Identification and mutational analysis of the immunodominant IgE binding epitopes of the major peanut allergen Ara h 2

Peanut allergens

Peanut allergens have the potential to negatively impact on the health and quality of life of millions of consumers worldwide. The seeds of the peanut plant Arachis hypogaea contain an array of allergens that are able to induce the production of specific IgE antibodies in predisposed individuals. A lot of effort has been focused on obtaining the sequences and structures of these allergens due to the high health risk they represent. At present, 16 proteins present in peanuts are officially recognized as allergens. Research has also focused on their in-depth immunological characterization as well as on the design of modified hypoallergenic derivatives for potential use in clinical studies and the formulation of strategies for immunotherapy. Detailed research protocols are available for the purification of natural allergens as well as their recombinant production in bacterial, yeast, insect, and algal cells. Purified allergen molecules are now routinely used in diagnostic multiplex protein arrays for the detection of the presence of allergen-specific IgE. This review gives an overview on the wealth of knowledge that is available on individual peanut allergens.

Detection of the Peanut Allergens Ara h 2 and Ara h 6 in Human Breast Milk: Development of 2 Sensitive and Specific Sandwich ELISA Assays

BACKGROUND

Little is known about breast milk as a vehicle for tolerance development or sensitization to peanuts very early in life. Thus, well-characterized and highly sensitive detection systems for the reliable determination of peanut allergens in breast milk are mandatory.

METHODS

For the quantification of the marker allergens Ara h 2 and Ara h 6 in the low nanogram per milliliter range in breast milk samples of a German cohort, sensitive and highly specific sandwich ELISAs were optimized and validated.

RESULTS

The Ara h 2 ELISA revealed a limit of detection (LOD) of 1.3 ng Ara h 2/mL and a quantification range of 2.3-250 ng/mL, the Ara h 6 ELISA showed an LOD of 0.7 ng/mL and a working range of 1.1-14.4 ng/mL. The assays showed no relevant cross-reactivity against other potentially cross-reactive legume, seed, and tree nut extracts (<0.01%, except for Ara h 1 in the Ara h 2 ELISA <0.1%). Ara h 2 was detectable in breast milk samples from 14/40 (35%) of the participants in concentrations from 2.3 to 184 ng/mL, Ara h 6 appeared in 9/40 (22.5%) of the lactating mothers between 1.1 and 9.7 ng/mL, and 1 highly positive sample with 79 ng/mL. Both allergens appeared at the same time points, but Ara h 6 in lower concentrations than Ara h 2.

CONCLUSIONS

Sensitive and specific diagnostic tools for the determination of Ara h 2 and Ara h 6 in human breast milk were established. The kinetics of secreted Ara h 2 and Ara h 6 seem to be similar but with a difference in concentration. Follow-up investigations on their tolerogenic or sensitizing properties in breast milk become now accessible.

Identification of a common Ara h 3 epitope recognized by both the capture and the detection monoclonal antibodies in an ELISA detection kit

Allergy to peanuts has become a common and severe problem, especially in westernized countries. In this study, we evaluated the target and epitope specificity of the capture and detection mouse monoclonal antibodies (mAbs) used in a commercial peanut allergen detection platform. We first identified the target of these antibodies as Ara h 3 and then used an overlapping peptide array of Ara h 3 to determine the antibody-binding epitopes. Further amino acids critical for the binding via alanine substitutions at individual amino acid residues within the epitope were mapped. Finally, inhibition ELISA and inhibition immunoblotting using a recombinant Ara h 3 protein were performed to confirm these results. Surprisingly, the capture and detection mAbs showed identical binding characteristics and were presumed to represent two isolates of the same clone, a notion supported by both isoelectric focusing electrophoresis and Liquid chromatography–mass spectrometry experiments. The simultaneous binding of a pair of identical mAbs to an individual allergen such as Ara h3 is attributed to the multivalency of the analyte and has implications for developing diagnostic assays for additional multimeric allergens.

Cloning, Expression, and the Effects of Processing on Sarcoplasmic-Calcium-Binding Protein: An Important Allergen in Mud Crab

Shellfish allergy is a prevalent, long-lasting disorder usually persisting throughout life. However, the allergen information is incomprehensive in crab. This study aimed to identify a novel allergen in crab, show its potential in diagnosis and reduce the allergenicity by food processing. A 21-kDa protein was purified from Scylla paramamosain and confirmed as sarcoplasmic calcium binding protein (SCP) by matrix-assisted laser desorption ionization-time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF-MS). Total RNA was isolated from crab muscle, and a rapid amplification of cDNA was performed to obtain an ORF of 579 bp that coded for 193 amino acid residues. According to the results of circular dichroism analysis and ELISA assay, the recombinant SCP (rSCP) expressed in Escherichia coli showed similar physicochemical and immunoreactive properties to native SCP (nSCP). Additionally, the extensive cross reactivity of SCP among different species and the bidirectional IgE cross-reactivity between nSCP and rSCP were detected by iELISA. The allergenicity of rSCP was reduced via Maillard reaction or enzymatic cross-linking reaction, which was confirmed by the results of scanning electron microscopy, dot blot, and digestion assay. A straightforward and reproducible way was developed to obtain high yields of rSCP that maintains structural integrity and full IgE reactivity, which could compensate the low specific IgE-titers of most patient sera for future diagnosis. Furthermore, the Maillard reaction and enzymatic cross-linking reaction were effective approaches for the production of hypoallergenic seafood.

