Mapping of conformational IgE epitopes of food allergens

Mutation of Disulfide Bond Sites Reduces the Immunoreactivity of Cra a 4 by Changing the Structural Characteristics

Sarcoplasmic calcium-binding protein (Cra a 4) from Crassostrea angulata belongs to the EF-hand superfamily, and understanding of its structure-allergenicity relationship is still insufficient. In this study, chemical denaturants were used to destroy the structure of Cra a 4, showing that disruption of the structure reduced its IgG-/IgE-binding activity. To explore which critical amino acid site affects the allergenicity of Cra a 4, the mutants were obtained by site-directed mutations in the disulfide bonds site (C97), conformational epitopes (I105, D114), or Ca2+-binding region (D106, D110) and their IgG-/IgE-binding activity was reduced significantly using serological tests. Notably, C97A had the lowest immunoreactivity. In addition, two conformational epitopes of Cra 4 were verified. Meanwhile, the increase of the α-helical content, surface hydrophobicity, and surface electrostatic potential of C97A affected its allergenicity. Overall, the understanding of the structure-allergenicity relationship of Cra a 4 allowed the development of a hypoallergenic mutant.

Insight into the allergenicity and structure changes of parvalbumin from Trachinotus ovatus induced by dense-phase carbon dioxide

Parvalbumin (PV) is a major allergen in fish, and traditional treatments cannot reduce its sensitization. The effects of dense-phase carbon dioxide (DPCD) treatment on the sensitization and spatial structure of PV in Trachinotus ovatus were evaluated in this study. Western blotting and indirect ELISA were used to determine the allergenicity changes and spatial conformations of PV treated by DPCD. Tris-tricine-SDS-PAGE, circular dichroism, surface hydrophobicity, endogenous fluorescence, UV spectrophotometry, free amino group, total sulfhydryl group and SEM analyses were applied to characterize PV structure. The results showed that DPCD treatment (15 MPa, 30 min, 50 °C) could reduce PV-induced allergic reactions by 39-41 %, which destroyed the normal conformational epitopes and reduced the risk of PV-induced allergy. The secondary structure changed from ordered to disordered with a decreased content of α-helical groups, while the internal hydrophobic groups were exposed. The total sulfhydryl group content decreased significantly (P < 0.05). The surface hydrophobicity and ultraviolet absorption spectrum were enhanced, and the endogenous fluorescence peak shifted to a long wavelength. Meanwhile, the content of free amino groups increased significantly (P < 0.05). This study could provide a theoretical basis and a promising technical approach for reduction of PV allergenicities.

An update on recent developments and highlights in food allergy

While both the incidence and general awareness of food allergies is increasing, the variety and clinical availability of therapeutics remain limited. Therefore, investigations into the potential factors contributing to the development of food allergy (FA) and the mechanisms of natural tolerance or induced desensitization are required. In addition, a detailed understanding of the pathophysiology of food allergies is needed to generate compelling, enduring, and safe treatment options. New findings regarding the contribution of barrier function, the effect of emollient interventions, mechanisms of allergen recognition, and the contributions of specific immune cell subsets through rodent models and human clinical studies provide novel insights. With the first approved treatment for peanut allergy, the clinical management of FA is evolving toward less intensive, alternative approaches involving fixed doses, lower maintenance dose targets, coadministration of biologicals, adjuvants, and tolerance-inducing formulations. The ultimate goal is to improve immunotherapy and develop precision-based medicine via risk phenotyping allowing optimal treatment for each food-allergic patient.

