Protein microarrays for the diagnosis of allergic diseases: state-of-the-art and future development

Detection of Allergenic Proteins in Foodstuffs: Advantages of the Innovative Multiplex Allergen Microarray-Based Immunoassay Compared to Conventional Methods

Several factors can affect the allergen content and profile of a specific food, including processing procedures often leading to a decrease in allergenicity, although no change, or even an increase, have also been reported. Evaluation of the effectiveness of a processing procedure requires the availability of reliable methodologies to assess the variation in molecules able to induce allergic reactions in the analyzed food. Conventional and innovative strategies and methodologies can be exploited to identify allergenic proteins in foodstuffs. However, depending on the specific purposes, different methods can be used. In this review, we have critically reviewed the advantages of an innovative method, the multiplex allergen microarray-based immunoassay, in the detection of allergens in foodstuffs. In particular, we have analyzed some studies reporting the exploitation of an IgE-binding inhibition assay on multiplex allergen biochips, which has not yet been reviewed in the available literature. Unlike the others, this methodology enables the identification of many allergenic proteins, some of which are still unknown, which are recognized by IgE from allergic patients, with a single test. The examined literature suggests that the inhibition test associated with the multiplex allergen immunoassay is a promising methodology exploitable for the detection of IgE-binding proteins in food samples.

Multiplex component-based allergen microarray in recent clinical studies

During the last decades component-resolved diagnostics either as singleplex or multiplex measurements has been introduced into the field of clinical allergology, providing important information that cannot be obtained from extract-based tests. Here we review recent studies that demonstrate clinical applications of the multiplex microarray technique in the diagnosis and risk assessment of allergic patients, and its usefulness in studies of allergic diseases. The usefulness of ImmunoCAP ISAC has been validated in a wide spectrum of allergic diseases like asthma, allergic rhinoconjunctivitis, atopic dermatitis, eosinophilic esophagitis, food allergy and anaphylaxis. ISAC provides a broad picture of a patient's sensitization profile from a single test, and provides information on specific and cross-reactive sensitizations that facilitate diagnosis, risk assessment, and disease management. Furthermore, it can reveal unexpected sensitizations which may explain anaphylaxis previously categorized as idiopathic and also display for the moment clinically non-relevant sensitizations. ISAC can facilitate a better selection of relevant allergens for immunotherapy compared with extract testing. Microarray technique can visualize the allergic march and molecular spreading in the preclinical stages of allergic diseases, and may indicate that the likelihood of developing symptomatic allergy is associated with specific profiles of sensitization to allergen components. ISAC is shown to be a useful tool in routine allergy diagnostics due to its ability to improve risk assessment, to better select relevant allergens for immunotherapy as well as detecting unknown sensitization. Multiplex component testing is especially suitable for patients with complex symptomatology.

Evaluation of a novel automated allergy microarray platform compared with three other allergy test methods

Microarray platforms, enabling simultaneous measurement of many allergens with a small serum sample, are potentially powerful tools in allergy diagnostics. We report here the first study comparing a fully automated microarray system, the Microtest allergy system, with a manual microarray platform, Immuno-Solid phase Allergen Chip (ISAC), and two well-established singleplex allergy tests, skin prick test (SPT) and ImmunoCAP, all tested on the same patients. One hundred and three adult allergic patients attending the allergy clinic were included into the study. All patients were tested with four allergy test methods (SPT, ImmunoCAP, Microtest and ISAC 112) and a total of 3485 pairwise test results were analysed and compared. The four methods showed comparable results with a positive/negative agreement of 81-88% for any pair of test methods compared, which is in line with data in the literature. The most prevalent allergens (cat, dog, mite, timothy, birch and peanut) and their individual allergen components revealed an agreement between methods with correlation coefficients between 0·73 and 0·95. All four methods revealed deviating individual patient results for a minority of patients. These results indicate that microarray platforms are efficient and useful tools to characterize the specific immunoglobulin (Ig)E profile of allergic patients using a small volume of serum sample. The results produced by the Microtest system were in agreement with diagnostic tests in current use. Further data collection and evaluation are needed for other populations, geographical regions and allergens.

Molecular-based diagnosis of respiratory allergic diseases in children from Curitiba, a city in Southern Brazil

BACKGROUND

Prevalence of respiratory allergic diseases has increased worldwide. Identification of the aeroallergens involved in allergenic sensitisation is important for diagnosis, treatment and prevention.

OBJECTIVE

To verify the molecular pattern of sensitisation to aeroallergens in patients with allergic respiratory diseases using microarray technique for specific IgE antibody detection.

METHODS

Cross-sectional study of 101 children with allergic rhinitis was followed in an outpatient clinic. All patients had positive skin prick tests (SPT) to at least one of the following antigens: Dermatophagoides pteronyssinus, Blomia tropicalis, Blattella germanica, Lolium multiflorum, and dog and cat epithelium. Serum specific IgE antibodies (sIgE) to mites, animal epithelia, fungi, cockroach and pollens components were determined by ImmunoCAP ISAC.