Determination of Crucial Immunogenic Epitopes in Major Peanut Allergy Protein, Ara h2, via Novel Nanoallergen Platform

Current methods for detection and diagnosis of allergies do not provide epitope specific immunogenic information and hence lack critical information that could aid in the prediction of clinical responses. To address this issue, we developed a nanoparticle based platform, called nanoallergens that enable multivalent display of potential allergy epitopes for determining the immunogenicity of each IgE binding epitope. By synthesizing nanoallergens that present various epitopes from the major peanut allergen, Ara h2, we directly determined the immunogenicity of each epitope, alone and in combination with other epitopes, using patient sera. This information provided insights on which epitopes are most critical for physiological responses to Ara h2 and revealed the importance of both high and low affinity epitopes for allergic responses. We anticipate the nanoallergen platform to be used to provide information regarding allergic reactions and therefore potentially aid in more accurate diagnosis and design of personalized treatment options.

Recombinant Allergens in Structural Biology, Diagnosis, and Immunotherapy

The years 1988-1995 witnessed the beginning of allergen cloning and the generation of recombinant allergens, which opened up new avenues for the diagnosis and research of human allergic diseases. Most crystal and solution structures of allergens have been obtained using recombinant allergens. Structural information on allergens allows insights into their evolutionary biology, illustrates clinically observed cross-reactivities, and makes the design of hypoallergenic derivatives for allergy vaccines possible. Recombinant allergens are widely used in molecule-based allergy diagnosis such as protein microarrays or suspension arrays. Recombinant technologies have been used to produce well-characterized, noncontaminated vaccine components with known biological activities including a variety of allergen derivatives with reduced IgE reactivity. Such recombinant hypoallergens as well as wild-type recombinant allergens have been used successfully in several immunotherapy trials for more than a decade to treat birch and grass pollen allergy. As a more recent application, the development of antibody repertoires directed against conformational epitopes during immunotherapy has been monitored by recombinant allergen chimeras. Although much progress has been made, the number and quality of recombinant allergens will undoubtedly increase and keep improving our knowledge in basic scientific investigations, diagnosis, and therapy of human allergic diseases.

Effect of acid treatment on allergenicity of peanut and egg

BACKGROUND

Many food experts have studied various treatments or processing techniques in order to develop hypoallergenic foods. In a previous study, acid treatment dramatically mitigated the allergenicity of peanut, especially Ara h 2.

RESULTS

Gel electrophoresis showed that most protein bands of acid-treated peanut were not detected, but protein bands of egg white became weaker and broader by acid treatment. In immunoblotting using a rabbit antibody, the antigenicity against ovalbumin or ovomucoid in acid-treated egg white was decreased but the antigenicity against Ara h 1 or Ara h 2 in peanut treated with pH 2 acetic acid was completely undetected. The allergenicity of ovalbumin and peanut fell significantly to 1/10²² and 1/5380, respectively, when measured as IC₅₀ in the sample treated with pH 2.0 acetic acid.

CONCLUSION

This study showed that acid treatment was more effective in peanut and barely effective in ovomucoid. This may contribute to the development of hypoallergenic food and clinical management of food allergy. © 2016 Society of Chemical Industry.

Lactobacillus buchneri S-layer as carrier for an Ara h 2-derived peptide for peanut allergen-specific immunotherapy

Peanut allergy is an IgE-mediated severe hypersensitivity disorder. The lack of a treatment of this potentially fatal allergy has led to intensive research on vaccine development. Here, we describe the design and initial characterization of a carrier-bound peptide derived from the most potent peanut allergen, Ara h 2, as a candidate vaccine. Based on the adjuvant capability of bacterial surface (S-) layers, a fusion protein of the S-layer protein SlpB from Lactobacillus buchneri CD034 and the Ara h 2-derived peptide AH3a42 was produced. This peptide comprised immunodominant B-cell epitopes as well as one T cell epitope. The fusion protein SlpB-AH3a42 was expressed in E. coli, purified, and tested for its IgE binding capacity as well as for its ability to activate sensitized rat basophil leukemia (RBL) cells. The capacity of Ara h 2-specific IgG rabbit-antibodies raised against SlpB-AH3a42 or Ara h 2 to inhibit IgE-binding was determined by ELISA inhibition assays using sera of peanut allergic patients sensitized to Ara h 2. IgE specific to the SlpB-AH3a42 fusion protein was detected in 69% (25 of 36) of the sera. Despite the recognition by IgE, the SlpB-AH3a42 fusion protein was unable to induce β-hexosaminidase release from sensitized RBL cells at concentrations up to 100ng per ml. The inhibition of IgE-binding to the natural allergen observed after pre-incubation of the 20 sera with rabbit anti-SlpB-AH3a42 IgG was more than 30% for four sera, more than 20% for eight sera, and below 10% for eight sera. In comparison, anti-Ara h 2 rabbit IgG antibodies inhibited binding to Ara h 2 by 48% ±13.5%. Our data provide evidence for the feasibility of this novel approach towards the development of a peanut allergen peptide-based carrier-bound vaccine. Our experiments further indicate that more than one allergen-peptide will be needed to induce a broader protection of patients allergic to Ara h 2.

