ABCB6 and atherosclerosis: Conversely, knockout of the cholesterol exporters Abca1 and Abcg1 increased macrophage proliferation in atherosclerosis, but also resulted in increased rates of apoptosis, suggesting that apoptosis dominates over proliferation of Mac-Abc-DKO macrophages (perhaps due to endoplasmic reticulum stress [9]), leading to a decrease in their number in advanced atherosclerosis.