Human IgE against the major allergen Bet v 1--defining an epitope with limited cross-reactivity between different PR-10 family proteins

A genome-wide association study for allergen component sensitizations identifies allergen component-specific and allergen protein group-specific associations

Background

Allergic diseases are some of the most common diseases worldwide. Genome-wide association studies (GWASs) have been conducted to elucidate the genetic factors of allergic diseases. However, no GWASs for allergen component sensitization have been performed.

Objective

We sought to detect genetic variants associated with differences in immune responsiveness against allergen components.

Methods

The participants of the present study were recruited from the Tokyo Children's Health, Illness, and Development study, and allergen component-specific IgE level at age 9 years was measured by means of allergen microarray immunoassays. We performed GWASs for allergen component sensitization against each allergen (single allergen component sensitization, number of allergen components analyzed, n = 31), as well as against allergen protein families (allergen protein group sensitization, number of protein groups analyzed, n = 16).

Results

We performed GWAS on 564 participants of the Tokyo Children's Health, Illness, and Development study and found associations between Amb a 1 sensitization and the immunoglobulin heavy-chain variable gene on chromosome 14 and between Phl p 1 sensitization and the HLA class II region on chromosome 6 (P < 5.0 × 10-8). A GWAS-significant association was also observed between the HLA class II region and profilin sensitization (P < 5.0 × 10-8).

Conclusions

Our data provide the first demonstration of genetic risk for allergen component sensitization and show that this genetic risk is related to immune response genes including immunoglobulin heavy-chain variable gene and HLA.

Targeting immunodominant Bet v 1 epitopes with monoclonal antibodies prevents the birch allergic response

BACKGROUND

Blocking the major cat allergen, Fel d 1, with mAbs was effective in preventing an acute cat allergic response.

OBJECTIVES

This study sought to extend the allergen-specific antibody approach and demonstrate that a combination of mAbs targeting Bet v 1, the immunodominant and most abundant allergenic protein in birch pollen, can prevent the birch allergic response.

METHODS

Bet v 1-specific mAbs, REGN5713, REGN5714, and REGN5715, were isolated using the VelocImmune platform. Surface plasmon resonance, x-ray crystallography, and cryo-electron microscopy determined binding kinetics and structural data. Inhibition of IgE-binding, basophil activation, and mast cell degranulation were assessed via blocking ELISA, flow cytometry, and the passive cutaneous anaphylaxis mouse model.

RESULTS

REGN5713, REGN5714, and REGN5715 bind with high affinity and noncompetitively to Bet v 1. A cocktail of all 3 antibodies, REGN5713/14/15, blocks IgE binding to Bet v 1 and inhibits Bet v 1- and birch pollen extract-induced basophil activation ex vivo and mast cell degranulation in vivo. Crystal structures of the complex of Bet v 1 with immunoglobulin antigen-binding fragments of REGN5713 or REGN5715 show distinct interaction sites on Bet v 1. Cryo-electron microscopy reveals a planar and roughly symmetrical complex formed by REGN5713/14/15 bound to Bet v 1.

CONCLUSIONS

These data confirm the immunodominance of Bet v 1 in birch allergy and demonstrate blockade of the birch allergic response with REGN5713/14/15. Structural analyses show simultaneous binding of REGN5713, REGN5714, and REGN5715 with substantial areas of Bet v 1 exposed, suggesting that targeting specific epitopes is sufficient to block the allergic response.

Suppression function against environmental dust exposure after Dermatophagoides pteronyssinus immunotherapy is associated with production of specific and cross-reactive immunoglobulin G4

BACKGROUND

Whether Dermatophagoides pteronyssinus (Der-p) allergen immunotherapy (AIT) can induce Dermatophagoides farina (Der-f) specific immunoglobulin (sIg) G4 production and tolerance to environmental allergens has not been fully investigated.

OBJECTIVE

We aimed to determine serum Der-p-sIgG4 and Der-f-sIgG4 levels in asthma and/or rhinitis patients undergoing Der-p AIT and their ability to reduce immune responses triggered by indoor-dust extracts.