Structural Characterization of the Allergenic 2S Albumin Cor a 14: Comparing Proteoform Patterns across Hazelnut Cultivars

The hazelnut allergen Cor a 14 belongs to the 2S albumins, a family of heterodimeric seed storage proteins exhibiting a high degree of structural diversity. Given its relevance as an allergen and the potential to elicit severe reactions, elucidation of the sequence heterogeneity of naturally occurring Cor a 14 is essential for the development of reliable diagnostics and risk evaluation. We therefore performed a comprehensive survey on the proteoforms of Cor a 14 and determined their quantitative distribution in three different hazelnut cultivars by a combinatory HPLC-HRMS approach including bottom-up and intact mass analysis. Compared with the Cor a 14 prototype sequence, we identified three sequence polymorphisms, two of the small and one of the large subunit, and elucidated their specific pairing on the protein level. Furthermore, we located a pronounced microheterogeneity on the protein termini and, for the first time, provide data on varying proteoform patterns between different cultivars of an allergenic seed. Together, these data present the basis for a more detailed investigation on the allergenicity of Cor a 14 in different cultivars and constitute, to be best of our knowledge, the largest set of proteoforms so far reported for a 2S albumin.

Peanut protein extraction conditions strongly influence yield of allergens Ara h 1 and 2 and sensitivity of immunoassays

The clinical importance of peanut (Arachis hypogaea) allergies demands standardized allergen extraction protocols. We determined the effectiveness of common extraction conditions (20 buffers, defatting reagents, extraction time/temperatures, processing, extraction repeats) on crude protein and Ara h 1 and 2 yields. Despite similar 1D-gel profiles, defatting with n-hexane resulted in significantly higher yields of crude protein, Ara h 1, and Ara h 2 than with diethyl ether. The yields were affected by the composition and pH of the extraction buffers and other conditions, but crude protein yield did not always correlate with Ara h 1 and 2 yields. Denaturants, reducing agents, acidic buffers, and thermal processing of peanuts perturbed allergen quantification in ELISAs, probably via exposure of additional epitopes. Allergen detection in 2D-Western blots with PBS resulted in greater sensitivity than with TBS or Tris. We recommend that allergen extraction conditions be selected based on the research question being investigated.

Crosslinking of peanut allergen Ara h 2 by polyphenol oxidase: digestibility and potential allergenicity assessment

BACKGROUND

Peanut is one of the eight major food allergens. Its allergen, Ara h 2, can be recognized by over 90% of serum IgE samples from peanut-allergic patients. Therefore, reducing the allergenicity of Ara h 2 is especially important.

RESULTS

In the present study, polyphenol oxidase (PPO), a protein cross-linking reaction catalyst that acts on tyrosine residue, was used to modify Ara h 2. After crosslinking, the microstructure, digestibility, IgG binding capability and IgE binding capability of Ara h 2 were analyzed. Cross-linking decreased the potential allergenicity of Ara h 2 by masking the allergen epitope, while the antigenicity of Ara h 2 changed slightly. After crosslinking, the apparent diameter of Ara h 2 was altered from 300 to 1700 nm or 220 nm, indicating that polymerization could either be inter- or intramolecular. Regarding digestibility, crosslinked Ara h 2 was relatively more easily digested by gastric fluid compared with the untreated Ara h 2, but much more difficult in the intestinal fluid.

CONCLUSION

The crosslinking reaction catalyzed by PPO, as a non-thermal process, may be beneficial for avoiding food allergy. The reaction could mask allergen epitopes, decreasing the allergenicity of Ara h 2. © 2015 Society of Chemical Industry.

Conformational stability of digestion-resistant peptides of peanut conglutins reveals the molecular basis of their allergenicity

Conglutins represent the major peanut allergens and are renowned for their resistance to gastro-intestinal digestion. Our aim was to characterize the digestion-resistant peptides (DRPs) of conglutins by biochemical and biophysical methods followed by a molecular dynamics simulation in order to better understand the molecular basis of food protein allergenicity. We have mapped proteolysis sites at the N- and C-termini and at a limited internal segment, while other potential proteolysis sites remained unaffected. Molecular dynamics simulation showed that proteolysis only occurred in the vibrant regions of the proteins. DRPs appeared to be conformationally stable as intact conglutins. Also, the overall secondary structure and IgE-binding potency of DRPs was comparable to that of intact conglutins. The stability of conglutins toward gastro-intestinal digestion, combined with the conformational stability of the resulting DRPs provide conditions for optimal exposure to the intestinal immune system, providing an explanation for the extraordinary allergenicity of peanut conglutins.

Immunotherapy using algal-produced Ara h 1 core domain suppresses peanut allergy in mice

Peanut allergy is an IgE-mediated adverse reaction to a subset of proteins found in peanuts. Immunotherapy aims to desensitize allergic patients through repeated and escalating exposures for several months to years using extracts or flours. The complex mix of proteins and variability between preparations complicates immunotherapy studies. Moreover, peanut immunotherapy is associated with frequent negative side effects and patients are often at risk of allergic reactions once immunotherapy is discontinued. Allergen-specific approaches using recombinant proteins are an attractive alternative because they allow more precise dosing and the opportunity to engineer proteins with improved safety profiles. We tested whether Ara h 1 and Ara h 2, two major peanut allergens, could be produced using chloroplast of the unicellular eukaryotic alga, Chlamydomonas reinhardtii. C. reinhardtii is novel host for producing allergens that is genetically tractable, inexpensive and easy to grow, and is able to produce more complex proteins than bacterial hosts. Compared to the native proteins, algal-produced Ara h 1 core domain and Ara h 2 have a reduced affinity for IgE from peanut-allergic patients. We further found that immunotherapy using algal-produced Ara h 1 core domain confers protection from peanut-induced anaphylaxis in a murine model of peanut allergy.

