the primary ligand for p-selectin is p-selectin glycoprotein ligand-1 (psgl-1) which is expressed on almost all leukocytes, although p-selectin also binds to heparan sulfate and fucoidans. psgl-1 is situated on various hematopoietic cells such as neutrophils, eosinophils, lymphocytes, and monocytes, in which it mediates tethering and adhesion of these cells. however, psgl-1 is not specific for p-selectin, as it can also function as a ligand for both e- and l-selectin.