IgE reactivity against a cross-reactive allergen in crustacea and mollusca: Evidence fev tropomyosin as the common allergen

Background: Although cross-reactivity between mollusks and other crustaceans in shrimp-sensitive subjects has been reported, the mechanism of this allergenic cross-reactivity has not been studied in detail. Objective: To investigate this cross-reactivity in vitro, we have taken advantage of a complementary DNA that expresses tropomyosin, the immunodominant shrimp allergen. Methods: Serum IgE from nine patients with known anaphylaxis to shrimp and five normal volunteers were analyzed by immunoblotting against 13 distinct crustaceans and mollusks. As additional antigens, muscle preparations were isolated from grasshopper, cockroach, fruit fly, chicken and mouse. Results: Sera from all patients, but not control subjects, reacted specifically with a 38 kd protein in all crustaceans and mollusks studied. In addition, 8 of 9 sera from patients, but from none of the normal control subjects, recognized proteins of various other molecular weights among the mollusk extracts studied. The 38 kd protein was identified as tropomyosin and was shown to share immunodominant epitopes among all species of crustaceans and mollusks tested by specific absorption studies. Moreover, sera from all nine subjects with shrimp allergy demonstrated IgE reactivities against grasshopper, cockroach, and fruit fly but not chicken or murine muscle. Conclusion: The allergic epitopes on tropomyosin are conserved among invertebrates including not only shellfish but also insects. This latter observation suggests that persons sensitive to shrimp should undergo further study for potential cross-reactive inhalant or ingested insect sensitivity.