Effect of Structural Targeted Modifications on the Potential Allergenicity of Peanut Allergen Ara h 2

Protein structure affects allergenicity, and critical structural elements, especially conformational epitopes that determine allergenicity, have attracted a great deal of interest. In this study, we aimed to identify the localized structure that affects the potential allergenicity of protein by making targeted modifications of Ara h 2 and comparing the structure and allergenicity of mutants with those of the wide-type allergen. The structures of the allergen and its mutants were characterized by circular dichroism and ultraviolet absorption spectroscopy and simulated by molecular dynamics. The allergenicity was assessed by Western blotting, an indirect competitive enzyme-linked immunosorbent assay, a cell model, and a mouse model. Then, the structures that affect allergenicity were analyzed and screened. Our results showed that mutations in amino acids changed the nearby localized structure and the overall structures. The structural changes affected the IgE binding capacity of the allergen and reduced its potential allergenicity. The solvent accessible surface area (SASA) of aromatic residues was positively correlated with the IgE binding capacity. The integrity of the disulfide bond is also critical for the binding of IgE to allergens. Interestingly, different mutations induced similar electrostatic potential and allergenicity changes, such as localized structure R⁶²DPYSPSQDPYSPS⁷⁵. In conclusion, the disulfide bond and the SASA of aromatic residues are important for the allergenicity of Ara h 2. The localized structure R⁶²DPYSPSQDPYSPS⁷⁵ is also crucial for the allergenicity of Ara h 2.

Immunodominant conformational and linear IgE epitopes lie in a single segment of Ara h 2

BACKGROUND

Contribution of conformational epitopes to the IgE reactivity of peanut allergens Ara h 2 and Ara h 6 is at least as important as that of the linear epitopes. However, little is known about these conformational IgE-binding epitopes.

OBJECTIVE

We investigated the distribution of conformational epitopes on chimeric 2S-albumins.

METHODS

Recombinant chimeras were generated by exchanging structural segments between Ara h 2 and Ara h 6. Well-refolded chimeras, as verified by circular dichroism analysis, were then used to determine the epitope specificity of mAbs by performing competitive inhibition of IgG binding. Furthermore, we delineated the contribution of each segment to the overall IgE reactivity of both 2S-albumins by measuring the chimeras' IgE-binding capacity with sera from 21 patients allergic to peanut. We finally assessed chimeras' capacity to trigger mast cell degranulation.

RESULTS

Configuration of the conformational epitopes was preserved in the chimeras. Mouse IgG mAbs, raised against natural Ara h 6, and polyclonal human IgE antibodies recognized different conformational epitopes distributed all along Ara h 6. In contrast, we identified human IgG mAbs specific to different Ara h 2 linear or conformational epitopes located in all segments except the C-terminal one. The major conformational IgE-binding epitope of Ara h 2 was located in a segment located between residues 33 and 81 that also contains the major linear hydroxyproline-containing epitope. Accordingly, this segment is critical for the capacity of Ara h 2 to induce mast cell degranulation.

CONCLUSIONS

Chimeric 2S-albumins provide new insights on the conformational IgE-binding epitopes of Ara h 2 and Ara h 6. Proximity of the immunodominant linear and conformational IgE-binding epitopes probably contributes to the high allergenic potency of Ara h 2.

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.

Structure-based prediction of the IgE epitopes of the major dog allergen Can f 1

Allergy to dogs has become increasingly prominent worldwide. Seven dog allergens have been identified, including Canis familiaris allergen 1-7 (Can f 1-7). Although Can f 1 is a major dog allergen sensitized to 50-75% of dog-allergic subjects, its IgE epitopes have not been identified. The structural analysis of an allergen is important to identify conformational epitopes. In this study, we generated a recombinant Can f 1 protein and determined its crystal structure using X-ray crystallography. Can f 1 had a typical lipocalin fold, which is composed of an eight-stranded β-barrel and α-helix, and has high similarity to Can f 2, Can f 4, and Can f 6 in overall structure. However, the localizations of surface charges on these proteins were quite different. Based on sequence alignment and tertiary structure, we predicted five critical residues (His86, Glu98, Arg111, Glu138, and Arg152) for the IgE epitopes. The relevance of these residues to IgE reactivity was assessed by generating Can f 1 mutants with these residues substituted for alanine. Although the effects of the mutation on IgE binding depended on the sera of dog-allergic patients, H86A and R152A mutants showed reduced IgE reactivity compared with wild-type Can f 1. These results suggest that Can f 1 residues His86 and Arg152 are candidates for the IgE conformational epitope.

