IgG receptor FcRn large subunit p51 (FcRn)

The rat neonatal Fc receptor heavy chain (FcRn), encoded by the Fcgrt gene, is a transmembrane glycoprotein that forms a heterodimer with beta-2 microglobulin (B2M) [UniProt: P13599]. It is structurally related to MHC class I molecules but functions primarily as a transporter and recycler of immunoglobulin G (IgG) and albumin [PubMed: 25210042]. In neonatal rats, FcRn facilitates the transfer of maternal IgG from milk across the intestinal epithelium to the bloodstream, providing passive immunity [PubMed: 1613032]. In adults, it is expressed in endothelial and epithelial cells, where it rescues IgG and albumin from lysosomal degradation by binding them in acidic endosomes and releasing them back into the circulation at physiological pH [PubMed: 15546383]. This mechanism is responsible for the exceptionally long half-life of these proteins. Therapeutically, FcRn is a high-priority target for autoimmune diseases characterized by pathogenic IgG autoantibodies, such as myasthenia gravis and immune thrombocytopenia [PubMed: 30333301]. Inhibiting FcRn leads to a rapid reduction in circulating IgG levels, offering a targeted approach to clearing autoantibodies without broad immunosuppression. The rat model is frequently used in preclinical development to study the pharmacokinetics of Fc-containing biologics and the efficacy of FcRn antagonists [PubMed: 29113815].

Other names

Neonatal Fc receptor heavy chainFc fragment of IgG receptor and transporterFCGRTBrambell receptorMHC class I-like antigen

Competitive inhibition of the neonatal Fc receptor (FcRn) to prevent the recycling of immunoglobulin G (IgG), thereby accelerating the degradation of pathogenic autoantibodies.