Scavenger receptor class B type 1 (SRB1) also known as SR-BI is a protein that in humans is encoded by the SCARB1 gene. SR-BI functions as a receptor for high-density lipoprotein. SR-BI is an integral membrane protein found in numerous cell types/tissues, including enterocytes, the liver and adrenal gland. It is best known for its role in facilitating the uptake of cholesteryl esters from high-density lipoproteins in the liver. This process drives the movement of cholesterol from peripheral tissues towards the liver, where cholesterol can either be secreted via the bile duct or be used to synthesise steroid hormones. This movement of cholesterol is known as reverse cholesterol transport and is a protective mechanism against the development of atherosclerosis, which is the principal cause of heart disease and stroke. SR-BI is crucial in carotenoid and vitamin E uptake in the small intestine. SR-B1 is upregulated in times of vitamin A deficiency and downregulated if vitamin A status is in the normal range. SCARB1 along with CD81 is the receptor for the entry of the Hepatitis C virus into liver cells.