RESULTS

sIgE to group 1 and 2 mite allergens showed higher positive rates: Der p 1 (74.2%), Der p 2 (73.3%), Der f 1 (74.2%), Der f 2 (72.3%). sIgE to animal epithelia were less frequent, Can f 1, Can f 2, Can f 3 in 4.9%, 2.9%, 1.9% respectively and Fel d 1, Fel d 2, Fel d 4 in 16.8%, 0.9% and 1.9%. respectively. Sensitisation to fungi and cockroach were rare, except for Bla g 7, to which 16.8% were positive. There was no significant recognition for tree pollens group. For grass, sIgE were detected to Cyn d 1 in 16.8%, Phl p 1 and Phl p 4 in 14.8% and 12.9%, respectively.

CONCLUSION

Knowing that the pattern of allergic sensitisation varies according to environment and population, our results reinforce the need for local studies, using molecular-based diagnosis.

The EuroPrevall outpatient clinic study on food allergy: background and methodology

BACKGROUND

The EuroPrevall project aimed to develop effective management strategies in food allergy through a suite of interconnected studies and a multidisciplinary integrated approach. To address some of the gaps in food allergy diagnosis, allergen risk management and socio-economic impact and to complement the EuroPrevall population-based surveys, a cross-sectional study in 12 outpatient clinics across Europe was conducted. We describe the study protocol.

METHODS

Patients referred for immediate food adverse reactions underwent a consistent and standardized allergy work-up that comprised collection of medical history; assessment of sensitization to 24 foods, 14 inhalant allergens and 55 allergenic molecules; and confirmation of clinical reactivity and food thresholds by standardized double-blind placebo-controlled food challenges (DBPCFCs) to milk, egg, fish, shrimp, peanut, hazelnut, celeriac, apple and peach.

RESULTS

A standardized methodology for a comprehensive evaluation of food allergy was developed and implemented in 12 outpatient clinics across Europe. A total of 2121 patients (22.6% <14 years) reporting 8257 reactions to foods were studied, and 516 DBPCFCs were performed.

CONCLUSIONS

This is the largest multicentre European case series in food allergy, in which subjects underwent a comprehensive, uniform and standardized evaluation including DBPCFC, by a methodology which is made available for further studies in food allergy. The analysis of this population will provide information on the different phenotypes of food allergy across Europe, will allow to validate novel in vitro diagnostic tests, to establish threshold values for major allergenic foods and to analyse the socio-economic impact of food allergy.

Reconceiving autoimmunity: An overview

Three interconnected positions are advocated: (1) although serving as a useful model, the immune self does not exist as such; (2) instead of a self/nonself demarcation, the immune system 'sees' itself, i.e., it does not ignore the 'self' or attack the 'other;' but exhibits a spectrum of responses, which when viewed from outside the system appear as discrimination of 'self' and 'nonself' based on certain criteria of reactivity. When immune reactions are conceived in terms of normal physiology and open exchange with the environment, where borders dividing host and foreign are elusive and changing, host defense is only part of the immune system's functions, which actually comprise two basic tasks: protection, i.e., to preserve host integrity, and maintenance of organismic identity. And thus (3) if the spectrum of immunity is enlarged, differentiating low reactive 'autoimmune' reactions from activated immune responses against the 'other' is only a matter of degree. Simply, all immunity is 'autoimmunity,' and the pathologic state of immunity directed at normal constituents of the organism is a particular case of dis-regulation, which appropriately is designated, autoimmune. Other uses of 'autoimmunity' and its congeners function as the semantic remnants of Burnet's original self/nonself theory and should be replaced. A new nomenclature is proposed, concinnity, which more accurately designates the physiology of the animal's ordinary housekeeping economy mediated by the immune system than 'autoimmunity' when used to describe such normal functions.

Development of hydrogel biochip for in vitro allergy diagnostics

A hydrogel biochip was developed for the simultaneous quantitative determination of sIgE for 21 allergens and total IgE in human serum. The biochips are manufactured by photoinduced copolymerization of different molecules (allergens and antibodies) with gel-forming monomers resulting in the formation of three-dimensional hydrogel elements (1nl gel drops). After incubation of the biochip with the serum, the results are visualized using fluorescently labeled anti-IgE antibodies. Using biochips, serum samples from allergic patients and healthy donors were analyzed and good correlation with the results obtained using commercial EIA test systems of generally recognized quality (Dr. Fooke Laboratorien GmbH, Germany) was observed.

Population-based study of multiplexed IgE sensitization in relation to asthma, exhaled nitric oxide, and bronchial responsiveness

BACKGROUND

IgE sensitization is an important risk factor for the development of asthma.

