IgE Reactivity of Blue Swimmer Crab (Portunus pelagicus) Tropomyosin, Por p 1, and Other Allergens; Cross-Reactivity with Black Tiger Prawn and Effects of Heating

Study on the Sensitization and Antigenic Epitopes of Tropomyosin from Antarctic Krill (Euphausia superba)

Antarctic krill (Euphausia superba), a shrimp-like marine crustacean, has become a beneficial source of high-quality animal protein. Meanwhile, a special focus has been placed on its potential sensitization issue. In this study, a 35 kDa protein was purified and identified to be Antarctic krill tropomyosin (AkTM) by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The purified TM showed a strong IgE-binding capacity to shrimp/crab-allergic patients' sera, indicating that TM is the primary allergen in Antarctic krill. Simulated gastrointestinal digestion revealed that the digestion stability of TM to pepsin was higher than that to trypsin. The strong degranulation triggered by TM in RBL-2H3 cells suggested that AkTM has a strong sensitization capacity. The TM-sensitized BALB/c mice displayed severe anaphylactic symptoms; high levels of TM-specific IgE, sIgG1, and histamine; and increased IL-4, indicating that AkTM could provoke IgE-mediated allergic reactions. Bioinformatics prediction, indirect competition ELISA, and mast cell degranulation assay were used to map the antigenic epitopes of AkTM. Finally, nine peptides of T_43-58, T_88-101, T_111-125, T_133-143, T_144-155, T_183-197, T_223-236, T_249-261, and T_263-281 were identified as the linear epitopes of AkTM. The findings may help us develop efficient food processing techniques to reduce krill allergy and gain a deeper comprehension of the allergenicity of krill allergens.

EAACI Molecular Allergology User's Guide 2.0

Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE-mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE-mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well-defined, highly pure molecules for component-resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the "EAACI Molecular Allergology User's Guide" (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state-of-the-art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

Seafood allergy: Allergen, epitope mapping and immunotherapy strategy

Seafoods are fashionable delicacies with high nutritional values and culinary properties, while seafood belongs to worldwide common food allergens. In recent years, many seafood allergens have been identified, while the diversity of various seafood species give a great challenge in identifying and characterizing seafood allergens, mapping IgE-binding epitopes and allergen immunotherapy development, which are critical for allergy diagnostics and immunotherapy treatments. This paper reviewed the recent progress on seafood (fish, crustacean, and mollusk) allergens, IgE-binding epitopes and allergen immunotherapy for seafood allergy. In recent years, many newly identified seafood allergens were reported, this work concluded the current situation of seafood allergen identification and designation by the World Health Organization (WHO)/International Union of Immunological Societies (IUIS) Allergen Nomenclature Sub-Committee. Moreover, this review represented the recent advances in identifying the IgE-binding epitopes of seafood allergens, which were helpful to the diagnosis, prevention and treatment for seafood allergy. Furthermore, the allergen immunotherapy could alleviate seafood allergy and provide promising approaches for seafood allergy treatment. This review represents the recent advances and future outlook on seafood allergen identification, IgE-binding epitope mapping and allergen immunotherapy strategies for seafood allergy prevention and treatment.

Understanding the Mechanism of Increased IgG/IgE Reactivity but Decreased Immunodetection Recovery in Thermally Induced Shrimp (Litopenaeus vannamei) Tropomyosin via Multispectroscopic and Molecular Dynamics Simulation Techniques

Despite the fact that tropomyosin (TM) has highly stable structural characteristics, thermal processing can adversely influence its immunodetection, and the mechanism involved has not been elucidated. Purified TM was heated at various temperatures, and then the IgG/IgE-binding capacity and immunodetection recovery were determined; meanwhile, the structural alterations were analyzed via spectroscopic and molecular dynamics simulation techniques. The obtained results demonstrated that heat-treated TM showed significantly increased IgG/IgE reactivity, confirmed by indirect ELISA and immunoblotting analysis, which might be attributed to the increased structural flexibility, and thus allowed TM to be recognized IgG/IgE easily. However, these structural alterations during thermal processing would contribute to the masking of some epitopes located in TM's surface due to the presence of curled or folded conformation with a considerable reduction of the solvent-accessible surface and radius of gyration, which primarily caused immunodetection recovery reduction in the sandwich ELISA (sELISA) test. The number of antigen binding sites might play a crucial role in a sandwich immunodetection system for sensitive and precise analysis in processed foods.

Crustacean shellfish allergens: influence of food processing and their detection strategies

Despite the increasing popularity of crustacean shellfish among consumers due to their rich nutrients, they can induce a serious allergic response, sometimes even life-threatening. In the past decades, a variety of crustacean allergens have been identified to facilitate the diagnosis and management of crustacean allergies. Although food processing techniques can ease the risk of crustacean shellfish allergy, no available processing methods to tackle crustacean allergies thoroughly. Strict dietary avoidance of crustacean shellfish and its component is the best option for the protection of sensitized individuals, which should rely on the compliance of food labeling and, as such, on their verification by sensitive, reliable, and accurate detection techniques. In this present review, the physiochemical properties, structure aspects, and immunological characteristics of the major crustacean allergens have been described and discussed. Subsequently, the current research progresses on how various processing techniques cause the alterations and modifications in crustacean allergens to produce hypoallergenic crustacean food products were summarized and discussed. Particularly, various analytical methodologies employed in crustacean shellfish allergen detection, and the effect of food processing and matrix on these techniques, are also herein emphasized for the appropriate selection of analytical detection tools to safeguard consumers safety.

