Membrane-bound immunoglobulin E CεmX domain (CεmX domain)

The CεmX domain is a 52-amino acid membrane-proximal extracellular sequence unique to membrane-bound IgE (mIgE) present on the surface of human B cells, but absent from soluble IgE and other immunoglobulins. It is generated by alternative splicing of the IgE heavy chain transcript and plays a regulatory role in B cell receptor function — restricting surface expression and limiting cell activation. The domain is intrinsically disordered, allowing antibodies to target flexible peptide segments for cell-specific cytotoxicity. Because mIgE-expressing B cells are essential for sustained IgE production and allergic pathology, the CεmX domain has become a promising target for monoclonal antibody therapies aiming to selectively eliminate these cells, thereby reducing IgE levels and modulating allergic responses. Drugs such as quilizumab exploit this mechanism, showing potential in clinical trials for severe allergies and asthma.

Other names

CεmX domainM1' regionExtracellular membrane-proximal domain (EMPD) of membrane-bound IgE

Binding to and cross-linking of the CεmX domain on mIgE-expressing B cells can induce: - B cell lysis (cytolytic effect) - Downregulation of IgE production - Antibody-dependent cellular cytotoxicity (ADCC) - Complement-mediated cytotoxicity (CDC)