OBJECTIVE

The aim of this study was to investigate the IgE antibody profile for a broad spectrum of allergen molecules in asthmatic patients.

METHODS

Participants from the European Community Respiratory Health Survey II (n=467) were tested with ImmunoCAP ISAC against 103 allergen molecules. The presence of bronchial hyperresponsiveness was measured with a methacholine challenge test and bronchial inflammation with fraction of exhaled nitric oxide (Feno).

RESULTS

A total of 38% of the controls and 72% of the asthmatic patients were sensitized against at least 1 of the allergen components (P<.0001). Asthma was independently related to having IgE antibodies against pollen (odds ratio=2.2) and perennial airway allergens (odds ratio=5.6), increased Feno was independently related to having IgE antibodies against food allergens and perennial allergens, while bronchial responsiveness was independently associated with having IgE antibodies against only perennial allergens. Sensitization to food allergens was related to asthma and increased Feno if IgE antibody against pollen allergens was present. Simultaneous sensitization to perennial, pollen, and food allergens involves the highest risk of asthma (odds ratio=18.3), bronchial inflammation, and responsiveness.

CONCLUSIONS

Feno, bronchial responsiveness, and the risk of asthma increase with multiple sensitizations to different allergen groups. We show for the first time that the presence of IgE antibodies against food allergens is independently associated with increased Feno and increases the risk of asthma in subjects with simultaneous sensitization to pollen allergens.

Eosinophilic airway inflammation is increased in children with asthma and food allergies

BACKGROUND

Asthma is associated with food allergies in a significant number of children, with evidence linking allergies to asthma severity and morbidity. In this study, we tested our hypothesis that the eosinophilic lower airway inflammation is higher in asthmatic children with food allergies.

AIMS

The aims of the study were to compare the eosinophilic inflammatory markers in asthmatic children with and without food allergies.

MATERIALS AND METHODS

Children with asthma, with (n = 22) and (n = 53) without food allergies were included. All subjects were classified according to the GINA guidelines (2009) and had received at least 3 months of anti-inflammatory therapy prior to testing. Fractional exhaled nitric oxide and sputum differential counts were performed using standard techniques.

RESULTS

  Children with asthma and food allergies had significantly higher fractional exhaled nitric oxide median (range) [(22.4 (6.1-86.9) vs. 10.3 (2.7-38.7) (p = 0.01)] and sputum eosinophil percentage [15.5 (5.0-53.0) vs. 2.0 (0-20) (p < 0.001)] compared with asthmatic children without allergies.

CONCLUSION

These results suggest that the children with asthma and food allergies have increased eosinophilic inflammation of the airways.

Bet v 1-like pollen allergens of multiple Fagales species can sensitize atopic individuals

BACKGROUND

In the temperate climate zone of the Northern hemisphere, Fagales pollen allergy represents the main cause of winter/spring pollinosis. Among Fagales trees, pollen allergies are strongly associated within the Betulaceae and the Fagaceae families. It is widely accepted that Fagales pollen allergies are initiated by sensitization against Bet v 1, the birch pollen major allergen, although evidence is accumulating that the allergenic activity of some Bet v 1-like molecules has been underestimated.

OBJECTIVE

To investigate the allergenic potential of the clinically most important Fagales pollen allergens from birch, alder, hazel, hornbeam, hop-hornbeam, oak, beech and chestnut.

METHODS

To obtain the full spectrum of allergens, the three previously unavailable members of the Bet v 1-family, hop-hornbeam Ost c 1, chestnut Cas s 1 and beech Fag s 1, were identified in the respective pollen extracts, cloned and produced as recombinant proteins in E. coli. Together with recombinant Bet v 1, Aln g 1, Car b 1, Cor a 1 and Que a 1, the molecules were characterized physicochemically, mediator release assays were performed and IgE cross-reactivity was evaluated by ELISA and Immuno Solid-phase Allergen Chip (ISAC) IgE inhibition assays.

RESULTS

All allergens showed the typical Bet v 1-like secondary structure elements, and they were all able to bind serum IgE from Fagales allergic donors. Strong IgE binding was observed for Betuloideae and Coryloideae allergens, however, cross-reactivity between the two subfamilies was limited as explored by inhibition experiments. In contrast, IgE binding to members of the Fagaceae could be strongly inhibited by serum pre-incubation with allergens of the Betuloideae subfamily.

CONCLUSIONS AND CLINICAL RELEVANCE

The data suggest that Bet v 1-like allergens of the Betuloideae and Coryloideae subfamily might have the potential to induce IgE antibodies with different specificities, while allergic reactions towards Fagaceae allergens are the result of IgE cross-reactivity.

