BACKGROUND:Shellfish are a major cause of food-induced anaphylaxis and crustaceans, especially crabs and prawns, are a common cause of shellfish allergy world-wide. Current diagnostic tests are limited by lack of knowledge of clinically relevant crustacean, in particular crab, allergens and there is no specific immunotherapy. Clinical co-allergy between crustacean species is often observed but whether this is due to multiple sensitivities or to IgE cross-reactivity is unclear. Adding complexity, thermal processing alters allergenicity of food proteins. Tropomyosin is a well-documented shellfish allergen and can contribute to IgE cross-reactivity between some crustaceans. However, knowledge of other clinically important cross-reactive shellfish allergens is limited. This project examined the IgE reactivity and cross-reactivity of proteins of four Australasian crustacean species: blue swimmer crab, mud crab, black tiger prawn and banana prawn, with a particular focus on the effect of thermal processing on allergenicity.
METHODS:Crustacean-allergic patients were selected on the basis of positive shrimp ImmunoCAP (specific IgE) and convincing clinical history. IgE reactivity of raw and cooked crustacean extracts was assessed using IgE ELISA, immunoblot and basophil activation. Blue swimmer crab tropomyosin was cloned and sequenced. IgE cross-reactivity between extracts was assessed by IgE inhibition ELISA and immunoblot.
RESULTS AND CONCLUSIONS:Differences in IgE reactivity were apparent between the crustacean species but cooked extracts consistently showed greater IgE reactivity than raw. Basophil activation tests confirmed clinical relevance of IgE reactivity. There was strong cross-reactivity between cooked extracts, particularly due to tropomyosin, but also evidence for crab-specific IgE reactivity. Blue swimmer crab tropomyosin, Por p 1, was identified as a novel allergen. These findings will advance more reliable diagnosis and management of potentially severe food allergy due to crustaceans.