From 1949-1966, a series of experimental studies by Professor F. W. Rogers Brambell (1901-1970; memoirs (1)) revealed the transmission of immunoglobulin from the mother to the fetus and newborn (2-4). In 1966, he published a review article in The Lancet describing that the selective transmission of γ-globulin from the mother to the offspring could occur before birth and also after birth and that this process required the Fc portion of the γ-globulin molecule. He speculated that the transmission involved the Fc portion of the γ-globulin molecule interacted with specific receptors on the cell (2). Electron microscopy and biochemical analyses later revealed the presence of a Fc receptor on neonatal rat small intestinal cells that selectively permitted the transport of immunoglobulin of the IgG subclasses across the intestinal epithelium in a pH-dependent manner (5-10). Finally, in 1989, Simister and Mostov affinity purified FcRn from an eleven-day old rat intestine; and identified two proteins with the relative molecular masses of about 14,000 Da and 45,000-53,000 Da which were identified as β2-microglobulin and neonatal Fc receptor (FcRn), respectively. Molecular analyses revealed the FcRn to have the predictive primary structure similar to that of class I major histocompatibility complex (MHC) antigens as it possessed three extracellular alpha domains, a single transmembrane region and a short cytoplasmic domain (11) which was later confirmed by X-ray crystallographic analyses (12, 13).