Comparison of conventional and component-resolved diagnostics by two different methods (Advia-Centaur/Microarray-ISAC) in pollen allergy

BACKGROUND

Component-resolved diagnostics (CRD) has recently been introduced into clinical allergology.

OBJECTIVE

The aim of this study was to assess the contribution that this new diagnostic technique makes to conventional diagnosis in patients with pollen allergy, comparing CRD with conventional technologies, and to compare 2 CRD methods, Advia-Centaur and Microarray-ISAC.

METHODS

Serum samples from 120 pollen-allergic patients were obtained. Immunoglobulin (Ig) E to total extracts (CAP System) and individual allergens using both CRD methods were determined.

RESULTS

The 3 diagnostic methods were in agreement in 62.5% of cases. In 30%, the CRD modified the conventional diagnosis either by detecting new relevant sensitizations (mainly to Olea) or by ruling out clinically irrelevant sensitizations caused by panallergens. The main differences between the 2 CRD methods were the deficiency in the ISAC version we used (ISAC-CRD-89) to detect sensitizations to Salsola and Plantago and that Advia-Centaur did not detect sensitizations to cypress. For all allergens except for Par j 1, a significant association in the frequency of sensitization was seen with the 2 CRD techniques and good agreement when comparing the results of the 2 methods in all cases. Significant correlation was found in the concentration of specific IgE in the 2 techniques for the most prevalent allergens in our setting. The results of the different profilins analyzed using Microarray-ISAC were superimposable although somewhat lower in the case of Phl p 12.

CONCLUSIONS

Component-resolved diagnostics modified the conventional diagnosis in 30% of cases. The results from the 2 CRD methods showed good agreement and correlation for most allergens.

Is aboriginal food less allergenic? Comparing IgE-reactivity of eggs from modern and ancient chicken breeds in a cohort of allergic children

BACKGROUND

Hen's egg allergy ranks among the most frequent primary food allergies in children. We aimed to investigate sensitization profiles of egg allergic patients and compare in vitro IgE reactivities of eggs from ancient chicken breeds (Araucana and Maran) with those from conventional laying hen hybrids.

METHODOLOGY

Egg allergic children (n = 25) were subjected to skin prick test, double blind placebo controlled food challenge, and sensitization profiles to Gal d 1-5 were determined by allergen microarray. IgE binding and biological activity of eggs from different chicken breeds were investigated by immunoblot, ELISA, and mediator release assays.

PRINCIPAL FINDINGS

We found that Gal d 1 and Gal d 2 are generally major egg allergens, whereas Gal d 3-5 displayed high sensitization prevalence only in patients reacting to both, egg white and yolk. It seems that the onset of egg allergy is mediated by egg white allergens expanding to yolk sensitization in later stages of disease. Of note, egg white/yolk weight ratios were reduced in eggs from Auraucana and Maran chicken. As determined in IgE immunoblots and mass analysis, eggs from ancient chicken breeds did not differ in their protein composition. Similar IgE-binding was observed for all egg white preparations, while an elevated allergenicity was detected in egg yolk from Araucana chicken.

CONCLUSION/SIGNIFICANCE

Our results on allergenicity and biological activity do not confirm the common assumption that aboriginal food might be less allergenic. Comprehensive diagnosis of egg allergy should distinguish between reactivity to hen's egg white and yolk fractions to avoid unnecessary dietary restrictions to improve life quality of the allergic child and its family.

Sensitization profiles of a case of pollen-food allergy syndrome

A 13-year-old girl who had had pollinosis since the age of eight began to experience itching of the ears and vomiting after eating fresh fruits such as peach, apple and watermelon. This occurred at 10 years of age. The girl displayed positive reactions to six kinds of pollens, eleven kinds of fruits, numerous vegetables and to recombinant: rBet v2 present in specific IgE antibodies. She also reacted positively to several pollens, fruits and rBet v2 in the skin prick test. In the component-resolved diagnosis (CRD) using microarray technology, she also tested positive for profilin, a pan-allergen among plants. It is reported that profilin cross-reacts between pollen, fruits, vegetables and latex. From these results, we concluded that the allergic reactions to multiple kinds of foodstuff and pollens observed in this subject were due to cross-reactivity induced by profilin. Our results demonstrate that CRD by microarray is a reliable test in the diagnosis of PFAS.

Proteomic analysis in the identification of allergenic molecules

Conventional and innovative strategies can be exploited to identify and characterize new allergenic proteins. With the aim of obtaining suggestions for future improvements, this article describes our attempt to understand and describe some of the advantages and pitfalls of the methodologies and procedures often used in this field. The analysis includes the protein extract preparation, starting from the allergenic source, the separation of the proteins contained in a mixture and the detection, identification and characterization of IgE-binding molecules. Classic and emerging proteomic technologies, including mass spectrometry-based methodologies, Edman degradation procedure, microarray-based techniques and bioinformatics search strategies, have been explored. A comparative analysis of biochemistry-based proteomics and molecular biology strategies has also been given.

