The present invention provides a polypeptide dimeric protein containing two monomers, each of which contains an extracellular domain (FcεRIa-ECD) of an alpha subunit of an IgE Fc receptor. The dimeric protein according to the present invention has advantages that an excellent binding ability to IgE is exhibited as compared with a conventional therapeutic agent containing an anti-IgE antibody, and less other side effects are exhibited due to lack of ADCC and CDC functions. Thus, the dimeric protein can be applied to a medical product for treating or preventing an IgE-mediated allergic disease.本發明提供一種含有二個單體之多肽二聚蛋白，該單體各含有IgE Fc受體之α次單元的胞外區域(FcεRIa-ECD)。根據本發明之二聚蛋白的優點在於，相較於含有抗IgE抗體之習用治療劑，表現出極佳的IgE結合能力，以及由於無ADCC與CDC之功能，故表現出較少的其它副作用。因此，該二聚蛋白可應用於醫療產品，用於治療或預防IgE介導的過敏性疾病。
