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 endotheial 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.