A monoclonal antibody to human platelet glycoprotein IIIa detects a related protein in cultured human endothelial cells

Abstract

We have previously described a series of monoclonal antibodies against platelet membrane glycoproteins. Two of the antibodies, B59.2 and B2.12, recognize the glycoprotein IIb-IIIa complex. These two antibodies react specifically with glycoprotein (GP) IIIa, as shown by immunoblotting of sodium dodecyl sulfate-polyacrylamide gels of solubilized platelet membranes. Monoclonal B2.12, but not B59.2, binds to cultured human endothelial cells obtained from umbilical vein, internal iliac artery, and inferior vena cava. At saturation ~100,000 binding sites were detected per human umbilical vein endothelial cell. When solubilized radioiodinated cells were chromatographed on a column of agarose-bound B2.12, a single radiolabeled protein was obtained whose apparent molecular weight is slightly larger than that of platelet GP IIIa. This protein incorporated [35S]methionine when endothelial cells were labeled metabolically. These results demonstrate that human endothelial cell membranes synthesize a protein immunologically related to platelet GP IIIa.