The platelet glycoprotein Ia-IIa-associated Br-alloantigen system is expressed by cultured endothelial cells.

To obtain information on the immunological relationship between the endothelial and platelet glycoprotein (GP)Ia-IIa (VLA-2) complex, we studied whether endothelial GPIa-IIa was able to express the platelet GPIa-IIa-associated Br-alloantigen system. Therefore, we tested antisera to both allelic forms of the Br system (Bra and Brb) on platelets (by an assay based on monoclonal antibody-specific immobilization of platelet antigens, MAIPA) and on cultured umbilical vein endothelial cells (by immunoprecipitation experiments) from the same individual. Endothelial cells from a platelet Br(a + b +), and from a platelet Br(a - b +) individual were studied. Our results indicate that endothelial GPIa-IIa is indistinguishable from platelet GPIa-IIa in its ability to express the Bra and Brb alloantigens. The association of Br alloantigens with endothelial GPIa-IIa was confirmed by the results of an assay based on monoclonal antibody-specific immobilization of endothelial antigens (MAIEA). These data further illustrate the structural and immunologic similarity of platelet and endothelial cell GPIa-IIa (VLA-2).