METHODS

We performed a real-world prospective trial and enrolled patients with allergic rhinitis and/or asthma in Guangzhou, China. These patients received either Der-p AIT (SCIT group) or routine medications (non-SCIT group) for 156 weeks. Clinical outcomes were assessed by the combined symptom medication score (SMS) and FEV₁ % changes. House dust samples were collected to analyze allergen levels. Serum levels of Der-p-sIgG4 and Der-f-sIgG4, serum inhibitory capacity against Der-p, Der-f, and indoor dust extract by sIgE-facilitated allergen binding to B cells (IgE-FAB), and serum blocking indoor dust extract-induced basophil activation inhibition assays (BATI) in peripheral blood monocytes were carried out at weeks 0, 4, 12, 16, 52, 104, and 156 after the initiations of the treatments.

RESULTS

Our study enrolled a total of 60 participants, with 30 patients in each group. Patients in the SCIT group had significantly improved SMS when compared with the baseline and the patients in the non-SCIT group. Median levels of Der-p 1 and Der-f 1 in indoor dust extract were 1.86 μg/g and 4.74 μg/g, respectively. Serum Der-p-sIgG4 and Der-f-IgG4 levels in SCIT patients showed a significant increase from week 12 to week 156. Serum in these SCIT patients could significantly block Der-p, Der-f, and indoor dust extract formation of allergen-sIgE complex and reduced the threshold of IgE-FAB from 16 weeks after the initiation of the treatment. The capacity to inhibit Der-p, Der-f, and indoor dust extract BATI was observed in SCIT serum after 12 weeks. Der-p-sIgG4 and Der-f-sIgG4 had a significant correlation with IgE-FAB and BATI in SCIT patients at all time points.

CONCLUSION

Single Der-p immunotherapy induced both Der-p-sIgG4 and Der-f-sIgG4 production, which might cross-reactively induce tolerance against environmental allergen exposure in patients with asthma and/or rhinitis.

Microscale Thermophoresis Reveals Oxidized Glutathione as High-Affinity Ligand of Mal d 1

Pathogenesis-related (PR)-10 proteins, due to their particular secondary structure, can bind various ligands which could be important for their biological function. Accordingly, the PR-10 protein Mal d 1, the major apple allergen, probably also binds molecules in the hydrophobic cavity of its secondary structure, but it has not yet been investigated in this respect. In this study, various natural products found in apples such as flavonoids, glutathione (GSH), and glutathione disulfide (GSSG) were investigated as possible ligands of Mal d 1 using microscale thermophoresis. Dissociation constants of 16.39 µM, 29.51 µM, 35.79 µM, and 0.157 µM were determined for catechin, quercetin-3-O-rhamnoside, GSH, and GSSG, respectively. Molecular docking was performed to better understand the underlying binding mechanism and revealed hydrophobic interactions that stabilize the ligands within the pocket while hydrophilic interactions determine the binding of both GSH derivatives. The binding of these ligands could be important for the allergenicity of the PR-10 protein and provide further insights into its physiological role.

Isotype-specific binding patterns of serum antibodies to multiple conformational epitopes of Bet v 1

BACKGROUND

Birch pollen is an important elicitor of respiratory allergy. The major allergen, Bet v 1, binds IgE exclusively via conformational epitopes.

OBJECTIVE

To identify Bet v 1-specific epitope repertoires of IgE and IgG from birch pollen-allergic and non-allergic subjects.

METHODS

Chimeric proteins were created by grafting individual epitope-sized, contiguous surface patches of Bet v 1 onto a non-allergenic structural homologue and expressed in Escherichia coli. Binding of IgE, IgG1 and IgG4 from sera of 30 birch pollen-allergic and 11 non-allergic subjects to Bet v 1, 13 chimeric proteins and four bacterial Bet v 1 homologues were measured by ELISA. The proportion of epitope-specific in total Bet v 1-specific IgE and the cross-reactivity of Bet v 1-specific IgE with bacterial homologues were determined by competitive ELISA.

RESULTS

Thirteen soluble, correctly folded chimeric proteins were produced. IgE from 27/30 birch pollen-allergic patients bound to 1-12 chimeric proteins (median 4.0) with patient-specific patterns. Three chimeras binding IgE from the majority of sera were identified, whose pgrafted patches overlapped with previously published epitopes. Patterns of IgG1 and IgG4 binding to the chimeric proteins did not correspond to the binding patterns of IgE. Sera of 19/30 birch pollen-allergic patients contained low amounts of IgE to bacterial homologues. Bacterial proteins were able to partially inhibit IgE binding to Bet v 1.

