The CREATE project: development of certified reference materials for allergenic products and validation of methods for their quantification

A comparison of in vitro potency between European and Mexican allergen extracts and US (CBER/FDA) reference extracts

BACKGROUND

The most important allergen manufacturers are based in Europe and in the US. In some countries local products are also sold. No comparison between European, US and local products has been made until now.

AIM OF THE STUDY

To determine total protein content and total specific IgE binding capacity or major allergen content of diagnostic extracts from European, US and Mexican origins relative to the CBER/FDA reference extracts for Dermatophagoides pteronyssinus (Dpt), Bermuda grass and cat (10,000(B) AU/mL).

METHODS

Diagnostic extracts were purchased from various manufacturers, blinded and shipped to the analysing laboratory, where the following assays were conducted: total protein concentration (Bradford), specific IgE competition ELISA (Dpt and Bermuda grass) and determination of Fel d 1 U/mL. When available, CBER/FDA recommended tests and reagents were used.

RESULTS

Total protein content of US reference extracts was higher than all other extracts. Relative potency of European and US-bought Dpt extracts 3,300-4,400 AU/mL, Bermuda grass 800-2,500 BAU/mL and cat 2.1-4.4 Fel d IU/mL (Ref. 19 U/mL), with one exception. Locally produced Mexican products were almost all below 1,000 (B)AU/mL.

CONCLUSIONS

Three diagnostic extracts from European manufacturers and from Mexican providers which obtain extracts in US have a <50% relative potency compared to 10,000 (B)AU/mL US extracts. Locally produced Mexican extracts have much lower total protein content and specific IgE binding capacity. These in vitro results must be complemented with other in vitro and in vivo skin prick tests to obtain a more complete picture of comparison of potency. Nevertheless results are quite consistent for the allergens tested here.

Skin prick test evaluation of Dermatophagoides pteronyssinus diagnostic extracts from Europe, Mexico, and the United States

BACKGROUND

Previous Food and Drug Administration (FDA)-approved enzyme-linked immunosorbent assay testing of Dermatophagoides pteronyssinus diagnostic extracts showed potencies of 36% to 44% for 3 European extracts relative to the FDA standard (10,000 AU/mL).

OBJECTIVE

To compare biological activity of various European D pteronyssinus diagnostic extracts against an FDA-validated extract using quantitative skin prick tests.

METHODS

Six diagnostic D pteronyssinus extracts (1 reference extract, which was made up of 10,000 AU/mL of the FDA-approved extract; 3 European extracts; 1 US-Mexican extract, which is imported as raw material from the United States and sold in Mexico; and 1 Mexican extract) were tested during 2 skin prick test sessions as a concentrate and 2 serial 2-fold dilutions, in quadruplicate, on the backs of 19 patients with D pteronyssinus allergic rhinitis. The Wilcoxon test for linked random samples was used in each group to investigate whether the distribution of the reference extract differed from each of the test extracts to a statistically significant degree (test level alpha = .05).

RESULTS

Extracts showed good dose response in wheal size for the concentrate compared with the 2 dilutions (steep part of the curve). All 3 European extracts (2-sided asymptotic significance, P = .003, P = .009, and P = .01, respectively) and 1 Mexican (P < .001) extract were less potent than the reference extract. European extracts varied in potency from 5,400 to 6,126 AU/mL, the US-Mexican extract had a potency of 7,444 AU/mL, and the Mexican extract had a potency of 2,099 AU/mL.

CONCLUSIONS

Our study confirmed the results from previous in vitro testing. Various diagnostic extracts of D pteronyssinus used in Europe and Mexico are less potent than those used in the United States. Similar comparisons using therapeutic extracts would be of interest.

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.

Tolerance induction after specific immunotherapy with pollen allergoids adjuvanted by monophosphoryl lipid A in children

Specific immunotherapy (SIT) is a well-established and clinically effective treatment for allergic diseases. A pollen allergoid formulated with the T helper type 1 (Th1)-inducing adjuvant monophosphoryl lipid A (MPL) facilitates short-term SIT. Little is known about mechanisms of tolerance induction in this setting. In a prospective study, 34 patients allergic to grass pollen (25 male, nine female, median age 10.2 years) received a total of 44 SIT courses (20 in the first, 24 in the second) with MPL-adjuvanted pollen allergoids. Immunogenicity was measured by levels of specific immunoglobulin G (IgG(grass)) and IgG4(grass) by antibody blocking properties on basophil activation, and by induction of CD4(+), CD25(+) and forkhead box P3 (FoxP3(+)) regulatory T cells (T(reg)). Specific IgG and IgG4 levels increased only slightly in the first year of SIT. In the second year these changes reached significance (P < 0.0001). In keeping with these findings, we were able to show an increase of T(reg) cells and a decreased release of leukotrienes after the second year of treatment. In the first year of treatment we found little evidence for immunological changes. A significant antibody induction was seen only after the second course of SIT. Short-course immunotherapy with pollen allergoids formulated with the Th1-inducing adjuvant MPL needs at least two courses to establish tolerance.

