Quantification in mass units of group 1 grass allergens by a monoclonal antibody-based sandwich ELISA

Multiple grass mixes as opposed to single grasses for allergen immunotherapy in allergic rhinitis

Grass pollen allergy affects approximately 40% of allergic patients. Subcutaneous allergen immunotherapy (SCIT) is the only allergen-specific and disease-modifying treatment available. Currently available therapeutic vaccines for the treatment of grass pollen allergy are based on natural grass pollen extracts which are either made from pollen of one cross-reactive grass species or from several related grass species. Clinical studies have shown that SCIT performed with timothy grass pollen extract is effective for the treatment of grass pollen allergy. Moreover, it has been demonstrated that recombinant timothy grass pollen allergens contain the majority of relevant epitopes and can be used for SCIT in clinical trials. However, recent in vitro studies have suggested that mixes consisting of allergen extracts from several related grass species may have advantages for SCIT over single allergen extracts. Here, we review current knowledge regarding the disease-relevant allergens in grass pollen allergy, available clinical studies comparing SCIT with allergen extracts from timothy grass or from mixes of several related grass species of the Pooideae subfamily, in vitro cross-reactivity studies performed with natural allergen extracts and recombinant allergens and SCIT studies performed with recombinant timothy grass pollen allergens. In vitro and clinical studies performed with natural allergen extracts reveal no relevant advantages of using multiple grass mixes as opposed to single grass pollen extracts. Several studies analysing the molecular composition of natural allergen extracts and the molecular profile of patients' immune responses after SCIT with allergen extracts indicate that the major limitation for the production of a high quality grass pollen vaccine resides in intrinsic features of natural allergen extracts which can only be overcome with recombinant allergen-based technologies.

An antibody-based ELISA for quantification of Ani s 1, a major allergen fromAnisakis simplex

Anisakis simplexis a nematode parasite that can infect humans who have eaten raw or undercooked seafood. Larvae invading the gastrointestinal mucosa excrete/secrete proteins that are implicated in the pathogenesis of anisakiasis and can induce IgE-mediated symptoms. Since Ani s 1 is a potent secreted allergen with important clinical relevance, its measurement could assess the quality of allergenic products used in diagnosis/immunotherapy ofAnisakisallergy and track the presence ofA. simplexparasites in fish foodstuffs. An antibody-based ELISA for quantification of Ani s 1 has been developed based on monoclonal antibody 4F2 as capture antibody and biotin-labelled polyclonal antibodies against Ani s 1 as detection reagent. The dose-response standard curves, obtained with natural and recombinant antigens, ranged from 4 to 2000 ng/ml and were identical and parallel to that of theA. simplexextract. The linear portion of the dose-response curve with nAni s 1 was between 15 and 250 ng/ml with inter-assay and intra-assays coefficients of variation less than 20% and 10%, respectively. The assay was specific since there was no cross-reaction with other extracts (exceptAscarisextracts) and was highly sensitive (detection limit of 1·8 ng/ml), being able to detect Ani s 1 in fish extracts from codfish and monkfish.

Quantification of the major allergen from cypress (Cupressus arizonica) pollen, Cup a 1, by monoclonal antibody-based ELISA

BACKGROUND

Cypress pollen allergy is an important cause of rhinoconjunctivitis and asthma in Mediterranean countries. Cypress allergenic extracts are difficult to produce since they have low protein and high carbohydrate content, thus accurate standardization of them is essential to guarantee their quality. The aim of this study is to develop a sandwich ELISA for the quantification of Cup a 1, the major allergen of cypress (Cupressus arizonica) pollen extract.

METHODS

Monoclonal antibodies directed to purified Cup a 1 were produced. Two of them (9C7 as capture antibody and 3D2 as the tracer) were selected to develop a quantitative sandwich ELISA. This ELISA was subsequently evaluated and compared with other techniques.