CONCLUSION

Epitopes recognized by Bet v 1-specific antibodies from birch pollen-allergic patients are specific to each patient and differ between IgE, IgG1 and IgG4.

Structural Aspects of the Allergen-Antibody Interaction

The development of allergic disease involves the production of IgE antibodies upon allergen exposure in a process called sensitization. IgE binds to receptors on the surface of mast cells and basophils, and subsequent allergen exposure leads to cross-linking of IgE antibodies and release of cell mediators that cause allergy symptoms. Although this process is quite well-understood, very little is known about the epitopes on the allergen recognized by IgE, despite the importance of the allergen-antibody interaction for the allergic response to occur. This review discusses efforts to analyze allergen-antibody interactions, from the original epitope mapping studies using linear peptides or recombinant allergen fragments, to more sophisticated technologies, such as X-ray crystallography and nuclear magnetic resonance. These state-of-the-art approaches, combined with site-directed mutagenesis, have led to the identification of conformational IgE epitopes. The first structures of an allergen (egg lysozyme) in complex with Fab fragments from IgG antibodies were determined in the 1980s. Since then, IgG has been used as surrogate for IgE, due to the difficulty of obtaining monoclonal IgE antibodies. Technical developments including phage display libraries have contributed to progress in epitope mapping thanks to the isolation of IgE antibody constructs from combinatorial libraries made from peripheral blood mononuclear cells of allergic donors. Most recently, single B cell antibody sequencing and human hybridomas are new breakthrough technologies for finally obtaining human IgE monoclonal antibodies, ideal for epitope mapping. The information on antigenic determinants will facilitate the design of hypoallergens for immunotherapy and the investigation of the fundamental mechanisms of the IgE response.

Allergome-wide peptide microarrays enable epitope deconvolution in allergen-specific immunotherapy

BACKGROUND

The interaction of allergens and allergen-specific IgE initiates the allergic cascade after crosslinking of receptors on effector cells. Antibodies of other isotypes may modulate such a reaction. Receptor crosslinking requires binding of antibodies to multiple epitopes on the allergen. Limited information is available on the complexity of the epitope structure of most allergens.

OBJECTIVES

We sought to allow description of the complexity of IgE, IgG₄, and IgG epitope recognition at a global, allergome-wide level during allergen-specific immunotherapy (AIT).

METHODS

We generated an allergome-wide microarray comprising 731 allergens in the form of more than 172,000 overlapping 16-mer peptides. Allergen recognition by IgE, IgG₄, and IgG was examined in serum samples collected from subjects undergoing AIT against pollen allergy.

RESULTS

Extensive induction of linear peptide-specific Phl p 1- and Bet v 1-specific humoral immunity was demonstrated in subjects undergoing a 3-year-long AIT against grass and birch pollen allergy, respectively. Epitope profiles differed between subjects but were largely established already after 1 year of AIT, suggesting that dominant allergen-specific antibody clones remained as important contributors to humoral immunity following their initial establishment during the early phase of AIT. Complex, subject-specific patterns of allergen isoform and group cross-reactivities in the repertoires were observed, patterns that may indicate different levels of protection against different allergen sources.

CONCLUSIONS

The study highlights the complexity and subject-specific nature of allergen epitopes recognized following AIT. We envisage that epitope deconvolution will be an important aspect of future efforts to describe and analyze the outcomes of AIT in a personalized manner.