Molecular characterization of Api g 2, a novel allergenic member of the lipid-transfer protein 1 family from celery stalks

SCOPE

Celery represents a relevant cross-reactive food allergen source in the adult population. As the currently known allergens are not typical elicitors of severe symptoms, we aimed to identify and characterize a non-specific lipid transfer protein (nsLTP).

METHODS AND RESULTS

MS and cDNA cloning were applied to obtain the full-length sequence of a novel allergenic nsLTP from celery stalks. The purified natural molecule consisted of a single isoallergen designated as Api g 2.0101, which was recombinantly produced in Escherichia coli Rosetta-gami. The natural and recombinant molecules displayed equivalent physicochemical and immunological properties. Circular dichroism revealed a typical α-helical fold and high thermal stability. Moreover, Api g 2 was highly resistant to simulated gastrointestinal digestion. As assessed by ELISA, thermal denaturation did not affect the IgE binding of Api g 2. Natural and recombinant Api g 2 showed similar allergenic activity in mediator release assays. Api g 2-specific IgE antibodies cross-reacted with peach and mugwort pollen nsLTPs.

CONCLUSION

Based on our results, it can be anticipated that inclusion of recombinant Api g 2 in the current panel of allergens for molecule-based diagnosis will facilitate the evaluation of the clinical relevance of nsLTP sensitization in celery allergy and help clinicians in the management of food allergic patients.

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.

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.

Latex-allergic patients sensitized to the major allergen hevein and hevein-like domains of class I chitinases show no increased frequency of latex-associated plant food allergy

Allergies to certain fruits such as banana, avocado, chestnut and kiwi are described in 30–70% of latex-allergic patients. This association is attributed to the cross-reactivity between the major latex allergen hevein and hevein-like domains (HLDs) from fruit class I chitinases. We aimed to assess the extent of cross-reactivity between hevein and HLDs using sera from latex-allergic patients with and without plant food allergy. Hevein and HLDs of latex, banana, and avocado chitinases were expressed in Escherichia coli as fusion proteins with the maltose-binding protein and purified by affinity chromatography. IgE binding to these proteins was studied in sera from 59 latex-allergic patients and 20 banana-allergic patients without latex allergy by ELISA and ELISA inhibition. Additionally, 16,408 allergic patients’ sera were tested for IgE binding to hevein, latex chitinase, and wheat germ agglutinin using an allergen microarray. Hevein-specific IgE was detected in 34/59 (58%) latex-allergic patients’ sera. HLDs of latex, banana, and avocado chitinases were recognized by 21 (36%), 20 (34%), and 9 (15%) sera, respectively. In contrast, only one of 20 banana-allergic patients without latex allergy was sensitized to chitinase HLDs. In most tested latex-allergic patients’ sera, IgE binding to hevein was only partially reduced by preincubation with HLDs. Among hevein-sensitized, latex-allergic patients, the percentage of plant food allergy (15/34 = 44%) was equal to latex-allergic patients without hevein sensitization (11/25 = 44%). In the general allergic population, 230 of 16,408 sera (1.4%) reacted to hevein and/or a hevein-like allergen. Of these, 128 sera showed an isolated sensitization to hevein, whereas only 17 bound to latex chitinase or wheat germ agglutinin without hevein sensitization. In conclusion, the IgE response to HLDs is elicited by hevein as sensitizing allergen in most cases. Despite considerable cross-reactivity between these allergens, no correlation between latex-associated plant food allergy and sensitization to hevein or HLDs was found.

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.

Crystal structure of the dog lipocalin allergen Can f 2: implications for cross-reactivity to the cat allergen Fel d 4

The dog lipocalin allergen Can f 2 is an important cause of allergic sensitization in humans worldwide. Here, the first crystal structure of recombinant rCan f 2 at 1.45 A resolution displays a classical lipocalin fold with a conserved Gly-Xaa-Trp motif, in which Trp19 stabilizes the overall topology of the monomeric rCan f 2. Phe38 and Tyr84 localized on the L1 and L5 loops, respectively, control access to the highly hydrophobic calyx. Although the rCan f 2 calyx is nearly identical with the aero-allergens MUP1, Equ c 1 and A2U from mouse, horse and rat, respectively, no IgE cross-reactivity was found using sera from five mono-sensitized subjects. However, clear IgE cross-reactivity was demonstrated between Can f 2 and the cat allergen Fel d 4, although they share less than 22% sequence identity. This suggests a role for these allergens in co-sensitization between cat- and dog-allergic patients.

A protein allergen microarray detects specific IgE to pollen surface, cytoplasmic, and commercial allergen extracts

Background

Current diagnostics for allergies, such as skin prick and radioallergosorbent tests, do not allow for inexpensive, high-throughput screening of patients. Additionally, extracts used in these methods are made from washed pollen that lacks pollen surface materials that may contain allergens.

