Antibody reactivity to the major fish allergen parvalbumin is determined by isoforms and impact of thermal processing

Fish Allergenicity Ladder and Parvalbumin Epitopes for Predicting Clinical Cross-Reactivity and Reintroduction in Chinese Population

BACKGROUND

IgE-mediated fish allergy has long been considered an umbrella term due to the high cross-reactivity of parvalbumin, the major fish allergen. Yet, clinical tolerance to certain fish highlights allergenicity differences. In this study, we sought to construct a fish allergenicity ladder and identify fish parvalbumin epitopes to improve the diagnosis of fish allergy.

METHODS

Reported clinical history and the serum-specific IgE (sIgE) responses of 200 Chinese subjects with suspected fish allergy were collected and analyzed, while the relative parvalbumin content in different fish was measured for the construction of a fish allergenicity ladder. Double-blind placebo-controlled food challenge (DBPCFC) and open challenge against salmon, grass carp, and grouper were performed in 58 selected patients for validation of the ladder. Epitope mapping was performed by peptide array against parvalbumins of salmon (both β-1 and β-2), cod, grouper, and grass carp with sera from fish allergic (n = 11), partial fish tolerant (n = 12), and complete fish tolerant (n = 5) patients diagnosed based on oral food challenge outcome.

RESULTS

The distribution pattern of reported history of fish allergy and tolerance, sIgE and molecular data, as well as their strong positive correlation led to the construction of a 3-step fish allergenicity ladder comprising: step 1 of the least allergenic fishes (tuna, halibut, salmon and cod), steps 2 of moderately allergenic fishes (herring and grouper) to step 3 of highly allergenic fishes (catfish, grass carp and tilapia). Epitope mapping revealed one epitope from grouper parvalbumin (AA64-78) for diagnosing general fish allergy and one epitopic region from salmon parvalbumin (AA19-33) as a biomarker of specific fish tolerance. Only epitope-specific IgE differentiated these patients but not sIgE to fish extract or parvalbumin.

CONCLUSION

The fish ladder and epitopes discovery can precisely differentiate fish-allergic and tolerant subjects and guide fish reintroduction by stepping up the ladder, which innovates fish allergy care in the next millennium.

A Comparison of the Structural Changes and IgG Immunobinding Activity of Parvalbumin in Salangid Icefish (Neosalanx taihuensis) After Glycation and Ultra-High Pressure Treatment

The aim of this study was to compare the effects of glycation and ultra-high pressure (UHP) treatment on the structure and IgG immunobinding activity of Salangidae icefish PV. The Circular Dichroism (CD) and Fluorescence Spectroscopy (FS) findings indicated that the glycation significantly affected both the secondary and tertiary structures of PV. However, the impact of UHP processing on the structure of PV was found to be less significant compared to the glycation. Western Blot analysis also revealed that the glycation markedly reduced the antigen specificity of PV. Conversely, UHP treatments at 300 MPa and 400 MPa slightly decreased the antigen specificity, whereas lower or excessively high pressures did not have a substantial impact. This research contributes valuable insights into strategies for reducing the allergenic potential of Salangid icefish.

Development of an indirect competitive ELISA based on the common epitope of fish parvalbumin for its detection

A common epitope (AGSFDHKKFFKACGLSGKST) of parvalbumin from 16 fish species was excavated using bioinformatics tools combined with the characterization of fish parvalbumin binding profile of anti-single epitope antibody in this study. A competitive enzyme-linked immunosorbent assay (ELISA) based on the common epitope was established with a limit of detection of 10.15 ng/mL and a limit of quantification of 49.29 ng/mL. The developed ELISA exhibited a narrow range (71% to 107%) of related cross-reactivity of 15 fish parvalbumin. Besides, the recovery, the coefficient of variations for the intra-assay and the inter-assay were 84.3% to 108.2%, 7.4% to 13.9% and 8.5% to 15.6%. Our findings provide a novel idea for the development of a broad detection method for fish allergens and a practical tool for the detection of parvalbumin of economic fish species in food samples.

Characterization, Epitope Confirmation, and Cross-Reactivity Analysis of Parvalbumin from Lateolabrax maculatus by Multiomics Technologies

Spotted seabass (Lateolabrax maculatus) is the second largest maricultural fish species in China and is the main trigger of food-related allergic reactions. Nevertheless, studies on the allergens of L. maculatus are limited. This study aimed to characterize pan-allergen parvalbumin from L. maculatus. Two proteins of about 11 kDa were purified and confirmed as parvalbumins by mass spectrometry. The IgG- and IgE-binding activities were evaluated through an immunoblotting assay. The molecular characteristics of β-parvalbumin were investigated by combining proteomics, genomics, and immunoinformatics approaches. The results indicated that β-parvalbumin consists of 109 amino acids with a molecular weight of 11.5 kDa and is the major allergen displaying strong IgE-binding capacity. In silico analysis and a dot blotting assay confirmed seven linear B cell epitopes distributed mainly on α-helixes and the calcium-binding loops. In addition, the cross-reactivity among 26 commonly consumed fish species was analyzed. The in-house generated anti-L. maculatus parvalbumin polyclonal antibody recognized 100% of the 26 fish species, demonstrating cross-reactivity and better binding capacity than the anticod parvalbumin antibody. Together, this study provides an efficient protocol to characterize allergens with multiomics methods and supports parvalbumin from L. maculatus as a candidate for fish allergen determination and allergy diagnosis.

