Uptake ability of hepatic sinusoidal endothelial cells and enhancement by lipopolysaccharide

The liver is one of the major organs that remove exogenous substances and waste products from the blood circulation. Hepatic macrophages (Kupffer cells) and sinusoidal endothelial cells are responsible for the scavenger function of the liver. The sinusoidal endothelial cells, called scavenger endothelial cells, are believed to take up only soluble substances and nanometer-sized particles under normal conditions, while Kupffer cells can ingest larger particles and whole cells. However, the sinusoidal endothelial cells may have the potential to take up considerably large particles under special conditions. In this morphological study, we compared the uptake ability between sinusoidal endothelial cells and Kupffer cells after intravenous injections of latex beads (20 nm, 100 nm and 500 nm in diameter), bovine serum albumin (BSA) and dextran. Under normal conditions, the sinusoidal endothelial cells vigorously took up 100-nm-sized latex beads as well as 20-nm latex beads. BSA and dextran were ingested by the endothelial cells but not the Kupffer cells. The administration of lipopolysaccharide (LPS), which mimics inflammation, stimulated the uptake by endothelial cells. The uptake of latex beads by Kupffer cells was also elevated under LPS-stimulated conditions, but the uptake of BSA and dextran by them was not. These findings suggest that the sinusoidal endothelial cells can ingest not only soluble substances but also larger particles than those expected, and their uptake ability is strengthened under inflammatory conditions.