How Accurate and Safe Is the Diagnosis of Hazelnut Allergy by Means of Commercial Skin Prick Test Reagents?

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.

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.

Hazelnut Allergy

Background and Objectives: Hazelnuts are frequently involved in IgE-mediated reactions and represent the main culprit of nut allergy in Europe. The clinical presentation varies from mild symptoms limited to the oropharynx [oral allergy syndrome (OAS)], due to the cross-reaction with homologues in pollen allergens and more severe events caused by the primary sensitization to highly stable molecules contained in hazelnuts. The aim of this review is to summarize the most relevant concepts in the field of hazelnut allergy and to provide a practical approach useful in the clinical practice Materials and Methods: References were identified by PubMed searches dating from January 2000 up to November 2020 using the search terms: “component resolved diagnosis” and “Hazelnut allergy. Results: The storage proteins Cor a 9 and Cor a 14 resulted highly specific for primary hazelnut allergy and strongly associated with severe reactions, while the cross reactive Cor a 1, an homolog of the birch Bet v1, were related to OAS. Any cut-off has shown a specificity and sensitivity pattern as high as to replace the oral food challenge (OFC), which still remains the gold standard in the diagnosis of hazelnut allergy. To date there is still no definitive treatment. Hazelnut free-diet and treatment of symptoms with emergency management, including the prescription of auto-injective epinephrine, still represent the main approach. Oral allergen immunotherapy (AIT) appears a promising therapeutic strategy and the definition of individual clinical threshold would be useful for sensitized individuals, caregivers, and physicians to reduce social limitation, anxiety, and better manage food allergy. Conclusions: An accurate diagnostic work-up including clinical history, in vivo and in vitro test including component resolved diagnosis and OFC are essential to confirm the diagnosis, to assess the risk of a severe reaction, and to prescribe an adequate diet and treatment.

Development of a protein microarray-based diagnostic chip mimicking the skin prick test for allergy diagnosis

Protein microarrays have been successfully used for detection of allergen-specific IgE in patient sera. Here, we demonstrate proof-of-concept of a solid-phase technique coupling the high-throughput potential of protein microarrays with the biologically relevant readout provided by IgE reporter cells, creating a novel allergic sensitization detection system. Three proteins (κ-casein, timothy grass pollen extract, polyclonal anti-human IgE) were printed onto three different polymer-coated surfaces (aldehyde-, epoxy- and NHS ester-coated). ToF-SIMs analysis was performed to assess printed protein stability and retention during washing steps. NFAT-DsRed rat basophil leukemia cell attachment and retention during washing steps was assessed after treatment with various extracellular matrix proteins. NFAT-DsRed IgE reporter cells were sensitized with serum of an allergic donor, incubated on the printed slides, and cell activation determined using a microarray laser scanner. NFAT DsRed IgE reporter cell binding was significantly increased on all polymer surfaces after incubation with fibronectin and vitronectin, but not collagen or laminin. All surfaces supported printed protein stability during washing procedure, with epoxy- and NHS ester-coated surfaces showing best protein retention. Cell activation was significantly higher in NHS ester-coated slides after timothy grass pollen extract stimulation appearing a suitable substrate for further development of an automated allergy diagnosis system.

Component-Resolved Diagnosis in Allergic Rhinitis and Asthma

BACKGROUND

Allergic rhinitis and asthma are highly prevalent chronic inflammatory diseases leading to restrictions in the patient's quality of life and high costs for healthcare systems. Both diseases are associated with the presence of specific IgE (sIgE) against aeroallergens. This review aims to examine the importance of molecular allergy diagnostics in the assessment and management of these disorders.

CONTENT

The "U-shaped" approach, proposed by the European Academy of Allergy and Clinical Immunology, combines conventional allergy diagnostics with the benefits of component-resolved diagnosis (CRD) and offers important additional information regarding the patient's sensitization pattern, especially in complex clinical cases such as polysensitization or idiopathic reactions, thus avoiding overuse of in vitro and in vivo IgE diagnostics. CRD may help the clinician to identify the cause of an allergy and, in the case of complex polysensitization, uncover possible cross-reactivity. Polysensitization, especially to inhalant allergens, is associated with the clinical appearance of asthma and allergic rhinitis; important risk factors for the latter are the major allergens Fel d 1 and Can f 1. Importantly, information on molecular sensitization patterns significantly influences the choice of specific immunotherapy and reduces its overprescription.

CONCLUSION

At present, allergy diagnostics largely rely on clinical history, physical examination, and in vivo IgE testing. However, in vitro diagnostics including CRD are currently finding their way into the clinical routine and can offer additional information on the patient's sensitization profile and treatment responsiveness.

Allergen Extracts for In Vivo Diagnosis and Treatment of Allergy: Is There a Future?