What Characteristics Confer Proteins the Ability to Induce Allergic Responses? IgE Epitope Mapping and Comparison of the Structure of Soybean 2S Albumins and Ara h 2

Ara h 2, a peanut 2S albumin, is associated with severe allergic reactions, but a homologous protein, soybean 2S albumin, is not recognized as an important allergen. Structural difference between these proteins might explain this clinical discrepancy. Therefore, we mapped sequential epitopes and compared the structure of Ara h 2, Soy Al 1, and Soy Al 3 (Gly m 8) to confirm whether structural differences account for the discrepancy in clinical responses to these two proteins. Commercially synthesized peptides covering the full length of Ara h 2 and two soybean 2S albumins were analyzed by peptide microarray. Sera from 10 patients with peanut and soybean allergies and seven non-atopic controls were examined. The majority of epitopes in Ara h 2 identified by microarray are consistent with those identified previously. Several regions in the 2S albumins are weakly recognized by individual sera from different patients. A comparison of allergenic epitopes on peanut and soybean proteins suggests that loop-helix type secondary structures and some amino acids with a large side chain including lone electron pair, such as arginine, glutamine, and tyrosine, makes the peptides highly recognizable by the immune system. By utilizing the peptide microarray assay, we mapped IgE epitopes of Ara h 2 and two soybean 2S albumins. The use of peptide microarray mapping and analysis of the epitope characteristics may provide critical information to access the allergenicity of food proteins.

Nanoallergens: A multivalent platform for studying and evaluating potency of allergen epitopes in cellular degranulation

Degranulation caused by type I hypersensitivity (allergies) is a complex biophysical process, and available experimental models for studying relevant immunoglobulin E binding epitopes on allergen proteins lack the ability to adequately evaluate, rank, and associate these epitopes individually and with each other. In this study, we propose a new allergy model system for studying potential allergen epitopes using nanoallergens, liposomes modified to effectively display IgE binding epitopes/haptens. By utilizing the covalently conjugated lipid tails on two hapten molecules (dinitrophenol and dansyl), hapten molecules were successfully incorporated into liposomes with high precision to form nanoallergens. Nanoallergens, with precisely controlled high-particle valency, can trigger degranulation with much greater sensitivity than commonly used bovine serum albumin conjugates. In rat basophil leukemia cell experiments, nanoallergens with only 2% hapten loading were able to trigger degranulation in vitro at concentrations as low as 10 pM. Additionally, unlike bovine serum albumin-hapten conjugates, nanoallergens allow exact control over particle size and valency. By varying the nanoallergen parameters such as size, valency, monovalent affinity of hapten, and specific IgE ratios, we exposed the importance of these variables on degranulation intensity while demonstrating nanoallergens' potential for evaluating both high- and low-affinity epitopes. The data presented in this article establish nanoallergen platform as a reliable and versatile allergy model to study and evaluate allergen epitopes in mast cell degranulation.

Antigenic Determinants of the Bilobal Cockroach Allergen Bla g 2

Bla g 2 is a major indoor cockroach allergen associated with the development of asthma. Antigenic determinants on Bla g 2 were analyzed by mutagenesis based on the structure of the allergen alone and in complex with monoclonal antibodies that interfere with IgE antibody binding. The structural analysis revealed mechanisms of allergen-antibody recognition through cation-π interactions. Single and multiple Bla g 2 mutants were expressed in Pichia pastoris and purified. The triple mutant K132A/K251A/F162Y showed an ∼100-fold reduced capacity to bind IgE, while preserving the native molecular fold, as proven by x-ray crystallography. This mutant was still able to induce mast cell release. T-cell responses were assessed by analyzing Th1/Th2 cytokine production and the CD4(+) T-cell phenotype in peripheral blood mononuclear cell cultures. Although T-cell activating capacity was similar for the KKF mutant and Bla g 2 based on CD25 expression, the KKF mutant was a weaker inducer of the Th2 cytokine IL-13. Furthermore, this mutant induced IL-10 from a non-T-cell source at higher levels that those induced by Bla g 2. Our findings demonstrate that a rational design of site-directed mutagenesis was effective in producing a mutant with only 3 amino acid substitutions that maintained the same fold as wild type Bla g 2. These residues, which were involved in IgE antibody binding, endowed Bla g 2 with a T-cell modulatory capacity. The antigenic analysis of Bla g 2 will be useful for the subsequent development of recombinant allergen vaccines.

Common food allergens and their IgE-binding epitopes

Food allergy is an adverse immune response to certain kinds of food. Although any food can cause allergic reactions, chicken egg, cow's milk, wheat, shellfish, fruit, and buckwheat account for 75% of food allergies in Japan. Allergen-specific immunoglobulin E (IgE) antibodies play a pivotal role in the development of food allergy. Recent advances in molecular biological techniques have enabled the efficient analysis of food allergens. As a result, many food allergens have been identified, and their molecular structure and IgE-binding epitopes have also been identified. Studies of allergens have demonstrated that IgE antibodies specific to allergen components and/or the peptide epitopes are good indicators for the identification of patients with food allergy, prediction of clinical severity and development of tolerance. In this review, we summarize our current knowledge regarding the allergens and IgE epitopes in the well-researched allergies to chicken egg, cow's milk, wheat, shrimp, and peanut.

Epitope analysis of Ara h 2 and Ara h 6: characteristic patterns of IgE-binding fingerprints among individuals with similar clinical histories

BACKGROUND

Ara h 2 and Ara h 6 are moderately homologous and highly potent peanut allergens.

OBJECTIVE

To identify IgE-binding linear epitopes of Ara h 6, compare them to those of Ara h 2, and to stratify binding based on clinical histories.

