FcRN (the neonatal Fc receptor) is a transmembrane MHC class I-like glycoprotein that is widely expressed on endothelial and epithelial cells. Mouse FcRN binds with high affinity to IgG from mouse, human, rat, rabbit, guinea pig, bovine, and sheep, while human FcRN binds IgG with significantly lower affinity and is much more restricted in terms of species recognition. It additionally binds to Albumin and beta 2-Microglobulin. FcRN is involved in recycling endocytosed IgG and Albumin, the bidirectional transport of IgG across epithelial and endothelial barriers, and intestinal uptake of maternal antibodies by the fetus. In the kidney, FcRN recycles Albumin to the serum but removes IgG from the glomular basement membrane and promotes its excretion into the urine. FcRN can also enhance IgG-mediated phagocytosis and antigen presentation by neutrophils and myeloid antigen presenting cells.