Antigen-specific immunotherapy against allergic rhinitis: the state of the art

Allergic rhinitis is the most prevalent type I allergy in industrialized countries. Pollen scattering from trees or grasses often induces seasonal allergic rhinitis, which is known as pollinosis or hay fever. The causative pollen differs across different areas and times of the year. Impaired performance due to pollinosis and/or medication used for treating pollinosis is considered to be an important reason for the loss of concentration and productivity in the workplace. Antigen-specific immunotherapy is an only available curative treatment against allergic rhinitis. Subcutaneous injection of allergens with or without adjuvant has been commonly used as an immunotherapy; however, recently, sublingual administration has come to be considered a safer and convenient alternative administration route of allergens. In this review, we focus on the safety and protocol of subcutaneous and sublingual immunotherapy against seasonal allergic rhinitis. We also describe an approach to selecting allergens for the vaccine so as to avoid secondary sensitization and adverse events. The biomarkers and therapeutic mechanisms for immunotherapy are not fully understood. We discuss the therapeutic biomarkers that are correlated with the improvement of clinical symptoms brought about by immunotherapy as well as the involvement of Tr1 and regulatory T cells in the therapeutic mechanisms. Finally, we focus on the current immunotherapeutic approach to treating Japanese cedar pollinosis, the most prevalent pollinosis in Japan, including sublingual immunotherapy with standardized extract, a transgenic rice-based edible vaccine, and an immunoregulatory liposome encapsulating recombinant fusion protein.

Comparison of allergen immunotherapy practice patterns in the United States and Europe

OBJECTIVE

To discuss important differences and similarities in the allergen specific immunotherapy (SIT) treatment practices for aeroallergen sensitivity in the United States and Europe.

DATA SOURCES

Information on regulation and standardization in the United States and Europe was obtained from a Food and Drug Administration Allergenic Products Advisory Committee meeting, published literature, personal communications, and information obtained from the extract manufacturers.

STUDY SELECTION

Information from the published literature included articles known to the authors and acknowledged consultants, textbooks, and PubMed, with search terms dependent on the particular subtopic.

RESULTS

Key differences between Europe and the United States include allergen extract regulation, standardization, formulation, types of allergen extracts, routes of administration, and reimbursement. Most SIT is formulated in US allergists' offices, whereas virtually all SIT is formulated by extract manufacturers in Europe. Sublingual immunotherapy represents a significant percentage of SIT treatment in Europe (approximately 45%), but only a small percentage of US allergists (approximately 5.9%) prescribe sublingual immunotherapy. Similarities between European and US allergist specialists lie in their perception of SIT and approach to providing optimal SIT care, which is detailed in their practice guidelines.

CONCLUSION

Significant differences and similarities exist in SIT practice patterns of US and European allergy specialists. The differences lie primarily in the availability of allergen extracts and how these extracts are formulated. A key similarity is that both recognize the need for ongoing research focused on developing safer and more effective SIT.

Characterization and comparison of commercially available mite extracts for in vivo diagnosis

BACKGROUND

Assessment of sensitization by allergen-specific IgE testing and skin prick testing (SPT) are primary tools in routine clinical diagnosis of allergies. To perform a correct diagnosis, it is critical that the allergen reagent used contains an adequate amount of all relevant components. This study aimed at evaluating commercially available mite extracts for in vivo diagnosis from eight manufacturers.

METHODS

Eight extracts from Dermatophagoides pteronyssinus and eight from Dermatophagoides farinae were analysed for total protein content by Bradford and for major allergen content by ELISA. SDS-PAGE, immunoblotting and SPT were also carried out.

RESULTS

The protein amount ranged from 27.7 microg/ml extract to 361.1 microg/ml (D. pteronyssinus) and from 20.3 to 353.0 microg/ml (D. farinae). In regards major allergen concentration, Der p 1 ranged from 9.6 to 36.2 microg/ml, Der f 1 26.5-196.1 microg/ml, mite group 2 0.7-31.7 microg/ml in D. pteronyssinus and 1.3-10.4 microg/ml in D. farinae. SDS-PAGE experiments showed that some components are poorly represented or absent in extracts from most manufacturers. Similar results were obtained by IgE-immunoblotting and SPT with 10 mite allergic patients confirmed a broad spectrum of reactivity of the extracts in the same subject.