Today, in vivo allergy diagnosis and allergen-specific immunotherapy (AIT) are still based on allergen extracts obtained from natural allergen sources. Several studies analyzing the composition of natural allergen extracts have shown severe problems regarding their quality such as the presence of undefined nonallergenic materials, contaminants as well as high variabilities regarding contents and biological activity of individual allergens. Despite the increasing availability of sophisticated analytical technologies, these problems cannot be overcome because they are inherent to allergen sources and methods of extract production. For in vitro allergy diagnosis problems related to natural allergen extracts have been largely overcome by the implementation of recombinant allergen molecules that are defined regarding purity and biological activity. However, no such advances have been made for allergen preparations to be used in vivo for diagnosis and therapy. No clinical studies have been performed for allergen extracts available for in vivo allergy diagnosis that document safety, sensitivity, and specificity of the products. Only for very few therapeutic allergen extracts state-of-the-art clinical studies have been performed that provide evidence for safety and efficacy. In this article, we discuss problems related to the inconsistent quality of products based on natural allergen extracts and share our observations that most of the products available for in vivo diagnosis and AIT do not meet the international standards for medicinal products. We argue that a replacement of natural allergen extracts by defined recombinantly produced allergen molecules and/or mixtures thereof may be the only way to guarantee the supply of clinicians with state-of-the-art medicinal products for in vivo diagnosis and treatment of allergic patients in the future.

Tree nut allergens

Tree nuts are considered as part of a healthy diet due to their high nutritional quality. However, they are also a potent source of allergenic proteins inducing IgE mediated hypersensitivity often causing serious, life-threatening reactions. The reported prevalence of tree nut allergy is up to 4.9% worldwide. The general term "tree nuts" comprises a number of nuts, seeds, and drupes, derived from trees from different botanical families. For hazelnut and walnut several allergens have been identified which are already partly applied in component resolved diagnosis, while for other tree nuts such as macadamia, coconut, and Brazil nut only individual allergens were identified and data on additional allergenic proteins are missing. This review summarizes the current knowledge on tree nut allergens and describes their physicochemical and immunological characterization and clinical relevance.

NUT Co Reactivity - ACquiring Knowledge for Elimination Recommendations (NUT CRACKER) study

BACKGROUND

Ambiguities exist regarding the diagnosis of tree-nut allergy, necessitating either their elimination or the performance of oral food challenges (OFCs).

OBJECTIVE

To examine the coincidences of allergies among tree-nuts and improve diagnostic testing to minimize the need for OFC.

METHODS

Eighty-three patients prospectively evaluated for walnut, pecan, cashew, pistachio, hazelnut, and almond allergy. A history of previous reactions was obtained, and standardized skin prick tests (SPTs) using finely ground tree-nut solution and basophil activation tests (BAT) were performed. Patients underwent OFC for each tree-nut they eliminated and to which a reaction in the previous 2 years was not documented.

RESULTS

While most patients were sensitized to 5-6 tree-nuts, over 50% were allergic to only 1-2 tree-nuts. The highest rate of allergy in sensitized patients was observed for walnut (74.6%) and cashew (65.6%). The rate of co-allergy for most tree-nuts was <30%. Two-thirds of walnut- and cashew-allergic patients were also allergic to pecan and pistachio, respectively, while all pecan- and pistachio-allergic patients were allergic to walnut and cashew, respectively. Receiver-operating characteristic analysis for SPT and BAT was tree-nut dependent and yielded area under the curve (AUC) values ranging from 0.75 to 0.94. Knowledge of coincident allergies in these pairs along with the combination of SPT and BAT correctly distinguished allergic from tolerant patients for walnut (87%), pecan (66%), cashew (71%), and pistachio (79%).

CONCLUSION

The data presented here should assist in differentiating between allergic and tolerant patients, decrease the need for OFC, and allow for appropriate elimination recommendations.

The Lancet Weight Determines Wheal Diameter in Response to Skin Prick Testing with Histamine

BACKGROUND

Skin prick test (SPT) is a common test for diagnosing immunoglobulin E-mediated allergies. In clinical routine, technicalities, human errors or patient-related biases, occasionally results in suboptimal diagnosis of sensitization.

OBJECTIVE

Although not previously assessed qualitatively, lancet weight is hypothesized to be important when performing SPT to minimize the frequency of false positives, false negatives, and unwanted discomfort.

METHODS

Accurate weight-controlled SPT was performed on the volar forearms and backs of 20 healthy subjects. Four predetermined lancet weights were applied (25 g, 85 g, 135 g and 265 g) using two positive control histamine solutions (1 mg/mL and 10 mg/mL) and one negative control (saline). A total of 400 SPTs were conducted. The outcome parameters were: wheal size, neurogenic inflammation (measured by superficial blood perfusion), frequency of bleeding, and the lancet provoked pain response.

RESULTS

The mean wheal diameter increased significantly as higher weights were applied to the SPT lancet, e.g. from 3.2 ± 0.28 mm at 25 g to 5.4 ± 1.7 mm at 265 g (p<0.01). Similarly, the frequency of bleeding, the provoked pain, and the neurogenic inflammatory response increased significantly. At 265 g saline evoked two wheal responses (/160 pricks) below 3 mm.

CONCLUSION AND CLINICAL RELEVANCE

The applied weight of the lancet during the SPT-procedure is an important factor. Higher lancet weights precipitate significantly larger wheal reactions with potential diagnostic implications. This warrants additional research of the optimal lancet weight in relation to SPT-guidelines to improve the specificity and sensitivity of the procedure.

