new, hypoallergenic vaccines for therapy of allergic disease. Here we describe important provocation methods (skin prick test, intradermal test, atopy patch test, nasal provocation, colonoscopic provocation test) and give an overview of the clinical provocation studies which have been performed with recombinant allergens so far.

Ara h 6 complements Ara h 2 as an important marker for IgE reactivity to peanut

The similarities of two major peanut allergens, Ara h 2 and Ara h 6, in molecular size, amino acid sequence, and structure have made it difficult to obtain natural Ara h 6 free of Ara h 2. The objectives of this study were to purify natural Ara h 6 that is essentially free of Ara h 2 and to compare its IgE reactivity and potency in histamine release assays to Ara h 2. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the highly purified allergen (<0.01% Ara h 2) revealed a single 14.5 kD band, and the identity of Ara h 6 was confirmed by liquid chromatography-tandem mass spectrometry. Ara h 6 showed a higher seroprevalence in chimeric IgE enzyme-linked immunosorbent assay (n = 54) but a weaker biological activity in basophil histamine release assays than Ara h 2. Purified Ara h 6 will be useful for diagnostic IgE antibody assays as well as molecular and cellular studies to investigate the immunological mechanisms of peanut allergy.

Prevalence of immediate-type food allergy in early childhood in seoul

PURPOSE

There are scanty epidemiologic data on the prevalence of food allergy (FA) among preschool children in Asia. We performed this study to determine the prevalence and causative foods of immediate-type FA in early childhood in Korea.

METHODS

A questionnaire-based, cross-sectional study was performed between September and October 2011. Children aged 0-6 years were recruited from 301 public child care centers in Seoul. Parents were asked to complete a questionnaire on FA. Children with FA were classified into "perceived FA, ever," "immediate-type FA, ever," and "immediate-type FA, current" according to the algorithm.

RESULTS

A total of 16,749 children were included in this study. The prevalence of "perceived FA, ever," "immediate-type FA, ever," and "immediate-type FA, current" was 15.1%, 7.0%, and 3.7%, respectively. "Immediate-type FA, current" was reported by 182 (4.9%) out of 3,738 children aged ≤2 years, 262 (3.4%) of 7,648 children aged 3-4 years, and 177 (3.3%) of 5,363 children aged 5-6 years. Hen's egg (126/621) was the most frequent cause as the individual food item, followed by cow's milk (82/621) and peanut (58/621). Among the food groups, fruits (114/621), tree nuts (90/621) and crustaceans (85/621) were the most common offending foods. The three leading causes of food-induced anaphylaxis were hen's egg (22/47), cow's milk (15/47), and peanut (14/47).

CONCLUSIONS

The prevalence of immediate-type FA in early childhood is 3.7%, and is higher in younger children. The most common offending foods differed with age.

The optimal diagnostic workup for children with suspected food allergy

Food allergy is defined as an abnormal immunologic reaction to food proteins that causes an adverse clinical reaction. In addition to well-known acute allergic reactions and anaphylaxis triggered by immunoglobulin E antibody-mediated immune responses to food proteins, there is an increasing recognition of cell-mediated disorders such as eosinophilic esophagitis and food protein-induced enterocolitis syndrome. More than 90% of food allergies in childhood are caused by eight foods: cow's milk, hen's egg, soy, peanuts, tree nuts, wheat, fish, and shellfish. The diagnostic workup for a child with suspected food allergy includes a detailed medical history, physical examination, food allergy screening tests, and responses to an elimination diet and an oral food challenge. None of the screening tests, alone or in combination, can definitely diagnose or exclude a food allergy. Novel diagnostic methods including those that focus on immune responses to specific food proteins or epitopes of specific proteins are under active study. Unconventional diagnostic methods are increasingly used, but they lack scientific rationale, standardization, and reproducibility. In selected cases, such as eosinophilic esophageal gastroenteropathies or food protein-induced gastroesophageal reflux disease, invasive procedures are mandatory for an accurate diagnosis. Properly done, an oral food challenge is still the gold standard in the diagnostic workup. An incorrect diagnosis is likely to result in unnecessary dietary restrictions, which, if prolonged, may adversely affect the child's nutritional status and growth.

