Background
Fish is one of the most frequent causes of food-induced allergy alongside cow’s milk, hen’s egg, peanut, tree nut and shellfish, and has been included in the European mandatory labeling legislation together with 13 other allergens1. Fish is a valuable source of healthy nutrients such as omega-3 fatty acids with increasing global demand. Fish allergy affects 0.1-0.4% of the world’s population2,3, has an early onset and tends to persist throughout life4. Allergic reactions are mainly provoked through ingestion but also by skin contact or by inhalation of fish steam during fish processing. The allergic reactions triggered by fish can be life-threatening and even fatal resulting in a heavy socioeconomic burden and negative impact on quality of life5,6
β-parvalbumin represents the major fish allergen accounting for up to 90% of sensitization and has been described and characterized in a wide range of fish species7-10. Parvalbumins are 8-12kDa calcium-binding muscle proteins with extreme thermal stability and shared 55-95% amino acid sequence homology among various fish species. This might account for the cross-reactivity among fish species but case reports have shown mono-sensitization and clinical allergy to single fish species11,12. Alongside parvalbumin, collagen, aldolase, enolase, pyruvate kinase, glucose-6-phosphate isomerase (G-6-PI), creatine kinase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), triosephosphate isomerase (TPI) and tropomyosin are other registered fish allergens in the World Health Organization and International Union of Immunological Societies (WHO/IUIS) database13. Among these allergens, collagen, aldolase and enolase are more well-characterized. Collagen is another heat stable protein, with reports showing anaphylaxis provoked by collagen and illustrating IgE binding to collagen only but not parvalbumin14,15. Enolase and aldolase, on the other hand, are identified as major heat-labile fish allergens in cod, salmon and tuna16.
The current diagnostic workup of fish allergy relies on skin prick test (SPT), measurement of specific IgE and when indicated, an oral food challenge17. Although a number of fish extracts are available on the ImmunoCAP platform, only parvalbumins from cod and common carp are available for IgE testing and other identified fish allergens have not been included for diagnosis due to the insufficient understanding of their allergenic properties and clinical relevance especially in the Asian populations with high fish consumption. Yet a considerable number of studies have illustrated the low specificity of SPT and specific IgE measurement while safety has always been a concern in oral food challenges18. Together with the reports of monosensitization to some fish species and parvalbumin-independent IgE sensitization19, a testing panel inclusive of the relevant fish allergens for precision component-resolve diagnosis (CRD) will be of great value.
This study identified fish allergens of salmon (Salmo salar ) and grass carp (Ctenopharyngodon idella ), which are among the most commonly farmed and consumed seawater and freshwater fishes in Asia. We compared the sensitization pattern towards the four major allergens, β-parvalbumin, enolase, aldolase and collagen, from both salmon and grass carp in fish allergic subjects from Hong Kong and Japan. Based on our results, we further characterized the allergen profiles in salmon meat cooked at the same core temperature by different methods to dissect the link between dietary preferences and allergen sensitization profiles.