cDNA cloning and molecular identification of the major oyster allergen from the Pacific oyster Crassostrea gigas

Physicochemical characterization and identification of major linear epitopes of sarcoplasmic calcium-binding protein (SCP) allergen from Pacific oyster (Crassostrea gigas)

BACKGROUND

Food allergy is a serious public nutritional health problem that has attracted extensive worldwide attention. Shellfish allergy is a long-lasting disorder that has a lifelong impact on health. Sarcoplasmic calcium-binding protein (SCP) plays a vital role in cell and muscle functions and has been identified as an allergen in oyster.

RESULTS

In this study, recombinant SCP (rSCP) with a molecular mass of 21 kDa was produced and identified based on SCP amino acid sequencing of Pacific oyster (Crassostrea gigas), and was used as a follow-up experimental material. Its physicochemical characterization showed that purified rSCP is highly stable to heat and acid-alkali and trypsin digestion but less resistant to pepsin digestion. We established an animal sensitization model and rSCP displayed stronger Immunoglobulin E (IgE)-binding activity with rat serum in the rSCP + cholera toxin (CT) group compared with the CT group and a control group. Five epitope peptides were identified as linear immunodominant epitopes by indirect competitive enzyme-linked immunosorbent assay (icELISA) for the first time. We also found that conformational epitopes may play a major role in the immunoreactivity of SCP.

CONCLUSION

These results are significant for understanding hypersensitization of humans to oyster and offer available preventive measures and treatment programs in further research. © 2021 Society of Chemical Industry.

Physicochemical characterization and linear epitopes identification of arginine kinase allergen from Crassostrea gigas

BACKGROUND

Molluscan shellfish, including oysters, often cause allergic reactions in sensitive people throughout the world. It has been demonstrated that arginine kinase (AK) is one of the major allergens of oyster. The present study aimed to evaluate the immunoreactivity and structure of oyster AK as affected by heat treatment, pH change, and in vitro digestion. What is more, the immunoglobulin E-binding epitopes of this allergen were also predicted and validated.

RESULTS

Thermal and pH assays revealed that AK was unstable at temperature >40 °C or pH ≤5.0 by sodium dodecyl sulfate polyacrylamide gel electrophoresis and circular dichroism, and the digestibility assays suggested that AK was more easily digested by pepsin than by trypsin and chymotrypsin. The potential epitopes were predicted through immunoinformatics tools, and seven linear epitopes were identified by indirect competition enzyme-linked immunosorbent assay with pooled sera and individual serum from oyster-allergic patients. The critical amino acids in each epitope were also confirmed using mutant peptides. These linear epitopes and critical amino acids were apt to distribute on the outer surface of homology-based AK model. Moreover, the three denaturants (sodium dodecyl sulfate, β-mercaptoethanol, and urea) can destroy the spatial structure of AK and increase or reduce its allergenicity by denaturation treatments.

CONCLUSION

Processing conditions lay the foundation for the variation of allergenicity. Seven linear epitopes and their critical amino acids were identified by indirect competitive enzyme-linked immunosorbent assay. These findings will be helpful in allergy diagnosis and development of hypoallergenic products in the near future. © 2021 Society of Chemical Industry.

Recombinant Tropomyosin from the Pacific Oyster (Crassostrea gigas) for Better Diagnosis

The Pacific oyster is a commercially important mollusc and, in contrast to most other shellfish species, frequently consumed without prior heat treatment. Oysters are rich in many nutrients but can also cause food allergy. Knowledge of their allergens and cross-reactivity remains very limited. These limitations make an optimal diagnosis of oyster allergy difficult, in particular to the Pacific oyster (Crassostrea gigas), the most cultivated and consumed oyster species worldwide. This study aimed to characterise IgE sensitisation profiles of 21 oyster-sensitised patients to raw and heated Pacific oyster extract using immunoblotting and advanced mass spectrometry, and to assess the relevance of recombinant oyster allergen for improved diagnosis. Tropomyosin was identified as the major allergen recognised by IgE from 18 of 21 oyster-sensitised patients and has been registered with the WHO/IUIS as the first oyster allergen (Cra g 1). The IgE-binding capacity of oyster-sensitised patients’ IgE to purified natural and recombinant tropomyosin from oyster, prawn, and dust mite was compared using enzyme-linked immunosorbent assay. The degree of IgE binding varied between patients, indicating partial cross-sensitisation and/or co-sensitisation. Amino acid sequence alignment of tropomyosin from these three species revealed five regions that contain predicted IgE-binding epitopes, which are most likely responsible for this cross-reactivity. This study fully biochemically characterises the first and major oyster allergen Cra g 1 and demonstrates that the corresponding recombinant tropomyosin should be implemented in improved component-resolved diagnostics and guide future immunotherapy.

