Expression of the Alloantigen Zwa(or P1A1) on Human Vascular Smooth Muscle Cells and Foreskin Fibroblasts: A Study on Normal Individuals and a Patient With Glanzmann’s Thrombasthenia

The cytoadhesin family consists of platelet glycoprotein (GP) IIb-IIIa and the endothelial vitronectin receptor. The β subunit (GP IIIa) of these complexes expresses the alloan-tigen Zwa(or PIA1). This alloantigen is not expressed by members of other integrin subfamilies. By using immuno-precipitation and immunoblot techniques, we found that the β subunit of a heterodimer, expressed by cultured human arterial smooth muscle cells and cultured foreskin fibroblasts, carries the Zwaantigenic determinant. Furthermore, the mobilities of the aand βsubunits of these two heterodimers are indistinguishable from those of the aand βsubunits of the endothelial vitronectin receptor. Therefore, we propose that the smooth muscle cell and fibroblast heterodimer are members of the cytoadhesin family. In Glanzmann's thrombasthenia, platelet GP IIb-IIIa is absent or severely reduced. Previously, we showed that endothe- lial cells from a thrombasthenic patient normally synthesize and express a GP IIb-IIIa-related molecule (the vitronectin receptor). Here we show that arterial smooth muscle cells, obtained from the same patient, express a surface molecule indistinguishable from the endothelial vitronectin receptor. We also demonstrate that both the endothelial and the smooth muscle cell GP IIIa-related molecule in this Glanzmann patient express Zwa. Our data indicate that (a) GP IIb-IIIa-related molecules on cell types other than platelets and endothelial cells can express Zwa in vitro, and (b) patients with Glanzmann's disease can express the Zwa. antigen. This study substantiates our view that the defect in Glanzmann's disease is restricted to the megakaryo-cytes/platelets.