Background The presence of specific IgE antibodies to invertebrates is common among patients with rhinitis and asthma. Tropomyosin has been described as an invertebrate cross-reactive allergen. We have recently characterized an allergenic extract from silverfish (Lepisma saccharina). Since this insect could be a new source of tropomyosin in the indoor environment, we have thought important to clone and characterize the tropomyosin from it.
Methods Recombinant tropomyosin was cloned and characterized by means of immunoblotting with tropomyosin-specific monoclonal antibodies, rabbit polyclonal antibodies and IgE from allergic patients. Its allergenic activity was investigated in histamine release assays. Immunoblotting and ELISA inhibition were carried out to identify the natural tropomyosin in the silverfish extract and to study the cross-reactivity among other arthropod tropomyosins.
Results Tropomyosin-specific antibodies recognized in immunoblotting the natural tropomyosin in the insoluble fraction of silverfish extract. The silverfish tropomyosin (Lep s 1) was cloned and fully expressed. It shared high homology with other arthropod tropomyosins. rLep s 1 was recognized by tropomyosin-specific monoclonal and polyclonal antibodies and by IgE of allergic patients. It was able to inhibit the IgE binding to the insoluble fraction of silverfish extract, and to induce histamine release by an arthropod-allergic serum. Inhibition experiments revealed IgE cross-reactivity between rLep s 1 and other arthropod tropomyosins.
Conclusion rLep s 1 is the first allergen cloned and characterized from silverfish extract. It enabled us to identify the natural counterpart in the insoluble fraction of silverfish extract, suggesting that the tropomyosin is not readily extractable with a classic aqueous extraction procedure. rLep s 1 displayed biological activity, suggesting that it could be regarded as a useful tool to study the role of silverfish tropomyosin in the sensitization to invertebrate allergic sources.