D3.272 - Selective Sensitization to Prawn with Absence of Cross-Reactivity to Fish: Molecular Identification of Hemocyanin (Pen m 7) and Sarcoplasmic Calcium-Binding Protein (Pen m 4) in a Patient with Recurrent Urticaria

Shellfish and fish allergies often coexist clinically, yet their molecular profiles are distinct and cross-reactivity is frequently overestimated. The molecular analysis using SDS-PAGE and Western Blot is highly relevant for understanding the relationships established between the different species and determining whether cross-sensitization may occur.

We report a patient with recurrent urticaria and systemic symptoms after eating selected seafood dishes, in whom a complete protein-level evaluation resolved diagnostic inconsistencies between skin testing, serum IgE and clinical episodes.

Protein extracts from raw prawn and shrimp, raw and cooked tuna and sea bass were prepared using standardized extraction and purification protocols. SDS-PAGE, IgE–Western blot and inhibition assays were performed using the patient’s serum.

The SDS-PAGE demonstrated clear protein patterns for prawn and shrimp, but the IgE–Western blot showed no IgE-reactive bands in shrimp, consistent with negative skin tests and clinical tolerance. In contrast, in the prawn extracts, different bands around ~75 kDa and ~20 kDa are recognized, which, according to the databases, it could correspond to hemocyanin at 76 kDa (Pen m 7) and sarcoplasmic calcium-binding protein at 21 kDa (Pen m 4) under both reducing and non-reducing conditions. Fish extracts showed IgE recognition of 45 kDa (aldolase) and 50 kDa (enolase) bands in raw samples only, consistent with thermal lability. Inhibition assays demonstrated that neither raw nor cooked fish extracts reduced IgE binding to prawn allergens, confirming absence of cross-reactivity between fish proteins and the patient’s prawn allergens.

This case demonstrates true species-selective sensitization to prawn, probably mediated by hemocyanin and sarcoplasmic calcium-binding protein, with complete absence of IgE cross-reactivity to fish. These findings explain the patient’s clinical reactions and highlight the diagnostic value of IgE–Western blot and inhibition assays when standard tests are inconclusive.