CONCLUSIONS

Immunochemical analysis showed a heterogeneous amount of component/s among mite extracts from different manufacturers. These data were confirmed by in vivo testing, suggesting that, for some of the patient tested, the absence of relevant allergens could strongly affect the diagnosis.

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.

Component-resolved diagnosis of pollen allergy based on skin testing with profilin, polcalcin and lipid transfer protein pan-allergens

BACKGROUND

Allergy diagnosis needs to be improved in patients suffering from pollen polysensitization due to the existence of possible confounding factors in this type of patients.

OBJECTIVE

To evaluate new diagnostic strategies by comparing skin responses to pan-allergens and conventional allergenic extracts with specific IgE (sIgE) to purified allergen molecules.

METHODS

One thousand three hundred and twenty-nine pollen-allergic patients were diagnosed by a combination of an in vitro method with a panel of 13 purified allergens, including major allergens and pan-allergens, using a high-capacity screening technology (ADVIA-Centaur) and skin prick test (SPT) to pan-allergens and conventional extracts.

RESULTS

There was a high concordance (kappa index) between in vitro (sIgE to major allergens) and in vivo (SPT to conventional extracts) methods in patients who were not sensitized to pan-allergens, but SPT with conventional extracts failed to diagnose patients with sensitization to pan-allergens. In patients who were simultaneously sensitized to polcalcins and profilins, there was a duplication both in the number of sensitizations to major allergens and in the years of disease evolution. There was a statistical association between sensitization to profilins and/or lipid transfer proteins and food allergy (P<0.0001).

CONCLUSION

The novel diagnostic strategy has proven to be a valuable tool in daily clinical practice. Introduction of routine SPT to pan-allergens is a simple and feasible way of improving diagnostic efficacy. Patients sensitized to pan-allergens should be tested by an adequate panel of allergenic molecules in order to identify the allergens that are responsible for the allergic disease.

The CONSORT statement checklist in allergen-specific immunotherapy: a GA2LEN paper

The methodology of randomized clinical trials is essential for the critical assessment and registration of therapeutic interventions. The CONSORT (Consolidated Standards of Reporting Trials) statement was developed to alleviate the problems arising from the inadequate reporting of randomized controlled trials. The present article reflects on the items that we believe should be included in the CONSORT checklist in the context of conducting and reporting trials in allergen-specific immunotherapy. Only randomized, blinded (in particular blinding of patients, health care providers, and outcome assessors), placebo-controlled Phase III studies in this article. Our analysis focuses on the definition of patients' inclusion and exclusion criteria, allergen standardization, primary, secondary and exploratory outcomes, reporting of adverse events and analysis.

GA(2)LEN skin test study I: GA(2)LEN harmonization of skin prick testing: novel sensitization patterns for inhalant allergens in Europe

BACKGROUND

Skin prick testing is the standard for diagnosing IgE-mediated allergies. However, different allergen extracts and different testing procedures have been applied by European allergy centres. Thus, it has been difficult to compare results from different centres or studies across Europe. It was, therefore, crucial to standardize and harmonize procedures in allergy diagnosis and treatment within Europe.

AIMS

The Global Asthma and Allergy European Network (GA(2)LEN), with partners and collaborating centres across Europe, was in a unique position to take on this task. The current study is the first approach to implement a standardized procedure for skin prick testing in allergies against inhalant allergens with a standardized pan-European allergen panel.

METHODS

The study population consisted of patients who were referred to one of the 17 participating centres in 14 European countries (n = 3034, median age = 33 years). Skin prick testing and evaluation was performed with the same 18 allergens in a standardized procedure across all centres.

RESULTS

The study clearly shows that many allergens previously regarded as untypical for some regions in Europe have been underestimated. This could partly be related to changes in mobility of patients, vegetation or climate in Europe.

CONCLUSION

The results of this large pan-European study demonstrate for the first time sensitization patterns for different inhalant allergens in patients across Europe. The standardized skin prick test with the standardized allergen battery should be recommended for clinical use and research. Further EU-wide monitoring of sensitization patterns is urgently needed.

Allergen content of grass pollen preparations for skin prick testing and sublingual immunotherapy

BACKGROUND

The allergen content of diagnostics and immunotherapeutics is crucial for effective diagnosis and treatment. The aim of this study was to quantify and compare the allergen content of different grass pollen preparations for skin prick testing and sublingual immunotherapy (SLIT).