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

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

Au@Ag Core-Shell Nanoparticles for Colorimetric and Surface-Enhanced Raman-Scattering-Based Multiplex Competitive Lateral Flow Immunoassay for the Simultaneous Detection of Histamine and Parvalbumin in Fish

Foodborne allergies and illnesses represent a major global health concern. In particular, fish can trigger life-threatening food allergic reactions and poisoning effects, mainly caused by the ingestion of parvalbumin toxin. Additionally, preformed histamine in less-than-fresh fish serves as a toxicological alert. Consequently, the analytical assessment of parvalbumin and histamine levels in fish becomes a critical public health safety measure. The multiplex detection of both analytes has emerged as an important issue. The analytical detection of parvalbumin and histamine requires different assays; while the determination of parvalbumin is commonly carried out by enzyme-linked immunosorbent assay, histamine is analyzed by high-performance liquid chromatography. In this study, we present an approach for multiplexing detection and quantification of trace amounts of parvalbumin and histamine in canned fish. This is achieved through a colorimetric and surface-enhanced Raman-scattering-based competitive lateral flow assay (SERS-LFIA) employing plasmonic nanoparticles. Two distinct SERS nanotags tailored for histamine or β-parvalbumin detection were synthesized. Initially, spherical 50 nm Au@Ag core-shell nanoparticles (Au@Ag NPs) were encoded with either rhodamine B isothiocyanate (RBITC) or malachite green isothiocyanate (MGITC). Subsequently, these nanoparticles were bioconjugated with anti-β-parvalbumin and antihistamine, forming the basis for our detection and quantification methodology. Additionally, our approach demonstrates the use of SERS-LFIA for the sensitive and multiplexed detection of parvalbumin and histamine on a single test line, paving the way for on-site detection employing portable Raman instruments.

Thermostable allergens in canned fish: Evaluating risks for fish allergy

BACKGROUND

Major fish allergens, including parvalbumin (PV), are heat stable and can withstand extensive cooking processes. Thus, the management of fish allergy generally relies on complete avoidance. Fish-allergic patients may be advised to consume canned fish, as some fish-allergic individuals have reported tolerance to canned fish. However, the safety of consuming canned fish has not been evaluated with comprehensive immunological and molecular analysis of canned fish products.

METHODS

We characterized the in vitro immunoreactivity of serum obtained from fish-allergic subjects to canned fish. Seventeen canned fish products (salmon n = 8; tuna n = 7; sardine n = 2) were assessed for the content and integrity of PV using allergen-specific antibodies. Subsequently, the sIgE binding of five selected products was evaluated for individual fish-allergic patients (n = 53). Finally, sIgE-binding proteins were identified by mass spectrometry.

RESULTS

The canned fish showed a markedly reduced PV content and binding to PV-specific antibodies compared with conventionally cooked fish. However, PV and other heat-stable fish allergens, including tropomyosin and collagen, still maintained their sIgE-binding capacity. Of 53 patients, 66% showed sIgE binding to canned fish proteins. The canned sardine contained proteins bound to sIgE from 51% of patients, followed by canned salmon (43%-45%) and tuna (8%-17%). PV was the major allergen in canned salmon and sardine. Tropomyosin and/or collagen also showed sIgE binding.

CONCLUSION

We showed that canned fish products may not be safe for all fish-allergic patients. Canned fish products should only be considered into the diet of individuals with fish allergy, after detailed evaluation which may include in vitro diagnostics to various heat-stable fish allergens and food challenge conducted in suitable environments.

On-Chip Discovery of Allergens from the Exudate of Large Yellow Croaker (Larimichthys Crocea) Muscle Food by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

It is extremely crucial to establish facile, accurate, and fast methods for testing allergenic proteins (allergens) in seafood. The current study focuses on the evaluation of fish muscle exudate proteins in an effort to discover potential allergens in fish exudate for allergy tests. Large yellow croaker (Larimichthys crocea) was studied as a seafood model. Magnetic beads (MBs) modified with an IgE antibody were utilized to isolate allergens existing in the exudate sample. Immunoglobulin E (IgE) in blood is a class of antibodies that is mainly associated with allergic reactions. Potential allergens in the muscle exudate were fished by IgE-biofunctional MBs in microfluidic channels. The protein-attached MBs were isolated under a magnetic field, eluted, and collected. The collected eluent was digested and analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to identify allergens. Eight allergens from large yellow croaker exudate were identified, i.e., parvalbumin beta, parvalbumin, protein S100, histone H4, cytochrome c, fatty acid binding protein 3 (FABP3), microsomal glutamate S-transfer 3 (MGST3), and C-C motif chemokine 21 (CCL21). The presently proposed microfluidic-magnetic-based allergen extraction protocol enables a facile and rapid test of potentials of seafood allergies, providing a solution to circumvent food safety issues, especially for allergic populations.

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.

