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 hepatocy tes 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. Inco rporation of SAA into HDL at concentrations equivalent to those found physi ologically in moderate inflammation mediated a 1.5-fold increase in the bin ding of HDL to adherent peripheral blood mononuclear cells but had no effec t 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 macro phages and an endothelial cell line, which may have functional significance in lipid metabolism or other macrophage responses during inflammation.