Irradiation technology: An effective and promising strategy for eliminating food allergens

Food allergies are one of the major health concerns worldwide and have been increasing at an alarming rate in recent times. The elimination of food allergenicity has been an important issue in current research on food. Irradiation is a typical nonthermal treatment technology that can effectively reduce the allergenicity of food, showing great application prospects in improving the quality and safety of foods. In this review, the mechanism and remarkable features of irradiation in the elimination of food allergens are mainly introduced, and the research progress on reducing the allergenicity of animal foods (milk, egg, fish and shrimp) and plant foods (soybean, peanut, wheat and nuts) using irradiation is summarized. Furthermore, the influencing factors for irradiation in the elimination of food allergens are analyzed and further research directions of irradiation desensitization technology are also discussed. This article aims to provide a reference for promoting the application of irradiation technology in improving the safety of foods.

Components of plant-derived food allergens: Structure, diagnostics, and immunotherapy

A large number of plant-derived food allergen components have been identified to date. Although these allergens are diverse, they often share common structural features such as numerous disulfide bonds or oligomeric structures. Furthermore, some plant-derived food allergen components cross-react with pollen allergens. Since the relationship between allergen components and clinical symptoms has been well characterized, measurements of specific IgE to these components have become useful for the accurate clinical diagnosis and selection of optimal treatment methods for various allergy-related conditions including allergy caused by plant-derived foods. Herein, I have described the types and structures of different plant allergen components and outlined the diagnosis as well as treatment strategies, including those reported recently, for such substances. Furthermore, I have also highlighted the contribution of allergen components to this field.

Effects of the Maillard reaction on the epitopes and immunoreactivity of tropomyosin, a major allergen in Chlamys nobilis

Scallop (Chlamys nobilis) causes an IgE-mediated food allergy; however, studies of the allergens in its musculus are not sufficiently comprehensive. In this context, the target protein was purified from scallops and confirmed to be the major allergen tropomyosin (TM) using proteomic technology and serological testing. Subsequently, seven potential IgE epitopes of TM were obtained using phage display technology with IgE enrichment from the serum of scallop-sensitized patients and identified via inhibition enzyme-linked immunosorbent assays. A method for the Maillard reaction of TM and xylose was established, and Maillard-reacted TM (MR-TM) showed significantly decreased immunobinding activity and CD63 and CD203c expression in basophils compared with TM. Furthermore, shotgun proteomics analysis showed that eleven specific amino acids (K12, R15, K28, K76, R125, R127, K128, R133, R140, K146, and K189) of the six IgE epitopes of TM were modified after the Maillard reaction. Overall, the immunoactivity of MR-TM was reduced, which provides a theoretical reference for the development of hypoallergenic foods.

Advances and novel developments in molecular allergology

The continuous search for new allergens and the design of allergen derivatives improves the understanding of their allergenicity and aids the design of novel diagnostic and immunotherapy approaches. This article discusses the recent developments in allergen and epitope discovery, allergy diagnostics and immunotherapy. Structural information is crucial for the elucidation of cross-reactivity of marker allergens such as the walnut Jug r 6 or that of nonhomologous allergens, as shown for the peanut allergens Ara h 1 and 2. High-throughput sequencing, liposomal nanoallergen display, bead-based assays, and protein chimeras have been used in epitope discovery. The binding of natural ligands by the birch pollen allergen Bet v 1 or the mold allergen Alt a 1 increased the stability of these allergens, which is directly linked to their allergenicity. We also report recent findings on the use of component-resolved approaches, basophil activation test, and novel technologies for improvement of diagnostics. New strategies in allergen-specific immunotherapy have also emerged, such as the use of virus-like particles, biologics or novel adjuvants. The identification of dectin-1 as a key player in allergy to tropomyosins and the formyl peptide receptor 3 in allergy to lipocalins are outstanding examples of research into the mechanism of allergic sensitization.