Food allergy

Food allergy appears to be increasing in prevalence and is estimated to affect >2% and possibly up to 10% of the population. Food allergies are defined by an immune response triggered by food proteins. Emerging data suggest that carbohydrate moieties on food proteins, specifically mammalian meats, may also elicit allergic responses. Food is the most common trigger of anaphylaxis in the community, which can be fatal. The underlying mechanisms of food allergy usually involve food-specific immunoglobulin E antibodies, but cell-mediated disorders account for a variety of chronic or subacute skin and gastrointestinal reactions. Eosinophilic esophagitis is an emerging food-related chronic disorder. The diagnosis of food allergy is complicated by the observation that detection of food-specific immunoglobulin E (sensitization) does not necessarily indicate clinical allergy. Diagnosis requires a careful medical history, laboratory studies, and, in many cases, oral food challenges to confirm a diagnosis. Novel diagnostic methods, many of which rely upon evaluating immune responses to specific food proteins or epitopes, may improve diagnosis and prognosis in the future. Current management relies upon allergen avoidance and preparation to promptly treat severe reactions with epinephrine. Studies suggest that some children with milk or egg allergy might tolerate extensively heated forms, for example milk or egg baked into muffins, without symptoms and possibly with some immunotherapeutic benefits. Novel therapeutic strategies are under study, including oral and sublingual immunotherapy, Chinese herbal medicine, anti-immunoglobulin E antibodies, and modified vaccines.

Food allergy: recent advances in pathophysiology and diagnosis

Approximately 5% of young children and 3-4% of adults exhibit adverse immune responses to foods in westernized countries, with a tendency to increase. The pathophysiology of food allergy (FA) relies on immune reactions triggered by epitopes, i.e. small amino-acid sequences able to bind to antibodies or cells. Some food allergens share specific physicochemical characteristics that allow them to resist digestion, thus enhancing allergenicity. These allergens encounter specialized dendritic cell populations in the gut, which leads to T-cell priming. In case of IgE-mediated allergy, this process triggers the production of allergen-specific IgE by B cells. Tissue-resident reactive cells, including mast cells, then bind IgE, and allergic reactions are elicited when these cells, with adjacent IgE molecules bound to their surface, are re-exposed to allergen. Allergic reactions occurring in the absence of detectable IgE are labeled non-IgE mediated. The abrogation of oral tolerance which leads to FA is likely favored by genetic disposition and environmental factors (e.g. increased hygiene or enhanced allergenicity of some foods). For an accurate diagnosis, complete medical history, laboratory tests and, in most cases, an oral food challenge are needed. Noticeably, the detection of food-specific IgE (sensitization) does not necessarily indicate clinical allergy. Novel diagnostic methods currently under study focus on the immune responses to specific food proteins or epitopes of specific proteins. Food-induced allergic reactions represent a large array of symptoms involving the skin and gastrointestinal and respiratory systems. They can be attributed to IgE-mediated and non-IgE-mediated (cellular) mechanisms and thus differ in their nature, severity and outcome. Outcome also differs according to allergens.

Microarray of allergenic component-based diagnosis in food allergy

PURPOSE OF REVIEW

The determination of specific IgE (sIgE) against allergenic components fixed in a solid support that is provided as a microarray of high capacity and allows a more precise evaluation in the food allergy diagnosis. In this review, we will analyze the results obtained to date with this technology applied to the component-based diagnosis of food allergy.

RECENT FINDINGS

Microarrays of proteins or glycoproteins allow us to know the profile of sensitization of a patient with food allergy. At present, a commercially available technique exists which allows sIgE to be detected against 103 allergenic molecules. Several laboratories worldwide have explored and optimized this technique for few allergen extracts and the results have been promising with high reliabilities and sensitivities and above all, good correlations with previous existing conventional assays.

