**Apolipoprotein A1 (ApoA1)** is the primary structural protein component of High-Density Lipoprotein (HDL), commonly known as "good cholesterol." Produced mainly in the liver and intestine, ApoA1 plays a critical role in **reverse cholesterol transport**—a protective process where excess cholesterol is collected from peripheral tissues and artery walls, then transported back to the liver for excretion. Additionally, ApoA1 acts as a cofactor for lecithin-cholesterol acyltransferase (LCAT), an enzyme essential for converting free cholesterol into esterified forms for transport. Higher circulating levels of ApoA1 are strongly associated with reduced cardiovascular risk, anti-inflammatory defense, and improved vascular endothelial function.