Methodology/Principal Findings

We sought to develop a high-throughput assay to rapidly measure allergen-specific IgE in sera and to explore the relative allergenicity of different pollen fractions (i.e. surface, cytoplasmic, commercial extracts). To do this, we generated a protein microarray containing surface, cytoplasmic, and commercial extracts from 22 pollen species, commercial extracts from nine non-pollen allergens, and five recombinant allergenic proteins. Pollen surface and cytoplasmic fractions were prepared by extraction into organic solvents and aqueous buffers, respectively. Arrays were incubated with <25 uL of serum from 176 individuals and bound IgE was detected by indirect immunofluorescence, providing a high-throughput measurement of IgE. We demonstrated that the allergen microarray is a reproducible method to measure allergen-specific IgE in small amounts of sera. Using this tool, we demonstrated that specific IgE clusters according to the phylogeny of the allergen source. We also showed that the pollen surface, which has been largely overlooked in the past, contained potent allergens. Although, as a class, cytoplasmic fractions obtained by our pulverization/precipitation method were comparable to commercial extracts, many individual allergens showed significant differences.

Conclusions/Significance

These results support the hypothesis that protein microarray technology is a useful tool for both research and in the clinic. It could provide a more efficient and less painful alternative to traditionally used skin prick tests, making it economically feasible to compare allergen sensitivity of different populations, monitor individual responses over time, and facilitate genetic studies on pollen allergy.

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.

Magnetic bead-based detection of autoimmune responses using protein microarrays

In the present study, a magnetic bead-based detection approach for protein microarrays is described as an alternative approach to the commonly used fluorescence-based detection system. Using the bead-based detection approach with applied magnetic force, it was possible to perform the detection step more rapidly as a result of the accelerated binding between the captured analyte in the microspot and the detection antibody, which was coupled to the magnetic beads. The resulting strong opacity shift on the microspots could be recorded with an ordinary flatbed scanner. In the context of autoimmunity, a set of 24 serum samples was analyzed for the presence of antibodies against 12 autoantigens using standard fluorescence and magnetic bead-based detection methods. Dynamic range, sensitivity, and specificity were determined for both detection methods. We propose from our findings that the magnetic bead-based detection option provides a simplified and cost effective readout method for protein microarrays.

A systems immunology approach to the host-tumor interaction: large-scale patterns of natural autoantibodies distinguish healthy and tumor-bearing mice

Traditionally, immunology has considered a meaningful antibody response to be marked by large amounts of high-affinity antibodies reactive with the specific inciting antigen; the detection of small amounts of low-affinity antibodies binding to seemingly unrelated antigens has been considered to be beneath the threshold of immunological meaning. A systems-biology approach to immunology, however, suggests that large-scale patterns in the antibody repertoire might also reflect the functional state of the immune system. To investigate such global patterns of antibodies, we have used an antigen-microarray device combined with informatic analysis. Here we asked whether antibody-repertoire patterns might reflect the state of an implanted tumor. We studied the serum antibodies of inbred C57BL/6 mice before and after implantation of syngeneic 3LL tumor cells of either metastatic or non-metastatic clones. We analyzed patterns of IgG and IgM autoantibodies binding to over 300 self-antigens arrayed on slides using support vector machines and genetic algorithm techniques. We now report that antibody patterns, but not single antibodies, were informative: 1) mice, even before tumor implantation, manifest both individual and common patterns of low-titer natural autoantibodies; 2) the patterns of these autoantibodies respond to the growth of the tumor cells, and can distinguish between metastatic and non-metastatic tumor clones; and 3) curative tumor resection induces dynamic changes in these low-titer autoantibody patterns. The informative patterns included autoantibodies binding to self-molecules not known to be tumor-associated antigens (including insulin, DNA, myosin, fibrinogen) as well as to known tumor-associated antigens (including p53, cytokeratin, carbonic anhydrases, tyrosinase). Thus, low-titer autoantibodies that are not the direct products of tumor-specific immunization can still generate an immune biomarker of the body-tumor interaction. System-wide profiling of autoantibody repertoires can be informative.

Clinical usefulness of microarray-based IgE detection in children with suspected food allergy

BACKGROUND

Component-resolved diagnostics using microarray technology has recently been introduced into clinical allergology, but its applicability in children with food allergy has hardly been investigated so far. The aim of this study was to evaluate the utility of microarray-based IgE detection in the diagnostic workup of food allergy and to compare this new diagnostic tool with established methods of allergen-specific IgE detection.

METHODS

We investigated 130 infants and children with suspected allergy to cow's milk (CM) or hen's egg (HE). Serum IgE measurements, skin prick tests, allergen microarray assays and controlled oral food challenges with HE and CM were performed.