EAACI Molecular Allergology User's Guide

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

Position paper of the EAACI: food allergy due to immunological cross-reactions with common inhalant allergens

In older children, adolescents, and adults, a substantial part of all IgE-mediated food allergies is caused by cross-reacting allergenic structures shared by inhalants and foods. IgE stimulated by a cross-reactive inhalant allergen can result in diverse patterns of allergic reactions to various foods. Local, mild, or severe systemic reactions may occur already after the first consumption of a food containing a cross-reactive allergen. In clinical practice, clinically relevant sensitizations are elucidated by skin prick testing or by the determination of specific IgE in vitro. Component-resolved diagnosis may help to reach a diagnosis and may predict the risk of a systemic reaction. Allergy needs to be confirmed in cases of unclear history by oral challenge tests. The therapeutic potential of allergen immunotherapy with inhalant allergens in pollen-related food allergy is not clear, and more placebo-controlled studies are needed. As we are facing an increasing incidence of pollen allergies, a shift in sensitization patterns and changes in nutritional habits, and the occurrence of new, so far unknown allergies due to cross-reactions are expected.

Molecular approach to allergy diagnosis and therapy

Presently, allergy diagnosis and therapy procedures are undergoing a transition phase in which allergen extracts are being step-by-step replaced by molecule-based products. The new developments will allow clinicians to obtain detailed information on sensitization patterns, more accurate interpretation of allergic symptoms, and thus improved patients' management. In this respect, recombinant technology has been applied to develop this new generation of molecule-based allergy products. The use of recombinant allergens allows full validation of identity, quantity, homogeneity, structure, aggregation, solubility, stability, IgE-binding and the biologic potency of the products. In contrast, such parameters are extremely difficult to assay and standardize for extract-based products. In addition to the possibility of bulk production of wild type molecules for diagnostic purposes, recombinant technology opened the possibility of developing safer and more efficacious products for allergy therapy. A number of molecule-based hypoallergenic preparations have already been successfully evaluated in clinical trials, bringing forward the next generation of allergy vaccines. In this contribution, we review the latest developments in allergen characterization, molecule-based allergy diagnosis, and the application of recombinant allergens in therapeutic setups. A comprehensive overview of clinical trials using recombinant allergens as well as synthetic peptides is presented.

Oil body-associated hazelnut allergens including oleosins are underrepresented in diagnostic extracts but associated with severe symptoms

BACKGROUND

Oil body-associated allergens such as oleosins have been reported for important allergenic foods such as peanut, sesame and hazelnut. Here we investigate whether oil body associated proteins (OAPs) are linked with specific clinical phenotypes and whether they are represented in skin prick test (SPT) reagents.

METHODS

A hazelnut OAP fraction was characterized by mass-spectrometry (MS) to identify its major constituents. Polyclonal rabbit antibodies were generated against hazelnut OAPs. The presence of OAPs in commercially available hazelnut SPTs was studied by immunoblot and spiking experiments. OAP-specific IgE antibodies were measured in sera from patients with a convincing history of hazelnut allergy by RAST (n = 91), immunoblot (n = 22) and basophil histamine release (BHR; n = 14).

RESULTS

Hazelnut OAPs were analysed by MS and found to be dominated by oleosins at ~14 and ~17 kDa, and a 27 kDa band containing oleosin dimers and unidentified protein. In 36/91 sera specific IgE against hazelnut OAPs was detected, and confirmed to be biologically active by BHR (n = 14). The majority (21/22) recognized the oleosin bands at 17 kDa on immunoblot, of which 11 exclusively. These OAP-specific IgE responses dominated by oleosin were associated with systemic reactions to hazelnut (OR 4.24; p = 0.015) and negative SPT (χ2 6.3, p = 0.012). Immunoblot analysis using OAP-specific rabbit antiserum demonstrated that commercial SPT reagents are virtually devoid of OAPs, sometimes (3/9) resulting in false-negative SPT. Spiking of SPT reagents with OAP restored serum IgE binding of these false-negative patients on immunoblot at mainly 17 kDa.

CONCLUSION

Hazelnut allergens found in oil bodies dominated by oleosin are associated with more severe systemic reactions and negative SPT. Defatted diagnostic extracts are virtually devoid of these allergens, resulting in poor sensitivity for detection of IgE antibodies against these clinically relevant molecules.

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.

Colonoscopic allergen provocation test with rBet v 1 in patients with pollen-associated food allergy

BACKGROUND

After consumption of fruits, nuts, and vegetables, several patients with pollen allergy experience gastrointestinal (GI) tract symptoms that are possibly caused by pollen-associated food allergy. The aim of this study was to evaluate the colonoscopic allergen provocation (COLAP) test using the recombinant birch pollen allergen Bet v 1 (rBet v 1) for in vivo diagnosis of pollen-associated food allergy manifesting in the GI tract.

METHODS

Thirty-four patients with a history of adverse reactions to food, GI tract symptoms, and birch pollen pollinosis and five healthy controls underwent COLAP test. Twenty minutes after endoscopic challenge of the cecal mucosa with rBet v 1, the mucosal wheal and flare reaction was registered semiquantitatively, and tissue biopsy specimens were examined for eosinophil mucosal activation.

RESULTS

The mucosal reaction to rBet v 1 was correlated with the presence of pollinosis (P = 0.004), history of adverse reaction to Bet v 1-associated food allergens (P = 0.001), and tissue eosinophils' activation (P < 0.001). A wheal and flare reaction in the COLAP test was observed in 13 of 16 patients (81%) with a history of GI tract symptoms associated with the ingestion of Bet v 1-related foods and in four of 18 (22%) patients with a negative history (P < 0.001). The control group did not develop visible mucosal reactions to rBet v 1. Systemic anaphylactic reactions did not occur.

