Trem1−/− mice were backcrossed onto the atherosclerosis-susceptible Apoe−/− background and 6–8-week-old female Trem1−/−Apoe−/− and Trem1+/+Apoe−/− mice were concurrently placed on a high-fat, high-cholesterol-containing diet (HFCD). This evidence concerns the gene APOE and atherosclerosis.