RESULTS

The described ELISA is very sensitive with a detection limit of 8.7 ng/ml and a practical working range of 62.5-1,000 ng/ml. The assay is also highly reproducible with intra-assay and interassay coefficients of variation of less than 10%. The purified Cup a 1, used as standard, presents pectate lyase enzymatic activity. The assay also detected Cup a 1-like proteins in pollen from other Cupressaceae. A good correlation was obtained between Cup a 1 content of 12 C. arizonica pollen extracts and their IgE-binding activity.

CONCLUSIONS

The described Cup a 1 ELISA is sensitive, specific and reproducible and can be used for the quantification of Cup a 1 in C. arizonica and other related pollen extracts. It also provides a reliable indication of the allergenic activity of the whole cypress pollen extract.

Human monoclonal antibody–based quantification of group 2 grass pollen allergens

BACKGROUND

Grasses belong to the most potent allergen sources worldwide. Group 2 grass pollen allergens are recognized by more than 100 million allergic patients.

OBJECTIVE

The aim was to develop an assay for the specific detection and quantification of group 2 grass pollen allergens.

METHODS

We have isolated a monoclonal human IgE Fab specific for group 2 grass pollen allergens by combinatorial cloning from lymphocytes of a grass pollen-allergic patient. This Fab was converted into a complete human IgG1 antibody and used together with rPh1 p 2 to develop a competitive ELISA for the specific measurement of group 2 allergens. ELISA plate-bound purified recombinant human Ph1 p 2-specific IgG1 is incubated with a constant amount of biotinylated rPh1 p 2 competing with increasing concentrations of group 2 allergens to be determined. Defined concentrations of purified rPhl p 2 are used to establish a standard curve. The concentration of unlabeled group 2 allergens can thus be deduced from the displacement of biotinylated rPh1 p 2, which can be detected with peroxidase-labeled streptavidin.

RESULTS

The competition-ELISA measured rPh1 p 2 concentrations ranging from 10 ng/mL to 500 ng/mL and allowed to quantify group 2 allergens from 9 different grass families. The results were in good agreement with immunoblot data.

CONCLUSIONS

The described assay can be used for standardization of diagnostic and therapeutic vaccines as well as for the quantification of group 2 allergens in environmental samples.

Proteomics of allergens

The present state of proteomics research is generally outlined and the character of allergenic compounds briefly elucidated. The principles of experimental approaches to isolation, purification, identification and characterization of allergens and to monitoring of their biological activity are described, with emphasis on the most modern methods. Selected examples are given for illustration and important results are summarized in tables.

Purification and characterization of Pla a 1, a major allergen from Platanus acerifolia pollen

BACKGROUND

Plane trees, as Platanus acerifolia, are an important source of airborne allergens in cities of the United States and Western Europe. Little is known about the relevant allergens of this pollen. The aim of this study was to identify relevant allergens from P. acerifolia pollen and purify and characterize a major allergen of 18 kDa.

METHODS

P. acerifolia pollen extract was fractionated using ion exchange, gel filtration, and reverse-phase chromatography. Analyzes were carried out by EAST, SDS-PAGE, isoelectric focusing, immunoblotting and amino-acid sequencing.

RESULTS

An 18-kDa protein from the P. acerifolia pollen extract, which we named Pla a 1, was purified. This nonglycosylated protein had an isoelectric point value higher than 9.3 and was recognized by up to 92% of monosensitized Platanus allergic patients and 83% of polyzensitized patients. Sequencing of its N-terminal yielded an amino acid sequence which showed no homology to the known proteins in the databases. Other relevant allergens detected in monosensitized patients were proteins of 43 and 52 kDa, with immunoglobulin (Ig)E-binding prevalences of 83 and 42%, respectively. Profilin was an important allergen in polyzensitized patients.

CONCLUSIONS

The most relevant allergens from the P. acerifolia pollen have been determined. A major allergen, specific of this pollen, and named Pla a 1, has been purified and characterized.