Seafood allergy: Allergen, epitope mapping and immunotherapy strategy

Deciphering the Cross-Reactivity of Tropomyosin across Three Molluscan Species: Insights into the Role of Conserved T-Cell and B-Cell Epitopes

Haliotis discus hannai tropomyosin (HTM), Alectryonella plicatula tropomyosin (ATM), and Mimachlamys nobilis tropomyosin (MTM) were reported as significant seafood allergens capable of eliciting severe allergic reactions. However, studies of cross-reactivity and epitope mapping among them are notably limited. This study discovered their cross-reactivity property through inhibition of IgG/IgE binding capacity and promotion of specific CD4+T-cell proliferation. For T-cell epitopes, 3, 4, and 3 epitopes were identified from the splenocytes of mice immunized with HTM, ATM, and MTM, respectively. In terms of B-cell epitopes, a combination of bioinformatics techniques and serological assays identified 4, 3, and 4 epitopes for HTM, ATM, and MTM, respectively. Sequence logo analysis revealed 2 conserved T-cell epitopes and 5 conserved B-cell epitopes, which may be critical for the observed cross-reactivity property. In conclusion, these findings provide crucial molecular evidence that could enhance the prevention of allergic reactions to aquatic mollusks.

Molecular Allergology: Epitope Discovery and Its Application for Allergen-Specific Immunotherapy of Food Allergy

The prevalence of food allergy continues to rise, posing a significant burden on health and quality of life. Research on antigenic epitope identification and hypoallergenic agent design is advancing allergen-specific immunotherapy (AIT). This review focuses on food allergens from the perspective of molecular allergology, provides an overview of integration of bioinformatics and experimental validation for epitope identification, highlights hypoallergenic agents designed based on epitope information, and offers a valuable guidance to the application of hypoallergenic agents in AIT. With the development of molecular allergology, the characterization of the amino acid sequence and structure of the allergen at the molecular level facilitates T-/B-cell epitope identification. Alignment of the identified epitopes in food allergens revealed that the amino acid sequence of T-/B-cell epitopes barely overlapped, providing crucial data to design allergen molecules as a promising form for treating (FA) food allergy. Manipulating antigenic epitopes can reduce the allergenicity of allergens to obtain hypoallergenic agents, thereby minimizing the severe side effects associated with AIT. Currently, hypoallergenic agents are mainly developed through synthetic epitope peptides, genetic engineering, or food processing methods based on the identified epitope. New strategies such as DNA vaccines, signaling molecules coupling, and nanoparticles are emerging to improve efficiency. Although significant progress has been made in designing hypoallergenic agents for AIT, the challenge in clinical translation is to determine the appropriate dose and duration of treatment to induce long-term immune tolerance.

Insight into the anti-allergic impacts of fucoidan from Gracilaria lemaneiformis in mitigating allergic reactions induced by shrimp tropomyosin via regulating Th1/Th2 cytokines and T cell subsets

Fucoidan is a natural sulfated polysaccharide with immunoregulatory function. In this work, the anti-allergic impacts of Gracilaria lemaneiformis fucoidan (GLF) in mitigating allergic reactions induced by shrimp tropomyosin were investigated. As the results, GLF performed significant hyaluronidase inhibition ability (IC50 = 0.272 mg/mL), alleviated the allergic reactions of RAW 264.7 macrophage cells via decreasing the secretion of TNF-α and NO by 58.75 % and 46.17 %, respectively, and mitigated the degranulation degree and secretion of IL-4, TNF-α and histamine as well as promoted IL-10 secretion in RBL-2H3 mast cells. In BALB/c mouse, after gavage of GLF, the mouse allergic symptoms got significantly alleviated, the secretion of IgE and IgG1 got reduced, IgG2a got promoted, the IL-4 secretion from mouse spleen lymphocytes (SLP) significantly declined, and IL-10 and IFN-γ secretion in SLP got improved, which indicated GLF performed significantly anti-allergic functions via transforming Th2 response into Th1 and Treg response. Moreover, the SLP cells treated by GLF had lower expression of GATA-3, higher T-bet and Foxp3 expression, which indicated GLF could mitigate allergic reactions via regulating T-bet, GATA3 and Foxp3 transcription factor expression of T cell subsets. Therefore, GLF could serve as anti-allergic substances for shrimp-induced allergy via regulating Th1/Th2 cytokines and T cell subsets.