SUMMARY

In recent years, as a result of advances in molecular biology, together with the development of new technologies of producing high-capacity solid-phase matrices such as microarrays, the diagnosis of food allergy has improved and the basic situation of analyzing sIgE against an allergenic source has now become real the possibility of analyzing sIgE against an allergenic protein or glycoprotein. This change has not only led to a more precise diagnosis of sensitization, but can also be used to explain the different hazards of certain molecular sensitizations, crossreactivity phenomena in many cases and can even change the clinical management according to the information provided. Further studies are clearly needed to evaluate more precisely the scope of this new technique.

Molecular diagnosis of fruit and vegetable allergy

PURPOSE OF REVIEW

The purpose of this paper is to review and discuss studies on molecular diagnosis in fruit and vegetable allergy.

RECENT FINDINGS

Celeriac, carrot and tomato are the most prevalent allergenic vegetables, whereas fruit allergy is mainly induced by apple, peach and kiwi. Component-resolved molecular diagnosis has been recently applied in two well-defined patient groups with kiwifruit and celeriac allergy, respectively. In kiwifruit allergy Act d 1 and Act d 3 were identified as potential marker allergens for severe symptoms. For celeriac allergy, however, such markers are still missing. In both studies component-resolved molecular diagnosis approach improved in particular sensitivity compared to extract-based diagnostic test assays.

SUMMARY

Food and vegetable allergy can be acquired both via a direct sensitization over the gastrointestinal tract and via a primary sensitization to pollen or latex. The diagnosis of fruit and vegetable allergy in birch pollen-sensitized patients should not be excluded on a negative IgE testing to extracts. Bet v 1-related allergens are often under-represented in extracts. Few recombinant allergens derived from fruits and vegetables are nowadays commercially available and facilitate diagnosis of fruit and vegetable allergies.

Age-related sensitization profiles for hazelnut (Corylus avellana) in a birch-endemic region

BACKGROUND

Symptoms of hazelnut allergy seem related to geographic and possibly age variations in allergen recognition.

OBJECTIVE

To investigate sensitization profiles of hazelnut allergy in different age groups in a birch-endemic region using component resolved diagnosis (CRD) by microarray.

METHODS

Sixty-five patients with hazelnut allergy, 27 healthy control individuals tolerant to hazelnut, and 34 birch pollen allergic but hazelnut tolerant individuals were included. All blood samples were analyzed using ISAC microarray.

RESULTS

Twenty-nine patients with hazelnut allergy suffered from a systemic reaction (17 preschool children with a median age of 2 years, six school children, and six adults), whereas 36 patients reported an oral allergy syndrome (OAS; three preschool and nine school children and 24 adults). In the hazelnut allergic preschool children with systemic reactions, 65% were sensitized to Cor a 9, 12% to Cor a 8, 18% to Cor a 1.04, 6% to Cor a 1.0101, and 29% to Bet v 1. Of the school-aged systemic reactors, 50% were sensitized to Cor a 9, 17% to Cor a 8, 50% to Cor a 1.04 and Cor a 1.0101, and 67% to Bet v 1. In adults with hazelnut allergy, 3.3% were sensitized to Cor a 9, 6.7% to Cor a 8, 90% to Cor a 1.04 and Bet v 1, and 87% to Cor a 1.0101. In regard to systemic reactors in this group, 17% were sensitized to Cor a 9, 33% to Cor a 8 and Cor a 1.0101, and 50% to Cor a 1.04 and Bet v 1. In the patients with OAS, irrespective the age group, all were sensitized to Bet v 1 and over 97% to Cor a 1.04 and Cor a 1.0101. No sensitization to Cor a 9 or Cor a 8 was found in patients with only an OAS. Of the patients with birch pollen allergy, tolerant to hazelnut, none were sensitized to Cor a 9 or Cor a 8, 56% to Cor a 1.0101, 82% to Cor a 1.04, and 92% to Bet v 1. In healthy controls, no sensitization to components of hazelnut, hazel pollen or birch pollen was demonstrable.