Characterization, Epitope Identification, and Cross-reactivity Analysis of Tropomyosin: An Important Allergen of Crassostrea angulata

Oyster is a common shellfish product in China, which is associated with food allergy. However, there is still lack of research on allergens in oysters. In this study, tropomyosin (TM), an important allergen of Crassostrea angulata, was purified and identified by mass spectrometry. Subsequently, TM was cloned and expressed, with a sequence of size 852 bp, encoding 284 amino acid residues. The results of circular dichroism, digestion assay, inhibition enzyme-linked immunosorbent assay, and basophil activation test showed that recombinant TM had similar physicochemical properties and immunological properties to native TM. Furthermore, two conformational mimotopes were obtained and 10 IgE linear epitopes were verified. Meanwhile, different degrees of cross-reactivity were observed between C. angulata TM and the other 8 shellfish TMs using antibodies and serological analysis, which may relate to the 3 conserved epitope regions. These findings are expected to provide a theoretical basis for the molecular diagnosis of oyster allergy and cross-reactivity among shellfish.

Food Allergies: Immunosensors and Management

Food allergies (FA) are commonly depicted as immune responses. The mechanism of allergic reactions involves immunoglobulin E (IgE) and non-immunoglobulin E (non-IgE)-related responses caused by contact with specific foods. FAs can be fatal, have negative effects and have become the subject of fanaticism in recent years. In terms of food safety, allergic compounds have become a problem. The immune response to allergens is different to that from food intolerance, pharmacological reactions, and poisoning. The most important allergenic foods are soybeans, milk, eggs, groundnuts, shellfishes, tree nuts, cereals and fish, which together are known as the “Big Eight”. This review will introduce and discuss FAs in milk, peanuts, nuts, shellfishes, eggs and wheat and their detections and potential treatments will also be provided. We believe that this review may provide important information regarding food-induced allergies for children who have allergic reactions and help them avoid the allergenic food in the future.

An overview of tropomyosin as an important seafood allergen: Structure, cross-reactivity, epitopes, allergenicity, and processing modifications

Tropomyosin (TM) is a major allergen in crustaceans, which often causes allergy and is fatal to some consumers. Currently, the most effective treatment is to avoid ingesting TM, although most adverse events occur in accidental ingestion. In this review, the molecular characterization, epitopes, cross-reactivity, and pathogenesis of TM are introduced and elucidated. Modification of TM by traditional processing methods such as heat treatment and enzymatic hydrolysis, and innovative processing technologies including high-pressure treatment, cold plasma (CP), ultrasound, pulsed electric field (PEF), pulsed ultraviolet, microwave and irradiation are discussed in detail. Particularly, enzymolysis, PEF, and CP technologies show great potential for modifying TM and more studies are needed to verify their effectiveness for the seafood industry. Possible mechanisms and the advantages/disadvantages of these technologies for the mitigation of TM allergenicity are also highlighted. Further work should be conducted to investigate the allergenicity caused by protein segments such as epitopes, examine the interaction sites between the allergen and the processing techniques and reveal the reduction mechanism of allergenicity.

Molecular and allergenic characterization of recombinant tropomyosin from mud crab Scylla olivacea

BACKGROUND

Tropomyosin is a major allergen in crustaceans, including mud crab species, but its molecular and allergenic properties in Scylla olivacea are not well known. Thus, this study aimed to produce the recombinant tropomyosin protein from S. olivacea and subsequently investigate its IgE reactivity.

METHODS AND RESULTS

The tropomyosin gene was cloned and expressed in the Escherichia coli system, followed by SDS-PAGE and immunoblotting test to identify the allergenic potential of the recombinant protein. The 855-base pair of tropomyosin gene produced was found to be 99.18% homologous to Scylla serrata. Its 284 amino acids matched the tropomyosin of crustaceans, arachnids, insects, and Klebsiella pneumoniae, ranging from 79.03 to 95.77%. The tropomyosin contained 89.44% alpha-helix folding with a tertiary structure of two-chain alpha-helical coiled-coil structures comprising a homodimer heptad chain. IPTG-induced histidine tagged-recombinant tropomyosin was purified at the size of 42 kDa and confirmed as tropomyosin using anti-tropomyosin monoclonal antibodies. The IgE binding of recombinant tropomyosin protein was reactive in 90.9% (20/22) of the sera from crab-allergic patients.

CONCLUSIONS

This study has successfully produced an allergenic recombinant tropomyosin from S. olivacea. This recombinant tropomyosin may be used as a specific allergen for the diagnosis of allergy.

