Apolipoprotein-E (ApoE) is composed of 299 amino acids and transports lipoproteins, fat-soluble vitamins, and cholesterol into the lymph system and then into the blood. It is synthesized principally in the liver, but has also been found in other tissues such as the brain, kidneys, and spleen. In the nervous system, non-neuronal cell types, most notably astroglia and microglia, are the primary producers of ApoE, while neurons preferentially express the ApoE receptors. There are seven currently identified mammalian receptors for ApoE which belong to the evolutionarily conserved low density lipoprotein receptor gene family.