Component-resolved diagnosis of wheat flour allergy in baker's asthma

EAACI Molecular Allergology User's Guide 2.0

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

Critical structural elements for the antigenicity of wheat allergen LTP1 (Tri a 14) revealed by site-directed mutagenesis

Lipid transfer proteins (LTPs) were identified as allergens in a large variety of pollens and foods, including cereals. LTPs belong to the prolamin superfamily and display an α-helical fold, with a bundle of four α-helices held together by four disulfide bonds. Wheat LTP1 is involved in allergic reactions to food. To identify critical structural elements of antibody binding to wheat LTP1, we used site-directed mutagenesis on wheat recombinant LTP1 to target: (i) sequence conservation and/or structure flexibility or (ii) each disulfide bond. We evaluated the modifications induced by these mutations on LTP1 secondary structure by synchrotron radiation circular dichroism and on its antigenicity with patient's sera and with mouse monoclonal antibodies. Disruption of the C28-C73 disulfide bond significantly affected IgE-binding and caused protein denaturation, while removing C13-C27 bond decreased LTP1 antigenicity and slightly modified LTP1 overall folding. In addition, we showed Lys72 to be a key residue; the K72A mutation did not affect global folding but modified the local 3D structure of LTP1 and strongly reduced IgE-binding. This work revealed a cluster of residues (C13, C27, C28, C73 and K72), four of which embedded in disulfide bonds, which play a critical role in LTP1 antigenicity.

Endotyping asthma related to three different work exposures

BACKGROUND

Work exposures play a significant role in adult-onset asthma, but mechanisms of work-related asthma are not fully elucidated.

OBJECTIVE

We aimed to reveal the molecular mechanisms of work-related asthma associated with flour (FA), isocyanate (IA) or welding fume (WA) exposures and identify potential biomarkers that distinguish these groups from each other.

METHODS

We used a combination of clinical tests, transcriptomic analysis and associated pathway analyses to investigate underlying disease mechanisms of the blood immune cells and the airway epithelium of 61 men.

RESULTS

Compared to the healthy controls, the WA patients had more differentially expressed genes than the FA and IA patients both in the airway epithelia and in the blood immune cells. In the airway epithelia, active inflammation was detected only in WA patients. In contrast, large number of differentially expressed genes were detected in all asthma groups in blood cells. Disease-related immune functions in blood cells were suppressed in all the asthma groups including leukocyte migration and inflammatory responses and decreased expression of upstream cytokines such as TNF and IFNγ. In transcriptome-phenotype correlations, hyperresponsiveness (R∼|0.6|) had the highest clinical relevance and associated with a set of exposure-group specific genes. Finally, biomarker subsets of only 5 genes specifically distinguished each of the asthma exposure group.

CONCLUSIONS

This study provides novel data on the molecular mechanisms underlying work-related asthma. We identified set of 5 promising biomarkers in asthma related to flour, isocyanate and welding exposure to be tested and clinically validated in future studies.

Performance of specific immunoglobulin E tests for diagnosing occupational asthma: a systematic review and meta-analysis

OBJECTIVES

To determine the test performance parameters for the retrievable range of high-molecular-weight (HMW) and low-molecular-weight (LMW) occupational allergens and to evaluate the impact of allergenic components and the implementation of measures for test validation.

METHODS

A protocol with predefined objectives and inclusion criteria was the basis of an electronic literature search of MEDLINE and EMBASE (time period 1967-2016). The specific inhalation challenge and serial peak flow measurements were the reference standards for the specific IgE (sIgE) test parameters. All of the review procedures were reported according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

RESULTS

Seventy-one studies were selected, and 62 entered meta-analysis. Pooled pairs analysis indicated a sensitivity of 0.74(95% CI 0.66 to 0.80) and specificity of 0.71(95% CI 0.63 to 0.77) for HMW allergens and a sensitivity of 0.28(95% CI 0.18 to 0.40) and specificity of 0.89(95% CI 0.77 to 0.95) for LMW allergens. Component-specific analysis improved the test parameters for some allergens. Test validation was handled heterogeneously among studies.

CONCLUSION

sIgE test performance is rather satisfactory for a wide range of HMW allergens with the potential for component-specific approaches, whereas sensitivity for LMW allergens is considerably lower, indicating methodological complications and/or divergent pathomechanisms. A common standard for test validation is needed.

Identification and molecular characterization of allergenic non-specific lipid-transfer protein from durum wheat (Triticum turgidum)

BACKGROUND

Common wheat (Triticum aestivum) and durum wheat (T. turgidum) are both involved in Baker's asthma (BA) and food allergy (FA) including wheat-dependent exercise-induced asthma (WDEIA). However, allergens in durum wheat have not been described, and the over-expression of T. turgidum non-specific lipid-transfer protein (nsLTPs) is considered to increase resistance to phytopathogens.

