Platelet-specific alloantigens have been implicated in the pathogenesis of two well-characterized thrombocytopenic disorders: neonatal alloimmune thrombocytopenic purpura and post-transfusion purpura. The overall goal of this proposal is to investigate the biochemical properties of the human platelet alloantigens, P1A1, Leka and Baka, in order to determine the structural features that are responsible for their antigenicity. To address this issue, three related studies will be conducted. The first study will examine the role of carbohydrate moieties in the structure and antigenicity of the Bak and Lek alloantigen systems. Oligosaccharides will be systematically removed from GPIIb and GPIIIa and the deglycosylated proteins will be assayed for their retention of specific antigenic determinants. In the second study, I will attempt to isolate and characterize small immunologically reactive fragments derived from platelet membrane glycoproteins IIIa and IIb that contain the P1A, Lek and Bak antigenic determinants. These will be compared by isoelectric focusing, amino acid compositional and, if possible, amino acid sequence analysis to determine the specific structural heterogeneity between the alleles in these three alloantigen systems. Finally, I intend to produce murine monoclonal antibodies that are specific for the P1A1 and Baka epitopes. These antibodies will be used as both research reagents for further characterization of the structural and functional regions of GPIIb and GPIIIa involved in alloantigenicity, and also as extremely useful typing reagents for consistent, reproducible clinical detection of these alloantigens on patient platelets. Together, these three interrelated projects comprise a research program that should yield valuable, timely new information about the detailed structure of human platelet alloantigens. This knowledge will contribute to our understanding of the specific morphological features of these glycoproteins that are responsible for eliciting an alloimmune response, as well as to a greater understanding of platelet membrane glycoprotein structure and function. This should, in turn, lead to improvements in transfusion therapy, platelet storage and our understanding and management of congenital platelet functional disorders.