Production of allergen-specific immunotherapeutic agents for the treatment of food allergy

Allergen-specific immunotherapy (IT) is emerging as a viable avenue for the treatment of food allergies. Clinical trials currently investigate raw or slightly processed foods as therapeutic agents, as trials using food-grade agents can be performed without the strict regulations to which conventional drugs are subjected. However, this limits the ability of standardization and may affect clinical trial outcomes and reproducibility. Herein, we provide an overview of methods used in the production of immunotherapeutic agents for the treatment of food allergies, including processed foods, allergen extracts, recombinant allergens, and synthetic peptides, as well as the physical and chemical processes for the reduction of protein allergenicity. Commercial interests currently favor producing standardized drug-grade allergen extracts for therapeutic use, and clinical trials are ongoing. In the near future, recombinant production could replace purification strategies since it allows the manufacturing of pure, native allergens or sequence-modified allergens with reduced allergenicity. A recurring issue within this field is the inadequate reporting of production procedures, quality control, product physicochemical characteristics, allergenicity, and immunological properties. This information is of vital importance in assessing therapeutic standardization and clinical safety profile, which are central parameters for the development of future therapeutic agents.

Identification and Cross-reactivity Analysis of Sarcoplasmic-Calcium-Binding Protein: A Novel Allergen in Crassostrea angulata

Oysters are an important shellfish group known to cause food allergy; however, knowledge of their sensitization components and cross-reactivity is limited. This study aimed to identify a novel allergen in Crassostrea angulata and investigate its cross-reactivity. To this end, a 20 kDa protein was purified from oyster and confirmed to be a sarcoplasmic-calcium-binding protein (SCP) by LC-MS/MS. A 537 bp open reading frame was obtained from oyster SCP total RNA, which encoded 179 amino acids, and was expressed in Escherichia coli. According to the circular dichroism results, digestion assay, and inhibition ELISA, the recombinant SCP (rSCP) exhibited similar physicochemical properties and IgG-binding activity to native SCP. rSCP displayed stronger IgE-binding activity by immunological method. Moreover, a different intensity of cross-reactivity and sequence homology were demonstrated between shellfish species. Collectively, these findings provide novel insight into shellfish allergens, which can be used to aid in the in vitro diagnosis of oyster-sensitized patients.

Effect of acid and in vitro digestion on conformation and IgE-binding capacity of major oyster allergen Cra g 1 (tropomyosin)

INTRODUCTION AND OBJECTIVES

The production and consumption of oysters is increasing annually because it can provide essential nutrients and benefit for human health, leading to frequent occurrence of severe allergic reactions observed in sensitized individuals. The aim of the present study was to investigate the effects of acid and protease treatment on the conformation and IgE-binding capacity of recombinant Crassostrea gigas tropomyosin (Cra g 1).

RESULTS

Under acidic conditions, Cra g 1 did not undergo degradation, however, the changes obvious in the intensity of CD signal and ANS-binding fluorescence were observed, which was associated with a decrease in antibody reactivity. In simulated gastrointestinal fluid (SGF) and simulated intestinal fluid (SIF) digestion system, acid-treated Cra g 1 was relatively resistant to digestion, but the degradative patterns were very different. Moreover, owing to alterations of secondary structure and hydrophobic surface of the protein during digestive processing, antigenicity of acid-induced Cra g 1 reduced in SGF while it increased significantly in SIF.

CONCLUSION

To our knowledge, this is the first study reporting that antigenicity of acid-treated oyster tropomyosin increased after SIF digestion. These results revealed that treatment with acid and pepsin, rather than trypsin, was an effective way of reducing IgE-binding capacity of tropomyosin from oyster.