CONCLUSIONS

The mucosal administration of rBet v 1 by COLAP test provides a new diagnostic tool that might support the diagnosis of Bet v 1-associated food allergy manifesting in the GI tract.

Lentil (Lens culinaris) lipid transfer protein Len c 3: a novel legume allergen

BACKGROUND

Lentils are increasingly consumed in many parts of the world.Two allergens, Len c 1 and 2, have been reported previously. Recently, peanut and green bean lipid transfer proteins (LTPs) have been identified as the first two members of an important group of allergens that might be associated with severe food allergies.

OBJECTIVE

To investigate lentil LTP as a potential new allergen.

METHODS

Efficacy of LTP extraction was monitored at different acidic pH values, using immunoblotting with cross-reactive anti-peach LTP antiserum. Natural LTP was purified from lentil extract and expressed as recombinant allergen in Escherichia coli. Sera from 10 lentil-allergic and/or -sensitized patients (Spain: 6, Italy: 1 and the Netherlands: 3) were used to further characterize lentil LTP.

RESULTS

Natural lentil LTP, purified from the homogenized germinated seeds and optimally extracted at pH 3, was identified and designated as allergen Len c 3. By CAP, 9/10 sera showed specific IgE to Len c 3. Recombinant (r) Len c 3 was successfully purified. The natural (n) Len c 3 CAP was completely inhibited by rLen c 3/rPru p 3. IgE binding to lentil pH 3 extract blot was completely inhibited by rLen c 3.

CONCLUSION

The availability of immunochemically active nLen/rLen c 3 as a novel legume allergen facilitates further development and implementation of a third (next to peanut and green bean) legume LTP in component-resolved diagnosis strategies and contributes to evaluate the clinical importance of legume LTPs. Preferential extraction of Len c 3 (pH 3) will affect the production of sensitive extract-based diagnostic tests.

Generation and characterization of anti-chitinase monoclonal antibodies

Class IV chitinase, an allergenic protein of Vitis vinifera (grape), was purified by anion exchange chromatography and used for immunization of Balb/c mice. Monoclonal antibodies (MAbs) were raised by hybridoma technology using Sp2/0 myeloma cells. Finally after three limiting dilutions, six stable clones were generated. Antibody isotyping showed that IgG(2a), IgG(2b), and IgM were produced by one, two, and three of the clones, respectively. All of the MAbs had kappa light chain. The affinities were in the range of 3 × 10(8) to 1.2 × 10(9) M(-1). The MAbs were specific for grape chitinase as confirmed by Western blotting. In conclusion, we successfully produced several MAbs against grape class IV chitinase, which could be used for assessment of this allergen in different grape cultivars.

Microarrayed allergen molecules for the diagnosis of allergic diseases

IgE-mediated allergic diseases are among the most prevalent diseases worldwide. The use of extracts in the skin test and the additional use of IgE testing still represent the current basis for the diagnostic work-up. During the past 30 years, knowledge of the molecular structure of allergens has increased dramatically, and the characterization and production of allergenic molecules, as natural purified compounds or recombinant products, is allowing us to approach the allergy diagnostic work-up differently. Much of this is based on the adoption of microtechnology since the first release of a biochip for IgE detection. Its use has prompted the development of new concepts linked to the diagnosis of allergic diseases. This review describes the background of allergy diagnosis and the tools currently used for specific IgE detection. It gives insight into the most recent advancement in the field of biotechnology leading to allergenic molecule availability, microtechnology leading to the routine use of protein biochips for IgE detection, and how they should be combined with information technology.

A search for biomarkers as diagnostic tools for food allergy: a pilot study in peanut-allergic patients

BACKGROUND

The impact of peanut allergy is large and accidental ingestion of peanut can lead to severe reactions. Currently used diagnostic tests, such as skin prick tests (SPT) and determination of specific immunoglobulins (IgE) have, however, limited sensitivity and specificity. Therefore, new tools have to be developed to improve the accuracy of the diagnostic work-up of food-allergic patients. Comprehensive metabolite analysis may provide biomarkers for diagnosing food allergy as metabolite levels reflect actual physiological conditions. We investigated whether metabolites can be found that discriminate between peanut-allergic patients and non-peanut-allergic subjects. Such metabolites may be used for future diagnostic purposes.

METHODS

Plasma and saliva samples were obtained from 23 participants (12 peanut allergic and 11 peanut tolerant) prior to and after a peanut challenge and measured with (1)H nuclear magnetic resonance (NMR) spectroscopy with subsequent multivariate data analysis.

RESULTS

Clear differences were observed between NMR spectra of peanut-allergic and peanut-tolerant subjects in plasma as well as saliva. Allergic patients already showed aberrant metabolite levels prior to peanut ingestion, thus before the onset of allergic reactions.

CONCLUSION

This pilot study shows that aberrant metabolite levels as determined by NMR in combination with multivariate statistics may serve as novel biomarkers for food allergy.

