Fc fragment of IgG receptor and transporter (FcRn)

Murine FcRn, or the neonatal Fc receptor, is a heterodimeric transmembrane protein composed of a heavy chain (encoded by the Fcgrt gene) and a light chain (beta-2-microglobulin). It is structurally related to MHC class I molecules and plays a pivotal role in regulating the homeostasis of immunoglobulin G (IgG) and albumin by protecting them from lysosomal degradation. This protection occurs via a pH-dependent recycling mechanism where FcRn binds ligands in acidic endosomes and releases them back into the bloodstream at neutral pH. In mice, FcRn is also responsible for the transfer of maternal antibodies to neonates across the intestinal epithelium, providing passive immunity. Therapeutically, FcRn is a major target for treating IgG-mediated autoimmune diseases, such as myasthenia gravis and immune thrombocytopenia, where inhibitors are used to accelerate the clearance of pathogenic autoantibodies. Furthermore, the receptor is a key focus in pharmacokinetics, as engineering therapeutic proteins for higher FcRn affinity can significantly extend their serum half-life.

Other names

Neonatal Fc receptorFcgrtIgG receptor FcRn large subunit p51Fc receptor IgG alpha chain transporterIgG Fc fragment receptor transporter alpha chainp51

Inhibition of the FcRn-IgG interaction to accelerate the catabolism of pathogenic IgG antibodies through a pH-dependent recycling pathway.