Allergen immunotherapy for food allergy from the Asian perspective: key challenges and opportunities

Introduction: Prevalence of food allergy is rising in different regions of the world. Asia has not been spared from this epidemic, but epidemiological data have revealed a different pattern of food allergens in this continent. Allergen-specific immunotherapy (AIT) for food allergy, which has been revolutionary as the main focus of research in recent years, needs to be adapted for the different populations in Asia. Areas covered: Recent evidence shows increasing popularity and superiority of AIT over strict food avoidance as the cornerstone of food allergy management. Asia is a distinctive continent with specific food allergy triggers, in particular, seafood, and wheat. Peanut, on the contrary, is not a common food allergen in most parts of Asia. The common Asian food allergens, as well as the rapidly developing food-specific AIT in this region will be covered in this article. Expert commentary: Evidence on oral immunotherapy for wheat allergy and preclinical data on shellfish AIT are promising. Further work should be done on resolving cross-sensitization between environmental allergens with wheat and shellfish allergens, and a modified AIT approach to enhance the safety and effectiveness of food-specific immunotherapy.

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.

Diagnosis of fish and shellfish allergies

Seafood allergy is a hypersensitive disorder with increasing prevalence worldwide. Effective and accurate diagnostic workup for seafood allergy is essential for clinicians and patients. Parvalbumin and tropomyosin are the most common fish and shellfish allergens, respectively. The diagnosis of seafood allergies is complicated by cross-reactivity among fish allergens and between shellfish allergens and other arthropods. Current clinical diagnosis of seafood allergy is a complex algorithm that includes clinical assessment, skin prick test, specific IgE measurement, and oral food challenges. Emerging diagnostic strategies, such as component-resolved diagnosis (CRD), which uses single allergenic components for assessment of epitope specific IgE, can provide critical information in predicting individualized sensitization patterns and risk of severe allergic reactions. Further understanding of the molecular identities and characteristics of seafood allergens can advance the development of CRD and lead to more precise diagnosis and improved clinical management of seafood allergies.

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.

Shellfish Allergy: a Comprehensive Review

Shellfish allergy is of increasing concern, as its prevalence has risen in recent years. Many advances have been made in allergen characterization. B cell epitopes in the major allergen tropomyosin have been characterized. In addition to tropomyosin, arginine kinase, sarcoplasmic calcium-binding protein, and myosin light chain have recently been reported in shellfish. All are proteins that play a role in muscular contraction. Additional allergens such as hemocyanin have also been described. The effect of processing methods on these allergens has been studied, revealing thermal stability and resistance to peptic digestion in some cases. Modifications after Maillard reactions have also been addressed, although in some cases with conflicting results. In recent years, new hypoallergenic molecules have been developed, which constitute a new therapeutic approach to allergic disorders. A recombinant hypoallergenic tropomyosin has been developed, which opens a new avenue in the treatment of shellfish allergy. Cross-reactivity with species that are not closely related is common in shellfish-allergic patients, as many of shellfish allergens are widely distributed panallergens in invertebrates. Cross-reactivity with house dust mites is well known, but other species can also be involved in this phenomenon.

Seafood-Associated Shellfish Allergy: A Comprehensive Review

Shellfish are diverse, serve as main constituents of seafood, and are extensively consumed globally because of their nutritional values. Consequently, increase in reports of IgE-mediated seafood allergy is particularly food associated to shellfish. Seafood-associated shellfish consists of crustaceans (decapods, stomatopods, barnacles, and euphausiids) and molluskans (gastropods, bivalves, and cephalopods) and its products can start from mild local symptoms and lead to severe systemic anaphylactic reactions through ingestion, inhalation, or contact like most other food allergens. Globally, the most commonly causative shellfish are shrimps, crabs, lobsters, clams, oysters, and mussels. The prevalence of shellfish allergy is estimated to be 0.5-2.5% of the general population but higher in coastal Asian countries where shellfish constitute a large proportion of the diet. Diversity in allergens such as tropomyosin, arginine kinase, myosin light chain, and sarcoplasmic binding protein are from crustaceans whereas tropomyosin, paramyosin, troponin, actine, amylase, and hemoyanin are reported from molluskans shellfish. Tropomyosin is the major allergen and is responsible for cross-reactivity between shellfish and other invertebrates, within crustaceans, within molluskans, between crustaceans vs. molluskans as well as between shellfish and fish. Allergenicity diagnosis requires clinical history, in vivo skin prick testing, in vitro quantification of IgE, immunoCAP, and confirmation by oral challenge testing unless the reactions borne by it are life-threatening. This comprehensive review provides the update and new findings in the area of shellfish allergy including demographic, diversity of allergens, allergenicity, their cross-reactivity, and innovative molecular genetics approaches in diagnosing and managing this life-threatening as well as life-long disease.

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.

