A minimal receptor-Ig chimera of human FcεRI α-chain efficiently binds secretory and membrane IgE

We constructed a soluble minimal receptor-Ig chimera in which the two extracellular domains of human FceRI αchain (D1 and D2) were fused to the dimerizing C-terminal domain of human IgG1 heavy chain (γ1-CH3). The protein was expressed and actively secreted by Chinese hamster ovary (CHO) cells as a fully glycosylated soluble dimeric protein. It showed efficient binding both to human membrane-bound IgE isoforms and to the two secretory IgE isoforms. Moreover, the dimeric receptor binds IgE with the expected 1:2 stoichiometry. The receptor-Ig chimera, in 2-fold molar excess, inhibited engagement of secretory IgE to rat basophilic leukemia cells expressing the human αβγ receptor. Full self-nature and inability to bind Fcγ receptors make this protein an attractive candidate for clinical applications and a novel biotechnological tool for atopic allergy research.