Mapping and IgE-binding capacity analysis of heat/digested stable epitopes of mud crab allergens

Mud crab (Scylla paramamosain) is widely consumed after thermal processing. It is necessary to comprehensively evaluate of the allergenic potential and epitopes of allergens in high temperature-pressure (HTP) treated S. paramamosain. Tropomyosin and arginine kinase presented higher prevalence (30.77% and 42.13%) than the other three important crab allergens by component-resolved diagnosis. The surface expression of basophils CD63 and CD203c were decreased in HTP treated crab, an effect that was even more evident after digestion and absorption by the intestinal Caco-2 cell model. Of the 35 stable epitope, six were for the first time identified in shellfish. Seven heat/digested stable peptides of tropomyosin retained IgE-binding capacity and were shown to interact with MHC-II. Five epitopes (amino acids 19-29, 99-109, 153-162, 170-188 and 211-221) were the first identified in crab. The study provides insight into prevention and therapy of crab allergy, as well as helps to reduce crab allergenicity during thermal processing.

Managing food allergy and anaphylaxis: A new model for an integrated approach

There is an increasing public concern on food allergy and related anaphylactic reactions that occur mainly at the community level. The perception of the disease is huge among parents who believe that 1 out of 20 children suffers from severe food allergy. The discrepancy between this self-reported prevalence and the real one when a food challenge is performed, points out the gap in the implementation of guidelines for clinical practice. Health professionals as well show scarce adherence to the guidelines both at the Emergency Departments and at the primary care level. Anaphylactic reaction are not recognized, adrenaline is under-used and self-injectable devices are not prescribed. Although education and training are limited to local, spontaneous initiatives from patient's organization and few allergists, the data so far available demonstrate that improvement in knowledge and attitudes can be achieved further to a structured program. There is the need to establish good evidence -based practices for educational intervention that should be adopted in the context of public health policies for food allergy. This would imply a change in legislation in many countries to prevent prosecution for liability of lay people administering adrenaline when properly trained. In parallel an integrated clinical care pathway should be developed by multidisciplinary and multi-professional teams in the context of national Centres of Excellence -CoE. These CoE could drive the progression to digital health create, creating networks of CoE for best practices of care and for clinical trials.

Development of hypoallergenic variants of the major horse allergen Equ c 1 for immunotherapy by rational structure based engineering

The use of recombinant allergens is a promising approach in allergen-specific immunotherapy (AIT). Considerable limitation, however, has been the ability of recombinant allergens to activate effector cells leading to allergic reactions. Recombinant hypoallergens with preserved protein folding and capacity to induce protective IgG antibodies binding effectively to the native allergen upon sensitization would be beneficial for safer AIT. In this study, hypoallergen variants of the major horse allergen Equ c 1 were designed by introducing one point mutation on the putative IgE epitope region and two mutations on the monomer-monomer interface of Equ c 1 dimer. The recombinant Equ c 1 wild type and the variants were produced and purified to homogeneity, characterized by size-exclusion ultra-high performance liquid chromatography and ultra-high resolution mass spectrometry. The IgE-binding profiles were analyzed by a competitive immunoassay and the biological activity by a histamine release assay using sera from horse allergic individuals. Two Equ c 1 variants, Triple 2 (V47K + V110E + F112K) and Triple 3 (E21Y + V110E + F112K) showed lower allergen-specific IgE-binding capacity and decreased capability to release histamine from basophils in vitro when using sera from six allergic individuals. Triple 3 showed higher reduction than Triple 2 in IgE-binding (5.5 fold) and in histamine release (15.7 fold) compared to wild type Equ c 1. Mutations designed on the putative IgE epitope region and monomer-monomer interface of Equ c 1 resulted in decreased dimerization, a lower IgE-binding capacity and a reduced triggering of an allergic response in vitro.