Current immunological and molecular biological perspectives on seafood allergy: a comprehensive review

Seafood is an important component in human diet and nutrition worldwide. However, seafood also constitutes one of the most important groups of foods in the induction of immediate (type I) food hypersensitivity, which significantly impacts the quality of life and healthcare cost. Extensive efforts within the past two decades have revealed the molecular identities and immunological properties of the major fish and shellfish allergens. The major allergen involved in allergy and cross-reactivity among different fish species was identified as parvalbumin while that responsible for shellfish (crustaceans and mollusks) allergy was identified as tropomyosin. The cloning and expression of the recombinant forms of these seafood allergens facilitate the investigation on the detailed mechanisms leading to seafood allergies, mapping of IgE-binding epitopes, and assessment of their allergenicity and stability. Future research focusing on the immunological cross-reactivity and discovery of novel allergens will greatly facilitate the management of seafood allergies and the design of effective and life-long allergen-specific immunotherapies.

Immunization with Hypoallergens of shrimp allergen tropomyosin inhibits shrimp tropomyosin specific IgE reactivity

Designer proteins deprived of its IgE-binding reactivity are being sought as a regimen for allergen-specific immunotherapy. Although shrimp tropomyosin (Met e 1) has long been identified as the major shellfish allergen, no immunotherapy is currently available. In this study, we aim at identifying the Met e 1 IgE epitopes for construction of hypoallergens and to determine the IgE inhibitory capacity of the hypoallergens. IgE-binding epitopes were defined by three online computational models, ELISA and dot-blot using sera from shrimp allergy patients. Based on the epitope data, two hypoallergenic derivatives were constructed by site-directed mutagenesis (MEM49) and epitope deletion (MED171). Nine regions on Met e 1 were defined as the major IgE-binding epitopes. Both hypoallergens MEM49 and MED171 showed marked reduction in their in vitro reactivity towards IgE from shrimp allergy patients and Met e 1-sensitized mice, as well as considerable decrease in induction of mast cell degranulation as demonstrated in passive cutaneous anaphylaxis assay. Both hypoallergens were able to induce Met e 1-recognizing IgG antibodies in mice, specifically IgG2a antibodies, that strongly inhibited IgE from shrimp allergy subjects and Met e 1-sensitized mice from binding to Met e 1. These results indicate that the two designer hypoallergenic molecules MEM49 and MED171 exhibit desirable preclinical characteristics, including marked reduction in IgE reactivity and allergenicity, as well as ability to induce blocking IgG antibodies. This approach therefore offers promises for development of immunotherapeutic regimen for shrimp tropomyosin allergy.

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.:

Reduction of the number of major representative allergens: from clinical testing to 3-dimensional structures

Vast amounts of allergen sequence data have been accumulated, thus complicating the identification of specific allergenic proteins when performing diagnostic allergy tests and immunotherapy. This study aims to rank the importance/potency of the allergens so as to logically reduce the number of allergens and/or allergenic sources. Meta-analysis of 62 allergenic sources used for intradermal testing on 3,335 allergic patients demonstrated that in southern China, mite, sesame, spiny amaranth, Pseudomonas aeruginosa, and house dust account for 88.0% to 100% of the observed positive reactions to the 62 types of allergenic sources tested. The Kolmogorov-Smironov Test results of the website-obtained allergen data and allergen family featured peptides suggested that allergen research in laboratories worldwide has been conducted in parallel on many of the same species. The major allergens were reduced to 21 representative allergens, which were further divided into seven structural classes, each of which contains similar structural components. This study therefore has condensed numerous allergenic sources and major allergens into fewer major representative ones, thus allowing for the use of a smaller number of allergens when conducting comprehensive allergen testing and immunotherapy treatments.

Group 10 allergens (tropomyosins) from house-dust mites may cause covariation of sensitization to allergens from other invertebrates

Group 10 allergens (tropomyosins) have been assumed to be a major cause of cross-reactivity between house-dust mites (HDMs) and other invertebrates. Despite all of the published data regarding the epidemiology, percent IgE binding and level of sensitization in the population, the role of tropomyosin as a cross-reactive allergen in patients with multiple allergy syndrome still remains to be elucidated. Homology between amino acid sequences reported in allergen databases of selected invertebrate tropomyosins was determined with Der f 10 as the reference allergen. The 66.9 and 54.4% identities were found with selected crustacean and insect species, respectively, whereas only 20.4% identity was seen with mollusks. A similar analysis was performed using reported B-cell IgE-binding epitopes from Met e1 (shrimp allergen) and Bla g7 (cockroach allergen) with other invertebrate tropomyosins. The percent identity in linear sequences was higher than 35% in mites, crustaceans, and cockroaches. The polar and hydrophobic regions in these groups were highly conserved. These findings suggest that tropomyosin may be a major cause of covariation of sensitization between HDMs, crustaceans, and some species of insects and mollusks.