RESULTS

We analyzed 145 oral challenges that served as reference parameters for assay performance assessment. On this basis, the panel of microarrayed allergen components was shown to represent a comprehensive repertoire of clinically relevant CM and HE proteins. Additionally, the implemented CM and HE components respectively sufficed for equivalent test performance as compared to the corresponding fluorescence enzyme immunoassay extract and skin testing. However, component-resolved diagnostics for HE and CM allergy did not make oral food challenges superfluous. Clinical IgE decision points predicting positive oral food challenges could be calculated for both in vitro test methods.

CONCLUSIONS

Allergen microarrays provide a new tool to diagnose symptomatic CM and HE allergy. They show performance characteristics comparable to the current diagnostic tests and may be indicated in small children in whom only small blood volumes are obtainable. However, they are not capable of replacing double-blind, placebo-controlled food challenges in most cases.

When does a protein become an allergen? Searching for a dynamic definition based on most advanced technology tools

Since the early beginning of allergology as a science considerable efforts have been made by clinicians and researchers to identify and characterize allergic triggers as raw allergenic materials, allergenic sources and tissues, and more recently basic allergenic structures defined as molecules. The last 15–20 years have witnessed many centres focusing on the identification and characterization of allergenic molecules leading to an expanding wealth of knowledge. The need to organize this information leads to the most important question ‘when does a protein become an allergen?’ In this article, I try to address this question by reviewing a few basic concepts of the immunology of IgE-mediated diseases, reporting on the current diagnostic and epidemiological tools used for allergic disease studies and discussing the usefulness of novel biotechnology tools (i.e. proteomics and molecular biology approaches), information technology tools (i.e. Internet-based resources) and microtechnology tools (i.e. proteomic microarray for IgE testing on molecular allergens). A step-wise staging of the identification and characterization process, including bench, clinical and epidemiological aspects, is proposed, in order to classify allergenic molecules dynamically. This proposal reflects the application and use of all the new tools available from current technologies.

The serum bank of EuroPrevall - the prevalence, cost and basis of food allergy across Europe

EuroPrevall is an EU-funded multidisciplinary project including 62 institutions from 22 countries. EuroPrevall studies the prevalence and distribution of food allergies in infants, children, adolescents, and adults in Europe, threshold doses for allergenic foods, the role of the environment in food allergy, the socioeconomic impact of food allergy, and novel diagnostic tools for food allergies. The EuroPrevall serum bank (EPASB), containing samples from approximately 70,000 subjects, is a major tool to achieve these goals. EPASB is coordinated by the Paul-Ehrlich-Institut, Langen, Germany. Local sera collections are administered at the University of Amsterdam (NL), the University Hospital of Manchester (UK), Charité Hospital (DE) and the Paul-Ehrlich-Institut. The EPASB coordinator and managing partners distribute samples for experimental work and regulate access. The overall aim is to provide sera to fulfil EuroPrevall research goals. The EPASB coordinator and managing partners suggest appropriate sera for addressing specific scientific and diagnostic questions. The serum bank will be maintained after termination of the project, but subsequent investigations must be in accordance with the original research goals of EuroPrevall. Thus, the contributors of the sera retain control over their future use. This rule prevents investigation of questions outside the scope of EuroPrevall, e.g. the allergenicity of genetically-modified foods.

[Protein arrays and perspectives of medical applications]

Protein microarrays make it possible to detect molecular interactions with various partners (proteins, peptides, nucleic acids, sugars, etc.). Their advantages are crucial for high-throughput analysis of proteomes of different organisms. Moreover, the recent data reveal the performance of microarrays over current immunological methods. Therefore, the antigen and antibody microarrays become indispensable for medical applications, in particular, for diagnosis and prognosis of microbial infections, autoimmune and allergic diseases. The further technological progress might provide the extension of the miniaturized assays for multiparametric monitoring of human pathologies in practical medicine.

Bioinformatics applied to allergy: allergen databases, from collecting sequence information to data integration. The Allergome platform as a model

Allergens are proteins or glycoproteins that are recognized by IgE produced by the immune system of allergic individuals. Until now around 1,500 allergenic structures have been identified and this number seems not have reached a plateau after 3-4 decades of research and the advent of molecular biology. Several allergen databases are available on Internet. Different aims and philosophies lead to different products. Here we report about main feature of web sites dedicated to allergens and we describe in more details our current work on the Allergome platform. The web server Allergome (www.allergome.org) represent a free independent open resource whose goal is to provide an exhaustive repository of data related to all the IgE-binding compounds. The main purpose of Allergome is to collect a list of allergenic sources and molecules by using the widest selection criteria and sources. A further development of the Allergome platform has been represented by the Real Time Monitoring of IgE sensitization module (ReTiME) that allows uploading of raw data from both in vivo and in vitro testing, thus representing the first attempt to have IT applied to allergy data mining. More recently, a new module (RefArray) representing a tool for literature mining has been released.

