Macrophages internalize aggregated low density lipoprotein (LDL) byReceived January 22, 1990; revision accepted July 13, 1991. (LDL) by the LDL receptor. 2 When excess cholesterol accumulates, cholesterol synthesis is repressed and the number of LDL receptors is downregulated, thereby decreasing the internalization of LDL. Because LDL receptor activity is tightly coupled to the amount of free cholesterol in cells, it is likely that a pathway distinct from LDL receptor-mediated endocytosis is responsible for the pathological accumulation of cholesterol. 1 -2 Apolipoprotein B-100 is the ligand for the binding of LDL to its receptor. 2 When the lysine residues of apolipoprotein B-100 are acetylated, LDL receptor recognition is lost. 1 -3 Macrophages possess another cell-surface receptor, the scavenger receptor, that binds and internalizes altered forms of LDL, including acetylated LDL, malondialdehyde-modified LDL, and oxidized LDL. 1 -3 -5 -7 In contrast to the LDL Downloaded from http://ahajournals.org by on April 3, 2019