THE PLATELET ALLOANTIGEN Zw^a (P1^A1) IS EXPRESSED BY CULTURED ENDOTHELIAL CELLS

Zw^a (P1^A1) 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 Zw^a. 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 Zw^a on platelets, isolated from umbilical cord blood, with the expression of Zw^a 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 Zw^a (Zw^a positive individuals) or lacked expression of Zw^a (Zw^a negative individuals). These findings strongly suggest that endothelial-and platelet Zwa are encoded by the same genes.

Thus, Zw^a is not exclusively expressed by platelets, also endothelial cells express this alloantigen.

An important consequence could be, that in alloimmunologic disorders in which the Zw^a antigen is implicated, not only the platelets, but also the vessel wall is involved.