CONCLUSION

Hazelnut allergy in a birch-endemic region exhibits age-related sensitization profiles with distinct clinical outcomes that can be identified using CRD. The majority of hazelnut allergic preschool and school children in a birch-endemic region show systemic reactions on consumption of processed hazelnut, mostly being sensitized to the hazelnut legumin-like allergen Cor a 9 but unrelated to birch pollen allergy. In contrast, adults generally suffer from an OAS apparently as a result of cross-reactivity between Cor a 1.04 from hazelnut and Bet v 1 from birch pollen.

Component resolved testing for allergic sensitization

Component resolved diagnostics introduces new possibilities regarding diagnosis of allergic diseases and individualized, allergen-specific treatment. Furthermore, refinement of IgE-based testing may help elucidate the correlation or lack of correlation between allergenic sensitization and allergic disease. Novel tools to predict severe outcomes and to plan for allergen-specific treatment are necessary, and because only a small amount of blood is needed to test for a multitude of allergens and allergenic components, component resolved diagnostics is promising. A drawback is the risk of overdiagnosis and misinterpretation of the complex results of such tests. Also, the practical use and selection of allergenic components need to be evaluated in large studies including well-characterized patients and healthy, sensitized controls and with representation of different geographical regions.

Allergen cross reactions: a problem greater than ever thought?

BACKGROUND

Cross reactions are an often observed phenomenon in patients with allergy. Sensitization against some allergens may cause reactions against other seemingly unrelated allergens. Today, cross reactions are being investigated on a per-case basis, analyzing blood serum specific IgE (sIgE) levels and clinical features of patients suffering from cross reactions. In this study, we evaluated the level of sIgE compared to patients' total IgE assuming epitope specificity is a consequence of sequence similarity.

METHODS

Our objective was to evaluate our recently published model of molecular sequence similarities underlying cross reactivity using serum-derived data from IgE determinations of standard laboratory tests. We calculated the probabilities of protein cross reactivity based on conserved sequence motifs and compared these in silico predictions to a database consisting of 5362 sera with sIgE determinations.

RESULTS

Cumulating sIgE values of a patient resulted in a median of 25-30% total IgE. Comparing motif cross reactivity predictions to sIgE levels showed that on average three times fewer motifs than extracts were recognized in a given serum (correlation coefficient: 0.967). Extracts belonging to the same motif group co-reacted in a high percentage of sera (up to 80% for some motifs).

CONCLUSIONS

Cumulated sIgE levels are exaggerated because of a high level of observed cross reactions. Thus, not only bioinformatic prediction of allergenic motifs, but also serological routine testing of allergic patients implies that the immune system may recognize only a small number of allergenic structures.

[Detection of allergen specific IgE by AdvanSure Allergy Screen test]

BACKGROUND

In vitro serum allergen-specific IgE tests have been routinely used in the clinical diagnosis of allergic diseases. We evaluated the clinical usefulness of a newly introduced multiple antigen screen test, Advansure Allergy Screen (LG Life Science, Korea) (LG-Screen) for the detection of allergen specific IgE.

METHODS

A total of 180 sera (80 for inhalant and 100 for food panels) were tested by LG-Screen and RIDA Allergy Screen (R-biopharm, Germany) (RIDA-Screen) assays. According to the 58-60 specific allergens or allergen groups, the positive rates and agreement rates were analyzed using the cut off levels of class 2. For the quantitation of total IgE and specific IgE, nephelometry and ImmunoCAP test were performed in the sera showing discrepant results between the two allergy screen assays.

