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Birch pollinosis is often accompanied by adverse reactions to food due to pollen-allergen specific IgE cross-reacting with homologous food allergens. The tertiary structure of Pru av 1, the major cherry (Prunus avium) allergen, for example, is nearly identical with Bet v 1, the major birch (Betula verrucosa) pollen allergen. In order to define cross-reactive IgE epitopes, we generated and analysed mutants of Pru av 1 and Api g 1.0101, the major celery (Apium graveolens) allergen, by immunoblotting, EAST (enzyme allergosorbent test), CD and NMR spectroscopy. The mutation of Glu 45 to Trp 45 in the P-loop region, a known IgE epitope of Bet v 1, significantly reduced IgE binding to Pru av 1 in a subgroup of cherry-allergic patients. The backbone conformation of Pru av 1 wild-type is conserved in the three-dimensional structure of Pru av 1 Trp 45 , demonstrating that the side chain of Glu 45 is involved in a cross-reactive IgE epitope. Accordingly, for a subgroup of celery-allergic patients, IgE binding to the homologous celery allergen Api g 1.0101 was enhanced by the mutation of Lys 44 to Glu. The almost complete loss of IgE reactivity to the Pru av 1 Pro 112 mutant is due to disruption of its tertiary structure. Neither the mutation Ala 112 nor deletion of the Cterminal residues 155-159 influenced IgE binding to Pru av 1. In conclusion, the structure of the P-loop partially explains the crossreactivity pattern, and modulation of IgE-binding by site-directed mutagenesis is a promising approach to develop hypo-allergenic variants for patient-tailored specific immunotherapy.

Background: This study was performed to get further insights into antibody responses to cross–reactive carbohydrate determinants (CCD), including initial experiments to prove the biological activity of anti–CCD IgE. Earlier studies have shown that IgE specific for CCD occurs in about 25% of celery–allergic patients. The clinical significance of these antibody specificities is doubtful. Methods: Patient sera were selected on the basis of a positive case history of celery allergy and multiple binding to high molecular weight celery allergens on immunoblots. Specific IgE to native and heated celery tuber was determined by the enzyme allergosorbent test (EAST). N–glycans were purified after extensive digestion of specific glycoproteins, such as pineapple stem bromelain, bovine fibrin, and human IgG, and used as antigens in an IgE ELISA as well as in EAST and immunoblotting inhibition experiments. Dose–related histamine release was performed with BSA neoglycoproteins containing 3–4 units of the purified glycopeptides. Results: Seven celery–allergic patients were identified who clearly presented IgE against the N–glycan purified from bromelain which is a common structure within the plant kingdom. Chemical defucosylation showed that α1,3–fucose is a key structure for IgE binding. In patients with anti–CCD IgE, the maximal inhibition of celery EAST by the bromelain glycan ranged from 22 to 100%. Inhibition of celery immunoblots by preincubation of patient serum with this glycan led to a quenching of multiple bands at masses >40 kD. After linking the bromelain glycopeptide to BSA, a strong dose–related histamine release was obtained in a celery–allergic patient, occurring at lower concentrations than with the recombinant major protein allergen from celery, Api g 1. Conclusions: Our results demonstrate that IgE specific for CCD is common in celery–allergic patients, and can represent the major proportion of IgE against this food. α1,3–fucose was confirmed to be an essential part of the IgE epitope. Immunoblotting inhibition indicated the presence of this carbohydrate determinant on multiple glycoproteins in celery extract. Although histamine release was only performed in 1 patient, our data show that proteins carrying multiple glycan units can be biologically active in patients sensitized to CCD.

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Allergen extracts have been used for diagnosis and treatment of allergy for around 100 years. During the second half of 20th century, the notion increasingly gained foothold that accurate standardization of such extracts is of great importance for improvement of their quality. As a consequence, manufacturers have implemented extensive protocols for standardization and quality control. These protocols have overall IgE-binding potencies as their focus. Unfortunately, each company is using their own in-house reference materials and their own unique units to express potencies. This does not facilitate comparison of different products. During the last decades, most major allergens of relevant allergen sources have been identified and it has been established that effective immunotherapy requires certain minimum quantities of these allergens to be present in the administered maintenance dose. Therefore, the idea developed to introduce major allergens measurements into standardization protocols. Such protocols based on mass units of major allergen, quantify the active ingredients of the treatment and will at the same time allow comparison of competitor products. In 2001, an EU funded project, the CREATE project, was started to support introduction of major allergen based standardization. The aim of the project was to evaluate the use of recombinant allergens as reference materials and of ELISA assays for major allergen measurements. This paper gives an overview of the achievements of the CREATE project.

SummaryPlant genetic engineering has the potential to introduce new allergenic proteins into foods but, at the same time, it can be used to remove established allergens. Here, we report the molecular characterization of Lyc e 3, a new tomato ( Lycopersicon esculentum ) allergen, and the efficient down-regulation of its expression in transgenic tomato plants. Ectopic expression of LTPG1 and LTPG2 in Escherichia coli , followed by immunoblotting, verified their IgE reactivity. Subsequently, transgenic tomato plants constitutively expressing LTPG1-or LTPG2-specific double-stranded RNA interference (dsRNAi) constructs were created and tested for the suppression of Lyc e 3 accumulation. Efficient silencing of Lyc e 3 was documented by Northern and Western blotting. In both cases, Lyc e 3 accumulation was decreased to levels below the detection limit (less than 0.5% of the wild-type protein).The allergenic potential of Lyc e 3-deficient tomato fruits was tested by measuring histamine release from sensitized human basophils stimulated with transgenic and parental lines.These assays revealed a strong (10-to 100-fold) decrease in histamine release of human basophils challenged with transgenic fruit extracts when compared with control extracts.These results demonstrate the feasibility of creating low allergenic tomato fruits by means of dsRNAi inhibition.

Our panel of recombinant allergens from carrot can provide a standardized tool for in vitro diagnosis of carrot allergy, and for epitope studies.