METHODS

Thirty highly peanut-allergic subjects were stratified by clinical history. Sera were diluted to contain the same amount of anti-peanut IgE. IgE binding to overlapping 20-mer peptides of Ara h 2 and Ara h 6 was assessed using microarrays.

RESULTS

Each subject had a unique IgE-binding fingerprint to peptides; these data were coalesced into epitope binding. IgE from subjects with a history of more severe reactions (n = 19) had a smaller frequency of binding events (BEs) for both Ara h 2 (52 BEs of 152 (19X8epitopes) possible BEs and Ara h 6 (13 BEs of 133 (19X7 epitopes) possible BEs) compared to IgE from those with milder histories (n = 11) (Ara h 2: 47 BEs of 88 (11X8 epitopes) possible BEs, P < 0.01; Ara h 6: 25 BEs of 77 (11X7 epitopes) possible BEs, P < 0.001). Using an unsupervised hierarchal cluster analysis, subjects with similar histories tended to cluster. We have tentatively identified a high-risk pattern of binding to peptides of Ara h 2 and Ara h 6, predominantly in subjects with a history of more severe reactions (OR = 12.6; 95% CI: 2.0-79.5; P < 0.01).

CONCLUSIONS AND CLINICAL RELEVANCE

IgE from patients with more severe clinical histories recognize fewer linear epitopes of Ara h 2 and Ara h 6 than do subjects with milder reactions and bind these epitopes in characteristic patterns. Close examination of IgE binding to epitopes of Ara h 2 and Ara h 6 may have prognostic value.

Ultrasensitive carbohydrate-peptide SPR imaging microarray for diagnosing IgE mediated peanut allergy

Severity of peanut allergies is linked to allergen-specific immunoglobulin E (IgE) antibodies in blood, but diagnostics from assays using glycoprotein allergen mixtures may be inaccurate. Measuring IgEs specific to individual peptide and carbohydrate epitopes of allergenic proteins is promising. We report here the first immunoarray for IgEs utilizing both peptide and carbohydrate epitopes. A surface plasmon resonance imaging (SPRi) microarray was equipped with peptide and β-xylosyl glycoside (BXG) epitopes from major peanut allergen glycoprotein Arachis hypogaea h2 (Ara-h2). A monoclonal anti-IgE antibody was included as positive control. IgEs were precaptured onto magnetic beads loaded with polyclonal anti-IgE antibodies to enhance sensitivity and minimize non-specific binding. As little as 0.1 attomole (0.5 pg mL(-1)) IgE was detected from dilute serum in 45 min. IgEs binding to Ara-h2 peptide and BXG were quantified in 10 μL of patient serum and correlated with standard ImmunoCAP values.

Single B-cell deconvolution of peanut-specific antibody responses in allergic patients

BACKGROUND

The frequencies, cellular phenotypes, epitope specificity, and clonal diversity of allergen-specific B cells in patients with food allergy are not fully understood but are of major pathogenic and therapeutic significance.

OBJECTIVE

We sought to characterize peanut allergen-specific B-cell populations and the sequences and binding activities of their antibodies before and during immunotherapy.

METHODS

B cells binding fluorescently labeled Ara h 1 or Ara h 2 were phenotyped and isolated by means of flow cytometric sorting from 18 patients at baseline and 13 patients during therapy. Fifty-seven mAbs derived from allergen-binding single B cells were evaluated by using ELISA, Western blotting, and peptide epitope mapping. Deep sequencing of the B-cell repertoires identified additional members of the allergen-specific B-cell clones.

RESULTS

Median allergen-binding B-cell frequencies were 0.0097% (Ara h 1) or 0.029% (Ara h 2) of B cells in baseline blood from allergic patients and approximately 3-fold higher during immunotherapy. Five of 57 allergen-specific cells belonged to clones containing IgE-expressing members. Almost all allergen-specific antibodies were mutated, and binding to both conformational and linear allergen epitopes was detected. Increasing somatic mutation of IgG4 members of a clone was seen in immunotherapy, whereas IgE mutation levels in the clone did not increase.

CONCLUSION

Most peanut allergen-binding B cells isolated by means of antigen-specific flow sorting express mutated and isotype-switched antibodies. Immunotherapy increases their frequency in the blood, and even narrowly defined allergen epitopes are recognized by numerous distinct B-cell clones in a patient. The results also suggest that oral immunotherapy can stimulate somatic mutation of allergen-specific IgG4.

In vitro evaluation of digestive and endolysosomal enzymes to cleave CML-modified Ara h 1 peptides

Ara h 1 is a major peanut allergen. Processing-induced modifications may modulate the allergenic potency of Ara h 1. Carboxymethyl lysine (CML) modifications are a commonly described nonenzymatic modification on food proteins. In the current study, we tested the ability of digestive and endolysosomal proteases to cleave CML-modified and unmodified Ara h 1 peptides. Mass spectrometric analyses of the digested peptides demonstrate that carboxymethylation of lysine residues renders these peptides refractory to trypsin digestion. We did not detect observable differences in the simulated gastric fluid or endolysosomal digestion between the parental and CML-modified peptides. One of the tested peptides contains a lysine residue previously shown to be CML modified laying in a previously mapped linear IgE epitope, but we did not observe a difference in IgE binding between the modified and parental peptides. Our findings suggest a molecular mechanism for the increased resistance of peanut allergens modified by thermal processing, such as Ara h 1, to digestion in intestinal fluid after heating and could help explain how food processing-induced modifications may lead to more potent food allergens by acting to protect intact IgE epitopes from digestion by proteases targeting lysine residues.

