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 ligan ds for E-selectin on HUT78, a skin-homing cutaneous T-cell lymphoma. T hese cells possessed high surface expression of the KM-93 epitope but not HECA 452 or CSLEX1 epitopes. The KM-93 antibody also blocked the b inding of HUT78 cells to E-selectin. All these antibodies are reported to recognize sialyl Lewis X (sLe(x))-like molecules. Using an E-selec tin affinity matrix, the main glycoprotein isolated from HUT78 cells w as a molecular species of 90000 MW. Other minor species of molecular w eights 40000, 60000, 100000, 120000 and 200000 were also identified as potential counter-receptors for E-selectin. Four of the purified coun terreceptors (90000, 100000, 120000 and 200000 MW) stained positive wi th the KM-93 antibody. Immunoblot analysis of these purified glycoprot eins established the identity of the 90000 MW glycoprotein as L-select in. Furthermore, an anti-L-selectin antibody inhibited the binding of HUT78 cells to E-selectin, probably by steric inhibition of the carboh ydrate 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.