Uncoupling in the expression of platelet GP IIb/IIIa in human endothelial cells and K562 cells: absence of immunologic crossreactivity between platelet GP IIb and the vitronectin receptor alpha chain.

Platelet glycoproteins (GP) IIb and IIIa exist as noncovalently associated Ca++-dependent heterodimer complexes within the platelet membrane and express the major platelet alloantigens Leka (Baka) and PIA1 (Zwa), which are genetic markers of GP IIb and GP IIIa, respectively. Since heterodimers immunologically related to platelet GP IIb/IIIa have been identified in a number of nucleated cell types, we tested anti-Leka and anti-PIA1 antiserum, polyclonal anti-platelet GP IIb/IIIa IgG, as well as a panel of 28 monoclonal anti-GP IIb, GP IIIa, or complex dependent anti-GP IIb/IIIa antibodies on endothelial cells, peripheral blood mononuclear cells, and the erythroleukemic cells HEL and K562 in order to determine whether nucleated cell GP IIb/IIIa related proteins and platelet GP IIb/IIIa are immunologically related. Using immunofluorescence, immunoblotting, and immunoprecipitation experiments, evidence is presented that (1) the alloantigen Leka is not expressed in endothelial cells of an individual whose platelets are of the Leka/PIA1 phenotype, whereas the PIA1 alloantigen is readily detectable in these cells, (2) that in contrast to HEL cells, which express platelet GP IIb/IIIa and are of the Leka/PIA1 phenotype, platelet GP IIb is immunologically undetectable in 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-treated K562 cells despite the presence of platelet GP IIIa, and (3) that peripheral blood mononuclear cells do not express platelet GP IIb or GP IIIa on their cell surface.