Recent developments and highlights in food allergy

The achievement of long-lasting, safe treatments for food allergy is dependent on the understanding of the immunological basis of food allergy. Accurate diagnosis is essential for management. In recent years, data from oral food challenges have revealed that routine allergy testing is poor at predicting clinical allergy for tree nuts, almonds in particular. More advanced antigen-based tests including component-resolved diagnostics and epitope reactivity may lead to more accurate diagnosis and selection of therapeutic intervention. Additional diagnostic accuracy may come from cellular tests such as the basophil activation test or mast cell approaches. In the context of clinical trials, cellular tests have revealed specific T-cell and B-cell populations that are more abundant in food-allergic individuals with distinct mechanistic features. Awareness of clinical markers, such as the ability to eat baked forms of milk and egg, continues to inform the understanding of natural tolerance development. Mouse models have allowed for investigation into multiple mechanisms of food allergy including modification of epithelial metabolism, and the induction of regulatory cell subsets and the microbiome. Increasing numbers of children who underwent food immunotherapy enlarged the body of evidence on mechanisms and predictors of treatment success. Experimental immunological markers in conjunction with clinical determinants such as lower age and lower initial specific IgE appear to be of benefit. More research on the optimal dose, preparation, and route of application integrating a high-level safety and efficacy is demanded. Alternatively, biologics blocking TSLP, IL-33, IL-4 and IL-13, or IgE may help to achieve that.

Food and drug allergy, and anaphylaxis in EAACI journals (2018)

The European Academy of Allergy and Clinical Immunology (EAACI) supports three journals: "Allergy," "Pediatric Allergy and Immunology (PAI)," and "Clinical and Translational Allergy (CTA)." One of the major goals of EAACI is to support health promotion in which prevention of allergy and asthma plays a critical role and to disseminate the knowledge of allergy to all stakeholders including the EAACI junior members. This paper summarizes the achievements of 2018 in anaphylaxis, and food and drug allergy. Main topics that have been focused are anaphylaxis, mechanisms of food allergy (FA), epidemiology of FA, food allergens, diagnosis of FA, prevention and control of FA, FA immunotherapy, drug allergy, and political agenda.

Future research trends in understanding the mechanisms underlying allergic diseases for improved patient care

The specialties of allergy and clinical immunology have entered the era of precision medicine with the stratification of diseases into distinct disease subsets, specific diagnoses, and targeted treatment options, including biologicals and small molecules. This article reviews recent developments in research and patient care and future trends in the discipline. The section on basic mechanisms of allergic diseases summarizes the current status and defines research needs in structural biology, type 2 inflammation, immune tolerance, neuroimmune mechanisms, role of the microbiome and diet, environmental factors, and respiratory viral infections. In the section on diagnostic challenges, clinical trials, precision medicine and immune monitoring of allergic diseases, asthma, allergic and nonallergic rhinitis, and new approaches to the diagnosis and treatment of drug hypersensitivity reactions are discussed in further detail. In the third section, unmet needs and future research areas for the treatment of allergic diseases are highlighted with topics on food allergy, biologics, small molecules, and novel therapeutic concepts in allergen‐specific immunotherapy for airway disease. Unknowns and future research needs are discussed at the end of each subsection.

Biomarkers in Food Allergy

PURPOSE OF REVIEW

To familiarize the reader with the concept of precision medicine in food allergy by dealing with the current biomarkers for the diagnosis, prognosis, and management of the disease.

RECENT FINDINGS

Many efforts have been devoted in order to characterize reliable biomarkers able to identify specific phenotypes and endotypes in food allergy. Specific IgE (sIgE), sIgE/total IgE ratios, and T cell assays are just a few candidates that have been investigated over time. With the advent of omics sciences, a new era is commencing. A better understanding of pathogenesis of food allergy and mechanisms of action of the different therapeutic options will allow the accurate selection of the appropriate patient. In the near future, advances in technologies and data interpretation will allow a better understanding of the pathogenesis of food allergy and the identification of proper biomarkers for a personalized treatment tailored on the specific patient's profile.