Filling the Antibody Pipeline in Allergy: PIPE Cloning of IgE, IgG1 and IgG4 against the Major Birch Pollen Allergen Bet v 1

Birch pollen allergy is among the most prevalent pollen allergies in Northern and Central Europe. This IgE-mediated disease can be treated with allergen immunotherapy (AIT), which typically gives rise to IgG antibodies inducing tolerance. Although the main mechanisms of allergen immunotherapy (AIT) are known, questions regarding possible Fc-mediated effects of IgG antibodies remain unanswered. This can mainly be attributed to the unavailability of appropriate tools, i.e., well-characterised recombinant antibodies (rAbs). We hereby aimed at providing human rAbs of several classes for mechanistic studies and as possible candidates for passive immunotherapy. We engineered IgE, IgG1, and IgG4 sharing the same variable region against the major birch pollen allergen Bet v 1 using Polymerase Incomplete Primer Extension (PIPE) cloning. We tested IgE functionality and IgG blocking capabilities using appropriate model cell lines. In vitro studies showed IgE engagement with FcεRI and CD23 and Bet v 1-dependent degranulation. Overall, we hereby present fully functional, human IgE, IgG1, and IgG4 sharing the same variable region against Bet v 1 and showcase possible applications in first mechanistic studies. Furthermore, our IgG antibodies might be useful candidates for passive immunotherapy of birch pollen allergy.

Characterization of epitope specificities of reference antibodies used for the quantification of the birch pollen allergen Bet v 1

BACKGROUND

Accurate allergen quantification is needed to document the consistency of allergen extracts used for immunotherapy. Herein, we characterize the epitope specificities of two monoclonal antibodies used in an ELISA for the quantification of the major birch pollen allergen Bet v 1, established as a reference by the BSP090 European project.

METHODS

The ability of mAbs 5B4 and 6H4 to recognize Bet v 1 isoforms was addressed by immunochromatography. The capacity of each mAb to compete with patients' IgE for binding to Bet v 1 was measured by ELISA inhibition. Epitope mapping was performed by pepscan analysis, site-directed mutagenesis, and hydrogen/deuterium exchange-mass spectrometry.

RESULTS

The 5B4 epitope corresponds to a peptide sequence (I56-K68) overlapping with the binding sites of patients' serum IgEs. Mutation of residues P59, E60, and K65 abolishes 5B4 binding to Bet v 1 and reduces the level of IgE recognition. In contrast, 6H4 recognizes a conformational epitope lying opposite to the 5B4 binding site, involving residues located in segments I44-K55 and R70-F79. Substitution of E45 reduces the binding capacity of 6H4, confirming that it is critical for the interaction. Both mAbs interact with >90% of Bet v 1 content present in the birch pollen extract, while displaying a weak cross-reactivity with other allergens of the PR-10 family.

CONCLUSIONS

MAbs 5B4 and 6H4 recognize structurally distinct epitopes present in the vast majority of Bet v 1 isoforms. These results support the relevance as a reference method of the Bet v 1-specific quantitative ELISA adopted by the European Pharmacopoeia.

Antibody Heavy Chain Variable Domains of Different Germline Gene Origins Diversify through Different Paths

B cells produce antibodies, key effector molecules in health and disease. They mature their properties, including their affinity for antigen, through hypermutation events; processes that involve, e.g., base substitution, codon insertion and deletion, often in association with an isotype switch. Investigations of antibody evolution define modes whereby particular antibody responses are able to form, and such studies provide insight important for instance for development of efficient vaccines. Antibody evolution is also used in vitro for the design of antibodies with improved properties. To better understand the basic concepts of antibody evolution, we analyzed the mutational paths, both in terms of amino acid substitution and insertions and deletions, taken by antibodies of the IgG isotype. The analysis focused on the evolution of the heavy chain variable domain of sets of antibodies, each with an origin in 1 of 11 different germline genes representing six human heavy chain germline gene subgroups. Investigated genes were isolated from cells of human bone marrow, a major site of antibody production, and characterized by next-generation sequencing and an in-house bioinformatics pipeline. Apart from substitutions within the complementarity determining regions, multiple framework residues including those in protein cores were targets of extensive diversification. Diversity, both in terms of substitutions, and insertions and deletions, in antibodies is focused to different positions in the sequence in a germline gene-unique manner. Altogether, our findings create a framework for understanding patterns of evolution of antibodies from defined germline genes.

