[Neonatal Fc receptor, key control of immunoglobulins biodistribution]

In 1969, Brambell, while studying the long serum half-life of IgG and their ability to cross the materno-foetal barrier, attributed these two properties to the existence of a specific Fc receptor, which was later denominated FcRn for neonatal Fc receptor. The resolution of its structure revealed that it is a MHC class-I-like molecule. FcRn is able to load IgG and albumin in a pH-dependent manner. It acts as an intracellular transport protein and as such is controling the serum half-life of these proteins (apical recycling of IgG and albumin in endothelial cells), IgG biodistribution (apical to basolateral and basolateral to apical transport of IgG in epithelial and endothelial cells) and it may also contribute to phagocytosis. FcRn is thus a key partner in the pharmacokinetics of therapeutic antibodies, opening interesting prospects for optimisation of their use.