Neonatal Fc receptor (FcRn) – not only transporter of maternal IgG

Abstract

The neonatal Fc receptor, (FcRn) is a transmembrane, heterodimeric glycoprotein with a structure similar to MHC class I molecules. In contrast to MHC class I antigens, FcRn does not bind to peptides (antigens) but interacts with the Fc fragment of IgG and albumin. The FcRn-IgG interaction as well as the FcRn-albumin interaction occur at acidic pH (optimally at pH 5.0-6.5) but not in physiological environment. These two ligands bind to distinct binding sites on the receptor molecule and by different mechanisms. Now, it is known that the expression of FcRn is not restricted to sites involved in the transport of maternal IgG, and this receptor is not responsible only for transfer the passive immunity from mother to the offspring. But FcRn has a much broader range of expression and function, throughout life and in many different cell types and tissues of humans and animals. This review summarizes the status of our knowledge on the expression, interaction with ligands and functions of the neonatal Fc receptor. This article shows also the possibilities of utilizing a current knowledge on FcRn for therapeutic purposes.