Fish and shellfish allergy in children: review of a persistent food allergy

The increased consumption of fish and shellfish has resulted in more frequent reports of adverse reactions to seafood, emphasizing the need for more specific diagnosis and treatment of this condition and exploring reasons for the persistence of this allergy. This review discusses interesting and new findings in the area of fish and shellfish allergy. New allergens and important potential cross-reacting allergens have been identified within the fish family and between shellfish, arachnids, and insects. The diagnostic approach may require prick to-prick tests using crude extracts of both raw and cooked forms of seafood for screening seafood sensitization before a food challenge or where food challenge is not feasible. Allergen-specific immunotherapy can be important; mutated less allergenic seafood proteins have been developed for this purpose. The persistence of allergy because of seafood proteins' resistance after rigorous treatment like cooking and extreme pH is well documented. Additionally, IgE antibodies from individuals with persistent allergy may be directed against different epitopes than those in patients with transient allergy. For a topic as important as this one, new areas of technological developments will likely have a significant impact, to provide more accurate methods of diagnosing useful information to patients about the likely course of their seafood allergy over the course of their childhood and beyond.

Recent developments with B-cell epitope identification for predictive studies

This review discusses currently available methods for predicting B-cell epitopes on proteins. The use of animals for assessing protein immunogenicity is addressed primarily to highlight the differences in B- and T-cell epitope recognition between species. These differences have to be considered when interpreting potential B-cell epitopes identified by the methods addressed here. "In vitro alternatives" focuses on the strengths and limitations of peptide-based technologies. Three types of computer-based methods for identifying potential B-cell epitopes are discussed: (i) methods applying physico-chemical and structural propensity scales for predicting linear epitopes from the primary structure of a protein, (ii) comparative methods basing prediction upon amino acid sequence and structural similarities between antigenically known and unknown proteins, and (iii) a method combining structural features with a B-cell epitope motif database for predicting linear and conformational antigenic determinants. With respect to human safety, the usefulness of antibody-based tests is limited to comparative studies between an antigenically known protein and variants thereof. Similarly, computer-based methods using data mining can address similarities in B-cell epitope profiles between related proteins, if a proper cut off can be defined for the minimal amino acid sequence similarity required for obtaining an acceptable accuracy. Among the physico-chemical and structural scales, scales identifying in a protein hairpin and non-specific turns seem useful for predicting epitopes with a continuous primary binding site. When conformational epitopes have to be identified as well, a novel computer-based tool seems to be the most promising alternative to X-ray crystallography. However, both methods remain to be extensively evaluated and validated. Thus, promising tools for B-cell epitope identification have been developed. But, no validated method for B-cell epitope identification on antigenically unknown proteins is available yet.

Rapid Detection of Shellfish Major Allergen Tropomyosin Using Superparamagnetic Nanoparticle-Based Lateral Flow Immunoassay

In this study, a competitive assay format using superparamagnetic nanoparticle-based lateral flow immunoassay (LFIA) was developed for rapid, quantitative detection of shellfish major allergen tropomyosin (Tm). Sartorius CN140 nitrocellulose membrane and 0.05mg/mL Tm immobilized in the test line (T line) were optimized in order to improve the performance of the LFIA system. Calibration curves for Tm under PBS-T diluents and carp muscle extraction diluents were established. Limit of detection (LOD) for Tm calibrated by carp muscle matrix was 12.4ng/mL with a work range of 0.01 to 20μg/mL. According to magnetic signals change with the time of sample flowing on the strip, the qualitative time of the LFIA was about 10min, while the quantitative time of the LFIA was about 25min. 30 food species were detected separately by the LFIA and Western blot method to evaluate the specificity of the LFIA. Overall relative agreement of the two methods was 96.7% (29/30). Moreover, intra- and inter-assay precisions of the LFIA for Tm detection were <10.20% and <12.34%, respectively. The average recovery range in different food matrices was 80.3~111.8%, within a reasonable range. Our data confirmed that the superparamagnetic nanoparticle-based LFIA method developed in this study is rapid, simple, high specificity and capable of quantitative test. Consequently, the LFIA has the potential application in the field of point-of-care test of shellfish major allergen Tm.