OBJECTIVE

To identify and assess the allergenicity of nsLTP from T. turgidum.

METHODS

Recombinant T. turgidum nsLTP Tri tu 14 was generated and tested for structural integrity (circular dichroism-spectroscopy) and purity (SDS-PAGE). Thirty-two wheat allergic patients were enrolled: 20 Spanish patients (BA) with positive bronchial challenge to wheat flour, and 12 Italian patients (wheat FA/WDEIA) with positive double-blind placebo-controlled food challenge/open food challenge (OFC) to pasta. IgE values to wheat, Tri tu 14, Tri a 14 (T. aestivum) and Pru p 3 (P. persica) were determined by ImmunoCAP testing. Allergenic potency (in vitro mediator release) and IgE cross-reactivity were investigated.

RESULTS

Tri tu 14 was found to share 49% and 52% amino acid identity with Tri a 14 and Pru p 3, respectively. Among 25 Tri a 14 CAP positive sera, 23 (92%) were reactive to wheat extract, 22 (88%) to Tri tu 14 and 20 (80%) to Pru p 3. The correlation between Tri a 14 and Tri tu 14 specific IgE levels was r = 0.97 (BA) and r = 0.93 (FA/WDEIA), respectively. FA/WDEIA patients showed higher specific IgE values to Tri tu 14 and Pru p 3 than BA patients. Tri tu 14 displayed allergenic activity by mediator release from effector cells and IgE cross-reactivity with Pru p 3. The degree of IgE cross-reactivity between the two wheat nsLTPs varied between individual patients.

CONCLUSIONS AND CLINICAL RELEVANCE

Sensitization to Tri tu 14 likely appears to be more important in wheat FA/WDEIA than in BA. Over-expression of Tri tu 14 in wheat would represent a risk for patients with nsLTP-mediated FA.

Component-resolved diagnosis in allergic disease: Utility and limitations

Component resolved diagnosis (CRD) is a microarray-based diagnostic solution capable of simultaneously analysing specific IgE antibodies against 112 allergenic components, providing sensitivity patterns for multi-sensitised or complex patients. The CRD is indicated for these patients, especially those with concomitant respiratory and food allergies. This study reivews the method, its utility, limitations, and our experience in allergic diseases with difficult etiologic diagnosis (eosinophilic esophagitis, occupational asthma and drug allergy).

Allergen component analysis as a tool in the diagnosis and management of occupational allergy

We are now in the epoch of "molecular allergology" and numerous clinically relevant allergenic molecules are available improving the performance of in vitro allergen tests and allergen detection methods. This review is focusing on characterized occupational allergens and their implementation into the in vitro diagnosis for occupational allergy and in allergen detection methods. More than 400 occupational agents are identified and documented as being 'respiratory sensitizers', but currently only a limited number of them are characterized on the molecular level and available for routine diagnosis as native or recombinant allergens. One exception, however, is natural rubber latex (NRL) from Hevea brasiliensis still remaining an important occupational allergen source. Characterization of 15 NRL allergens led to the development of assays for the determination of allergen content of NRL materials and the implementation of component-resolved diagnosis (CRD) for specific IgE antibody measurement. Microarray or singleplex using recombinant or native allergens are reliable tools for NRL allergy diagnosis. In addition, NRL allergy is an excellent model for improving extract-based specific IgE measurement by amplification of NRL extract preparation with stable recombinant major allergen rHev b 5. Despite the many efforts to characterize the occupationally relevant wheat allergens for baker's asthma, the most frequently occurring forms of occupational asthma, the results are highly diverse. Wheat sensitization profiles of bakers showed great interindividual variability and no wheat allergen could be classified as the major allergen. For diagnosis of baker's asthma, a whole wheat extract is still the best option for specific IgE determination. But single wheat allergens might help to discriminate between wheat-induced food allergy, grass pollen allergy and baker's asthma. For workplace-related allergens like coffee, wood, soybean, seafood and moulds allergens are characterized and few of them are available, but their relevance for occupational sensitization routes should be verified in the further studies.

Addressing Molecular Diagnosis of Occupational Allergies

PURPOSE OF REVIEW

Numerous clinically relevant allergenic molecules enhance the performance of specific (s) IgE tests and improve the specificity of allergy diagnosis. This review aimed to summarize our current knowledge of the high-molecular-weight allergens involved in the development of occupational asthma and rhinitis and to critically analyze the contribution of component-resolved diagnosis in the management of these conditions.