Insights into the immune manipulation mechanisms of pollen allergens by protein domain profiling

Plant pollens are airborne allergens, as their inhalation causes immune activation, leading to rhinitis, conjunctivitis, sinusitis and oral allergy syndrome. A myriad of pollen proteins belonging to profilin, expansin, polygalacturonase, glucan endoglucosidase, pectin esterase, and lipid transfer protein class have been identified. In the present in silico study, the protein domains of fifteen pollen sequences were extracted from the UniProt database and submitted to the interactive web tool SMART (Simple Modular Architecture Research Tool), for finding the protein domain profiles. Analysis of the data based on custom-made scripts revealed the conservation of pathogenic domains such as OmpH, PROF, PreSET, Bet_v_1, Cpl-7 and GAS2. Further, the retention of critical domains like CHASE2, Galanin, Dak2, DALR_1, HAMP, PWI, EFh, Excalibur, CT, PbH1, HELICc, and Kelch in pollen proteins, much like cockroach allergens and lethal viruses (such as HIV, HCV, Ebola, Dengue and Zika) was observed. Based on the shared motifs in proteins of taxonomicall-ydispersed organisms, it can be hypothesized that allergens and pathogens manipulate the human immune system in a similar manner. Allergens, being inanimate, cannot replicate in human body, and are neutralized by immune system. But, when the allergens are unremitting, the immune system becomes persistently hyper-sensitized, creating an inflammatory milieu. This study is expected to contribute to the understanding of pollen allergenicity and pathogenicity.

Antibodies and superantibodies in patients with chronic rhinosinusitis with nasal polyps

Background

Chronic rhinosinusitis with nasal polyps is associated with local immunoglobulin hyperproduction and the presence of IgE antibodies against Staphylococcus aureus enterotoxins (SAEs). Aspirin-exacerbated respiratory disease is a severe form of chronic rhinosinusitis with nasal polyps in which nearly all patients express anti-SAEs.

Objectives

We aimed to understand antibodies reactive to SAEs and determine whether they recognize SAEs through their complementarity-determining regions (CDRs) or framework regions.

Methods

Labeled staphylococcal enterotoxin (SE) A, SED, and SEE were used to isolate single SAE-specific B cells from the nasal polyps of 3 patients with aspirin-exacerbated respiratory disease by using fluorescence-activated cell sorting. Recombinant antibodies with “matched” heavy and light chains were cloned as IgG₁, and those of high affinity for specific SAEs, assayed by means of ELISA and surface plasmon resonance, were recloned as IgE and antigen-binding fragments. IgE activities were tested in basophil degranulation assays.

Results

Thirty-seven SAE-specific, IgG- or IgA-expressing B cells were isolated and yielded 6 anti-SAE clones, 2 each for SEA, SED, and SEE. Competition binding assays revealed that the anti-SEE antibodies recognize nonoverlapping epitopes in SEE. Unexpectedly, each anti-SEE mediated SEE-induced basophil degranulation, and IgG₁ or antigen-binding fragments of each anti-SEE enhanced degranulation by the other anti-SEE.

Conclusions

SEEs can activate basophils by simultaneously binding as antigens in the conventional manner to CDRs and as superantigens to framework regions of anti-SEE IgE in anti-SEE IgE-FcεRI complexes. Anti-SEE IgG₁s can enhance the activity of anti-SEE IgEs as conventional antibodies through CDRs or simultaneously as conventional antibodies and as “superantibodies” through CDRs and framework regions to SEEs in SEE–anti-SEE IgE-FcεRI complexes.

Developments in the field of allergy in 2014 through the eyes of Clinical and Experimental Allergy

The pathogenesis of asthma continues to be a major topic of interest to our authors with reviews and original papers on the role of viruses, mechanisms of inflammation, biomarkers, and phenotypes of asthma being major topics. A number of papers described new treatments for asthma focusing on blocking the Th2 response reflecting the fact that two decades of work in this area is finally bearing fruit. The pathogenesis of chronic rhinosinusitis is a growing area of interest, but there has been less on the genetics of airways disease than in previous years possibly reflecting the degree of rigour (and therefore a smaller body of work), with which these sorts of studies are now being undertaken. There continues to be a wide range of papers dealing with mechanisms of allergic disease ranging from clinical-based studies to basic research and the use of in vivo animal models especially mice. As before, mechanisms and new approaches to immunotherapy are common themes. Several were published in the allergens section investigating modification of allergens to increase their effectiveness and reduce the risk of adverse events. Risk factors for allergic disease was a common theme in the epidemiology section and food allergy a common theme in clinical allergy with papers on the development of protocols to induce tolerance and attempts to find biomarkers to distinguish sensitization from allergic disease. This was another exciting year for the editors, and we hope the readers of the journal.