Stability of transgene expression in reduced allergen peanut (Arachis hypogaea L.) across multiple generations and at different soil sulfur levels

Transgenic peanut (Arachis hypogaea L.) containing a gene designed for RNA interference (RNAi) showed stable complete silencing of Ara h 2 and partial silencing of Ara h 6, two potent peanut allergens/proteins, along with minimal collateral changes to other allergens, Ara h 1 and Ara h 3, across three generations (T3, T4, and T5) under field conditions. Different soil sulfur levels (0.012, 0.3, and 3.0 mM) differentially impacted sulfur-rich (Ara h 2, Ara h 3, and Ara h 6) versus sulfur-poor (Ara h 1) proteins in non-transgenic versus transgenic peanut. The sulfur level had no effect on Ara h 1, whereas low sulfur led to a significant reduction of Ara h 3 in transgenic and non-transgenic seeds and Ara h 2 and Ara h 6 in non-transgenic but not in transgenic peanuts because these proteins already were reduced by gene silencing. These results demonstrate stability of transgene expression and the potential utility of RNAi in allergen manipulation.

Developing therapies for peanut allergy

Peanut allergy is an IgE-mediated, persisting immune disorder that is of major concern worldwide. Currently, no routine immunotherapy is available to treat this often severe and sometimes fatal food allergy. Traditional subcutaneous allergen immunotherapy with crude peanut extracts has proven not feasible due to the high risk of severe systemic side effects. The allergen-specific approaches under preclinical and clinical investigation comprise subcutaneous, oral, sublingual and epicutaneous immunotherapy with whole-peanut extracts as well as applications of hypoallergenic peanut allergens or T cell epitope peptides. Allergen-nonspecific approaches include monoclonal anti-IgE antibodies, TCM herbal formulations and Toll-like receptor 9-based immunotherapy. The potential of genetically engineered plants with reduced allergen levels is being explored as well as the beneficial influence of lactic acid bacteria and soybean isoflavones on peanut allergen-induced symptoms. Although the underlying mechanisms still need to be elucidated, several of these strategies hold great promise. It can be estimated that individual strategies or a combination thereof will result in a successful immunotherapy regime for peanut-allergic individuals within the next decade.

Purification of Recombinant Peanut Allergen Ara h 1 and Comparison of IgE Binding to the Natural Protein

Allergic reactions to food are on the rise worldwide and there is a corresponding increase in interest to understand the molecular mechanisms responsible. Peanut allergies are the most problematic because the reaction often persists into adulthood and can be as severe as anaphylaxis and death. The purpose of the work presented here was to develop a reproducible method to produce large quantities of pure recombinant Ara h 1(rAra h 1) that will enable standardization of immunological tests for patients and allow structural and immunological studies on the wild type and mutagenized forms of the protein. Ara h 1 is initially a pre-pro-protein which, following two endoproteolytic cleavages, becomes the mature form found in peanut. The mature form however has flexible regions that make it refractory to some structural studies including crystallography. Therefore, independent purification of the mature and core regions was desirable. Expression constructs were synthesized cDNA clones for each in a pET plasmid vector without tags. Codons were optimized for expression in E. coli. High-level expression was achieved in BL21 strains. Purification to near homogeneity was achieved by a combination of ammonium sulfate precipitation and ion exchange chromatography. The purified rAra h 1 was then compared with natural Ara h 1 for IgE binding. All patients recognized both the folded natural and rAra h 1, but the IgE binding to the rArah1 was significantly reduced in comparison to the natural allergen, which could potentially make it useful for immunotherapeutic purposes.

Allergenicity of peanut component Ara h 2: Contribution of conformational versus linear hydroxyproline-containing epitopes

BACKGROUND

The 2S-albumin Ara h 2 is the most potent peanut allergen and a good predictor of clinical reactivity in allergic children. Posttranslational hydroxylation of proline residues occurs in DPYSP(OH)S motifs, which are repeated 2 or 3 times in different isoforms.

OBJECTIVES

We investigated the effect of proline hydroxylation on IgE binding and the relative contributions of linear and conformational epitopes to Ara h 2 allergenicity.

METHODS

Peptides containing DPYSP(OH)S motifs were synthesized. A recombinant variant of Ara h 2 without DPYSP(OH)S motifs was generated by means of deletion mutagenesis. IgE reactivity of 18 French and 5 American patients with peanut allergy toward synthetic peptides and recombinant allergens was assessed by using IgE-binding inhibition assays and degranulation tests of humanized rat basophilic leukemia cells.

RESULTS

Hydroxyproline-containing peptides exhibited an IgE-binding activity equivalent to that of the unfolded Ara h 2. In contrast, corresponding peptides without hydroxyprolines displayed a very weak IgE-binding capacity. Despite removal of the DPYSP(OH)S motifs, the deletion variant still displayed Ara h 2 conformational epitopes. The IgE-binding capacity of Ara h 2 was then recapitulated with an equimolar mixture of a hydroxylated peptide and the deletion variant. Hydroxylated peptides of 15 and 27 amino acid residues were also able to trigger cell degranulation.

CONCLUSIONS

Sensitization toward linear and conformational epitopes of Ara h 2 is variable among patients with peanut allergy. Optimal IgE binding to linear epitopes of Ara h 2 requires posttranslational hydroxylation of proline residues. The absence of hydroxyprolines could then affect the accuracy of component-resolved diagnostics by using rAra h 2.

