D1.65 - Selective Allergy to Large Prawn: Identification of a Projectin-Derived IgE-Binding Protein

Crustacean allergy is typically associated with tropomyosin-mediated cross-reactivity; however, species-specific allergic reactions are increasingly recognized. “Large prawn,” a commonly consumed commercial category in Spain, is poorly represented in allergen databases. We report a case of selective allergy to large prawn with tolerance to other crustaceans and describe the underlying molecular findings.

An 18-year-old man experienced reproducible episodes of abdominal heaviness, fatigue, and ocular tearing within minutes after ingestion of large prawn (Ploeticus muellirus), either grilled or in rice dishes. Symptoms resolved with oral antihistamines. He tolerated shrimp (Litopenaeus vannamei), langoustine, clams, mussels, squid, and fish. 

Protein extracts from large prawn and shrimp were prepared from shell, head, muscle, and cooking water (raw and cooked). Protein concentration was assessed by Bradford assay. SDS-PAGE and IgE–Western blot analyses were performed under reducing conditions. Additional proteic analysis was conducted to further characterize and tentatively identify the IgE-reactive high–molecular-weight protein detected.

Skin prick tests with commercial extracts (clam, mussel, shrimp, squid, tropomyosin) were negative. Prick-by-prick testing showed positive responses to raw and cooked large prawn (5×5 mm) and its head (7×7 mm), and to shrimp (5×5 mm), despite clinical tolerance to shrimp.

IgE–Western blot revealed no relevant IgE-binding proteins in shrimp extracts, apart from a faint 20 kDa band in raw muscle. In contrast, large prawn extracts showed a strong IgE-reactive band of approximately 150 kDa, consistently detected in shell, head, and cooking water extracts. This band was absent in shrimp and did not correspond to known major crustacean allergens. Proteic characterization suggested that the 150 kDa IgE-reactive band is compatible with a peptide derived from projectin, a high–molecular-weight (~621 kDa) myofibrillar protein described as non-majoritarian in crustaceans and not previously reported as an allergen. 

This case demonstrates selective allergy to large prawn associated with a species-specific IgE-binding protein distinct from tropomyosin. Proteomic analysis of the IgE-reactive band identified projectin, a giant myofibrillar protein not previously reported as an allergen. These findings provide the first evidence of IgE recognition of projectin-derived peptides in selective crustacean allergy and highlight the value of combining individualized extract preparation with molecular and proteomic approaches.