A Review of Food Allergy and Nutritional Considerations in the Food-Allergic Adult

In the United States, the prevalence of adults with food allergies is approximately 2% to 3%. Theoretically, any food can cause an allergic reaction; however, some foods are clearly more allergenic than others. In adults, peanuts, tree nuts, finned fish, crustaceans, fruit, and vegetables account for 85% of the food-allergic reactions. Currently, the only ways to manage food allergies are to avoid the allergen and initiate therapy for an allergic reaction if ingestion does occur. The presence of homologous proteins among animal or plant foods and between foods and certain airborne allergens may account for cross-sensitization that may be clinically relevant. For inpatients or outpatients with food allergies, nutrient and fluid requirements are the same as for individuals without food allergies. Since patients with adverse reactions to food may self-restrict intake or have been counseled on food avoidance, it is particularly important to determine dietary adequacy and to provide patients with appropriate food substitutions to provide nutrients that may be missing from a patient’s diet. This is of particular concern for individuals with multiple food allergies. Eating away from home and traveling also pose special problems for those with food allergies.

High level expression, purification and physico- and immunochemical characterisation of recombinant Pen a 1: a major allergen of shrimp

Well-characterised and immunologically active recombinant allergens are of eminent importance for improvement of diagnostic tools and immunotherapy of allergic diseases. The use of recombinant allergens has several advantages such as the more precise quantification of the active substance compared to allergen extracts and the reduced risk of contamination with other allergenic proteins compared to purified natural allergens. Optimised standard protocols for expression and purification and a detailed physico-chemical characterisation of such recombinant allergens are necessary to ensure consistent quality and comparability of results obtained with recombinant material. In this study the major allergen Pen a 1 of brown shrimp (Penaeus aztecus) was expressed in E. coli and purified in two steps by immobilised metal chelate-affinity chromatography (IMAC) and size-exclusion chromatography. Identity and purity were verified with N-terminal sequencing and peptide mass fingerprinting. Circular dichroism and NMR-spectroscopy indicated an alpha-helical flexible structure of rPen a 1 which is in accordance with the known structure of tropomyosins. Finally, the recombinant allergen proved to be immunologically reactive in IgE Western blot analysis and ELISA. This study provides a protocol for the preparation of recombinant shrimp tropomyosin in standardised quality.

Molluscan shellfish allergy

Food allergies affect approximately 3.5-4.0% of the worldwide population. Immediate-type food allergies are mediated by the production of IgE antibodies to specific proteins that occur naturally in allergenic foods. Symptoms are individually variable ranging from mild rashes and hives to life-threatening anaphylactic shock. Seafood allergies are among the most common types of food allergies on a worldwide basis. Allergies to fish and crustacean shellfish are very common. Molluscan shellfish allergies are well known but do not appear to occur as frequently. Molluscan shellfish allergies have been documented to all classes of mollusks including gastropods (e.g., limpet, abalone), bivalves (e.g., clams, oysters, mussels), and cephalopods (e.g., squid, octopus). Tropomyosin, a major muscle protein, is the only well-recognized allergen in molluscan shellfish. The allergens in oyster (Cra g 1), abalone (Hal m 1), and squid (Tod p 1) have been identified as tropomyosin. Cross-reactivity to tropomyosin from other molluscan shellfish species has been observed with sera from patients allergic to oysters, suggesting that individuals with allergies to molluscan shellfish should avoid eating all species of molluscan shellfish. Cross-reactions with the related tropomyosin allergens in crustacean shellfish may also occur but this is less clearly defined. Occupational allergies have also been described in workers exposed to molluscan shellfish products by the respiratory and/or cutaneous routes. With food allergies, one man's food may truly be another man's poison. Individuals with food allergies react adversely to the ingestion of foods and food ingredients that most consumers can safely ingest (Taylor and Hefle, 2001). The allergens that provoke adverse reactions in susceptible individuals are naturally occurring proteins in the specific foods (Bush and Hefle, 1996). Molluscan shellfish, like virtually all foods that contain protein, can provoke allergic reactions in some individuals.

Structural, immunological and functional properties of natural recombinant Pen a 1, the major allergen of Brown Shrimp, Penaeus aztecus

BACKGROUND

Recombinant allergens are considered the basis for new diagnostic approaches and development of novel strategies of allergen-specific immunotherapy. As Pen a 1 from brown shrimp Penaeus aztecus is the only major allergen of shrimp and binds up to 75% of all shrimp-specific IgE antibodies this molecule may be an excellent model for the usage of allergens with reduced IgE antibody-binding capacity for specific immunotherapy.