The high molecular weight glutenin subunit Bx7 allergen from wheat contains repetitive IgE epitopes

BACKGROUND

Wheat is one of the most common food allergen sources for children and adults. The aim of this study was to characterize new wheat allergens using an IgE discovery approach and to investigate their IgE epitopes.

METHODS

A cDNA expression library representing the wheat transcriptome was constructed in phage lambda gt11 and screened with IgE antibodies from wheat food allergic patients. IgE-reactive cDNA clones coding for portions of high molecular weight (HMW) glutenin subunits were identified by sequence analysis of positive clones. IgE epitopes were characterized using recombinant fragments from the HMW Bx7 and synthetic peptides thereof for testing of allergic patients' sera and in basophil degranulation assays.

RESULTS

We found that the major IgE-reactive areas of HMW glutenins are located in the repetitive regions of the protein and could show that two independent IgE-reactive fragments from HMW Bx7 contained repetitive IgE epitopes.

CONCLUSIONS

Our results demonstrate that IgE antibodies from wheat food allergic patients can recognize repetitive epitopes in one of the important wheat food allergens. Recombinant HMW Bx7 may be included into the panel of allergens for component-resolved diagnosis of wheat food allergy.

Comparative and evolutionary analysis of major peanut allergen gene families

Peanut (Arachis hypogaea L.) causes one of the most serious food allergies. Peanut seed proteins, Arah1, Arah2, and Arah3, are considered to be among the most important peanut allergens. To gain insights into genome organization and evolution of allergen-encoding genes, approximately 617 kb from the genome of cultivated peanut and 215 kb from a wild relative were sequenced including three Arah1, one Arah2, eight Arah3, and two Arah6 gene family members. To assign polarity to differences between homoeologous regions in peanut, we used as outgroups the single orthologous regions in Medicago, Lotus, common bean, chickpea, and pigeonpea, which diverged from peanut about 50 Ma and have not undergone subsequent polyploidy. These regions were also compared with orthologs in many additional dicot plant species to help clarify the timing of evolutionary events. The lack of conservation of allergenic epitopes between species, and the fact that many different proteins can be allergenic, makes the identification of allergens across species by comparative studies difficult. The peanut allergen genes are interspersed with low-copy genes and transposable elements. Phylogenetic analyses revealed lineage-specific expansion and loss of low-copy genes between species and homoeologs. Arah1 syntenic regions are conserved in soybean, pigeonpea, tomato, grape, Lotus, and Arabidopsis, whereas Arah3 syntenic regions show genome rearrangements. We infer that tandem and segmental duplications led to the establishment of the Arah3 gene family. Our analysis indicates differences in conserved motifs in allergen proteins and in the promoter regions of the allergen-encoding genes. Phylogenetic analysis and genomic organization studies provide new insights into the evolution of the major peanut allergen-encoding genes.

B-cell epitope engineering: A matter of recognizing protein features and motives

Using in vivo and in vitro studies B-cell epitopes have been identified on a number of proteins. These epitopes were used to develop predictive methods. After comparison of existing and emerging technologies, this review concludes that antigenicity is not described by physicochemical and structural characteristics of a protein alone. Molecular characteristics of the antigenic amino acids are required. How the structural context affects the selection of these amino acids by the antibody is unknown.:

Molecular approach to allergy diagnosis and therapy

Presently, allergy diagnosis and therapy procedures are undergoing a transition phase in which allergen extracts are being step-by-step replaced by molecule-based products. The new developments will allow clinicians to obtain detailed information on sensitization patterns, more accurate interpretation of allergic symptoms, and thus improved patients' management. In this respect, recombinant technology has been applied to develop this new generation of molecule-based allergy products. The use of recombinant allergens allows full validation of identity, quantity, homogeneity, structure, aggregation, solubility, stability, IgE-binding and the biologic potency of the products. In contrast, such parameters are extremely difficult to assay and standardize for extract-based products. In addition to the possibility of bulk production of wild type molecules for diagnostic purposes, recombinant technology opened the possibility of developing safer and more efficacious products for allergy therapy. A number of molecule-based hypoallergenic preparations have already been successfully evaluated in clinical trials, bringing forward the next generation of allergy vaccines. In this contribution, we review the latest developments in allergen characterization, molecule-based allergy diagnosis, and the application of recombinant allergens in therapeutic setups. A comprehensive overview of clinical trials using recombinant allergens as well as synthetic peptides is presented.

Basophil response to peanut allergens in Mediterranean peanut-allergic patients

Ara h 1, Ara h 2, and Ara h 3 are important sensitizers in peanut allergy. Ara h 9 has also been shown to be relevant in the Mediterranean area. We evaluated the basophil response to peanut allergens and Pru p 3 in Mediterranean patients: Group 1, peanut and peach allergy; Group 2, peanut allergy and tolerance to peach; Group 3, peach allergy and tolerance to peanut; Group 4, nonallergic subjects that tolerate both peanut and peach. Compared to controls (Group 4), there was an increased basophil activation with Ara h 2 (P = 0.031) and Pru p 3 (P = 0.009) in Group 1 and with Ara h 1 (P = 0.016), Ara h 2 (P = 0.001), and Ara h 9 (P = 0.016) in Group 2. Importantly, only Ara h 2 showed an increased activation (P = 0.009) in Group 2 compared to Group 3. Ara h 2 is the best discriminating allergen for peanut allergy diagnosis in a Mediterranean population showing two patterns: patients also allergic to peach, responding to Ara h 2 and Pru p 3, and patients allergic only to peanut, responding to Ara h 1, Ara h 2, and Ara h 9.

