Traditional Model of RCT in the Context of Atheroprotection (Adapted from Glomset and Ross).(2) 1) FC efflux from macrophages initiates the formation of discoidal nHDL, which contains FC, PL, and apo AI. 2) LCAT catalyzes the conversion of FC to CE, which forms a central core within spherical HDL. 3) SR-B1 selectively extracts lipids, especially FC and CE, from the mature HDL particle leaving an apo-rich remnant HDL (remHDL) particle and lipid-free apo AI that returns to another RCT cycle.