Sialyl lewis x

Sialyl LewisX, also known as sialyl LeX and SLeX, is a tetrasaccharide carbohydrate that is usually attached to O-glycans on the surface of cells. It is known to play a vital role in cell-to-cell recognition processes. It is also the means in which an egg attracts sperm - first to stick to it and eventually to bond with it and eventually form a fetus. The discovery of the essential role that this tetrasaccharide plays in the fertilization process was made in August of 2011.

Sialyl Lewis X is also one of the most important blood group antigens and is displayed on the terminus of glycolipids that are present on the cell surface. The Sialyl Lewis X determinant, E-selectin ligand carbohydrate structure, is constitutively expressed on granulocytes and monocytes and mediates inflammatory extravasation of these cells. Resting T and B lymphocytes lack its expression and are induced to strongly express sialyl Lewis X upon activation. The Sialyl Lewis X determinant is expressed preferentially on activated Th1 cells but not on Th2 cells.

Clinical significance
Defective synthesis of the sialyl Lewis X antigen results in immunodeficiency (leukocyte adhesion deficiency type 2). Defective synthesis can be caused by the loss of fucosyltransferase, impairing the glycosylation of the glycosphingolipid.