Ki67 has been extensively utilized to demonstrate lesion resident macrophage proliferation at various stages of human atherosclerosis, and it enables for accurate detection of cells that are actively proliferating that are not in the G0 phase of the cell cycle.22, 29, 30 We identified proliferating cells at various stages of lesion development in Apoe−/− mice fed a chow diet, with the predominant amount of cells appearing in the early (12 weeks old) and intermediate (24 weeks old) stages of atherosclerosis. The gene discussed is MKI67; the disease is atherosclerosis.