The molecular basis of peanut allergy

Peanut allergens can trigger a potent and sometimes dangerous immune response in an increasing number of people. The molecular structures of these allergens form the basis for understanding this response. This review describes the currently known peanut allergen structures and discusses how modifications both enzymatic and non-enzymatic affect digestion, innate immune recognition, and IgE interactions. The allergen structures help explain cross-reactivity among allergens from different sources, which is useful in improving patient diagnostics. Surprisingly, it was recently noted that similar short peptide sequences among unrelated peanut allergens could also be a source of cross-reactivity. The molecular features of peanut allergens continue to inform predictions and provide new research directions in the study of allergic disease.

Peanut allergens: an overview

Peanut is recognized as a potent food allergen producing one of the most frequent food allergies. This fact has originated the publication of an elevated number of scientific reports dealing with peanut allergens and, especially, the prevalence of peanut allergy. For this reason, the information available on peanut allergens is increasing and the debate about peanut allergy is always renewed. This article reviews the information currently available on peanut allergens and on the techniques used for their chemical characterization. Moreover, a general overview on the current biotechnological approaches used to reduce or eliminate peanut allergens is also provided.

Inhibition of weak-affinity epitope-IgE interactions prevents mast cell degranulation

Development of specific inhibitors of allergy has had limited success, in part, owing to a lack of experimental models that reflect the complexity of allergen-IgE interactions. We designed a heterotetravalent allergen (HtTA) system, which reflects epitope heterogeneity, polyclonal response and number of immunodominant epitopes observed in natural allergens, thereby providing a physiologically relevant experimental model to study mast cell degranulation. The HtTA design revealed the importance of weak-affinity epitopes in allergy, particularly when presented with high-affinity epitopes. The effect of selective inhibition of weak-affinity epitope-IgE interactions was investigated with heterobivalent inhibitors (HBIs) designed to simultaneously target the antigen- and nucleotide-binding sites on the IgE Fab. HBI demonstrated enhanced avidity for the target IgE and was a potent inhibitor of degranulation in vitro and in vivo. These results demonstrate that partial inhibition of allergen-IgE interactions was sufficient to prevent mast cell degranulation, thus establishing the therapeutic potential of the HBI design.

Food allergen selective thermal processing regimens may change oral tolerance in infancy

Food allergy can be considered a failure in the induction of oral tolerance. Recently, great interest has been focused on understanding the mechanisms and the contributing factors of oral tolerance development, hoping for new definitive interventions in the prevention and treatment of food allergy. Given that food processing may modify the properties and the nature of dietary proteins, several food processing methods could affect the allergenicity of these proteins and consequently may favour oral tolerance induction to food allergic children. Indeed, effective thermal food processing regimens of altering food proteins to reduce allergenicity have been recently reported in the literature. This article is mainly focused on the effect of selective thermal processing regimens on the main infant allergenic foods, with a potential clinical relevance on their allergenicity and therefore on oral tolerance induction. In the light of recent findings, the acquisition of tolerance in younger age and consequently the ability of young children to "outgrow" food allergy could be achieved through the application of selective thermal processing regimens on certain allergenic foods. Therefore, the ability of processed foods to circumvent clinical disease and at the same time to have an impact on the immune system and facilitate tolerance induction could be invaluable as a component of a successful therapeutic strategy. The opening in the new avenues of research in the use of processed foods in clinical practice for the amelioration of the impact on the quality of life of patients and possibly in food allergy prevention is warranted.

Nuts 'n' guts: transport of food allergens across the intestinal epithelium

The increase in the incidence of food allergy is a growing problem for the western world. This review will focus on the findings from several macromolecular epithelial transport experiments and drug permeability studies to provide a recent comprehension of food allergen intestinal epithelial cell transport and the allergen-epithelial relationship. Specifically, this review will aim to answer whether allergens can permeate the intestinal barrier directly via intestinal epithelial cells, and whether this mode of transport affects downstream immune reactions. By improving our understanding of the interactions which take place during exposure of food allergens with the intestinal epithelium, we can begin to understand whether the epithelial barrier plays a major role in the allergic sensitization process rather than simply restricting the entry of allergens to the underlying lamina propria.

Reduction and alkylation of peanut allergen isoforms Ara h 2 and Ara h 6; characterization of intermediate- and end products

Conglutins, the major peanut allergens, Ara h 2 and Ara h 6, are highly structured proteins stabilized by multiple disulfide bridges and are stable towards heat-denaturation and digestion. We sought a way to reduce their potent allergenicity in view of the development of immunotherapy for peanut allergy. Isoforms of conglutin were purified, reduced with dithiothreitol and subsequently alkylated with iodoacetamide. The effect of this modification was assessed on protein folding and IgE-binding. We found that all disulfide bridges were reduced and alkylated. As a result, the secondary structure lost α-helix and gained some β-structure content, and the tertiary structure stability was reduced. On a functional level, the modification led to a strongly decreased IgE-binding. Using conditions for limited reduction and alkylation, partially reduced and alkylated proteins were found with rearranged disulfide bridges and, in some cases, intermolecular cross-links were found. Peptide mass finger printing was applied to control progress of the modification reaction and to map novel disulfide bonds. There was no preference for the order in which disulfides were reduced, and disulfide rearrangement occurred in a non-specific way. Only minor differences in kinetics of reduction and alkylation were found between the different conglutin isoforms. We conclude that the peanut conglutins Ara h 2 and Ara h 6 can be chemically modified by reduction and alkylation, such that they substantially unfold and that their allergenic potency decreases.