Microarrays: molecular allergology and nanotechnology for personalised medicine (I)

The diagnosis of antibody-mediated allergic disorders is based on the clinical findings and the detection of allergen-specific IgE based on in vitro and in vivo techniques, together with allergen provocation tests. In vitro diagnostic techniques have progressed enormously following the introduction of the advances made in proteomics and nanotechnology--offering tools for the diagnosis and investigation of allergy at molecular level. The most advanced developments are the microarray techniques, which in genomics allowed rapid description of the human genetic code, and which now have been applied to proteomics, broadening the field for research and clinical use. Together with these technological advances, the characterisation of most of the different proteins generating specific IgE and which conform each natural allergen, as well as their purification or genetic engineering-based synthesis, have been crucial elements--offering the possibility of identifying disease-causing allergens at molecular level, establishing a component-resolved diagnosis (CRD), using them to study the natural course of the disease, and applying them to improvements in specific immunotherapy. Microarrays of allergic components offer results relating to hundreds of these allergenic components in a single test, and use a small amount of serum that can be obtained from capillary blood. The availability of new molecules will allow the development of panels including new allergenic components and sources, which will require evaluation for clinical use. The present study reviews these new developments, component-resolved diagnosis, and the development of microarray techniques as a critical element for furthering our knowledge of allergic disease.

The influence of recombinant production on the immunologic behavior of birch pollen isoallergens

BACKGROUND

Allergic reactions towards the birch major pollen allergen Bet v 1 are among the most common causes of spring pollinosis in the temperate climate zone of the Northern hemisphere. Natural Bet v 1 is composed of a complex mixture of different isoforms. Detailed analysis of recombinant Bet v 1 isoforms revealed striking differences in immunologic as well as allergenic properties of the molecules, leading to a classification of Bet v 1 isoforms into high, medium, and low IgE binding proteins. Especially low IgE binding Bet v 1 isoforms have been described as ideal candidates for desensitizing allergic patients with allergen specific immunotherapy (SIT). Since diagnosis and therapy of allergic diseases are highly dependent on recombinant proteins, continuous improvement of protein production is an absolute necessity.

METHODOLOGY

Therefore, two different methods for recombinant production of a low IgE binding Bet v 1 isoform were applied; one based on published protocols, the other by implementing latest innovations in protein production. Both batches of Bet v 1.0401 were extensively characterized by an array of physicochemical as well as immunological methods to compare protein primary structure, purity, quantity, folding, aggregation state, thermal stability, and antibody binding capacity.

CONCLUSION

The experiments demonstrated that IgE antibody binding properties of recombinant isoallergens can be significantly influenced by the production method directly affecting possible clinical applications of the molecules.

Molecular allergology approach to allergic diseases in the paediatric age

Identification, characterization, and purification of allergens are essential for the structural and immunologic studies needed to understand how these molecules induce specific IgE antibody production by the human immune system. Advances in molecular biology techniques have led to the production of recombinant allergens having constant properties, allowing detection of specific IgE directed against different molecular components of an allergenic source. Presence of homologous allergens in different sources is the reason for cross-reaction. Molecule-based diagnostic tools can lead to better interpretation of poly-sensitizations, observed by ST and in vitro tests using allergenic extracts as they were made before. Some examples IgE sensitization to major genuine allergens and panallergens will be presented.

Molecular composition and biological activity of commercial birch pollen allergen extracts

BACKGROUND

Commercial extracts used for diagnosis and treatment of allergy are currently prepared from natural allergen sources. The aim of this study was to analyse birch pollen allergen extracts produced for in vivo diagnosis of birch pollen allergy regarding their contents of individual birch pollen allergens (Bet v 1, Bet v 2 and Bet v 4).

METHODS

Protein contents were measured and the allergen composition was analysed by immunoblotting using antibody probes specific for Bet v 1, Bet v 2 and Bet v 4 in birch pollen extracts from five manufacturers of allergen extracts. The contents of the major birch pollen allergen, Bet v 1, were quantified with a specific two-site binding enzyme-linked immunosorbent assay with nanogram sensitivity for Bet v 1. The biological activities of the allergen extracts were evaluated by skin prick testing in birch pollen allergic patients and compared with their sensitization profiles.

RESULTS

A more than 10-fold variation regarding total protein contents (23.1-314 microg mL(-1)) and also regarding the amounts of the major birch pollen allergen, Bet v 1 (1.62-19.6 microg mL(-1)) was found. The highly cross-reactive Bet v 4 allergen was absent in three of the five tested extracts. Furthermore, varying skin test results were obtained in birch pollen allergic patients with the allergen extracts.

CONCLUSIONS

Commercial birch pollen extracts exhibit a considerable variability regarding allergen contents and hence deliver varying in vivo test results. These problems might be overcome with recombinant allergen-based preparations.

Component-resolved in vitro diagnosis of hazelnut allergy in Europe

BACKGROUND

Food allergy to hazelnut occurs both with and without concomitant pollen allergy.

OBJECTIVE

We sought to evaluate a panel of hazelnut allergens for diagnosis of hazelnut allergy in Spain, Switzerland, and Denmark.

METHODS

Fifty-two patients with a positive double-blind, placebo-controlled food challenge result with hazelnuts; 5 patients with a history of anaphylaxis; 62 patients with pollen allergy but hazelnut tolerance; and 63 nonatopic control subjects were included. Serum IgE levels to hazelnut extract, recombinant hazelnut allergens (rCor a 1.04, rCor a 2, rCor a 8, rCor a 11), and native allergens (nCor a 9, nCor a Bd8K, nCor a Bd11K) were analyzed by means of ImmunoCAP.