Investigation of conformational and epitope alterations of shrimp tropomyosin under α-dicarbonyl glycation and conformation-allergenicity relationship

The incidence of shrimp-induced food allergy is increasing yearly. Glycation has been reported to reduce shrimp tropomyosin (TM) allergenicity, and how advanced glycation end products (AGEs) impact TM allergenicity has garnered worldwide attention. This work investigated the conformational and epitope alterations of TM under α-dicarbonyl compounds (glyoxal (GO), methylglyoxal (MGO), butanedione (BU)) glycation and conformation-allergenicity relationship. As the results, α-dicarbonyl compounds glycation induced high glycation and TM conformational alterations. AGEs glycation sites on TM epitopes were identified by HPLC-MS/MS, with epitope destruction rates of 62.5 %, 50 % and 62.5 % for GO-TM, MGO-TM and BU-TM, respectively. Immunological results revealed TM glycated by α-dicarbonyls compounds performed weaker IgE binding by 33.38-33.86 %, while GO and MGO reduced IgG binding by 63.60 % and 77.72 %, respectively, suggesting α-dicarbonyls compounds reduced TM allergenicity via AGEs-induced epitope loss and conformational changes. This investigation could provide novel insights into how α-dicarbonyls compounds reduce TM allergenicity and prevent shrimp-induced allergy.

Effect of Maillard reaction on the allergenicity of crude extract of Mactra quadrangularis

Food allergy incidents resulting from the consumption of Mactra quadrangularis is frequently reported. Investigating the impact of the Maillard reaction on the allergenicity of M. quadrangularis allergens is beneficial for the development of hypoallergenic mollusks aquatic products. This study examined the effects of the reaction products (Mactra-Xyl) on the allergenicity using Maillard reaction between crude extract (Mactra) of M. quadrangularis and xylose. The IgE-binding activity with sera from M. quadrangularis allergic patients and allergenicity potential by a mouse food allergy model of Mactra-Xyl were evaluated. Structural changes of Mactra-Xyl were analyzed by UV spectroscopy and surface hydrophobicity assessment, and the amino acid modification sites of the major allergen tropomyosin were further identified using LC-MS/MS. The sera results showed that the IgE-binding activity of Mactra-Xyl was reduced by 56.66 % ± 15.48 % compared to Mactra. In the BALB/c mouse food allergy model, the levels of specific IgE antibody and CD4+IL-4+ cells were significantly decreased, whereas the levels of IgG2a antibody and CD4+IFN-γ+ cells were observably increased in Mactra-Xyl group compared to those observed in Mactra group, thereby alleviating the allergic response. Furthermore, the UV fluorescence intensity and protein surface hydrophobicity of Mactra-Xyl were decreased. LC-MS/MS results revealed that 6 amino acid residues (K21, R77, K86, R140, K189, N202) on 4 IgE epitopes of tropomyosin in Mactra-Xyl were modified, the finding explain the reduced allergenicity of Mactra-Xyl. Therefore, this study provided a theoretical basis for the development of hypoallergenic M. quadrangularis products.

A Crystal Structure of Pro c 2 Provides Insights into Cross-Reactivity of Aquatic Allergens from the Phosphagen Kinase Family

Arginine kinase (AK) from the phosphagen kinase family is a cross-reactive shellfish allergen. Structurally related cross-reactive allergens are involved in the pathogenesis of allergic symptoms. This study aimed to unravel the cross-reactivity of AK from a structural perspective. The crystal structure of Procambarus clarkii AK (Pro c 2) was resolved at 1.57 Å resolution, which showed a well-conserved structure not only to shellfish AKs but also to fish creatine kinase (CK), another allergen from the phosphagen kinase family. In Western blot, the CK corresponding protein in fish muscles was found to be reactive with AK-specific immunoglobulin (Ig) G. Recombinant Pro c 2 (rPro c 2) and CKs from Lateolabrax japonicus (rCK-L) and Ctenopharyngodon idell (rCK-C) were then produced, and the IgE reactivity of rCK-L and rCK-C, as well as their IgG/IgE cross-reactivity with rPro c 2, was confirmed by immunological assays. This study demonstrated the cross-reactivity among aquatic allergens from the phosphagen kinase family due to their structural similarity.