Occupational Allergic Sensitization Among Workers Processing King Crab (Paralithodes camtschaticus) and Edible Crab (Cancer pagurus) in Norway and Identification of Novel Putative Allergenic Proteins

Introduction: Asthma and allergy occur frequently among seafood processing workers, with the highest prevalence seen in the crustacean processing industry. In this study we established for the first time the prevalence of allergic sensitization in the Norwegian king- and edible crab processing industry and characterized the IgE-reactive proteins.

Materials and Methods: Two populations of crab processing workers participated; 119 king crab and 65 edible crab workers. The investigation included information on work tasks and health through a detailed questionnaire. Allergic sensitization was investigated by crab-specific IgE quantification and skin prick tests (SPT) to four in-house prepared crab extracts; raw meat, cooked meat, raw intestines and raw shell. Allergen-specific IgE binding patterns were analyzed by IgE immunoblotting to the four allergen extracts using worker serum samples. Total proteins in crab SPT extracts and immunoblot-based IgE binding proteins were identified by mass spectrometric analysis.

Results: Positive SPTs were established in 17.5% of king- and 18.1% of edible crab workers, while elevated IgE to crab were demonstrated in 8.9% of king- and 12.2% of edible crab processing workers. There was no significant difference between the king and edible crab workers with respect to self-reported respiratory symptoms, elevated specific IgE to crab or SPT results. Individual workers exhibited differential IgE binding patterns to different crab extracts, with most frequent binding to tropomyosin and arginine kinase and two novel IgE binding proteins, hemocyanin and enolase, identified as king- and edible crab allergens.

Conclusions: Occupational exposure to king- and edible crabs may frequently cause IgE mediated allergic sensitization. Future investigations addressing the diagnostic value of crab allergens including tropomyosin and arginine kinase and the less well-known IgE-binding proteins hemocyanin and enolase in a component-resolved diagnostic approach to crab allergy should be encouraged.

Allergens from Edible Insects: Cross-reactivity and Effects of Processing

PURPOSE OF REVIEW

The recent introduction of edible insects in Western countries has raised concerns about their safety in terms of allergenic reactions. The characterization of insect allergens, the sensitization and cross-reactivity mechanisms, and the effects of food processing represent crucial information for risk assessment.

RECENT FINDINGS

Allergic reactions to different insects and cross-reactivity with crustacean and inhalant allergens have been described, with the identification of new IgE-binding proteins besides well-known pan-allergens. Depending on the route of sensitization, different potential allergens seem to be involved. Food processing may affect the solubility and the immunoreactivity of insect allergens, with results depending on species and type of proteins. Chemical/enzymatic hydrolysis, in some cases, abolishes immunoreactivity. More studies based on subjects with a confirmed insect allergy are necessary to identify major and minor allergens and the role of the route of sensitization. The effects of processing need to be further investigated to assess the risk associated with the ingestion of insect-containing food products.

Clinical Management of Seafood Allergy

Seafood plays an important role in human nutrition and health. A good patient workup and sensitive diagnostic analysis of IgE antibody reactivity can distinguish between a true seafood allergy and other adverse reactions generated by toxins or parasites contaminating ingested seafood. The 2 most important seafood groupings include the fish and shellfish. Shellfish, in the context of seafood consumption, constitutes a diverse group of species subdivided into crustaceans and mollusks. The prevalence of shellfish allergy seems to be higher than that of fish allergy, with an estimate of up to 3% in the adult population and fin fish allergy prevalence of approximately 1%. Clinical evaluation of the seafood-allergic patient involves obtaining a detailed history and obtaining in vivo and/or in vitro testing with careful interpretation of results with consideration of cross-reactivity features of the major allergens. Oral food challenge is useful not only for the diagnosis but also for avoiding unnecessary dietary restrictions. In this review, we highlight some of the recent reports to provide solid clinical and laboratory tools for the differentiation of fish allergy from shellfish allergy, enabling best treatment and management of these patients.

Conservation Analysis of B-Cell Allergen Epitopes to Predict Clinical Cross-Reactivity Between Shellfish and Inhalant Invertebrate Allergens

Understanding and predicting an individual's clinical cross-reactivity to related allergens is a key to better management, treatment and progression of novel therapeutics for food allergy. In food allergy, clinical cross-reactivity is observed in patients reacting to unexpected allergen sources containing the same allergenic protein or antibody binding patches (epitopes), often resulting in severe allergic reactions. Shellfish allergy affects up to 2% of the world population and persists for life in most patients. The diagnosis of shellfish allergy is however often challenging due to reported clinical cross-reactivity to other invertebrates including mites and cockroaches. Prediction of cross-reactivity can be achieved utilizing an in-depth analysis of a few selected IgE-antibody binding epitopes. We combined available experimentally proven IgE-binding epitopes with informatics-based cross-reactivity prediction modeling to assist in the identification of clinical cross-reactive biomarkers on shellfish allergens. This knowledge can be translated into prevention and treatment of allergic diseases. To overcome the problem of predicting IgE cross-reactivity of shellfish allergens we developed an epitope conservation model using IgE binding epitopes available in the Immune Epitope Database and Analysis Resource (http://www.iedb.org/). We applied this method to a set of four different shrimp allergens, and successfully identified several non-cross-reactive as well as cross-reactive epitopes, which have been experimentally established to cross-react. Based on these findings we suggest that this method can be used for advanced component-resolved-diagnosis to identify patients sensitized to a specific shellfish group and distinguish from patients with extensive cross-reactivity to ingested and inhaled allergens from invertebrate sources.