RECENT FINDINGS

There is a lack of standardization and validation for most available extracts of occupational agents, and assessment of sIgE reactivity to occupational allergen components has been poorly investigated, with the notable exception of natural rubber latex (NRL) and wheat flour. In the case of NRL, the application of recombinant single allergens and amplification of natural extracts with stable recombinant allergens improved the test sensitivity. IgE-sensitization profile in patients with baker's asthma showed great interindividual variation, and extract-based diagnostic is still recommended. For other occupational allergens, it remains necessary to evaluate the relevance of single allergen molecules for the sensitization induced by occupational exposure. Progress has been made to characterize occupational allergens especially NRL and wheat, although there is still an unmet need to increase the knowledge of occupational allergens, to include standardized tools into routine diagnostic, and to evaluate their usefulness in clinical practice.

Allergen component analysis as a tool in the diagnosis of occupational allergy

PURPOSE OF REVIEW

Rapid developments have been seen in molecular allergy diagnosis, based on the detection and quantification of specific IgE to single allergens. This review summarizes and discusses studies on allergen component analysis as a tool in the diagnosis of occupational allergy.

RECENT FINDINGS

More than 400 agents are identified as sensitizers of occupational asthma, but only very few are characterized on the molecular level and available for routine diagnosis. Baker's asthma is one of the most frequently occurring forms of occupational asthma caused by workplace-related inhalation of cereal flour mainly wheat. Wheat sensitization profiles of bakers show great interindividual variability and no wheat allergen could be classified as the major allergen. Component-resolved diagnosis is a useful tool for diagnosing natural rubber latex (NRL) allergy. In cases with unexpected high-latex IgE but without clinical symptoms application of crossreactive carbohydrate determinants are helpful to clarify the cause of IgE binding.

SUMMARY

Latex is an excellent model for component-resolved diagnosis and demonstrates well how to improve the diagnosis by using single allergens. For diagnosis of baker's asthma, a whole wheat extract is still the best option for specific IgE determination, but single wheat allergens might help to discriminate between wheat-induced food allergy, grass-pollen allergy, and baker's asthma. New diagnostic tools and platforms are promising, but further knowledge of molecules relevant for occupational asthma (as in wood dust allergens, enzymes, laboratory animal allergens, etc.) and for occupational hypersensitivity pneumonitis is necessary to improve and standardize the diagnostic tools.

Recent advances in component resolved diagnosis in food allergy

Due to the high prevalence of food allergic diseases globally there are increasing demands in clinical practice for managing IgE-mediated conditions. During the last decade, component resolved diagnostics has been introduced into the field of clinical allergology, providing information that cannot be obtained from extract-based tests. Component resolved data facilitate more precise diagnosis of allergic diseases and identify sensitizations attributable to cross-reactivity. Furthermore it assists risk assessment in clinical practice as sensitization to some allergenic molecules is related to persistence of clinical symptoms and systemic rather than local reactions. The information may also aid the clinician in prescription of oral immunotherapy (OIT) in patients with severe symptoms, and in giving advice on food allergen avoidance or on the need to perform food challenges. The use of allergen components is rapidly evolving and increases our possibility to treat food allergic patients with a more individual approach. Using molecular allergology, we can already now better diagnose, prognose and grade the food allergy. In summary, daily routine molecular allergy diagnostics offers a number of benefits that give us a higher diagnostic precision and allow for better management of the patient.

New developments in work-related asthma

INTRODUCTION

Work-related asthma includes two subtypes: occupational asthma or asthma caused by specific agents (sensitizers or irritants) in the workplace, and work-exacerbated asthma or pre-existing asthma worsened by workplace exposures. Areas covered: This review provides an update on the definitions and the clinical features of the different work-related asthma subtypes as well as new insights into their etiology and the pathophysiological mechanisms involved. The diagnosis of work-related asthma should be made on objective basis using a constellation of clinical, physiologic and allergologic tests. Specific inhalation challenge with the suspected occupational agent(s) remains as the reference standard for diagnosis. A literature search was performed using the following terms: work-related asthma, occupational asthma, work-exacerbated asthma, irritant-induced asthma and etiological agents. Expert commentary: Studies focusing on the biological effects and mechanisms of environmental exposures in the development of sensitizer-induced or irritant-induced asthma in various workplace settings are of greatest interest. An integrative approach that combines clinical parameters with component-resolved diagnosis as well as inflammatory biomarkers appears to be very promising. Occupational allergy provides a good opportunity to understand the complex relationships between exposure to allergens in the workplace, interaction with genes and the co-exposures to other factors in the working environment.