AIM

The aim was to clone, express and characterize a full-length recombinant Pen a 1 molecule and compare it with natural Pen a 1 in regard to structural and immunological parameters such as IgE antibody capacity and ability to induce IgE-mediated mediator release.

METHODS

Total RNA was isolated from P. aztecus and a rapid amplification of cDNA ends (5' RACE) was performed to obtain full-length cDNA coding for Pen a 1. Using a gene-specific primer, PCR was performed and full-length cDNA was cloned and sequenced. Recombinant His-tagged Pen a 1 was isolated from Escherichia coli under native conditions by immobilized metal affinity chromatography. Secondary structure of natural and recombinant Pen a 1 was compared by circular dichroism (CD) spectroscopy, and the IgE antibody-binding capacity evaluated by RAST. The allergenic potency was tested by the capability of natural and recombinant Pen a 1 to induce mediator release in a murine and human in vitro model of IgE-mediated type I allergy.

RESULTS

The deduced amino-acid sequence was 284 residues long and amino-acid sequence identities with allergenic and non-allergenic tropomyosins ranged from 80% to 99% and 51% to 58%, respectively. The analysis of the secondary structure of natural and recombinant Pen a 1 by CD spectroscopic analysis showed that both nPen a 1 and rPen a 1 had alpha-helical conformation that is typical for tropomyosin. The IgE antibody binding capacities of nPen a 1 and r Pen a1 were found to be essentially identical by RAST. The mediator release experiments using both wild-type and humanized rat basophilic leukaemia 30/25 cells showed that rPen a 1 and nPen a 1 induced a similar level of mast cell activation.

CONCLUSIONS

Recombinant Pen a 1 and natural Pen a 1 are structurally and immunologically identical and rPen a 1 may be used as the basis for component-resolved diagnosis and the generation of modified shrimp tropomyosin for allergen-specific immunotherapy. The results of the animal studies indicate that C3H/HeJ mice that were sensitized with shrimp extract in combination with cholera toxin as adjuvant may be a suitable model to study shrimp allergy.

Heterogeneity and tissue specificity of tropomyosin isoforms from four species of bivalves

Heterogeneity and tissue specificity of tropomyosin isoforms obtained from four species of bivalves (Scapharca broughtonii (ark shell), Mytilus galloprovincialis (mussel), Atrina pectinata (surf clam) and Crassostrea gigas (Pacific oyster)), were examined. Tropomyosins were extracted from translucent and opaque portions of posterior adductor muscle, respectively, and cardiac muscle of each bivalve. There were two tropomyosin isoforms in the ark shell, the surf clam and the Pacific oyster. They were designated as TMa and TMb. In the ark shell, TMa was the common isoform and TMb was specific for the opaque portion of the adductor muscle. In the surf clam, TMb was the common isoform present in all tissues. TMa was found only in the translucent portion of muscle. In the Pacific oyster, TMb was the major component in both portions of adductor muscle and TMa was the major component in cardiac muscle, although both tropomyosins were included in all tissues. The mussel had only one tropomyosin.

Seafood allergy: lessons from clinical symptoms, immunological mechanisms and molecular biology

Food allergy consists of a wide range of disorders that result from adverse immune responses to dietary antigens. Manifestations of allergic response includes acute, potentially fatal anaphylactic reactions and a variety of chronic diseases that mainly affect the gastrointestinal tract, skin, and respiratory tract. Tools for clinical diagnosis and management, which have not changed much in the past two decades, include the clinical history, tests for specific IgE antibody to suspected foods, elimination diets, oral food challenges, and provision of medications such as epinephrine for emergency treatment. On the other hand, recent immunological and molecular biological research have enhanced our understanding of the mechanisms of these disorders and revealed the identities of many food allergens. Here, we will discuss seafood allergies with respect to the clinical manifestations, diagnosis, immunological mechanisms, and molecular biology of seafood allergens. Furthermore, potential applications and future directions in the clinical management of seafood allergies are discussed.

