Serum is a rich source of ligands for the scavenger receptor on hepatic sinusoidal endothelial cells

The present study was undertaken to characterize the substances in serum th at effectively inhibit endocytosis via the hepatic sinusoidal endothelial c ell (SEC) scavenger receptor (SR). Experiments with SEC in vitro showed tha t serum inhibits endocytosis of formaldehyde treated serum albumin and nido gen, that are ligands for the SR, by up to 80 %. Fractionation of serum on anion exchange and chromatofocusing chromatography revealed that the inhibi tory substances are several highly negatively charged macromolecules of var ying size. Endocytosis of non-SR ligands like mannan and collagen a-chains was not affected by fractionated serum. Intravenous injection of adduct-lab elled fractionated serum revealed that the liver was the main site for elim ination, and isolation of liver cells showed that SEC contained 75-80 % of liver radioactivity. Receptor specificity studies indicated that the negati vely charged serum fraction was internalized mainly by the SEC SR.