To test the hypothesis that enhanced cholesterol efflux in macrophages contributed to the reduction in the development of atherosclerosis in miR-33−/−Apoe−/− mice, cholesterol efflux to apoA-I and HDL-C was measured using 3H-cholesterol-labeled acetylated low-density lipoprotein (acLDL). This evidence concerns the gene APOA1 and atherosclerosis.