not-yet-known not-yet-known not-yet-known unknown 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 fish allergic patients were collected and analyzed, while the relative parvalbumin content in different fish were measured for the construction of 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 clinical, sIgE and molecular data and their strong positive correlation led to the construction of a 4-step fish allergenicity ladder comprising: step 1 of the least allergenic fishes (tuna, halibut, salmon), steps 2 (cod) and 3 (herring and grouper) of moderately allergenic fishes to step 4 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 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 innovate fish allergy care in the next millennium.

Background The current diagnostics of fish allergy lack sufficient accuracy such that more reliable tests such as component-resolved diagnosis (CRD) are urgently needed. This study aimed at identifying fish allergens of salmon and grass carp and evaluating the sensitization pattern towards the identified allergens in fish allergic subjects from two distinct populations in Asia. Methods One hundred and three fish allergic subjects were recruited from Hong Kong (67 subjects) and Japan (46 subjects). Western blot and mass spectrometry were used to identify allergens from salmon and grass carp. Fish allergens were purified and tested against 96 sera on ELISA to analyze patients’ sensitization pattern. The protein profiles of salmon meat prepared under different cooking methods until core temperature reached 80°C were evaluated by SDS-PAGE and mass spectrometry. Results Three common allergens between salmon and grass carp, namely enolase, glycerldehyde-3-phosphate dehydrogenase (GAPDH) and parvalbumin, and two salmon-specific allergens collagen and aldolase were identified. Parvalbumin was the major allergen for both fishes showing an overall sensitization rate of 74.7%, followed by collagen (38.9%), aldolase (38.5%) and enolase (17.8%). Japanese subjects showed more diverse allergen sensitization pattern and more frequent IgE-binding to heat-labile salmon allergens. Compared with steaming and boiling, cooking by baking and frying retained more fish proteins inclusive of heat-labile allergens. Conclusions Fish allergic patients from different Asian populations show varying fish allergen sensitization profiles. The relevant extracts and components for diagnosis are population-dependent but parvalbumin and collagen are important biomarkers. Cooking methods modify allergen composition of salmon and appear to influence patients’ allergic manifestations.