Cross-reactive monoclonal antibodies against fish parvalbumins as a tool for studying antigenic similarity of different parvalbumins and analysis of fish extracts

Fish parvalbumins are heat-stable calcium-binding proteins that are highly cross-reactive in causing allergy symptoms in fish-sensitized patients. The reactivities of parvalbumin-specific monoclonal or polyclonal antibodies with parvalbumins of different fish species allowed their application for development of various immunoassays for allergen identification in fish samples. In this study, monoclonal antibodies (MAbs) were generated against two parvalbumins - natural Atlantic cod parvalbumin and recombinant common carp β-parvalbumin expressed in E. coli. Large collections of recombinant parvalbumins and natural allergen extracts of different fish species and other animals were used to identify the specificities of these MAbs using ELISA, Western blot, and dot blot. MAbs demonstrated different patterns of cross-reactivities with recombinant parvalbumins. Their binding affinities were affected by the addition and removal of Ca²⁺ ions. Moreover, all MAbs showed a broad reactivity with the target antigens in natural fish, chicken, and pork extracts. The ability of two MAbs (clones 7B2 and 3F6) to identify and isolate native parvalbumins from allergen extracts was confirmed by Western blot. Epitope mapping using recombinant fragments of Atlantic cod parvalbumin (Gad m 1) and common carp parvalbumin (Cyp c 1) revealed that 4 out of 5 MAbs recognize parvalbumin regions that contain calcium binding sites. In conclusion, the generated broadly reactive well-characterized MAbs against fish β-parvalbumins could be applied for investigation of parvalbumins of fish and other animals and their detection in allergen extracts.

Parvalbumin: A Major Fish Allergen and a Forensically Relevant Marker

Parvalbumins (PVALBs) are low molecular weight calcium-binding proteins. In addition to their role in many biological processes, PVALBs play an important role in regulating Ca2+ switching in muscles with fast-twitch fibres in addition to their role in many biological processes. The PVALB gene family is divided into two gene types, alpha (α) and beta (β), with the β gene further divided into two gene types, beta1 (β1) and beta2 (β2), carrying traces of whole genome duplication. A large variety of commonly consumed fish species contain PVALB proteins which are known to cause fish allergies. More than 95% of all fish-induced food allergies are caused by PVALB proteins. The authentication of fish species has become increasingly important as the seafood industry continues to grow and the growth brings with it many cases of food fraud. Since the PVALB gene plays an important role in the initiation of allergic reactions, it has been used for decades to develop alternate assays for fish identification. A brief review of the significance of the fish PVALB genes is presented in this article, which covers evolutionary diversity, allergic properties, and potential use as a forensic marker.

Identification of Fish Species and Targeted Genetic Modifications Based on DNA Analysis: State of the Art

Food adulteration is one of the most serious problems regarding food safety and quality worldwide. Besides misleading consumers, it poses a considerable health risk associated with the potential non-labeled allergen content. Fish and fish products are one of the most expensive and widely traded commodities, which predisposes them to being adulterated. Among all fraud types, replacing high-quality or rare fish with a less valuable species predominates. Because fish differ in their allergen content, specifically the main one, parvalbumin, their replacement can endanger consumers. This underlines the need for reliable, robust control systems for fish species identification. Various methods may be used for the aforementioned purpose. DNA-based methods are favored due to the characteristics of the target molecule, DNA, which is heat resistant, and the fact that through its sequencing, several other traits, including the recognition of genetic modifications, can be determined. Thus, they are considered to be powerful tools for identifying cases of food fraud. In this review, the major DNA-based methods applicable for fish meat and product authentication and their commercial applications are discussed, the possibilities of detecting genetic modifications in fish are evaluated, and future trends are highlighted, emphasizing the need for comprehensive and regularly updated online database resources.

Identification of Potentially Tolerated Fish Species by Multiplex IgE Testing of a Multinational Fish-Allergic Patient Cohort

BACKGROUND

Although recent studies indicated that many fish-allergic patients may safely consume certain fish species, no clinical guidelines are available for identification of the exact species tolerated by specific patients.

OBJECTIVE

To investigate whether multiplex immunoglobulin E (IgE) testing reveals potentially tolerated fish through absence of IgE to parvalbumin (PV) and extracts from specific species.

METHODS

Sera from 263 clinically well-defined fish-allergic patients from Austria, China, Denmark, Luxembourg, Norway, and Spain were used in a research version of the ALEX² multiplex IgE quantification assay. Specific IgE to PVs from 10 fish species (9 bony and 1 cartilaginous), and to extracts from 7 species was quantified. The IgE signatures of individual patients and patient groups were analyzed using SPSS and R.

RESULTS

Up to 38% of the patients were negative to cod PV, the most commonly used molecule in fish allergy diagnosis. Forty-five patients (17%) tested negative to PVs but positive to the respective fish extracts, underlining the requirement for extracts for accurate diagnosis. Between 60% (Spain) and 90% (Luxembourg) of the patients were negative to PV and extracts from ray, a cartilaginous fish, indicating its potential tolerance. Up to 21% of the patients were negative to at least 1 bony fish species. Of the species analyzed, negativity to mackerel emerged as the best predictive marker of negativity to additional bony fish, such as herring and swordfish.

CONCLUSIONS

Parvalbumins and extracts from multiple fish species relevant for consumption should be used in fish-allergy diagnosis, which may help identify potentially tolerated species for individual patients.

