The neonatal Fc receptor (FCRN) is an approximately 45 kDa transmembrane glycoprotein with structural homology to MHC class I proteins. It is widely expressed in endothelial and epithelial cells and plays an important role in IgG homeostasis and antigen presentation by dendritic cells.FCGRT & B2M heterodimer protein (FcRn complex) consist of two subunits: p51, and p14 , and forms an MHC class I-like heterodimer.