THE PLATELET ALLOANTIGEN Zwa (P1A1) IS EXPRESSED BY CULTURED ENDOTHELIAL CELLS

Zwa (P1A1) is a platelet specific alloantigen, located on glycoprotein (GP) IIIa, and is of pathogenic importance in alloimmunologic disorders such as neonatal alloimmune thrombocytopenia and post transfusion purpura. As endothelial cells synthesize a plasma membrane protein complex which is structurally closely related to the platelet membrane GP IIb/IIIa complex, we examined whether these cells also express Zwa. Employing a variety of immunochemical techniques, our studies show that endothelial cells indeed can express this antigen at the plasma membrane surface.We also compared the expression of Zwa on platelets, isolated from umbilical cord blood, with the expression of Zwa on cultured endothelial cells, isolated from the same umbilical cord, of a number of neonates. Both platelets and endothelial cells obtained from the same individual, either expressed Zwa (Zwa positive individuals) or lacked expression of Zwa (Zwa negative individuals). These findings strongly suggest that endothelial-and platelet Zwa are encoded by the same genes.Thus, Zwa is not exclusively expressed by platelets, also endothelial cells express this alloantigen.An important consequence could be, that in alloimmunologic disorders in which the Zwa antigen is implicated, not only the platelets, but also the vessel wall is involved.