Fish Processing and Digestion Affect Parvalbumins Detectability in Gilthead Seabream and European Seabass

Consumption of aquatic food, including fish, accounts for 17% of animal protein intake. However, fish consumption might also result in several side-effects such as sneezing, swelling and anaphylaxis in sensitized consumers. Fish allergy is an immune reaction to allergenic proteins in the fish muscle, for instance parvalbumin (PV), considered the major fish allergen. In this study, we characterize PV in two economically important fish species for southern European aquaculture, namely gilthead seabream and European seabass, to understand its stability during in vitro digestion and fish processing. This information is crucial for future studies on the allergenicity of processed fish products. PVs were extracted from fish muscles, identified by mass spectrometry (MS), and detected by sandwich enzyme-linked immunosorbent assay (ELISA) after simulated digestion and various food processing treatments. Secondary structures were determined by circular dichroism (CD) after purification by anion exchange and gel filtration chromatography. In both species, PVs presented as α-helical and β-sheet structures, at room temperature, were shown to unfold at boiling temperatures. In European seabass, PV detectability decreased during the simulated digestion and after 240 min (intestinal phase) no detection was observed, while steaming showed a decrease (p < 0.05) in PVs detectability in comparison to raw muscle samples, for both species. Additionally, freezing (−20 °C) for up to 12 months continued to reduce the detectability of PV in tested processing techniques. We concluded that PVs from both species are susceptible to digestion and processing techniques such as steaming and freezing. Our study obtained preliminary results for further research on the allergenic potential of PV after digestion and processing.

Detection of Parvalbumin Fish Allergen in Canned Tuna by Real-Time PCR Driven by Tuna Species and Can-Filling Medium

Canned tuna is considered one of the most popular and most commonly consumed products in the seafood market, globally. However, in past decades, fish allergens have been detected as the main concern regarding food safety in these seafood products and are listed as the top eight food allergies. In the group of fish allergens, parvalbumin is the most common. As a thermally stable and calcium-binding protein, parvalbumin can be easily altered with changing the food matrices. This study investigated the effect of a can-filling medium (tomato sauce, spices, and brine solutions) on the parvalbumin levels in canned tuna. The effect of pH, calcium content, and the DNA quality of canned tuna was also investigated before the parvalbumin-specific encoded gene amplification. The presence of fish allergens was determined by melting curve analyses and confirmed by agarose gel electrophoresis. The obtained results showed that the presence of parvalbumin in commercially canned tuna was driven by can-filling mediums, thermal conductivity, calcium content, and the acidity of various ingredients in food matrices. The intra-specific differences revealed a variation in fish allergens that are caused by cryptic species. This study proved that allergens encoding gene analyses by agarose electrophoresis could be used as a reliable approach for other food-borne allergens in complex food matrices.

Comparative Analysis of Glycosylation Affecting Sensitization by Regulating the Cross-Reactivity of Parvalbumins in Turbot (Scophthalmus maximus), Conger Eel (Conger myriaster) and Sea Bass (Micropterus salmoides)

Parvalbumin (PV) is the most common allergen in fish. Some patients with fish allergy are allergic to only one species of fish but are tolerant to others; however, the underlying mechanism has not been identified. This study showed that three types of glycated fishes' PV showed a similar decrease in immunoglobulin E (IgE) binding. Glycosylation could improve the simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) digestion resistance of fishes' PV. We also discovered that the cross-reactivity between eel and turbot was weaker than that of bass; glycosylation can reduce cross-reactivity between eel/bass and turbot by downregulating Th2 cytokines and upregulating Th1 cytokines as well as downregulating the expression of G-T PV, G-E PV, G-B PV of IL-4 (94.31 ± 3.16, 73.26 ± 0.91, 94.95 ± 3.03 ng/mL), and IL-13 (38.84 ± 0.75, 33.77 ± 0.71, 36.51 ± 0.50 ng/mL) and upregulating the expression of IFN-γ (318.01 ± 3.46, 387.15 ± 3.30, 318.01 ± 4.21 ng/mL) compared with T PV, respectively. This study showed that glycosylation affected sensitization by regulating the cross-reactivity of parvalbumins.

Development of a sensitive sandwich ELISA with broad species specificity for improved fish allergen detection

A sensitive Enzyme-linked Immunosorbent Assay (ELISA) with improved broad species specificity was developed for the detection of southern hemisphere fish residues in processed foods. The polyclonal antibodies were raised against parvalbumins from 13 fish species representing 7 fish orders selected for their molecular diversity and immunoreactivity profile. The optimized ELISA-2 (based on the rabbit capture antibody (RB#4) - sheep detection antibody (S2#4) pair) displayed an improved detection limit of 0.6 μg/L (3.7 μg of /kg). Our immunoreactivity-directed species selection approach in the strategized antibody production significantly improved the detection of no or weakly immunoreactive fish species previously not detected immunochemically. Of 37 commercially important fish species tested, the ELISA-2 could detect 28 fish species (76%). The optimized sample extraction with a buffer additive achieved good protein recoveries of 87.2 - 117.3% (within the AOAC recommended range). The ELISA-2 was able to detect fish residues in five highly processed food products.

A comprehensive overview of emerging processing techniques and detection methods for seafood allergens

Seafood is rich in nutrients and plays a significant role in human health. However, seafood allergy is a worldwide health issue by inducing adverse reactions ranging from mild to life-threatening in seafood-allergic individuals. Seafood consists of fish and shellfish, with the major allergens such as parvalbumin and tropomyosin, respectively. In the food industry, effective processing techniques are applied to seafood allergens to lower the allergenicity of seafood products. Also, sensitive and rapid allergen-detection methods are developed to identify and assess allergenic ingredients at varying times. This review paper provides an overview of recent advances in processing techniques (thermal, nonthermal, combined [hybrid] treatments) and main allergen-detection methods for seafood products. The article starts with the seafood consumption and classification, proceeding with the prevalence and symptoms of seafood allergy, followed by a description of biochemical characteristics of the major seafood allergens. As the topic is multidisciplinary in scope, it is intended to provide information for further research essential for food security and safety.