Rapid Gluten Allergen Detection Using an Integrated Photoimaging Assay and Ionic Liquid Extraction Sensor

In recent years, food allergies and food sensitivities have remained critical public health problems that affect approximately 15% of the global population. Wheat is a major food source worldwide, but it is also a common food allergen. Celiac disease is chronic immune-mediated enteropathy triggered by exposure to dietary gluten in genetically predisposed individuals; it can be treated only through strict gluten avoidance. Therefore, rapid gluten detection is crucial for protecting the health of patients. Gluten contains two primary water-insoluble proteins: gliadin and glutenin. Gliadin is a key contributor to celiac disease and poses challenges for sample pretreatment owing to its insolubility, thereby reducing the accuracy and sensitivity of detection systems. Rapid sample processing is a critical problem in gliadin detection. In this report, we developed a gliadin sensor system called the integrated food allergy and microorganism sensor (iFAMs). The iFAMs comprises a gliadin lateral flow chip, a one-pot extraction solution, and an image assay app. The iFAMs enables gliadin extraction and detection in under 2 min with high sensitivity (0.04 mg/kg for gliadin, lower than the regulatory limit of 20 mg/kg). Users can easily measure gluten concentrations in samples and quantify gliadin levels using the smartphone-based image assay app. In samples collected from restaurants, the iFAMs successfully detected hidden gluten within "gluten-free" food items. The compact size and user-friendly design of the iFAMs render it suitable for not only consumers but also clinicians, food industries, and regulators to enhance food safety.

Antigenic epitopes and cross-reactivity analysis of tropomyosin from Oratosquilla oratorio

Tropomyosin (TM) has been determined as the major allergen in Oratosquilla oratoria. However, little information is available about its antigenic epitopes and cross-reactivity. In this study, recombinant TM was obtained through genetic engineering and its IgG-/IgE-binding activity was similar to native TM. Subsequently, four T-cell epitopes were identified by using bioinformatics technology combined with CD4+ T-cell proliferation assay, and seven B-cell epitopes were identified by bioinformatics technology combined with serological assay. Moreover, dot blot analysis showed that TM had cross-reactivity among O. oratoria and other shellfish by using IgE polycolonal antibody from sera of shrimp-sensitive individuals or O. oratoria TM-immunized mice. Interestingly, three T-cell epitopes (AA4-24, AA194-212, and AA221-243) and four B-cell epitopes (AA85-100, AA121-138, AA209-233, and AA242-259) of TM in O. oratoria were conserved between O. oratoria and other shellfish, which may be the main reason for the cross-reactivity between them. In summary, these findings could serve for the diagnosis and prevention of shrimp allergy.

Development of Hypoallergenic Derivatives of Cra a 1 with B Cell Epitope Deletion and T Cell Epitope Retention

Tropomyosin was reported as an important allergen in Crassostrea angulata and designated as Cra a 1. The localization of the T cell epitopes and the reduction of the immunoreactivity of Cra a 1 are still lacking. In this study, four T cell epitopes were identified by using wild-type Cra a 1 (wtCra a 1)-immunized mouse splenocytes cultured with synthetic peptides. The immunoreactivity was maintained after chemical denaturation treatment, indicating that the linear epitope is an immunodominant epitope of wtCra a 1. Furthermore, the hypoallergenic derivative (mCra a 1) was developed by the deletion of linear B cell epitopes and retention of T cell epitopes. mCra a 1 could stimulate CD4+T cell proliferation and upregulate interleukin-10 secretion. Overall, basophil activation by mCra a 1 was low, but its ability to induce T cell proliferation was retained, suggesting that mCra a 1 may serve as a viable candidate for treating oyster allergy.

A SILAC-based accurate quantification of shrimp allergen tropomyosin in complex food matrices using UPLC-MS/MS

The carryover of trace allergens in complex food matrices poses challenges for detection techniques. Here, we demonstrate an accurate UPLC-MS/MS quantification assay for the shrimp allergen tropomyosin with a full-length isotope-labelled recombinant tropomyosin (TM-I) internal standard in complex food matrices. The TM-I, expressed based on the SILAC technique, exhibited a high isotope labelling ratio (>99%), purity, and alignment with the natural sequence. This method determined the tropomyosin ranging from 0.2 to 100 ng/mL. Mean recoveries ranged from 89 to 116%, with intra- and inter-day RSDs below 12%, for three signature peptides across three types of commercially processed food matrices. The limits of quantitation were 1 μg/g in pop food and sauce, and 10 μg/g in surimi product, respectively. This study supports the use of recombinant full-length isotope-labelled proteins rather than stable-isotope labelling peptides as internal standards to achieve more accurate quantitation of food allergens as the digestion error is corrected.