Role of L-selectin on leukocytes in the binding of sialic acids on sperm surface during the phagocytosis of sperm in female reproductive tract.

In either natural fertilization or artificial insemination, hundreds of millions of sperm are ejaculated or inseminated and then deposited in the female reproductive tract, but only a few sperm reach the ampulla or the site of fertilization. This dramatic reduction in numbers clearly highlights the obstacles that sperm must overcome in order to reach the destination for egg fertilizing. Phagocytosis of sperm by leukocytes are repeatedly observed and generally considered to be one of the most important barriers, but the mechanism of the phagocytosis of sperm remains unclear. L-selectin is constitutively expressed on leukocytes, which can influence the behaviors of leukocytes when bind to ligands. Sialic acids are found as the outer most monosaccharide, capping the majority of glycans at the sperm surface, can act as recognition molecule. Since the sialic acids are considered as ligands of L-selectin, we propose that leukocytes bind to the sperm through the L-selectin on leukocytes and sialic acid on sperm surface during the sperm phagocytosis in female reproductive tract.