The first reptilian allergen and major allergen for fish-allergic patients: Crocodile β-parvalbumin

BACKGROUND

Clinical cross-reactivity between bony fish, cartilaginous fish, frog, and chicken muscle has previously been demonstrated in fish-allergic patients. In indicative studies, two reports of anaphylaxis following the consumption of crocodile meat and IgE-cross-binding were linked to the major fish allergen parvalbumin (PV). This study investigates IgE-binding proteins in crocodile meat with a focus on PV and their clinical relevance.

METHODS

Proteins were extracted from muscle tissue of crocodile, three bony fish, and two cartilaginous fish. A cohort of fish-allergic pediatric patients (n = 77) underwent allergen skin prick testing (SPT) to three fish preparations (n = 77) and crocodile (n = 12). IgE-binding proteins were identified and quantified by SDS-PAGE, mass spectrometric analyses, and immunoblotting using commercial and in-house antibodies, as well as individual and pooled patients' serum. PV isoforms were purified or recombinantly expressed before immunological analyses, including human mast cell degranulation assay.

RESULTS

Of the tissues analyzed, PV was most abundant in heated crocodile preparation, triggering an SPT of ≥3 mm in 8 of 12 (67%) fish-allergic patients. Seventy percent (31 of 44) of fish PV-sensitized patients demonstrated IgE-binding to crocodile PV. Crocodile β-PV was the major IgE-binding protein but 20-fold less abundant than α-PV. Cellular reactivity was demonstrated for β-PV and epitopes predicted, explaining frequent IgE-cross-binding of β-PVs. Both PV isoforms are now registered as the first reptile allergens with the WHO/IUIS (β-PV as Cro p 1 and α-PV as Cro p 2).

CONCLUSION

Fish-allergic individuals may be at risk of an allergy to crocodile and should seek specialist advice before consuming crocodilian meat.

Proteomics for Development of Food Allergy Vaccines

Food allergy is a hypersensitivity reaction to food products initiated by immunologic mechanisms, which represents one of the major concerns in food safety. New therapies for food allergies including oral and epicutaneous allergen-specific immunotherapy are required, and B cell epitope-based allergy vaccines are a good promise to improve this field. In this chapter, we describe a workflow for the design of food allergy vaccines using proteomic tools. The strategy is defined based on the characterization of B cell epitopes for a particular food allergen. For that, the workflow comprises five consecutive steps: (1) shotgun proteomics analysis of different protein isoforms for a particular food allergen, (2) downloading all protein sequences for the specific allergen included in UniProtKB database, (3) analysis by protein-based bioinformatics of B cell epitopes, (4) synthesizing of the selected B cell peptide epitopes, and (5) performing of immunoassays using sera from healthy and allergic patients. The results from this method provide a rationale repository of B cell epitopes for the design of new specific immunotherapies for a particular food allergen. The strategy was optimized for all the beta-parvalbumins (β-PRVBs), which are considered as the main fish allergens. Using this workflow, a total of 35 peptides were identified as B cell epitopes, among them the top 4 B cell peptide epitopes that may induce protective immune response were selected as potential peptide vaccine candidates for fish allergy.

Alternative Fish Species for Nutritional Management of Children with Fish-FPIES—A Clinical Approach

In the Mediterranean region, fish is a common cause of food protein-induced enterocolitis syndrome (FPIES) in children. No laboratory tests specific to FPIES are available, and oral food challenge (OFC) is the gold standard for its diagnosis and testing for achievement of tolerance. Children with FPIES to fish are usually advised to avoid all fish, regardless of the species. Fish are typically classified into bony and cartilaginous, which are phylogenetically distant species and therefore contain less cross-reacting allergens. The protein β-parvalbumin, considered a pan-allergenic, is found in bony fish, while the non-allergenic α-parvalbumin is commonly found in cartilaginous fish. Based on this difference, as a first step in the therapeutic process of children with FPIES caused by a certain fish in the bony fish category (i.e., hake, cod, perch, sardine, gilthead sea bream, red mullet, sole, megrim, sea bass, anchovy, tuna, swordfish, trout, etc.), an OFC to an alternative from the category of cartilaginous fish is suggested (i.e., blue shark, tope shark, dogfish, monkfish, skate, and ray) and vice versa. Regarding the increased mercury content in some sharks and other large species, the maximum limit imposed by the European Food Safety Authority (EFSA) for weekly mercury intake must be considered. An algorithm for the management of fish-FPIES, including alternative fish species, is proposed.

Development of a sensitive sandwich-ELISA assay for reliable detection of fish residues in foods

A new sandwich-type Enzyme-Linked Immunosorbent Assay (ELISA) method was developed based on goat IgG as capturing antibody and rabbit IgG as detecting antibody targeting soluble antigenic fish proteins in foods as detection targets. The assay has provided a relatively lower limit of quantitation (LoQ) for fish proteins with LoQ 0.5 ng/ml and appears highly sensitive. The analysis of 24 different substances, both raw and boiled, revealed no cross-reactivity above the cut-off point of the limit of quantitation. Recoveries of the SB spiked food matrixes were in the range of 83-131%. Assay precision testing proved that repeatability (<5%) and reproducibility (<11%) had an acceptable level of variation. The sandwich ELISA was capable of detecting all tested commercially important fish. As a potential analytical tool, the newly developed immunoenzymatic method is suitable for detecting undeclared fish residues in real food samples available in the market, thereby will help to reduce the incidents of fish allergies.

