HEAT-STABLE ANTIGEN (CD24) AS LIGAND FOR MOUSE P-SELECTIN

Heat-stable antigen (HSA)/CD24 is a cell surface molecule expressed by many cell types in the mouse. The molecule has an unusual structure b ecause of its small protein core and extensive glycosylation. In order to study the functional role of the HSA-associated glycoconjugates we have isolated different forms of HSA. Using lectin analysis we provid e evidence for extensive heterogeneity in carbohydrate composition and sialic acid linkage. Several HSA forms were recognized by mouse P-sel ectin-IgG but not E-selectin-IgG in ELISA. As expected, P-selectin-IgG also bound to L2/HNK-1-positive neural glycoproteins (L2-glycoprotein s) and sulfatides but not to gangliosides and other control glycoprote ins. The binding of P-selectin-IgG to L2-glycoproteins and HSA require d bivalent cations. The reactivity to HSA was sensitive to sialidase t reatment whereas the binding to L2-glycoproteins was not. Studies with alpha2-6 sialytransferase indicated that alpha2 - 6 linked sialic aci d was not involved in the P-selectin binding to HSA. Surprisingly, an L2/HNK-1 specific antibody was found to cross-react with some HSA glyc oforms and its binding correlated with P-selectin-IgG reactivity. L2/H NK-1-positive or L2/HNK-1-negative HSA glycoforms were also analyzed a fter coating to polystyrene beads. Only the L2/HNK-1-positive HSA coat ed beads were reactive with P-selectin-IgG and could bind to activated bend3 endothelioma cells expressing P-selectin whereas the L2/HNK-1-n egative HSA beads did not. It is suggested that in its L2/HNK-1 modifi ed form the HSA molecule on leukocytes could represent a ligand for P- selectin on endothelial cells or platelets.