A review on methodologies for extraction, identification and quantification of allergenic proteins in prawns

Prawn allergy is one of the most common food-borne allergies and current prevention is by avoidance. This review paper summarised different methodologies for the extraction, identification and quantification of prawn protein allergens, reported in various research studies. Following extraction, allergenic components have been analysed using well-established methodologies, such as SDS-PAGE, Immunoblotting, ELISA, CD Spectroscopy, HPLC, DBPCFC, SPT etc. Moreover, the preference towards Aptamer-based technique for allergenicity analysis has also been highlighted in this review paper. The summary of these methodologies will provide a reference platform for present and future research directions.

Basophil Activation Test: Old and New Applications in Allergy

PURPOSE OF REVIEW

The basophil activation test (BAT) using flow cytometry has supplanted traditional methods of measuring basophil degranulation using histamine and other mediator release, and can be used for clinical applications as well as to explore the immune mechanisms of effector cell response to allergen. This review discusses the advancements made in clinical, diagnostic and laboratory research of allergy utilizing an ever-evolving BAT.

RECENT FINDINGS

Being an in vitro surrogate of the allergic reaction that happens in vivo in the sick patient, the BAT can be used to support the diagnosis of various allergic conditions, such as food, drug, respiratory and insect venom allergies, and the assessment of clinical response to allergen-specific immunotherapy and other immunomodulatory treatments. The BAT can also be used for research purposes to explore the mechanisms of allergy and tolerance at the level of the basophil, for instance by manipulating IgE and IgG and their receptors and by studying intracellular signalling cascade in response to allergen. This review covers the applications of the BAT to the clinical management of allergic patients and the increased understanding of the mechanisms of immune response to allergens as well as technological advancements made in recent years.

Influence of thermal treatment on the characteristics of major oyster allergen Cra g 1 (tropomyosin)

BACKGROUND

Shellfish, including oysters, often cause allergic reactions in adults. Thermal treatment is one of the most common technologies for dealing with seafood, which may affect biological properties. The present study aimed to evaluate the impact of heating on the conformation and potential allergenicity of oyster-derived tropomyosin (Cra g 1).

RESULTS

Sodium dodecylsulphate-polyacrylamide gel electrophoresis showed that there was an apparent band at 35 kDa of raw tropomyosin after purification and more significant polymers appeared in the heated protein. Interestingly, obvious changes in the intensity of the circular dichroism signal and 1-anilino-8-naphthalene sulfonate-binding fluorescence were observed especially in the case of the roasted form, which was associated with an increase in antibody reactivity. The degree of immunoglobulin (Ig)E binding of this treatment was demonstrated in the order roasted > boiled > raw. Furthermore, sequence alignment and amino acid composition revealed that Cra g 1 shared relatively high homology to tropomyosins from other shellfish and was also abundant in lysine that was apt to be modified by reducing sugars during heating.

CONCLUSION

Heated Cra g 1 produces higher IgE reactivity than the raw form as a result of the denaturation and formation of polymers. These findings will benefit the diagnosis and management of potential allergenicity as a result of shellfish. © 2018 Society of Chemical Industry.

Analysis of the Allergenic Epitopes of Tropomyosin from Mud Crab Using Phage Display and Site-Directed Mutagenesis

Mud crab ( Scylla serrata), which is widely consumed, can cause severe allergic symptoms. Eight linear epitopes and seven conformational epitopes of tropomyosin (TM) from S. serrata were identified using phage display. The conformational epitopes were formed based on the coiled-coil structure of TM. Most of the epitopes were located in the regions where primary structures were conserved among crustacean TM. Twelve synthetic peptides were designed according to the epitopes and trypsin-cutting sites of TM, among them, three synthetic peptides (including one linear epitope and two conformational epitopes) were recognized by all of the patient sera using inhibitory dot blotting. A triple-variant (R90A-E164A-Y267A) was constructed based on the critical amino acids of the TM epitope. The IgE-binding activity of the triple-variant was significantly reduced compared with that of native TM. The results of phage display and site-directed mutagenesis offered new information regarding conformational epitopes of TM.

Effect of Heat Processing on IgE Reactivity and Cross-Reactivity of Tropomyosin and Other Allergens of Asia-Pacific Mollusc Species: Identification of Novel Sydney Rock Oyster Tropomyosin Sac g 1

SCOPE

Shellfish allergy is an increasing global health priority, frequently affecting adults. Molluscs are an important shellfish group causing food allergy but knowledge of their allergens and cross-reactivity is limited. Optimal diagnosis of mollusc allergy enabling accurate advice on food avoidance is difficult. Allergens of four frequently ingested Asia-Pacific molluscs are characterized: Sydney rock oyster (Saccostrea glomerata), blue mussel (Mytilus edulis), saucer scallop (Amusium balloti), and southern calamari (Sepioteuthis australis), examining cross-reactivity between species and with blue swimmer crab tropomyosin, Por p 1.

