Isolation and Immunologic Characterization of the Human Platelet Alloantigen, P1\u3csup\u3eA1\u3c/sup\u3e

An understanding of the mechanisms whereby platelets become susceptible to immunoinjury in vivo ultimately requires a precise knowledge of the molecular nature of the antigens and/or receptors involved. For this purpose, an immunochemical analysis of two clinically important platelet antigens (receptors), the platelet alloantigen P1A1 and the receptor which interacts with drug-dependent platelet-specific antibodies, was initiates. Platelets from patients with the hereditary disorder of platelet function, Glanzmann\u27s thrombasthenia, lack normal quantities of the integral membrane glycoproteins, GP IIb and GP IIIa. The expression of the alloantigen, P1A1, was studied in thirteen patients with this disorder. Less than 1% of normal amounts of P1A1 could be detected on platelets from ten of the thirteen individuals , while platelets from the three remaining individuals contained 12-33% of normal levels. The expression of other platelet antigenic markers (HLA antigen, receptor for drug-dependent antibodies, and the antigens reactive with antibodies from patients with Idiopathic Thromboeytopenic Purpura) was normal. These observations were consistent with the possibility, among others, that P1A1 is associated with either or both GP IIb and GP Illa. To address this question, the P1A1 antigen was isolated by sequential lectin affinity chromatography of~sodium deoxycholate extracts of platelet membranes, by indirect immunopreclpitation of Nonidet P40 extracts of lacto-peroxidase-iodinated intact platelets, and by preparative sodium dodecyl sulfate - polyacrylamide slab gel electrophoresis of solubilized membrane preparations. By each of the three separatory procedures, the P1A1 antigenic marker was shown to be associated with GP ma