METHODS

Five skin prick test (SPT) solutions and 10 sublingual immunotherapeutics were analysed for protein and allergen concentration by Bradford assay, inhibition of IgE-binding to Phleum pratense ImmunoCAPs and content of the main allergen Phl p 5 by two-site enzyme immunoassay. In addition, the grass pollen preparations were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analyses.

RESULTS

Protein concentrations of SPT solutions ranged from 15 to 427 microg/ml, and Phl p 5 concentrations ranged from 0.15 to 18.3 microg/ml. The ranking of SPT solutions concerning Phl p 5 content and IgE inhibition capacity was the same, and the ranking of protein and allergen content was closely correlated (r = 0.9). Protein content of the maintenance doses of the immunotheurapeutics ranged from 5 to 153 microg, Phl p 5 content ranged from 0.2 to 21.6 microg. IgE inhibition capacity of the maintenance doses was closely correlated to their Phl p 5 and protein content. SDS-PAGE and immunoblots confirmed the differences in protein and allergen content.

CONCLUSIONS

Grass pollen preparations for SPT and SLIT varied greatly concerning protein and allergen content. Whereas this result corresponds to previous analyses results of SPT solutions, it was the first comparison of grass pollen immunotherapeutics. For diagnosis and therapy, these differences should be taken into account.

Standardization of allergen products: 1. Detailed characterization of GMP-produced recombinant Bet v 1.0101 as biological reference preparation

BACKGROUND

Standardization of allergen extracts requires the availability of well-characterized recombinant allergens, which can be used as reference standards provided by the European regulatory authorities. The objective of this study was the detailed physicochemical and immunological characterization of rBet v 1.0101, which shall be used in a ring trial within the framework of the Biological Standardization Programme BSP090 of the European Directorate for Quality of Medicines and Healthcare.

METHODS

Recombinant Bet v 1.0101 Y0487 was produced under good manufacturing practice conditions and analysed by an array of physicochemical and immunological methods for identity, quantity, homogeneity, folding and denaturation, aggregation state and stability in solution, as well as biological activity.

RESULTS

Batch Y0487 was shown to contain monomeric and well-folded protein being identical with rBet v 1.0101, as determined by mass spectrometry. SDS-PAGE, isoelectric focusing, deamidation analysis and size-exclusion chromatography with light scattering revealed sample homogeneity of >99.9%. Upon storage at +4 degrees C batch Y0487 retained the monomeric state up to 3 months. Protein quantification determined by amino acid analysis was found coinciding with half-maximal inhibition of serum IgE in ELISA. Biological activity of batch Y0487 was shown to be comparable to natural Bet v 1 by IgG and IgE immunoblotting, as well as basophil and T-cell activation.

CONCLUSION

Recombinant Bet v 1.0101 Y0487 was characterized extensively by physicochemical and immunological methods. It was shown highly stable, monomeric and immunologically equivalent to its natural counterpart. Thus, it represents an appropriate candidate reference standard for Bet v 1.

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.

Mediator release assay for assessment of biological potency of German cockroach allergen extracts

BACKGROUND

Cockroach is an important allergen in inner-city asthma. The diagnosis and treatment of cockroach allergy has been impeded by the lack of standardized cockroach extracts.

OBJECTIVE

We investigated the utility of a mediator release assay based on rat basophil leukemia (RBL) cells for comparing the potency of German cockroach extracts.

METHODS

RBL cells (line 2H3) transfected with human FcepsilonRI were passively sensitized with sera from subjects with cockroach allergy and stimulated with serial dilutions of 3 commercial cockroach extracts (1:10 weight/volume). In addition, the in-house prepared extract was tested in separate experiments with pooled sera that produced optimal performance in the RBL assay. N-hexosaminidase release (NHR) was used as a marker of RBL cell degranulation and was examined in relation to the intradermal skin test (ID(50)EAL) and serum cockroach-specific and total IgE levels.

RESULTS

The median cockroach-specific IgE concentration in 60 subjects was 0.72 kU(A)/L (interquartile range, 0.35-2.97 kU(A)/L); 19 sera (responders) produced a minimum 10% NHR to more than 1 extract. Responders had higher median cockroach-specific IgE (7.4 vs 1.0 kU(A)/L) and total IgE (429 vs 300 kU/L) levels than nonresponders. Ranking of extract potency was consistent between the mediator release assay and the ID(50)EAL. For the in-house prepared cockroach extract, the dose-response curves were shifted according to the concentration of the extract. NHR was reproducible between different experiments by using pooled sera.