METHODS AND RESULTS

IgE ELISA showed that cooking increased IgE reactivity of mollusc extracts and basophil activation confirmed biologically relevant IgE reactivity. Immunoblotting demonstrated strong IgE reactivity of several proteins including one corresponding to heat-stable tropomyosin in all species (37-40 kDa). IgE-reactive Sydney rock oyster proteins were identified by mass spectrometry, and the novel major oyster tropomyosin allergen was cloned, sequenced, and designated Sac g 1 by the IUIS. Oyster extracts showed highest IgE cross-reactivity with other molluscs, while mussel cross-reactivity was weakest. Inhibition immunoblotting demonstrated high cross-reactivity between tropomyosins of mollusc and crustacean species.

CONCLUSION

These findings inform novel approaches for reliable diagnosis and improved management of mollusc allergy.

Seafood allergy: A comprehensive review of fish and shellfish allergens

Seafood refers to several distinct groups of edible aquatic animals including fish, crustacean, and mollusc. The two invertebrate groups of crustacean and mollusc are, for culinary reasons, often combined as shellfish but belong to two very different phyla. The evolutionary and taxonomic diversity of the various consumed seafood species poses a challenge in the identification and characterisation of the major and minor allergens critical for reliable diagnostics and therapeutic treatments. Many allergenic proteins are very different between these groups; however, some pan-allergens, including parvalbumin, tropomyosin and arginine kinase, seem to induce immunological and clinical cross-reactivity. This extensive review details the advances in the bio-molecular characterisation of 20 allergenic proteins within the three distinct seafood groups; fish, crustacean and molluscs. Furthermore, the structural and biochemical properties of the major allergens are described to highlight the immunological and subsequent clinical cross-reactivities. A comprehensive list of purified and recombinant allergens is provided, and the applications of component-resolved diagnostics and current therapeutic developments are discussed.

Detecting Allergens From Black Tiger Shrimp Penaeus monodon That Can Bind and Cross-link IgE by ELISA, Western Blot, and a Humanized Rat Basophilic Leukemia Reporter Cell Line RS-ATL8

Background

Black tiger shrimp Penaeus monodon is one of the common causes of shellfish allergy that is increasing worldwide. One of the important problems in the management of shellfish allergy is the lack of accurate diagnostic assay because the biological and immunological properties of allergens in black tiger shrimp have not been well characterized. This study aims to detect proteins with the ability to bind and cross-link immunoglobulin E (IgE) from black tiger shrimp by enzyme-linked immunosorbent assay (ELISA), Western blot, and a humanized rat basophilic leukemia reporter cell line RS-ATL8.

Methods

Sera from shrimp allergic subjects were subjected to ELISA and Western blots using raw or cooked shrimp extract as antigens. Pooled sera were used to sensitize the RS-ATL8 reporter cell line and cells were activated by shrimp extract. Eluted protein extracts separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) were tested on the RS-ATL8 cell line and subjected to mass spectrometry to identify potential candidate allergens.

Results

Allergic sera reacted stronger to raw shrimp extract than cooked shrimp extract (P=0.009). Western blot demonstrated that major IgE reactivity protein bands were at 32–39 kDa and 91–230 kDa in both raw and cooked shrimp extracts. The eluted protein bands at the molecular weight of 38 and 115 kDa from raw shrimp extract induced IgE cross-linking as assayed by the RS-ATL8 cell line. These protein bands were subjected to mass spectrometry for analysis. Ubiquitin-activating enzyme and crustacyanin were identified as potential candidate novel shrimp allergens.

Conclusions

The RS-ATL8 reporter cell line can be used to identify potential new shrimp allergens that can functionally cross-link IgE and induce mast cell degranulation.

Effects of daily food processing on allergenicity

Daily food processing has the potential to alter the allergenicity of foods due to modification of the physico-chemical properties of proteins. The degree of such modifications depends on factors such as processing conditions, type of food considered, allergenic content, etc. The impact of daily food processing like boiling, roasting, frying or baking on food allergenicity have been extensively studied. The influence of other thermal treatments such as microwave heating or pressure cooking on allergenicity has also been analyzed. Non-thermal treatment such as peeling impacts on the allergenic content of certain foods such as fruits. In this review, we give an updated overview of the effects of daily processing treatments on the allergenicity of a wide variety of foods. The different variables that contribute to the modification of food allergenicity due to processing are also reviewed and discussed.

