Complementary DNA of human lgE Icε fragment (residues 226–480) lacking the Cϕ domain was expressed in Escherichia coli and the product was purified by immunoaffinity chromatography on a monoclonal antibody (E12 0.02)-Affi-Gel 10 column. About 1.8 mg of an apparent dimer and 5.9 mg of a monomer were obtained from 65 g E. coli cells with 9.3% recovery. The purified products were found to lack more than half of the COOH-terminal portion of the Cε3 domain. The apparent dimer showed high immunological specific activity (3.6 × 106 U/mg protein) comparable to that of natural human IgE when measured by commercial human IgE determination kits.
