A sialoglycoprotein from human leukocytes functions as a ligand for P-selectin.

P-selectin (CD62P), a Ca(2+)-dependent lectin expressed on activated platelets and endothelial cells, functions as a receptor for myeloid and monocytoid cells. Previous reports have described a homodimeric sialoglycoprotein from human leukocytes and HL-60 cells specifically recognized by P-selectin. We describe here a panel of monoclonal antibodies prepared against high molecular weight fractions of HL-60 cell membranes. These antibodies are of IgM isotype, bind to a approximately 240-kDa protein from human leukocyte membranes which is also reactive with P-selectin. They recognize a Ca(2+)-dependent, sialidase-sensitive determinant on myeloid and monocytoid cell lines. Each antibody specifically inhibits adhesion of neutrophils or HL-60 cells to: 1) purified P-selectin, 2) thrombin-stimulated platelets, and 3) phorbol 12-myristate 13-acetate-activated endothelial cells. These results suggest that the sialoglycoprotein recognized by this panel of monoclonal antibodies may function as a cell surface ligand for P-selectin.