Acute Phase Serum Amyloid A Protein Increases High Density Lipoprotein Binding to Human Peripheral Blood Mononuclear Cells and an Endothelial Cell Line

Serum Amyloid A (SAA) is an acute-phase protein secreted mainly by hepatocytes and is largely associated with high-density lipoprotein (HDL) in plasma. It has been suggested that SAA alters HDL binding to the cell surface and that this in turn changes HDL-mediated cholesterol delivery to cells. Incorporation of SAA into HDL at concentrations equivalent to those found physiologically in moderate inflammation mediated a 1.5-fold increase in the binding of HDL to adherent peripheral blood mononuclear cells but had no effect on binding of the lipoprotein to the monocyte cell lines, U937 or THP-1. SAA incorporation also increased binding to an endothelial cell line, EA.hy.926. Hepatoma cells (HuH-7) showed no change in specific binding of the SAA-enriched HDL particle compared to normal HDL. These results suggest that a specific receptor for HDL-bound SAA is found on differentiated human macrophages and an endothelial cell line, which may have functional significance in lipid metabolism or other macrophage responses during inflammation.