Aptamer-Based Fluorescent Biosensor for the Rapid and Sensitive Detection of Allergens in Food Matrices

Food allergies have seriously affected the life quality of some people and even endangered their lives. At present, there is still no effective cure for food allergies. Avoiding the intake of allergenic food is still the most effective way to prevent allergic diseases. Therefore, it is necessary to develop rapid, accurate, sensitive, and reliable analysis methods to detect food allergens from different sources. Aptamers are oligonucleotide sequences that can bind to a variety of targets with high specificity and selectivity, and they are often combined with different transduction technologies, thereby constructing various types of aptamer sensors. In recent years, with the development of technology and the application of new materials, the sensitivity, portability, and cost of fluorescence sensing technology have been greatly improved. Therefore, aptamer-based fluorescence sensing technology has been widely developed and applied in the specific recognition of food allergens. In this paper, the classification of major allergens and their characteristics in animal and plant foods were comprehensively reviewed, and the preparation principles and practical applications of aptamer-based fluorescence biosensors are summarized. In addition, we hope that this article can provide some strategies for the rapid and sensitive detection of allergens in food matrices.

Development and Characterization of Monoclonal Antibodies for the Detection of Fish Protein

This study developed and characterized anti-fish monoclonal antibodies (mAbs) capable of detecting fish, a major allergenic food, in processed food products to protect fish sensitized individuals. Of the three mAbs raised against crude protein extract of cooked fish muscle, mAb 8F5 exhibited a positive reaction to all 50 common food fish species tested with no cross-reactions to shellfish, land animals, or food additives. Although the ELISA results were negative against swordfish and yellowfin tuna, western blot clearly detected both after cooking. The ~36 kDa antigenic protein of mAb 8F5, which was found in all fish species, was detectable by mAb 8F5 in all of the fish samples even after prolonged heat treatment (100 °C, up to 60 min). These findings suggest that mAb 8F5 has great potential utility as a probe for the immunochemical detection of fish tissue in cooked food.

Effect of Processing on Fish Protein Antigenicity and Allergenicity

Fish allergy is a life-long food allergy whose prevalence is affected by many demographic factors. Currently, there is no cure for fish allergy, which can only be managed by strict avoidance of fish in the diet. According to the WHO/IUIS Allergen Nomenclature Sub-Committee, 12 fish proteins are recognized as allergens. Different processing (thermal and non-thermal) techniques are applied to fish and fishery products to reduce microorganisms, extend shelf life, and alter organoleptic/nutritional properties. In this concise review, the development of a consistent terminology for studying food protein immunogenicity, antigenicity, and allergenicity is proposed. It also summarizes that food processing may lead to a decrease, no change, or even increase in fish antigenicity and allergenicity due to the change of protein solubility, protein denaturation, and the modification of linear or conformational epitopes. Recent studies investigated the effect of processing on fish antigenicity/allergenicity and were mainly conducted on commonly consumed fish species and major fish allergens using in vitro methods. Future research areas such as novel fish species/allergens and ex vivo/in vivo evaluation methods would convey a comprehensive view of the relationship between processing and fish allergy.

IgE and IgG4 epitopes revealed on the major fish allergen Lat c 1

BACKGROUND

The IgE- and IgG₄-binding patterns of the major fish allergen parvalbumins are not clearly understood. IgE antibody-binding to parvalbumin from Asian seabass, Lat c 1.01, is implicated in up to 90 % of allergic reactions, although the region of IgE or IgG4 epitopes are unknown. In the present study, we characterized the specific IgE- and IgG₄-binding regions of Lat c 1.01 using serum from pediatric and adult patients with clinically-confirmed fish allergy.

METHODS

A comparative investigation of patient IgE- and IgG₄-binding to recombinant Lat c 1.01 was performed by immunoblotting and indirect ELISA using serum from 15 children and eight adults with clinically confirmed IgE-mediated reactions to fish. The IgE- and IgG₄-binding regions of Lat c 1.01 were determined by inhibition ELISA using seven overlapping peptides spanning the entire 102 amino acid sequence. Elucidated IgE-binding regions were modelled and compared to known antibody-binding regions of parvalbumins from five other fish species.

RESULTS

Ninety five percent (22/23) patients demonstrated IgE-binding to rLat c 1.01, while fewer patients (10/15 children and 7/8 adults) demonstrated robust IgG₄ binding when determined by immunoblots. IgE-binding for both cohorts was significantly higher compared to IgG₄-binding by ELISA. All patients in this study presented individual IgE and IgG₄ epitope-recognition profiles. In addition to these patient-specific antibody binding sites, general IgE epitopes were also identified at the C- and N-terminal regions of this major fish allergen.

CONCLUSIONS AND CLINICAL RELEVANCE

Our findings demonstrate two specific IgE epitopes on parvalbumin from Asian seabass, while IgG₄ binding is much lower and patient specific. This study highlights the importance of advancement in epitope analysis regardless of the age group for diagnostics and immunotherapies for fish allergy.