Clinical presentation, allergens, and management of wheat allergy

IgE-mediated allergy to wheat proteins can be caused by exposure through ingestion, inhalation, or skin/mucosal contact, and can affect various populations and age groups. Respiratory allergy to wheat proteins is commonly observed in adult patients occupationally exposed to flour, whereas wheat food allergy is more common in children. Wheat allergy is of growing importance for patients with recurrent anaphylaxis, especially when exercise related. The diagnosis of wheat allergy relies on a consistent clinical history, skin prick testing with well-characterized extracts and specific IgE tests. The accuracy of wheat allergy diagnosis may be improved by measuring IgE responses to several wheat components. However, a high degree of heterogeneity has been found in the recognition pattern of allergens among patient groups with different clinical profiles, as well as within each group. Thus, oral provocation with wheat or the implicated cereal is the reference test for the definitive diagnosis of ingested wheat/cereal allergy.

Common food allergens and their IgE-binding epitopes

Food allergy is an adverse immune response to certain kinds of food. Although any food can cause allergic reactions, chicken egg, cow's milk, wheat, shellfish, fruit, and buckwheat account for 75% of food allergies in Japan. Allergen-specific immunoglobulin E (IgE) antibodies play a pivotal role in the development of food allergy. Recent advances in molecular biological techniques have enabled the efficient analysis of food allergens. As a result, many food allergens have been identified, and their molecular structure and IgE-binding epitopes have also been identified. Studies of allergens have demonstrated that IgE antibodies specific to allergen components and/or the peptide epitopes are good indicators for the identification of patients with food allergy, prediction of clinical severity and development of tolerance. In this review, we summarize our current knowledge regarding the allergens and IgE epitopes in the well-researched allergies to chicken egg, cow's milk, wheat, shrimp, and peanut.

Advances in adult asthma diagnosis and treatment in 2014

In 2014, new biologic therapies are emerging for severe asthma based on identification of relevant phenotypes. The exploration of nutritional supplements to treat asthma has been less successful.

Component-resolved diagnosis of baker's allergy based on specific IgE to recombinant wheat flour proteins

BACKGROUND

Sensitization to wheat flour plays an important role in the development and diagnosis of baker's asthma.

OBJECTIVES

We evaluated wheat allergen components as sensitizers for bakers with work-related complaints, with consideration of cross-reactivity to grass pollen.

METHODS

Nineteen recombinant wheat flour proteins and 2 cross-reactive carbohydrate determinants were tested by using CAP-FEIA in sera of 101 bakers with wheat flour allergy (40 German, 37 Dutch, and 24 Spanish) and 29 pollen-sensitized control subjects with wheat-specific IgE but without occupational exposure. IgE binding to the single components was inhibited with wheat flour, rye flour, and grass pollen. The diagnostic efficiencies of IgE tests with single allergens and combinations were evaluated by assessing their ability to discriminate between patients with baker's allergy and control subjects based on receiver operating characteristic analyses.

RESULTS

Eighty percent of bakers had specific IgE levels of 0.35 kUA/L or greater and 91% had specific IgE levels of 0.1 kUA/L or greater to at least one of the 21 allergens. The highest frequencies of IgE binding were found for thiol reductase (Tri a 27) and the wheat dimeric α-amylase inhibitor 0.19 (Tri a 28). Cross-reactivity to grass pollen was proved for 9 components, and cross-reactivity to rye flour was proved for 18 components. A combination of IgE tests to 5 components, Tri a 27, Tri a 28, tetrameric α-amylase inhibitor CM2 (Tri a 29.02), serine protease inhibitor-like allergen (Tri a 39), and 1-cys-peroxiredoxin (Tri a 32), produced the maximal area under the curve (AUC = 0.84) in receiver operating characteristic analyses, but this was still lower than the AUC for wheat- or rye flour-specific IgE (AUC = 0.89 or 0.88, respectively).

CONCLUSIONS

Component-resolved diagnostics help to distinguish between sensitization caused by occupational flour exposure and wheat seropositivity based on cross-reactivity to grass pollen. For routine diagnosis of baker's allergy, however, allergen-specific IgE tests with whole wheat and rye flour extracts remain mandatory because of superior diagnostic sensitivity.

Optimizing the diagnosis of food allergy

Accurately diagnosing a patient with a possible food allergy is important to avoid unnecessary dietary restrictions and prevent life-threatening reactions. Routine testing modalities have limited accuracy, and an oral food challenge is often required to make a definitive diagnosis. Given that they are labor intensive and risk inducing an allergic reaction, several alternative diagnostic modalities have been investigated. Testing for IgE antibodies to particular protein components in foods has shown promise to improve diagnostics and has entered clinical practice. Additional modalities show potential, including epitope binding, T-cell studies, and basophil activation.