protein_function: Binds to the Fc region of monomeric immunoglobulinsgamma. Mediates the selective uptake of IgG from milk and helpsnewborn animals to acquire passive immunity. IgG in the milk isbound at the apical surface of the intestinal epithelium. Theresultant FcRn-IgG complexes are transcytosed across theintestinal epithelium and IgG is released from FcRn into blood ortissue fluids.
The neonatal Fc receptor (FcRn), also known as the Brambell receptor, is a protein that in humans is encoded by the FCGRT gene. The neonatal Fc receptor is an Fc receptor which is similar in structure to the MHC class I molecule and also associates with beta-2-microglobulin. It was first discovered in rodents as a unique receptor capable of transporting IgG from mother"s milk across the epithelium of newborn rodent"s gut into the newborn"s bloodstream. Further studies revealed a similar receptor in humans, leading to the naming as a neonatal Fc receptor. In humans, however, it is found in the placenta to help facilitate transport of mother"s IgG to the growing fetus and it has also been shown to play a role in monitoring IgG turnover. Neonatal Fc receptor expression is up-regulated by the proinflammatory cytokine,TNF-??, and down-regulated by IFN-??.