Ligand binding modulates the structural dynamics and compactness of the major birch pollen allergen

Pathogenesis-related plant proteins of class-10 (PR-10) are essential for storage and transport of small molecules. A prominent member of the PR-10 family, the major birch pollen allergen Bet v 1, is the main cause of spring pollinosis in the temperate climate zone of the northern hemisphere. Bet v 1 binds various ligand molecules to its internal cavity, and immunologic effects of the presence of ligand have been discussed. However, the mechanism of binding has remained elusive. In this study, we show that in solution Bet v 1.0101 is conformationally heterogeneous and cannot be represented by a single structure. NMR relaxation data suggest that structural dynamics are fundamental for ligand access to the protein interior. Complex formation then leads to significant rigidification of the protein along with a compaction of its 3D structure. The data presented herein provide a structural basis for understanding the immunogenic and allergenic potential of ligand binding to Bet v 1 allergens.

Nanoparticle-allergen interactions mediate human allergic responses: protein corona characterization and cellular responses

Background

Engineered nanomaterials (ENMs) interact with different biomolecules as soon as they are in contact, resulting in the formation of a biomolecule ‘corona’. Hence, the ‘corona’ defines the biological identity of the ENMs and could affect the response of the immune system to ENM exposure. With up to 40 % of the world population suffering from type I allergy, a possible modulation of allergen effects by binding to ENMs is highly relevant with respect to work place and consumer safety. Therefore, the aim of this present study was to gain an insight into the interactions of gold nanoparticles with different seasonally and perennially occurring outdoor and indoor allergens.

Methods

Gold nanoparticles (AuNPs) were conjugated with the major allergens of birch pollen (Bet v 1), timothy grass pollen (Phl p 5) and house dust mite (Der p 1). The AuNP-allergen conjugates were characterized by means of TEM negative staining, dynamic light scattering (DLS), z-potential measurements and hyperspectral imaging. Furthermore, 3D models were constructed, based on the characterization data, to visualize the interaction between the allergens and the AuNPs surface. Differences in the activation of human basophil cells derived from birch/grass pollen- and house dust mite-allergic patients in response to free allergen and AuNP-allergen conjugates were determined using the basophil activation assay (BAT). Potential allergen corona replacement during BAT was controlled for using Western blotting. The protease activity of AuNP-Der p 1 conjugates compared to free Der p 1 was assessed, by an enzymatic activity assay and a cellular assay pertaining to lung type II alveolar epithelial cell tight junction integrity.

Results

The formation of a stable corona was found for all three allergens used. Our data suggest, that depending on the allergen, different effects are observed after binding to ENMs, including enhanced allergic responses against Der p 1 and also, for some patients, against Bet v 1. Moreover elevated protease activity of AuNP-Der p 1 conjugates compared to free Der p 1 was found.

Conclusion

In summary, this study presents that conjugation of allergens to ENMs can modulate the human allergic response, and that protease activity can be increased.

Graphical Abstract

Interfaces between allergen structure and diagnosis: know your epitopes

Allergy diagnosis is based on the patient's clinical history and can be strengthened by tests that confirm the origin of sensitization. In the past 25 years, these tests have evolved from the exclusive in vivo or in vitro use of allergen extracts, to complementary molecular-based diagnostics that rely on in vitro measurements of IgE reactivity to individual allergens. For this to occur, an increase in our understanding of the molecular structure of allergens, largely due to the development of technologies such as molecular cloning and expression of recombinant allergens, X-ray crystallography, or nuclear magnetic resonance (NMR), has been essential. New in vitro microarray or multiplex systems are now available to measure IgE against a selected panel of purified natural or recombinant allergens. The determination of the three-dimensional structure of allergens has facilitated detailed molecular studies, including the analysis of antigenic determinants for diagnostic purposes.

