CETP and atherosclerosis: For example, in contrast to humans, rats carry cholesterol mainly in HDL particles due to low level of cholesteryl ester transfer protein (CETP), while CETP promotes transferring cholesterol esters from HDL to very low-density lipoprotein/low-density lipoprotein (LDL), and the low level of CETP in rats may explain why rats never develop atherosclerosis.