CONCLUSION

The mediator release assay measures biologic potency and correlates with the ID(50)EAL. It should be further evaluated to determine whether it could be used to replace intradermal skin test titration for assessing the potency of cockroach extract.

Immunologic characterization of isoforms of Car b 1 and Que a 1, the major hornbeam and oak pollen allergens

BACKGROUND

Birch pollen allergy is one of the most common causes of spring pollinosis often associated with hypersensitivity reactions to pollen of other Fagales species. Yet, only the major disease eliciting allergens of alder and hazel have been fully characterized. Therefore, the aim of this study was to perform cloning, expression and immunologic characterization of the Bet v 1 homologues from oak (Que a 1) and hornbeam (Car b 1).

METHODS

The isoform pattern of Car b 1 and Que a 1 was analyzed by proteomics using 2D gel electrophoresis and LC ESI-QTOF MS. Isoallergens showing high IgE-binding were cloned and expressed in Escherichia coli. IgE-binding activity of the recombinant proteins was determined by enzyme-linked immunosorbent assay (ELISA) and basophil mediator release assays using serum samples from patients mainly exposed either to oak and hornbeam or to birch pollen. Cross-reactivity of the allergens was further investigated at the T-cell level.

RESULTS

Dominant isoforms of Car b 1 and Que a 1, identified by mass spectrometry, showed different IgE-binding properties when testing Fagales pollen-allergic patients living in birch-free areas as compared to birch-sensitized individuals.

CONCLUSION

Tree pollen-allergic patients who are primarily exposed to Fagales pollen other than birch reacted stronger with rCar b 1 and rQue a 1 than with rBet v 1, as determined by inhibition ELISA and basophil mediator release assays. Thus, rCar b 1 and rQue a 1 allergens should be considered for improving molecule-based diagnosis and therapy of tree pollen allergies manifesting in birch-free areas.

Subcutaneous and sublingual immunotherapy in children: complete update on controversies, dosing, and efficacy

For this review, articles on immunotherapy dosing in pediatric respiratory allergy were identified via PubMed, through congressional abstracts for 2008, in reference lists of recent review articles, and via personal communication with experts. In pediatric subcutaneous immunotherapy (SCIT), doses shown to be effective, mostly in aluminium-adsorbed preparations administered every 6 weeks, contain 20 microg of group 5 major allergen, 12 microg Bet v 1, 15 microg Fel d 1, and 5 to 20 microg Der p 1. Evidence indicates that SCIT prevents new sensitizations and asthma onset 7 years after discontinuation and reduces symptoms 12 years after a 5-year SCIT course, even though skin reactivity returns. Consistent evidence of effect exists for sublingual immunotherapy in pediatric respiratory allergy with daily 15- to 25-microg grass group 5 major allergen and 6 microg Bet v 1. Der p/f doses of 0.8/0.4 microg three times weekly (up to 27/57 microg daily) demonstrate inconsistent findings. Evidence of effect exists for SCIT in pediatric allergic rhinitis and asthma as treatment and preventive management. Evidence of effect exists for sublingual immunotherapy in pediatric allergic rhinoconjunctivitis and seasonal asthma. Similar results are doubtful for perennial asthma.

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.

The European Union CREATE project: a model for international standardization of allergy diagnostics and vaccines

Allergen measurements are used extensively in the formulation of allergy diagnostics and vaccines, yet no purified international allergen standards are available for calibration purposes. The aims of the European Union CREATE project were to develop international standards with verifiable allergen content. Purified natural and recombinant allergens were analyzed by means of SDS-PAGE, mass spectrometry, circular dichroism spectra, and small-angle x-ray scattering. IgE reactivity was assessed by means of direct RAST, RAST inhibition, immunoblotting, and basophil histamine release with sera from 961 allergic patients. Three recombinant allergens, rBet v 1, rPhl p 5a, and rDer p 2, were structurally indistinguishable from their natural counterparts and showed excellent IgE reactivity suitable for use as certified reference materials. A second tier of allergens (rPhl p 5b, rOle e1, rDer p 1, rDer f 1, and rDer f 2) was identified that could provide suitable candidates for certified reference materials with minor improvements to the recombinant proteins. Only rPhl p 1 was considered unsuitable as a reference material. Quantitative ELISAs were identified that accurately measured each allergen, except for rPhl p 1. The CREATE project has provided a major step forward in allergen standardization and provides a model for the development of a comprehensive panel of international reference preparations that will harmonize allergen measurements worldwide.

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.