Characterization of E-selectin-binding epitopes expressed by skin-homing T cells

The glycoprotein counter-receptors for E-selectin borne on skin-homing T cells are poorly defined. In this study we have used flow cytometry to investigate the surface expression of potential carbohydrate ligands for E-selectin on HUT78, a skin-homing cutaneous T-cell lymphoma. These cells possessed high surface expression of the KM-93 epitope but not HECA 452 or CSLEX1 epitopes. The KM-93 antibody also blocked the binding of HUT78 cells to E-selectin. All these antibodies are reported to recognize sialyl Lewis X (sLex)-like molecules. Using an E-selectin affinity matrix, the main glycoprotein isolated from HUT78 cells was a molecular species of 90 000 MW. Other minor species of molecular weights 40 000, 60 000, 100 000, 120 000 and 200 000 were also identified as potential counter-receptors for E-selectin. Four of the purified counter-receptors (90 000, 100 000, 120 000 and 200 000 MW) stained positive with the KM-93 antibody. Immunoblot analysis of these purified glycoproteins established the identity of the 90 000 MW glycoprotein as l-selectin. Furthermore, an anti-l-selectin antibody inhibited the binding of HUT78 cells to E-selectin, probably by steric inhibition of the carbohydrate ligand for E-selectin that is borne on the C-type lectin domain of l-selectin. These results suggest that a carbohydrate epitope on l-selectin may act as a ligand for E-selectin on skin-homing T cells.