L-Selectin is a type of protein found on the surface of certain white blood cells, particularly lymphocytes and neutrophils. It plays a crucial role in the immune system by helping these cells adhere to the walls of blood vessels, allowing them to exit the bloodstream and reach sites of inflammation or infection. This adhesion process is essential for the immune response, as it enables white blood cells to migrate to tissues where they are needed. L-Selectin interacts with specific carbohydrates on the endothelial cells lining blood vessels, facilitating the movement of immune cells to areas requiring defense against pathogens.