Role of tropomyosin in silkworm allergy

Silkworm pupae are widely consumed in Asian countries and allergic reactions following consumption have been described. However, false-positive responses in skin prick allergy tests or non-specifc immunoglobulin E (IgE) responses to total extract of silkworm pupa make diagnosis diffcult. Although improved allergy diagnosis is required, molecular characterization of silkworm allergens has not been performed to date, except for Bomb m 1, an arginine kinase. This study aimed to evaluate the allergenicity of tropomyosin, a well-established invertebrate pan-allergen, from silkworm pupa. The silkworm tropomyosin gene was cloned by reverse transcription and polymerase chain reaction, and the protein was overexpressed in Escherichia coli and purifed by affnity chromatography using Nickel-resin. IgE reactivity of the recombinant protein was examined by ELISA and competitive inhibition analyses. Silkworm pupa tropomyosin shared 73.5-92.3% amino acid sequence identity with previously identifed allergenic tropomyosins. Sera from eight of 15 patients with silkworm allergy (53.3%) exhibited binding of IgE to the recombinant protein. However, recombinant protein was able to inhibit less than 10% of IgE reactivity to silkworm pupa extract. Of the eight sera tested, six that specifcally reacted with silkworm tropomyosin also demonstrated IgE reactivity to shrimp and crab. In the present study, specifc IgE to silkworm tropomyosin was detected in patients with silkworm allergy, suggesting that it may be useful in diagnosis of allergy to silkworm pupa.