RESULTS

Among patients with hazelnut allergy, 91% (Switzerland/Spain, 100%; Denmark, 75%) had IgE to hazelnut extract, 75% to rCor a 1.04, 42% to rCor a 2, 28% to rCor a 8, and 2% to rCor a 11. The highest rate of sensitization to Cor a 1.04 was found in the northern regions (Switzerland/Denmark, 100%; Spain, 18%), whereas IgE to the lipid transfer protein rCor a 8 prevailed in Spain (Spain, 71%; Switzerland, 15%; Denmark, 5%). IgE to profilin rCor a 2 was equally distributed (40% to 45%). Among control subjects with pollen allergy, 61% had IgE to hazelnut extract, 69% to rCor a 1.04, 34% to rCor a 2, 10% to rCor a 8, and 6% to rCor a 11.

CONCLUSION

Component-resolved in vitro analyses revealed substantial differences in IgE profiles of hazelnut allergic and hazelnut tolerant patients across Europe.

Array-based profiling of ragweed and mugwort pollen allergens

BACKGROUND

Ragweed (Ambrosia artemisiifolia) and mugwort (Artemisia vulgaris) pollen is the main cause of allergic reactions in late summer and autumn. The differential diagnosis between ragweed and mugwort pollen allergy is a frequent problem encountered by allergologists in areas where both plants are present due to shared antigenic structures and overlapping flowering seasons.

OBJECTIVE

To evaluate the sensitization pattern of weed allergic patients towards a large panel of purified allergens in the microarray format and by enzyme-linked immunosorbent assay (ELISA).

METHODS

Eight ragweed and six mugwort pollen allergens were purified from natural source or expressed as recombinant proteins in Escherichia coli. Allergens were spotted on protein microarray slides or coated onto ELISA plates. Sera from 19 ragweed and/or mugwort allergic individuals were used to determine the reactivity towards single molecules in both assays.

RESULTS

All ragweed allergic individuals were sensitized to Amb a 1, among them 30% were monosensitized to the major ragweed allergen. Art v 1 and Art v 3 were recognized by 89% of mugwort pollen-allergic patients. Extensive cross-reactivity was observed for both patient groups mainly involving the pan-allergens profilin and nonspecific lipid transfer proteins. Comparable IgE profiles were obtained with both allergen microarray and ELISA methods.

CONCLUSIONS

Molecule-based diagnosis provides essential information for the differential diagnosis between ragweed and mugwort pollen allergy and for the selection of the appropriate allergen source for specific immunotherapy.

Purification and characterization of natural Ara h 8, the Bet v 1 homologous allergen from peanut, provides a novel isoform

The peanut allergen Ara h 8 is an important allergen for birch pollen allergic patients because of the cross-reactivity to the homologous Bet v 1. As the existence of Ara h 8 has been shown at the cDNA level so far (AY328088) and the allergen has indirectly been detected as natural protein, it was the aim of our study to identify natural Ara h 8 in peanut extract and to develop a purification strategy. This was achieved using a unique combination of purification steps, including optimized extraction conditions, size exclusion and ion exchange chromatography and treatment of the interfering contaminants with iodoacetic acid. A characterization of the protein by microsequencing showed discrepancies to the deduced amino acid sequence of AY328088. For this reason, we cloned and expressed a new Ara h 8 isoform from cDNA (EU046325). This IgE-reactive protein corresponds to the results of microsequencing, ESI-FTICR-MS and trypsin fingerprinting analysis of the authentic and purified nAra h 8. Apart from the ultimate use of recombinant allergens for diagnostic procedures, there is also a scientific need for the natural counterpart, as it represents an excellent reference point by which to compare protein characteristics and to standardize diagnostic and therapeutic allergens.

Hazelnut allergy: from pollen-associated mild allergy to severe anaphylactic reactions

PURPOSE OF REVIEW

Hazelnut allergy can vary between mild oral symptoms and potentially dangerous anaphylaxis. There is a need to predict which subjects are at risk for severe reactions. In this study, possibilities for 'component-resolved diagnosis', based on sensitization to different allergens in hazelnut, are discussed.

RECENT FINDINGS

One type of hazelnut allergy can be associated with sensitization to homologues of pollen allergens, predominantly birch, in hazelnut: Cor a 1 (Bet v 1) and Cor a 2 (profilin). These allergens account for relatively mild symptoms. However, subjects can also be sensitized to several other allergens in hazelnut that are related to more severe symptoms. These allergens are homologues of allergens in other nuts and peanut: Cor a 8 (lipid transfer protein) and Cor a 9 (11S globulin) and perhaps Cor a 11 (7S globulin). The clinical relevance of these and other potential hazelnut allergens has to be further defined. The diagnosis of hazelnut has to be confirmed by oral double-blind placebo-controlled food challenge.

SUMMARY

Sensitization to hazelnut can either be associated with mild oral symptoms, depending on sensitization to pollen, or with more serious allergic symptoms, related to sensitization to homologues of nut and peanut allergens.