Effect of thermal processing on T cell reactivity of shellfish allergens - Discordance with IgE reactivity

Crustacean allergy is a major cause of food-induced anaphylaxis. We showed previously that heating increases IgE reactivity of crustacean allergens. Here we investigate the effects of thermal processing of crustacean extracts on cellular immune reactivity. Raw and cooked black tiger prawn, banana prawn, mud crab and blue swimmer crab extracts were prepared and IgE reactivity assessed by ELISA. Mass spectrometry revealed a mix of several allergens in the raw mud crab extract but predominant heat-stable tropomyosin in the cooked extract. PBMC from crustacean-allergic and non-atopic control subjects were cultured with the crab and prawn extracts and proliferation of lymphocyte subsets was analysed by CFSE labelling and flow cytometry. Effector responses were assessed by intracellular IL-4 and IFN-γ, and regulatory T (CD4+CD25+CD127loFoxp3+) cell proportions in cultures were also compared by flow cytometry. For each crustacean species, the cooked extract had greater IgE reactivity than the raw (mud crab p<0.05, other species p<0.01). In contrast, there was a trend for lower PBMC proliferative responses to cooked compared with raw extracts. In crustacean-stimulated PBMC cultures, dividing CD4+ and CD56+ lymphocytes showed higher IL-4+/IFN-γ+ ratios for crustacean-allergic subjects than for non-atopics (p<0.01), but there was no significant difference between raw and cooked extracts. The percentage IL-4+ of dividing CD4+ cells correlated with total and allergen-specific IgE levels (prawns p<0.01, crabs p<0.05). Regulatory T cell proportions were lower in cultures stimulated with cooked compared with raw extracts (mud crab p<0.001, banana prawn p<0.05). In conclusion, cooking did not substantially alter overall T cell proliferative or cytokine reactivity of crustacean extracts, but decreased induction of Tregs. In contrast, IgE reactivity of cooked extracts was increased markedly. These novel findings have important implications for improved diagnostics, managing crustacean allergy and development of future therapeutics. Assessment of individual allergen T cell reactivity is required.

Allergens and molecular diagnostics of shellfish allergy: Part 22 of the Series Molecular Allergology

Shellfish belongs to "The Big 8" food groups causing allergy, which often does not outgrow during childhood. Shellfish is one of the main food allergens in adults and constitutes a diverse group of species subdivided into crustaceans and mollusks, which seem to include similar but also different allergens. Several pan-allergens are characterized in detail, including tropomyosin and arginine kinase, responsible for clinical cross-reactivity with other invertebrate allergen sources, embracing mites, insects, and parasites. Currently, at least seven different shellfish allergens have been identified, mostly from crustaceans. However, only three recombinant allergens are available for IgE-based routine diagnostic, including tropomyosin, arginine kinase, and sarcoplasmic Ca²⁺-binding protein. Other allergens include myosin light chain, troponin C, triosephosphate isomerase, and actin. This review summarizes the current advances on the molecular characterization of shellfish allergens, clinical cross-reactivity, and current diagnostic approaches for the management of this life-threatening disease.

Identification and Characterization of IgE-Binding Tropomyosins in Aedes aegypti

BACKGROUND

The mosquito Aedes aegypti is a potential source of important clinically relevant allergens. However, the allergenicity and cross-reactivity of most of these has not been fully described.

METHODS

Natural wild-type mosquito tropomyosin was purified by size exclusion and anionic-exchange chromatography from an A. aegypti extract. Further characterization was accomplished by MALDI-TOF/TOF. Two recombinant variants of tropomyosin were obtained by expression in Escherichia coli. Specific IgE measurement by ELISA and skin tests for mosquito extract were performed in 12 patients with asthma or allergy rhinitis residing on the Caribbean island of Martinique. Cross-reactivity between natural A. aegypti tropomyosin and recombinant tropomyosins from A. aegypti, house dust mite, shrimp and Ascaris lumbricoides was analyzed by ELISA competition.

RESULTS

Four variants of natural tropomyosin were purified. A band of 32 kDa in SDS-PAGE representing 2 tropomyosin variants (Aed a 10.0101 and Aed a 10.0201) reacted with specific IgE of 4 of the 12 (33%) allergic patients and with rabbit polyclonal anti-shrimp tropomyosin. A high degree of cross-reactivity (60-70%) was detected between natural mosquito tropomyosin and Blo t 10, Der p 10 and Lit v 1, and a lower degree with Asc l 3 from A. lumbricoides (<30%). rAed a 10.0101 inhibited IgE binding to natural A. aegypti tropomyosin; however, rAed a 10.0201 showed a low inhibitory capacity.

CONCLUSION

Tropomyosin is a new IgE-binding protein from A. aegypti. Two of the 4 variants identified showed different degree of cross-reactivity with tropomyosins from other arthropods. The potential allergenic role of each variant should be further investigated.

Identification and characterization of ovary development-related protein EJO1 (Eri s 2) from the ovary of Eriocheir sinensis as a new food allergen

SCOPE

Crab is a major source of shellfish allergens. Most studies have focused on allergens in crab muscle (CM) rather than on allergens in crab ovary (CO). This study aimed to identify potential allergens in CO from Eriocheir sinensis.