Novel monoclonal antibody-sandwich immunochromatographic assay based on Fe3O4/Au nanoparticles for rapid detection of fish allergen parvalbumin

In this study, a rapid sandwich immunochromatographic assay (ICA) was developed to detect parvalbumin (PV). Firstly, two optimum primary monoclonal antibody (mAb) against PV had been screened out: mAb1 was used as the capture antibody, and mAb2 conjugated to Fe₃O₄/Au nanoparticles (Fe₃O₄/AuNPs) that served as a detection reagent. Using this pair of mAbs, a sandwich ICA strip based on Fe₃O₄/AuNPs was developed. The results showed that the color intensity of test line positively correlated with the PV concentration in the standard or spiked sample. The limit of detection for qualitative (LOD) and quantitative detection (LOQ) were 2 ng/mL and 0.691 ng/mL, respectively. Besides, the detection time of this ICA strip was within 15 min. The recovery rates ranged from 104.0% to 117.4%, within an acceptable level (80-120%). Moreover, the developed assay also showed high cross reaction in different fish species. These results demonstrated that the established test strip has the potential to be used as a rapid screening tool for large scale determination of PV in foodstuffs.

A review on food processing and preparation methods for altering fish allergenicity

People eat many varieties of food to satiate their hunger. Among them, a few numbers of food cause overreaction of the body's immune system, and fish holds a permanent position on that list. Processing methods, including one treatment or a combination, can have different effects on the allergenic potential of food proteins. An important point to note, however, is that not all of these methods can eliminate the potential for protein allergy. Thus, it is essential to understand the risk involved with the consumption of processed fish and its derivatives. Fish could be prepared in various ways before come to the dining plate. It has shown some of these methods can effectively manipulate the allergenicity owing to the alterations occurred in the protein conformation. This article provides an overview of the impact of fish processing methods (thermal and non-thermal) on the allergenic potential of fish along with possible causative structural modification provokes allergen stability. The article begins with current trends related to fish consumption, proceeds with the prevalence and underlying mechanism of fish allergy. Properties of clinically relevant fish proteins, projected IgE epitopes of PV, cross-reactivity of fish allergens are also addressed in this context to understand and compare the behavioral patterns of PV profiles of different species on processing methods.

Commercial fish ELISA kits have a limited capacity to detect different fish species and their products

BACKGROUND

Fish is a major food and allergen source, requiring safety declarations on packages. Enzyme-linked immunosorbent assays (ELISAs) are often used to ensure that the product meets the required standards with regard to the presence of allergens. Over 1000 different fish species are traded and consumed worldwide, and they are increasingly provided by aquaculture. Up to 3% of the general population is at risk of sometimes fatal allergic reactions to fish, requiring strict avoidance of this commodity. The aim of this study is to evaluate the capacity of three commercially available ELISA tests to detect a wide variety of bony and cartilaginous fish and their products, which is essential to ensure reliable and safe food labeling.

RESULTS

The detection rates for 57 bony fish ranged from 26% to 61%. Common European and North American species, including carp, cod, and salmon species, demonstrated a higher detection rate than those from the Asia-Pacific region, including pangasius and several mackerel and tuna species. Among the 17 canned bony fish products, only 65% to 86% were detected, with tuna showing the lowest rate. None of the cartilaginous fish (n = 9), other vertebrates (n = 8), or shellfish (n = 5) were detected.

CONCLUSIONS

We demonstrated that three commercial fish ELISA kits had a limited capacity to detect fish and their products. The complexity of fish as a protein source that is increasingly utilized means that there is an urgent need for improved detection methods. This is crucial for the food industry to provide safe seafood products and comply with international legislation. © 2020 Society of Chemical Industry.

Reconstruction of fish allergenicity from the content and structural traits of the component β-parvalbumin isoforms

Most fish-allergic patients have anti-β-parvalbumin (β-PV) immunoglobulin E (IgE), which cross-reacts among fish species with variable clinical effects. Although the β-PV load is considered a determinant for allergenicity, fish species express distinct β-PV isoforms with unknown pathogenic contributions. To identify the role various parameters play in allergenicity, we have taken Gadus morhua and Scomber japonicus models, determined their β-PV isoform composition and analyzed the interaction of the IgE from fish-allergic patient sera with these different conformations. We found that each fish species contains a major and a minor isoform, with the total PV content four times higher in Gadus morhua than in Scomber japonicus. The isoforms showing the best IgE recognition displayed protease-sensitive globular folds, and if forming amyloids, they were not immunoreactive. Of the isoforms displaying stable globular folds, one was not recognized by IgE under any of the conditions, and the other formed highly immunoreactive amyloids. The results showed that Gadus morhua muscles are equipped with an isoform combination and content that ensures the IgE recognition of all PV folds, whereas the allergenic load of Scomber japonicus is under the control of proteolysis. We conclude that the consideration of isoform properties and content may improve the explanation of fish species allergenicity differences.

Fish Allergy Management: From Component-Resolved Diagnosis to Unmet Diagnostic Needs

Purpose of review

Fish is a common elicitor of IgE-mediated food allergy. Fish includes a large variety of foods, in terms of species and food processing, with marked distinction in local diets around the globe. Fish-allergic patients present with phenotypic diversity and major differences in levels of clinical cross-reactivity, features that pose an important challenge for the clinical diagnosis and management.

Recent findings

Parvalbumin is the major fish allergen. However, a single molecule is not sufficient but several homologs, allergens different from parvalbumin and allergen extracts, are needed for IgE-based diagnosis.

Summary

Parvalbumin-specific IgE are markers for clinical cross-reactions. Added value is provided by IgE typing to parvalbumin homologs from distantly related fish. IgE co-sensitization profiles (parvalbumin, enolase, aldolase) are referred as severity markers. The allergen panel seems to be not yet complete why fish extracts still play a crucial role in serum IgE analysis. Further clinical validation of a multiplex approach in molecular fish allergy diagnosis is needed for striving to avoid unnecessary food restrictions and in a further sense, improved patient care.