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

This article aims to critically review developments in food allergy diagnostics with regard to the verification of specific IgE antibodies and the identification of the responsible allergens. Results of IgE-binding tests with food extracts are hampered by cross-reactive proteins, low-quality test agents, or both. Specificity can be increased by defining adequate cutoff values, whereas sensitivity can be improved by using high-quality test agents. IgE-binding tests with purified allergens enabled reliable quantification of allergen-specific IgE titers, with higher levels found in individuals with food allergy compared with individuals without food allergy. However, the overlap in individual test reactivity between allergic and nonallergic subjects complicates interpretation. Recombinant allergens and synthetic sequential epitopes enabled detection of sensitization profiles, with IgE specific to several allergens and substructures now being suggested as markers of severity, persistence, or both. However, high-power quantitative studies with larger numbers of patients are required to confirm these markers. IgE-binding tests merely indicate sensitization, whereas the final proof of clinical relevance still relies on family/case history, physical examinations, and provocation tests. Novel technologies promise superior diagnostics. Microarray technology permits simultaneous measurement of multiple IgE reactivities regarding specificity, abundance, reactivity, or interaction. Improved functional tests might enable reliable estimation of the clinical relevance of IgE sensitizations at justifiable expenses.

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.

Optimized techniques for the extraction of grape allergens appropriate for in vivo and in vitro testing and diagnosis

Standardized allergen extracts are needed for diagnosis and therapy purposes. For grapes, standardization is hampered by low protein and high tannin and pectin concentrations. The aim of the current study was to develop an optimized method for the extraction of grape proteins and possibly extend this to other fruits. Several existing or modified extraction methods were compared by means of protein concentration determination, SDS-PAGE, immunoblotting and radioallergosorbent test (RAST). An optimized extraction protocol was obtained in which we combined a high concentration of plant tissue, a concentrated, enriched and neutral buffer able to remove sugars and keep proteins soluble and a bivalent buffer for pectin removal. Both the quantitative (protein concentration) and qualitative parameters (SDS-PAGE protein patterns and IgE reactivity) were compared to standard protocols and commercial extracts used as diagnostic tools in the clinical practice. This method proved to be the most efficient mainly compared to the standard Björksten protocol in extracting the low molecular weight proteins, including the major grape allergen (lipid transfer protein, Vit v 1). It proved to be an easy, low cost and reproducible method proposed to prepare grape extracts that could replace the commercially available ones, used for diagnosis and possibly extend the method to other fruits especially in extracting LTPs.

Mediator release assays based on human or murine immunoglobulin E in allergen standardization

BACKGROUND

The biological potency of allergens can be measured by provoking mediator release from effector cells. As established immunochemical methods in allergen standardization only determine inhibition potency or major allergen content, routine tests for biological potency may enhance standardization and batch control of allergen products.

OBJECTIVE

The general performance and application potential of biological in vitro assays in batch control and standardization of allergens and as a tool for verifying activity and stability of allergen standards were analysed.

METHODS

Allergen extracts of five clinically relevant allergens from three to five different manufacturers were investigated. A CAP-IgE-inhibition assay was compared with mediator release assay (MRA)s based on murine or human basophils. Rat basophilic leukaemia (RBL) cells were passively sensitized with pooled murine allergen-specific IgE-containing sera. Humanized RBL cells and human-stripped basophils were sensitized with pooled patient's sera, which were also used for the CAP-IgE-inhibition assay. Allergen specificity of the sera was determined by immunoblotting.

RESULTS

A good batch-to-batch consistency was found with each assay among all manufacturers and allergens tested. Between different manufacturers, the products showed differences in activity and the various assays indicated an almost identical ranking. However, the biological assays revealed qualitative differences of biological activity or composition of allergen preparations undetectable by IgE-inhibition assay.

CONCLUSIONS

MRAs provide refined information on allergen activity, either confirming the results of IgE-inhibition assay, or indicating differences requiring further investigation, and represent a highly sensitive novel tool in allergen standardization. By using permanently cultivated cell lines, repeated venepuncture to obtain human basophils is avoided. As in the RBL assay, the coefficient of variation for the release values were below 15% and for the ED50 below 25%, the assay is suitable to determine differences that are relevant for batch control purposes.

Allergen-specific IgE testing in the diagnosis of food allergy and the event of a positive match in the bioinformatics search

Current documents on risk assessment of genetically modified foods recommend including IgE-binding tests on sera from allergic patients. However, there is no generally accepted recommendation on technical aspects of the testing procedures or on the interpretation of the results, despite that fact that both false positive and false-negative results may be caused by variability of the test procedures. The present article discusses the state-of-the-art of serological test procedures for qualitative and quantitative determination of specific IgE and interpretation of test results. It is emphasized that the use of sera from clinically well-characterized subjects is of high importance. In the case of a positive test result, the biological activity of the detected IgE antibodies, i. e., the potential to trigger mediator release from basophils or mast cells in an allergen-specific manner, should be taken into account. However, present data also indicate that validation of such mediator release tests is required, both in terms of experimental protocols and with respect to correlation of the test results with the clinical situation. Further studies are also required to prove the usefulness of targeted serum screening, i. e., the testing of gene products from organisms not known to be allergenic with sera from subjects allergic to related species.