A simple, rapid, and sensitive integrated protein microarray for simultaneous detection of multiple antigens and antibodies of five human hepatitis viruses (HBV, HCV, HDV, HEV, and HGV)

Protein microarrays for parallel detection of multiple viral antigens and antibodies have not yet been described in the field of human hepatitis virus infections. Here, we describe a simple, rapid and sensitive integrated protein microarray with three different reaction models. The integrated protein microarray could simultaneously determine in human sera two viral antigens (HBsAg, HBeAg) and seven viral antibodies (HBsAb, HBcAb, HBeAb, HCVAb, HDVAb, HEVAb, HGVAb) of human hepatitis viruses within 20 min. The results of the protein microarray were assessed directly by the naked eye but can also be analyzed by a quantitative detector. The detection limit of this protein microarray was 0.1 ng/ml for HBsAg. Overall, >85% concordance was observed between the integrated protein microarrays and an enzyme-linked immunosorbent assay for above hepatitis viral antigen and antibody detections in human sera. This integrated protein microarray can be easily optimized for clinical use and epidemiological screening for multiple hepatitis virus infections.

Biotechnologies in new high-throughput food allergy tests: why we need them

The increase in prevalence of food allergies generates a need for more accurate and reliable quantitative allergy testing in order to help diagnosis. In this short review, we briefly outline the history of food allergy testing and extend our comments to current multiplex techniques. Particular emphasis is given to new developments in the protein microarray area, where the use of recent advances in biotechnology has the potential to produce high-throughput devices with improved clinical significance.

The role of protein glycosylation in allergy

The asparagine-linked carbohydrate moieties of plant and insect glycoproteins are the most abundant environmental immune determinants. They are the structural basis of what is known as cross-reactive carbohydrate determinants (CCDs). Despite some structural variation, the two main motifs are the xylose and the core-3-linked fucose, which form the essential part of two independent epitopes. Plants contain both epitopes, insect glycoproteins only fucose. These epitopes and other fucosylated determinants are also found in helminth parasites where they exert remarkable immunomodulatory effects. About 20% or more of allergic patients generate specific anti-glycan IgE, which is often accompanied by IgG. Even though antibody-binding glycoproteins are widespread in pollens, foods and insect venoms, CCDs do not appear to cause clinical symptoms in most, if not all patients. When IgE binding is solely due to CCDs, a glycoprotein allergen thus can be rated as clinical irrelevant allergen. Low binding affinity between IgE and plant N-glycans now drops out as a plausible explanation for the benign nature of CCDs. This rather may result from blocking antibodies induced by an incidental 'immune therapy' ('glyco-specific immune therapy') exerted by everyday contact with plant materials, e.g. fruits or vegetables. The need to detect and suppress anti-CCD IgE without interference from peptide epitopes can be best met by artificial glycoprotein allergens. Hydroxyproline-linked arabinose (single beta-arabinofuranosyl residues) has been identified as a new IgE-binding carbohydrate epitope in the major mugwort allergen. However, currently the occurrence of this O-glycan determinant appears to be rather restricted.

Diagnostic challenges for multiplexed protein microarrays

Multiplexed protein analysis using planar microarrays or microbeads is growing in popularity for simultaneous assays of antibodies, cytokines, allergens, drugs and hormones. However, this new assay format presents several new operational issues for the clinical laboratory, such as the quality control of protein-microarray-based assays, the release of unrequested test data and the use of diagnostic algorithms to transform microarray data into diagnostic results.

Component-resolved diagnostics in food allergy

PURPOSE OF REVIEW

The purpose of this paper is to review and discuss recent studies on component-resolved diagnostics in food allergy, involving panels of pure allergen molecules or arrays of peptides derived from allergen sequences, and to summarize the reporting of new food allergens during the past 2 years.

RECENT FINDINGS

Several component-resolved diagnostic studies in food allergy suggest that the use of panels of allergen molecules may allow refined clinical information to be obtained on the likelihood or severity of an allergic food reaction and regarding diagnostic specificity. Further, in some studies the use of pure allergen molecules has led to a clearly higher sensitivity of the immunoglobulin E immunoassay compared with conventional allergen extracts.

SUMMARY

While common diagnostic methods in allergy assess the presence or absence of allergen-specific sensitization, to date, no in-vitro or in-vivo test exists which exhibits full correlation with clinical food allergy. A multitude of recently reported findings and observations indicate that molecular analysis of allergen sensitization pattern may serve to enhance the clinical utility of immunoglobulin E antibody-based allergy diagnostics. Pure natural and recombinant allergen molecules as well as panels of synthetic peptides have been used for this purpose.