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Analysis of amino acid sequence variations and immunoglobulin E-binding epitopes of German cockroach tropomyosin

The allergenicities of tropomyosins from different organisms have been reported to vary. The cDNA encoding German cockroach tropomyosin (Bla g 7) was isolated, expressed, and characterized previously. In the present study, the amino acid sequence variations in German cockroach tropomyosin were analyzed in order to investigate its influence on allergenicity. We also undertook the identification of immunodominant peptides containing immunoglobulin E (IgE) epitopes which may facilitate the development of diagnostic and immunotherapeutic strategies based on the recombinant proteins. Two-dimensional gel electrophoresis and immunoblot analysis with mouse anti-recombinant German cockroach tropomyosin serum was performed to investigate the isoforms at the protein level. Reverse transcriptase PCR (RT-PCR) was applied to examine the sequence diversity. Eleven different variants of the deduced amino acid sequences were identified by RT-PCR. German cockroach tropomyosin has only minor sequence variations that did not seem to affect its allergenicity significantly. These results support the molecular basis underlying the cross-reactivities of arthropod tropomyosins. Recombinant fragments were also generated by PCR, and IgE-binding epitopes were assessed by enzyme-linked immunosorbent assay. Sera from seven patients revealed heterogeneous IgE-binding responses. This study demonstrates multiple IgE-binding epitope regions in a single molecule, suggesting that full-length tropomyosin should be used for the development of diagnostic and therapeutic reagents.

Preparation and Characterization of Monoclonal Antibody Against Abalone Allergen Tropomyosin

Muscle protein tropomyosin is a major and common allergen of mollusks. In order to develop immunoassays based on monoclonal antibody (MAb) for allergen characterization, a MAb against Japanese abalone (Haliotis discus) was prepared and characterized in the present study. In comparison with the IgE reactivities of sera from crustacean allergic individuals, the selected MAb AE9F9 showed specific reaction to the abalone allergenic tropomyosin. The MAb AE9F9 reacted to the crustaceans including lobster, crab, and shrimp, but not to the mollusks other than abalone. It was surprising that the MAb AE9F9 was also reactive to the vertebrate chicken tropomyosin and smooth muscle tropomyosin of chicken gizzard. Comparison of amino acid sequences of tropomyosins among abalone, other mollusks, crustaceans, and chicken showed that two regions (90-105 and 147-165) have a high identity among abalone, crustaceans, and chicken, but are polymorphic among mollusks. In the two regions, substitutions at residues 99-Leu, 149-Lys, and 160-Arg of abalone tropomyosin are observed only in mollusks, suggesting that these residues might be important for determining the abalone tropomyosin structure recognized by the AE9F9 antibody. Because of the distinct binding site, the MAb AE9F9 might be useful for abalone allergen detection and epitope mapping of allergen tropomyosin.

Improving diagnostic tests for food allergy with recombinant allergens

Food allergy is one important manifestation of atopic allergy. Primary food allergy mainly affects young children (class I), whereas adults frequently develop food allergy as a consequence of an inhalant sensitization (class II). At present, the diagnostic instrument for proving class II food allergy is not satisfactory. Skin tests as well as serological tests are in general neither very specific nor highly sensitive because they depend on food extracts, which differ in their content of individual allergens, vary between manufacturers, and even between different batches. Since the presence of food allergen-specific IgE antibodies does not always correlate with clinical symptoms against the respective food, oral provocation tests (ideally double-blind placebo-controlled food challenges) have to be performed to validate serological diagnosis or skin tests. However, oral provocation tests are connected to several practical problems and include a specific risk for the allergic patient. Applying DNA technology, up to 40 food allergens have been produced in recombinant form, which implies standardized quality and unlimited quantity of the respective proteins. Hence, such molecules might be used to solve problems of clinical and molecular allergology in diagnosis, research, and therapy of class II food allergies. First experiments with recombinant food allergens in this respect appear very promising.

SDAP: database and computational tools for allergenic proteins

SDAP (Structural Database of Allergenic Proteins) is a web server that provides rapid, cross-referenced access to the sequences, structures and IgE epitopes of allergenic proteins. The SDAP core is a series of CGI scripts that process the user queries, interrogate the database, perform various computations related to protein allergenic determinants and prepare the output HTML pages. The database component of SDAP contains information about the allergen name, source, sequence, structure, IgE epitopes and literature references and easy links to the major protein (PDB, SWISS-PROT/TrEMBL, PIR-ALN, NCBI Taxonomy Browser) and literature (PubMed, MEDLINE) on-line servers. The computational component in SDAP uses an original algorithm based on conserved properties of amino acid side chains to identify regions of known allergens similar to user-supplied peptides or selected from the SDAP database of IgE epitopes. This and other bioinformatics tools can be used to rapidly determine potential cross-reactivities between allergens and to screen novel proteins for the presence of IgE epitopes they may share with known allergens. SDAP is available via the World Wide Web at http://fermi.utmb.edu/SDAP/.