Expression of the drug-dependent antigen for quinine-dependent antiplatelet antibodies on GP IIIa but not that on GPIb, IIb or IX on human endothelial cells

In quinine- and quinidine-induced thrombocytopenic purpura IgG antibodies are known to react in a drug-dependent manner with different combinations of surface glycoproteins (GP) Ib, IIb, IIIa and IX. Because endothelial cells share a number of properties of platelets, including the presence of GIP IIIa and GPIb-like proteins, we have compared these two cell types for their quinine-dependent IgG binding abilities. By immunoblotting of endothelial cells, quinine-dependent IgG binding from four patient sera was observed only to a 93 kDa component corresponding to GP IIIa. Strong IgG binding independent of the drug was found at 170-180 kDa. Thus endothelial cells express the GP IIIa quinine-dependent epitope on platelet GP IIIa, but not those on other platelet glycoproteins.