D1.61 - Shrimp Tropomyosin as a Selective Allergen in a Case of Food Allergy: The Value of Individualized Molecular Analysis

Shellfish allergy is a common cause of IgE-mediated food hypersensitivity. Nevertheless, some patients exhibit selective or partial cross-tolerance among crustaceans and mollusks, posing diagnostic challenges. Tropomyosin is the major pan-allergen in crustaceans, yet its detectability may vary across commercial extracts and molecular assays, potentially leading to false-negative results.

A 44-year-old woman experienced respiratory symptoms immediately after ingesting small shrimps, while tolerating other crustaceans and all mollusks. Protein extracts were prepared from raw and cooked shrimp following standardized protocols. SDS-PAGE and Western blot were performed under reducing and non-reducing conditions, using the patient’s serum for IgE detection and a tropomyosin-specific IgG antibody to confirm protein identity.

Commercial skin prick tests for crustaceans and Anisakis were negative, whereas prick-to-prick testing with patient-provided fresh shrimp yielded a clear positive response. Serum IgE revealed sensitization to house dust mites but was negative for shrimp tropomyosin (rPen a 1) by molecular assay. SDS-PAGE of both raw and cooked extracts demonstrated a prominent ~37-kDa band. This band was recognized by the patient’s IgE in the Western blot, supporting its clinical relevance. Although rPen a 1 was negative on ISAC, the specific Western blot using anti-tropomyosin IgG confirmed that the reactive band corresponded to tropomyosin. These findings suggest selective recognition of isoforms present only in the shrimp species consumed by the patient.

This case underscores the diagnostic value of food-specific protein extracts when commercial assays yield negative results despite a suggestive clinical history. The identification of tropomyosin as the culprit allergen—despite negative commercial testing—highlights the importance of complementary techniques such as SDS-PAGE and IgE-Western blot for achieving precise, individualized allergological diagnoses. Tailored molecular analysis is essential to uncover clinically relevant sensitization patterns that standardized extracts or single-molecule assays may fail to detect.