Food processing and occupational respiratory allergy- An EAACI position paper

Occupational exposure to foods is responsible for up to 25% of cases of occupational asthma and rhinitis. Animal and vegetable high-molecular-weight proteins present in aerosolized foods during food processing, additives, preservatives, antioxidants, and food contaminants are the main inhalant allergen sources. Most agents typically cause IgE-mediated allergic reactions, causing a distinct form of food allergy (Class 3 food allergy). The allergenicity of a food protein, allergen exposure levels, and atopy are important risk factors. Diagnosis relies on a thorough medical and occupational history, functional assessment, assessment of sensitization, including component-resolved diagnostics where appropriate, and in selected cases specific inhalation tests. Exposure assessment, including allergen determination, is a cornerstone for establishing preventive measures. Management includes allergen exposure avoidance or reduction (second best option), pharmacological treatment, assessment of impairment, and worker's compensation. Further studies are needed to identify and characterize major food allergens and define occupational exposure limits, evaluate the relative contribution of respiratory versus cutaneous sensitization to food antigens, evaluate the role of raw versus cooked food in influencing risk, and define the absolute or relative contraindication of patients with ingestion-related food allergy, pollinosis, or oral allergy syndrome continuing to work with exposure to aerosolized food allergens.

Effect of tyrosinase and caffeic acid crosslinking of turbot parvalbumin on the digestibility, and release of mediators and cytokines from activated RBL-2H3 cells

Turbot can induce allergy in susceptible individuals due to the presence of parvalbumin (PV), a major fish allergen. This study aimed at evaluating the digestibility and the ability of PV to elicit the release of cellular degranulation, following treatment with tyrosinase (PV-Tyr), caffeic acid (PV-CA) and in combination (PV-Tyr/CA), using in vitro digestion and RBL-2H3 (passive rat basophil leukemia) cell line. The digestion assay products revealed that the stability of PV in simulated gastric fluid (SGF) was stronger, while in simulated intestinal fluid (SIF) was rather weak. Western blot analysis revealed that the IgG-binding abilities of the cross-linked PV were markedly reduced. Moreover, crosslinking hampered the release of cellular degranulation process in RBL-2H3 cell lines. PV-Tyr/CA showed highly significant reduction in the release rate of β-hexosaminidase (66.02%), histamine (35.01%), tryptase (29.25%), cysteinyl leukotrienes (29.72%), prostaglandin D₂ (34.96%), IL-4 (43.99%) and IL-13 (38.93%) and shown potential in developing hypoallergenic fish products.

Fish-derived low molecular weight components modify bronchial epithelial barrier properties and release of pro-inflammatory cytokines

The prevalence of fish allergy among fish-processing workers is higher than in the general population, possibly due to sensitization via inhalation and higher exposure. However, the response of the bronchial epithelium to fish allergens has never been explored. Parvalbumins (PVs) from bony fish are major sensitizers in fish allergy, while cartilaginous fish and their PVs are considered less allergenic. Increasing evidence demonstrates that components other than proteins from the allergen source, such as low molecular weight components smaller than 3 kDa (LMC) from pollen, may act as adjuvants during allergic sensitization.

We investigated the response of bronchial epithelial cells to PVs and to LMC from Atlantic cod, a bony fish, and gummy shark, a cartilaginous fish. Polarized monolayers of the bronchial epithelial cell line 16HBE14o- were stimulated apically with fish PVs and/-or the corresponding fish LMC. Barrier integrity, transport of PVs across the monolayers and release of mediators were monitored.

Intact PVs from both the bony and the cartilaginous fish were rapidly internalized by the cells and transported to the basolateral side of the monolayers. The PVs did not disrupt the epithelial barrier integrity nor did they modify the release of proinflammatory cytokines. In contrast, LMC from both fish species modified the physical and immunological properties of the epithelial barrier and the responses differed between bony and cartilaginous fish. While the barrier integrity was lowered by cod LMC 24 h after cell stimulation, it was increased by up to 2.3-fold by shark LMC. Furthermore, LMC from both fish species increased basolateral and apical release of IL-6 and IL-8, while CCL2 release was increased by cod but not by shark LMC.

In summary, our study demonstrated the rapid transport of PVs across the epithelium which may result in their availability to antigen presenting cells required for allergic sensitization. Moreover, different cell responses to LMC derived from bony versus cartilaginous fish were observed, which may play a role in different allergenic potentials of these two fish classes.

Identification and comparison of allergenicity of native and recombinant fish major allergen parvalbumins from Japanese flounder (Paralichthys olivaceus)

Compared with native parvalbumin, recombinant β-parvalbumin based on the optimized DNA sequence can be used in fish allergen confirmation.

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.

Classification of Food Allergens and Cross-Reactivity

Patients with specific food allergies are commonly sensitized to related foods, for example, shrimp with other shellfish and peanut with other legumes. In some instances, this represents a true allergy to the related food, defined as cross-reactivity, while in other instances, it represents a positive skin or IgE test only, in a patient who can eat the related food without difficulty. This is defined as cross-sensitization. It is extremely important that the clinician recognize these patterns of cross-sensitization and cross-reactivity, both to counsel patients on foods that should be avoided and to make sure that foods are not unnecessarily restricted from the diet. In fact, it is very common for patients to be instructed to avoid entire food groups based just on positive tests, which leads to unnecessary dietary restrictions with effects on food choices, nutrition, and quality of life.

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.