EXPRESSION OF PLATELET ALLOANTIGENS ON HUMAN ENDOTHELIAL CELLS AND HEL CELLS

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Analogs of platelet membrane glycoproteins IIb and IIIa (GPIIb-IIIa) have been shown to be synthesized and expressed by human endothelial cells (HEC), a human erythroleukemia cell line (HEL) and various other cells. Previous studies from our laboratory demonstrated that the platelet alloantigen P1A1, is expressed on HEC GPIIIa. Other alloantigen systems, namely, Pen and Bak, are known to be localized on platelet GPIIIa and GPIIb, respectively. Utilizing additional antibodies from patients with PTP specific for Pena, Baka, and Bakb allo-antigens, and isoantibodies (iso-ab) from a patient with Glanzmann's Thrombasthenia (GT), we have studied cultured HEC and HEL cells for expression of epitopes recognized by these antibodies. HEC and HEL cells were meta-bolically labeled with 35S-methionine and lysed in 0.5% TX-100 in the presence of 5mM EDTA. Soluble antigens were immunoprecipitated with these antibodies coupled to Protein A-Sepharose and subjected to SDS-PAGE and fluorography. Anti-Pena and the GT iso-ab reacted with the GPIIb-IIIa complex from both HEC and HEL lysates, but anti-Baka and anti-Bakb failed to immunoprecipitate GPIIb-IIIa analogs from either HEC or HEL. In an immunoblot assay, the GT iso-ab bound to GPIIIa of both HEC and HEL. Anti-Pena failed to react with SDS-denatured proteins. HEL GPIIIa migrates slightly faster than HEC GPIIIa and slightly slower than platelet GPIIIa. These results indicate that the epitopes of platelet GPIIIa recognized by alloantibodies and isoantibodies are shared by GPIIIa analogs of HEC and HEL. GPIIb-associated alloantigens are not expressed by HEC and HEL GPIIb analogs, an observation that is consistent with the decreased structural homology between GPIIb analogs derived from different cell types.