What a polyclonal antibody sees in von Willebrand factor

INTRODUCTION: Von Willebrand factor (VWF) plays a critical role in hemostasis by carrying factor VIII (FVIII) and binding to specific ligands on the surface of blood platelets and within the blood vessel wall. MATERIALS AND METHODS: We constructed a gene-specific phage display library containing small, random VWF fragments. Using this library, we mapped the repertoire of immune epitopes recognized by a commonly used commercial rabbit antihuman VWF polyclonal antibody. RESULTS: A total of eight discrete epitopes within the VWF protein were identified, including two dominant epitopes that account for 74% of immuno selected VWF fragments. Comparison with previously mapped epitopes for mouse monoclonal antibodies reveals four overlapping regions that may identify common antigenic determinants. The distribution of these epitopes was not readily predicted from primary amino acid sequence divergence among these mammalian species or standard algorithms for the prediction of antigenicity, hydrophobicity, or surface probability. CONCLUSION: Taken together with previous monoclonal antibody epitope mapping studies, our results suggest that a limited number of exposed domains on the surface of the human VWF protein may be the primary determinants of immunogenicity.