METHODS AND RESULTS

Dot blot and immunoblotting results revealed the differential reactivity of CM and CO extracts to positive sera from patients allergic to crabs. Four CO proteins showed good specific IgE-binding activities in 2-DE/immunoblotting analysis; mass spectrometry identified the proteins as hemocyanin, vitellogenin, ovary development-related protein EJO1and EJO2. The recently identified allergen EJO1 is named 'Eri s 2' in the World Health Organization and International Union of Immunological Societies (WHO/IUIS) allergen nomenclature database. Recombinant Eri s 2 exhibited good reactivity to positive sera, and pre-incubation with recombinant Eri s 2 abrogated the reactivity of positive sera from two patients to CO in a dose-dependent manner. Moreover, co-incubation of recombinant Eri s 2 with patient basophils dose-dependently promoted basophil activation, confirming the biological activity of Eri s 2.

CONCLUSION

CO tissue is an important allergen source, and Eri s 2 is a new crab allergen. This study provides insights that will be useful for component-resolved diagnostics for crab allergy.

EAACI Molecular Allergology User's Guide

The availability of allergen molecules ('components') from several protein families has advanced our understanding of immunoglobulin E (IgE)-mediated responses and enabled 'component-resolved diagnosis' (CRD). The European Academy of Allergy and Clinical Immunology (EAACI) Molecular Allergology User's Guide (MAUG) provides comprehensive information on important allergens and describes the diagnostic options using CRD. Part A of the EAACI MAUG introduces allergen molecules, families, composition of extracts, databases, and diagnostic IgE, skin, and basophil tests. Singleplex and multiplex IgE assays with components improve both sensitivity for low-abundance allergens and analytical specificity; IgE to individual allergens can yield information on clinical risks and distinguish cross-reactivity from true primary sensitization. Part B discusses the clinical and molecular aspects of IgE-mediated allergies to foods (including nuts, seeds, legumes, fruits, vegetables, cereal grains, milk, egg, meat, fish, and shellfish), inhalants (pollen, mold spores, mites, and animal dander), and Hymenoptera venom. Diagnostic algorithms and short case histories provide useful information for the clinical workup of allergic individuals targeted for CRD. Part C covers protein families containing ubiquitous, highly cross-reactive panallergens from plant (lipid transfer proteins, polcalcins, PR-10, profilins) and animal sources (lipocalins, parvalbumins, serum albumins, tropomyosins) and explains their diagnostic and clinical utility. Part D lists 100 important allergen molecules. In conclusion, IgE-mediated reactions and allergic diseases, including allergic rhinoconjunctivitis, asthma, food reactions, and insect sting reactions, are discussed from a novel molecular perspective. The EAACI MAUG documents the rapid progression of molecular allergology from basic research to its integration into clinical practice, a quantum leap in the management of allergic patients.

Assessment of the sensitizing capacity and allergenicity of enzymatic cross-linked arginine kinase, the crab allergen

SCOPE

The enzymatic cross-linking of an allergen by food processing may alter its sensitization potential. In this study, the IgE-binding activity and allergenicity of cross-linked thermal polymerized arginine kinase (CL-pAK) were investigated.

METHODS AND RESULTS

The IgE-binding activity and stability of CL-pAK were analyzed by immunological and proteomics methods. The sensitization and potency to induce oral tolerance of CL-pAK were tested using in vivo assays and a cell model. According to the results of inhibition of ELISA, the half inhibitory concentration of AK after cross-linking changed from 1.13 to 228.36 μg/mL. The results of in vitro digestion demonstrated that CL-pAK showed more resistance to gastrointestinal digestion than native AK. Low allergenicity and capacity to induce oral tolerance in mice were shown by the sera levels of AK-specific antibodies and T-cell cytokine production. Exposure of RBL-2H3 cells to CL-pAK compared with AK, resulted in lower levels of mast degranulation and histamine.

CONCLUSION

Enzymatic cross-linking with thermal polymerization of AK by tyrosinase and caffeic acid had high potential in mitigating IgE-binding activity and allergenicity, which were influenced by altering the molecular and immunological features of the shellfish protein.

Tropomyosin, the major tropical oyster Crassostrea belcheri allergen and effect of cooking on its allergenicity

BACKGROUND

Many types of shellfish including oysters are sometime cooked before ingestion and it has been demonstrated that cooking may affect the allergenicity of food. Therefore, the aim of our present study is to identify major and minor allergens of tropical oyster (Crassostrea belcheri) and to investigate the effect of different cooking processing on the allergenicity of this oyster.

METHODS

Raw, boiled, fried and roasted extracts of oyster were prepared. Protein profiles were analysed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Major and minor allergens and allergenicity patterns of all extracts were then determined by immunoblotting with sera from patients with positive skin prick tests (SPT) to the raw oyster extract. Mass-spectrometry was used to identify the major allergenic proteins of this oyster.