Cloning of oleosin, a putative new hazelnut allergen, using a hazelnut cDNA library

The clinical presentation of non-pollen related allergy to hazelnut can be severe and systemic. So far, only a limited number of non-pollen related hazelnut allergens have been identified and characterized. The aim of this study was to identify and clone new hazelnut allergens. A lambda ZAP cDNA library of hazelnut was constructed. The library was screened with serum of six hazelnut allergic patients displaying different IgE-binding patterns on hazelnut immunoblot. Rapid amplification of cDNA ends (RACE) protocols were applied to obtain full-length clones. Expression experiments were carried out in Eschericchia coli. Expression was monitored by SDS-PAGE, protein staining and immunoblotting. A hazelnut cDNA library was constructed. IgE screening resulted in the cloning of two isoforms of a novel putative hazelnut allergen. The clones were identified as oleosins, with theoretical molecular masses of 16.7 and 14.7 kDa and pI of 10.5 and 10.0, respectively. The isoforms demonstrated only 37% amino acid sequence identity but contained the typical hydrophobic stretch in the middle of the protein (53% identity) with the characteristic oleosin proline knot region (11/12 amino acids identical). Expression in E. coli of the longer isoform resulted in a clear band on SDS-PAGE. The expressed protein was recognized on an immunodot blot by IgE from serum that was used for screening the cDNA library. Hazelnut contains multiple isoforms of oleosin. IgE binding of a hazelnut-allergic patient to a recombinant version suggest that hazelnut oleosin is an allergen, as has been described for peanut and sesame.

Plant food allergies: a suggested approach to allergen-resolved diagnosis in the clinical practice by identifying easily available sensitization markers

BACKGROUND

Molecular biology techniques have led to the identification of a number of allergens in vegetable foods, but due to the lack of purified food proteins for routine diagnostic use, the detection of sensitizing allergens remains a nearly impossible task in most clinical settings. The allergen-resolved diagnosis of food allergy is essential because each plant-derived food may contain a number of different allergens showing different physical/chemical characteristics that strongly influence the clinical expression of allergy; moreover, many allergens may cross-react with homologue proteins present in botanically unrelated vegetable foods.

OBJECTIVE

Through a review of the available literature, this study aimed to detect "markers" of sensitization to specific plant food allergens that are easily accessible in the clinical practice.

RESULTS

There are several "markers" of sensitization to different allergenic proteins in vegetable foods that can be helpful in the clinical practice. Specific algorithms for patients allergic to Rosaceae and to tree nuts were built.

CONCLUSION

Clinical allergologists lacking the assistance of an advanced molecular biology lab may take advantage of some specific clinical data as well as of some "markers" in the difficult task of correctly diagnosing patients with plant food allergy and to provide them the best preventive advice.

The oral allergy syndrome: improved diagnostic and treatment methods

PURPOSE OF REVIEW

The aim of this article is to review recent clinical and molecular findings related to the oral allergy syndrome in order to define its relevance in the field of food allergy, describe current diagnostic approaches and discuss attempts to use specific immunotherapy for treatment.

RECENT FINDINGS

New allergenic sources causing the oral allergy syndrome have been reported. Their allergenic molecules have been identified. In most of those studies oral allergy syndrome is reported as a clinical manifestation among more severe ones. Some of the molecules generally considered not to be at risk for severe reactions have been demonstrated to pose a threat for inducing generalized reactions. Some studies tried to assess the usefulness of immunotherapy with birch pollen extract by either subcutaneous or sublingual routes for the treatment of associated food allergies. In most of the cases, a well defined study design and a molecular approach at different study levels are lacking and thus the value of the obtained results is limited. To date, no final conclusion can be drawn on the basis of reported results.

SUMMARY

The knowledge about the highly prevalent phenomenon of oral allergy syndrome is still incomplete, in respect to both, epidemiology and foods inducing symptoms. It is very important to reach consensus on several aspects of this food-induced allergic disease. Further studies are required to highlight whether immunotherapy using co-recognized inhalant allergens is an effective way of curative treatment, or if co-treatment with purified pollen-related food allergens will be required to obtain a long-lasting effect.

Clinical role of lipid transfer proteins in food allergy

Lipid transfer proteins are widespread plant food allergens, highly resistant to food processing and to the gastrointestinal environment, which have recently been described as true food allergens in the Mediterranean area, where they have been associated with severe allergic reactions to foods in patients without pollen allergy. In this review we analyze their molecular structure, biological function, and clinical relevance in food allergy.

Recombinant allergens for immunotherapy. Where do we stand?

PURPOSE OF REVIEW

This review is an update regarding the development of recombinant allergens from the laboratory bench to clinical applications. Special attention will be given to the potential improvement of allergen-specific immunotherapy through the use of recombinant allergens.

RECENT FINDINGS

Currently used therapeutic allergen extracts suffer from several important disadvantages and therefore may be replaced by recombinant allergens in the near future. Recent studies indicate that recombinant allergen-based diagnostic tests can be used for selection of patients for immunotherapy and to analyse the mechanisms underlying immunotherapy. Furthermore, recombinant and peptide technologies have been used for the generation of allergy vaccines with reduced allergenic activity. Applying the new technologies, the vaccines can be formulated to target either B cells or T cells, or both cell types. Very recently, encouraging results were obtained in an immunotherapy trial performed with genetically engineered allergens.

SUMMARY

Recombinant allergen-based diagnostic tests will improve the selection of patients for immunotherapy. The first immunotherapy trial with recombinant allergens provides information about mechanisms underlying immunotherapy and holds promise that new types of allergy vaccines based on recombinant allergens will become available soon.