title: Biophysical tools to assess the interaction of PF4 with polyanions.
abstract: The antigen in heparin-induced thrombocytopenia (HIT) is expressed on platelet factor 4 (PF4) when PF4 complexes with polyanions. In recent years, biophysical tools (e. g. circular dichroism spectroscopy, atomic force microscopy, isothermal titration calorimetry, x-ray crystallography, electron microscopy) have gained an important role to complement immunological and functional assays for better understanding the interaction of heparin with PF4. This allowed identification of those features that make PF4 immunogenic (e. g. a certain conformational change induced by the polyanion, a threshold energy of the complexes, the existence of multimeric complexes, a certain number of bonds formed by PF4 with the polyanion) and to characterize the morphology and thermal stability of complexes formed by the protein with polyanions. These findings and methods can now be applied to test new drugs for their potential to induce the HIT-like adverse drug effect by preclinical in vitro testing. The methods and techniques applied to characterize the antigen in HIT may also be helpful to better understand the mechanisms underlying other antibody-mediated disorders in thrombosis and hemostasis (e. g. acquired hemophilia, thrombotic thrombocytopenic purpura). Furthermore, understanding the mechanisms making the endogenous protein PF4 immunogenic may help to understand the mechanisms underlying other autoimmune disorders.
authors.affiliation: Mihaela Delcea, PhD, ZIK HIKE - Zentrum für Innovationskompetenz, "Humorale Immunreaktionen bei kardiovaskulären Erkrankungen", Ernst-Moritz-Arndt-Universität Greifswald, Fleischmannstrasse 42-44, 17489 Greifswald, Germany, Tel.: +49 3834 8622343, E-mail: delceam@uni-greifswald.de.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Delcea
authors.affiliation: Prof. Dr. med. Andreas Greinacher, MD, Institut für Immunologie und Transfusionsmedizin, Sauerbruchstrasse, 17475 Greifswald, Germany, Tel.: +49 3834 865482, E-mail: greinach@uni-greifswald.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Greinacher
mesh_terms: D006493:Heparin / Q000737:chemistry*; D006801:Humans; D010978:Platelet Factor 4 / Q000737:chemistry*; D000071228:Polyelectrolytes; D011108:Polymers / Q000737:chemistry*; D013921:Thrombocytopenia / Q000139:chemically induced*
chemical_list: D006493:Heparin; D010978:Platelet Factor 4; D000071228:Polyelectrolytes; D011108:Polymers
keywords: Platelet factor 4; biophysics of PF4/polyanion complexes; conformational changes; heparin; heparin-induced thrombocytopenia