RESULTS

SDS-PAGE of the raw extract showed 15 protein bands (20-180 kDa). In contrast, smaller numbers of protein bands were demonstrated in the boiled extract, those ranging between 40-42 and 55-150 kDa were denatured, whereas the protein profiles were altered to a similar degree by frying or roasting. The 37 kDa proteins had the highest frequency of IgE-binding (95 %), thus identified as the major allergen of this tropical oyster. Other minor IgE-binding proteins were observed at various molecular weights. Immunoblot of raw extract yielded 11 IgE-binding proteins. The cooked extracts showed only a single IgE-binding protein at 37 kDa. Mass spectrometry analysis of the 37 kDa major allergen identified this spot as tropomyosin.

CONCLUSIONS

Cooked extracts produce lower IgE-binding than raw extract, which suggest that thermal treatment can be used as a tool in attempting to reduce oyster allergenicity by reducing the number of IgE-reactive bands. The degree of allergenicity of this oyster was demonstrated in the order raw > boiled > fried ≈ roasted. A heat-resistent 37 kDa protein, corresponding to tropomyosin, was identified as the major allergen of this tropical oyster.

Tropomyosin and Actin Identified as Major Allergens of the Carpet Clam (Paphia textile) and the Effect of Cooking on Their Allergenicity

OBJECTIVES

To identify the major allergenic proteins of clam (Paphia textile) and to investigate the effect of different cooking methods on the allergenicity of these identified proteins.

METHODS

Clam protein extracts were separated by denaturing polyacrylamide gel electrophoresis. IgE reactive proteins were then analyzed by immunoblotting with sera from patients with positive skin prick tests (SPT) to the raw clam extract. Mass spectrometry was used to identify the major allergenic proteins of this clam.

RESULTS

Raw extract showed 12 protein bands (18-150 kDa). In contrast, fewer protein bands were seen in the boiled extract; those ranging from 40 to 150 kDa were denatured. The protein profiles were similarly altered by frying or roasting. The immunoblots of raw and boiled extracts yielded 10 and 2 IgE-binding proteins, respectively. The fried and roasted extracts showed only a single IgE-binding protein at 37 kDa. Mass spectrometry analysis of the 37 and 42 kDa major allergens indicated that these spots were tropomyosin and actin, respectively.

CONCLUSION

The two major allergens of Paphia textile were identified as the thermostable tropomyosin and a new thermolabile allergen actin.

Auto-induction for high yield expression of recombinant novel isoallergen tropomyosin from King prawn (Melicertus latisulcatus) for improved diagnostics and immunotherapeutics

Food allergies are increasing worldwide, demonstrating a considerable public health concern. Shellfish allergy is one of the major food groups causing allergic sensitization among adults and children, affecting up to 2% of the general world population. Tropomyosin (TM) is the major allergen in shellfish and frequently used in the diagnosis of allergic sensitization and the detection of cross-contaminated food. To improve and establish better and more sensitive diagnostics for allergies and immunotherapeutics, large quantities of pure allergens are required. To establish a reproducible method for the generation of pure recombinant tropomyosin we utilized in this study different Escherichia coli strains (NM522, TOP10 and BL21(DE3)RIPL). In addition, isopropyl-β-D-thiogalactoside (IPTG) induction was compared with a novel auto-induction system to allow the generation of larger quantities of recombinant allergen. We demonstrated that the B-strain of E. coli is better for the expression of TM compared to the K-strain. Moreover, a higher yield could be achieved when using the auto-induction system, with up to 62 mg/l. High yield expressed recombinant TM from King prawn (KP) was compared to recombinant TM from Black tiger prawn (Pen m 1). We demonstrated that recombinant TM from KP and known isoallergen Pen m 1 have very similar molecular and immunological characteristics. Overall, we demonstrate that auto-induction can be used to express larger quantities of recombinant allergens for the development of diagnostic, to quantify allergens as well as immunotherapeutics employing isoallergens.

Effect of heat processing on antibody reactivity to allergen variants and fragments of black tiger prawn: A comprehensive allergenomic approach

SCOPE

Prawn allergy is one of the leading causes of IgE-mediated hypersensitivity to food. Alterations of IgE-antibody reactivity to prawn allergens due to thermal processing are not fully understood. The aim of this study was to analyze the impact of heating on prawn allergens using a comprehensive allergenomic approach.

METHODS AND RESULTS

Proteins from raw and heat-processed black tiger prawn (Penaeus monodon) extracts as well as recombinant tropomyosin (rPen m1) were analyzed by SDS-PAGE and immunoblotting using sera from 16 shellfish allergic patients. IgE antibody binding proteins were identified by advanced mass spectroscopy, characterized by molecular structure analysis and their IgE reactivity compared among the prepared black tiger prawn extracts. Heat processing enhanced the overall patient IgE binding to prawn extracts and increased recognition of a number of allergen variants and fragments of prawn allergens. Allergens identified were tropomyosin, myosin light chain, sarcoplasmic calcium binding protein, and putative novel allergens including triose phosphate isomerase, aldolase, and titin.

CONCLUSION

Seven allergenic proteins are present in prawns, which are mostly heat-stable and form dimers or oligomers. Thermal treatment enhanced antibody reactivity to prawn allergens as well as fragments and should be considered in the diagnosis of prawn allergy and detection of crustacean allergens in processed food.