Macrophages have several pathways for efflux of cholesterol. They efflux free cholesterol to lipid-poor apoA-I via the ABCA1 pathway and to mature HDL via the ABCG1 pathway. Both ABCA1 and ABCG1 are regulated by the nuclear receptor LXR, which is activated by binding of oxysterols, derived from free cholesterol. SR-BI also has the capacity to efflux free cholesterol to mature HDL.