P-SELECTIN GLYCOPROTEIN LIGAND-1 IS THE MAJOR COUNTER-RECEPTOR FOR P-SELECTIN ON STIMULATED T-CELLS AND IS WIDELY DISTRIBUTED IN NONFUNCTIONAL FORM ON MANY LYMPHOCYTIC CELLS

P-selectin glycoprotein ligand-1 (PSGL-1) is the high affinity counter-receptor for P-selectin on myeloid cells (Sako, D., Chang, X. J., Barone, K. M., Vachino, G., White, H. M., Shaw, G., Veldman, G. M., Bean, K. M., Ahern, T. J., Furie, B., Cumming, D. A., and Larsen, G. R. (1993) Cell 75, 1179-1186). Here we demonstrate that PSGL-1 is also widely distributed on T- and B-lymphocytic tumor cell lines, resting peripheral blood T and B cells, and on stimulated peripheral blood T cell and intestinal intraepithelial lymphocyte (IEL) lines. However, the majority of PSGL-1-positive resting peripheral blood lymphocytic cells and lymphoid tumor cell lines do not display significant P-selectin binding. In contrast, in vitro stimulated peripheral blood T cell and IEL lines avidly bind P-selectin, and PSGL-1 is the sole high affinity counter-receptor mediating this binding. During the course of in vitro stimulation, cell surface expression levels of PSGL-1 do not change as P-selectin binding increases. Rather, the activities of two glycosyltransferases reportedly involved in the production of functional PSGL-1 in myeloid cells are substantially higher in the stimulated T-lymphocytic lines than in resting T lymphocytes, consistent with the hypothesis that activation-dependent post-translational events contribute to the expression of functional PSGL-1 on lymphocytes.