SLEX

Sialyl Lewis X (sLe^x) is a membrane-associated tetrasaccharide carbohydrate antigen with the structure Neu5Ac α2-3 Gal β1-4(Fuc α1-3) GlcNAc-R. It is carried on glycoproteins and glycolipids, particularly on leukocytes and endothelial cells, where its expression is regulated during development and inflammation.

sLe^x functions as a ligand for selectins, notably E-selectin and P-selectin, mediating the initial steps of leukocyte rolling and tethering on activated endothelium. This adhesive interaction facilitates leukocyte extravasation to sites of inflammation and, in some contexts, contributes to tumor cell adhesion to the vascular endothelium during metastasis.

Biosynthesis of sLe^x involves sequential glycosylation steps. First, a Lewis X motif (Gal β1-4 GlcNAc with Fuc α1-3) is formed by fucosyltransferases such as FUT3 and related enzymes. Then, sialylation by α2-3 sialyltransferases (e.g., ST3Gal family) adds the Neu5Ac to generate sLe^x. Expression on the cell surface is controlled by the activity of these glycosyltransferases, including FUT7, which is particularly important for leukocyte sLe^x presentation.

clinically, sLe^x is studied as a biomarker in inflammatory diseases and some cancers. Its presence on tumor cells can promote hematogenous spread by enabling binding to selectins on endothelium. Research continues on targeting selectin–sLe^x interactions for therapeutic purposes.

Detection methods include specific antibodies and lectins, flow cytometry, and mass spectrometry, used to quantify or localize sLe^x on cells and glycoproteins.