Cloning and characterization of recombinant tropomyosin of giant freshwater shrimp M. rosenbergii to determine major allergens causing allergic reactions among shrimp-allergic children.

BACKGROUND Seawater and freshwater shrimp are some of the most common causes of food allergy among children in Thailand. Tropomyosin has been reported as a major allergen for shrimp allergic populations around the world. Despite a high number of shrimp-allergic Thai children, however, it is unknown whether shrimp tropomyosin is a major cause of allergic reactions. OBJECTIVES To clone and characterize tropomyosin of giant freshwater shrimp Macrobrachium rosenbergii (Mr) and determine whether this tropomyosin is a major cross-reactive allergen for Thai children with shrimp allergy. METHODS Recombinant shrimp Mr tropomyosin (Mac r1.0101) was expressed in yeast Pichia pastoris. Secondary structure composition of purified recombinant Mac r1.0101 was determined by Circular Dichroism. IgE reactivity was examined by immunoblot, direct binding ELISA and inhibition of IgE ELISA using serum from shrimp-allergic children. RESULTS AND CONCLUSION The amino acid sequence of Mac r1.0101 showed 2 polymorphic amino acids (F44 and S45) indicating a variant of tropomyosin. Purified recombinant Mac r1.0101 obtained a nature-like α-helix structure which can be bound by serum-specific IgE. The binding affinity of serum-specific IgE to Mac r1.0101 based on the IC50 value was ~1.8 ng/ml. Ten of 13 shrimp-allergic Thai children had serum-specific IgE against Mac r1.0101, but at different levels. Results of the inhibition of specific IgE using Mac r1.0101 showed that 7 of the tested serum samples also had specific IgE against other shrimp allergens in addition to IgE against Mac r1.0101. Tropomyosin therefore appears to be a major cross-reactive allergen for Thai children who are allergic to both seawater and giant freshwater shrimp.