Figure 4.

FcRn in the liver is essential for vectorial delivery of albumin into the blood stream. (1) Hepatocytes are polarized epithelial cells of which the apical side (red) faces the bile duct, and the basolateral side (black) faces the fenestrated sinusoidal endothelium. The sinusoidal endothelium is populated by liver specific macrophages called Kupffer cells. Albumin is produced solely by hepatocytes. (2) FcRn in hepatocytes is required for delivery of newly synthesized albumin to the basolateral side of the cells, and subsequent secretion of albumin to the blood stream (left) (3) Absence of FcRn expression in hepatocytes results in increased albumin levels in the bile, its intracellular accumulation and lower circulating albumin levels (right). For simplicity, FcRn-mediated albumin recycling in hepatocytes is not depicted.