RESULTS

The agreement rate and kappa value (k) of total IgE between the two allergy screen assays was 73.9% and 0.333. LG-Screen showed higher agreement rate with nephelometry than RIDA-Screen. The positive rates to common outdoor inhalant and food allergens were significantly higher in RIDA-Screen. Overall agreement rate of specific IgE between the two allergy screen assays for 58 allergens was 86.7% (6,086/7,020) (k, 0.293). In samples showing discrepant results between the two allergy screen assays, concordance rate of allergy screen assay with ImmunoCAP assay was 70.9% (449/633) for LG-Screen (k, 0.585) and 29.1% (184/633) for RIDA-Screen (k, -0.303).

CONCLUSIONS

LG-Screen showed a favorable agreement with RIDA-Screen and ImmunoCAP assays, and it could be used for the detection of allergen specific IgE in the clinical laboratory.

A Review of Food Allergy and Nutritional Considerations in the Food-Allergic Adult

In the United States, the prevalence of adults with food allergies is approximately 2% to 3%. Theoretically, any food can cause an allergic reaction; however, some foods are clearly more allergenic than others. In adults, peanuts, tree nuts, finned fish, crustaceans, fruit, and vegetables account for 85% of the food-allergic reactions. Currently, the only ways to manage food allergies are to avoid the allergen and initiate therapy for an allergic reaction if ingestion does occur. The presence of homologous proteins among animal or plant foods and between foods and certain airborne allergens may account for cross-sensitization that may be clinically relevant. For inpatients or outpatients with food allergies, nutrient and fluid requirements are the same as for individuals without food allergies. Since patients with adverse reactions to food may self-restrict intake or have been counseled on food avoidance, it is particularly important to determine dietary adequacy and to provide patients with appropriate food substitutions to provide nutrients that may be missing from a patient’s diet. This is of particular concern for individuals with multiple food allergies. Eating away from home and traveling also pose special problems for those with food allergies.

Component-resolved allergy diagnosis by microarray: potential, pitfalls, and prospects

Diagnosis of IgE-mediated allergies is not always straightforward, as traditional tests can yield equivocal or negative results and provocation tests are hampered by several practical and ethical limitations. During the last decades two new in vitro techniques have entered the field of allergy diagnosis, that is, flow-assisted analysis of allergen-specific activated basophils and component-resolved diagnosis (CRD). This review focuses on component-resolved allergy diagnosis by microarray that has evolved from recent advances in molecular allergology and biochip technology. The technique allows a comprehensive analysis of individual sensitization profiles with multiplexed purified and recombinant allergens within a single run using only a minute amount of serum, providing information that largely exceeds the output from current sIgE capturing tools. Actually, multiplexing allows identification of diagnostic patterns that may facilitate the formulation of diagnostic algorithms. Although CRD by microarray sounds promising, the diagnostic performance requires further intensive assessment before it can enter mainstream application. In our opinion, the technique should currently be considered a complementary diagnostic tool rather than a first-line choice.

The role of immunoglobulin E-binding epitopes in the characterization of food allergy

PURPOSE OF REVIEW

Allergen-specific immunoglobulin E (IgE) antibodies play a central role in food allergic reactions. IgE epitope mapping of food allergens may provide information regarding patient's clinical history and contribute to food allergy diagnosis/prognosis. The goal of this article is to review recent developments in the methods for IgE epitope mapping and the role of IgE-binding epitopes in the characterization of food allergy.

RECENT FINDINGS

Recent studies have suggested a potential role for sequential IgE-binding epitopes as biomarkers for characterizing various phenotypes of food allergy. Studies of allergens in milk, peanut, egg and wheat have shown a correlation between IgE sequential epitope diversity and patients' allergy severity or persistence. Several informative epitopes in milk allergens have been identified as candidate biomarkers to predict the development of tolerance to milk. However, limitations with current methods of IgE-binding epitope identification need to be addressed before they can be applied in the diagnosis/prognosis of food allergy.

SUMMARY

IgE epitope mapping has the potential to become an additional tool for the diagnosis/prognosis of food allergy and lead to a better understanding of the pathogenesis and tolerance induction of food allergy.