Isolation of Mal d 1 and Api g 1 - specific recombinant antibodies from mouse IgG Fab fragment libraries - Mal d 1-specific antibody exhibits cross-reactivity against Bet v 1

Background

Around 3–5% of the population suffer from IgE-mediated food allergies in Western countries and the number of food-allergenic people is increasing. Individuals with certain pollen allergies may also suffer from a sensitisation to proteins in the food products. As an example a person sensitised to the major birch pollen allergen, Bet v 1, is often sensitised to its homologues, such as the major allergens of apple, Mal d 1, and celery, Api g 1, as well. Development of tools for the reliable, sensitive and quick detection of allergens present in various food products is essential for allergic persons to prevent the consumption of substances causing mild and even life-threatening immune responses. The use of monoclonal antibodies would ensure the specific detection of the harmful food content for a sensitised person.

Methods

Mouse IgG antibody libraries were constructed from immunised mice and specific recombinant antibodies for Mal d 1 and Api g 1 were isolated from the libraries by phage display. More detailed characterisation of the resulting antibodies was carried out using ELISA, SPR experiments and immunoprecipitation assays.

Results

The allergen-specific Fab fragments exhibited high affinity towards the target recombinant allergens. Furthermore, the Fab fragments also recognised native allergens from natural sources. Interestingly, isolated Mal d 1-specific antibody bound also to Bet v 1, the main allergen eliciting the cross-reactivity syndrome between the birch pollen and apple. Despite the similarities in Api g 1 and Bet v 1 tertiary structures, the isolated Api g 1-specific antibodies showed no cross-reactivity to Bet v 1.

Conclusions

Here, high-affinity allergen-specific recombinant antibodies were isolated with interesting binding properties. With further development, these antibodies can be utilised as tools for the specific and reliable detection of allergens from different consumable products. This study gives new preliminary insights to elucidate the mechanism behind the pollen-food syndrome and to study the IgG epitope of the allergens.

Enlarging the toolbox for allergen epitope definition with an allergen-type model protein

BACKGROUND

Birch pollen-allergic subjects produce polyclonal cross-reactive IgE antibodies that mediate pollen-associated food allergies. The major allergen Bet v 1 and its homologs in plant foods bind IgE in their native protein conformation. Information on location, number and clinical relevance of IgE epitopes is limited. We addressed the use of an allergen-related protein model to identify amino acids critical for IgE binding of PR-10 allergens.

METHOD

Norcoclaurine synthase (NCS) from meadow rue is structurally homologous to Bet v 1 but does not bind Bet v 1-reactive IgE. NCS was used as the template for epitope grafting. NCS variants were tested with sera from 70 birch pollen allergic subjects and with monoclonal antibody BV16 reported to compete with IgE binding to Bet v 1.

RESULTS

We generated an NCS variant (Δ29NCSN57/I58E/D60N/V63P/D68K) harboring an IgE epitope of Bet v 1. Bet v 1-type protein folding of the NCS variant was evaluated by 1H-15N-HSQC NMR spectroscopy. BV16 bound the NCS variant and 71% (50/70 sera) of our study population showed significant IgE binding. We observed IgE and BV16 cross-reactivity to the epitope presented by the NCS variant in a subgroup of Bet v 1-related allergens. Moreover BV16 blocked IgE binding to the NCS variant. Antibody cross-reactivity depended on a defined orientation of amino acids within the Bet v 1-type conformation.

CONCLUSION

Our system allows the evaluation of patient-specific epitope profiles and will facilitate both the identification of clinically relevant epitopes as biomarkers and the monitoring of therapeutic outcomes to improve diagnosis, prognosis, and therapy of allergies caused by PR-10 proteins.

The human IgE repertoire

IgE is a key mediator in allergic diseases. However, in strong contrast to other antibody isotypes, many details of the composition of the human IgE repertoire are poorly defined. The low levels of human IgE in the circulation and the rarity of IgE-producing B cells are important reasons for this lack of knowledge. In this review, we summarize the current knowledge on these repertoires both in terms of their complexity and activity, i.e. knowledge which despite the difficulties encountered when studying the molecular details of human IgE has been acquired in recent years. We also take a look at likely future developments, for instance through improvements in sequencing technology and methodology that allow the isolation of additional allergen-specific human antibodies mimicking IgE, as this certainly will support our understanding of human IgE in the context of human disease in the years to come.