Thromb Haemost 2016; 116(05): 783-791
DOI: 10.1160/TH16-04-0258
Theme Issue Article
Schattauer GmbH

Biophysical tools to assess the interaction of PF4 with polyanions

Mihaela Delcea
1  Institute for Immunology and Transfusion Medicine, University Medicine Greifswald, Greifswald, Germany
2  ZIK HIKE - Center for Innovation Competence, Humoral Immune Reactions in Cardiovascular Diseases, University of Greifswald, Greifswald, Germany
3  DZHK (German Centre for Cardiovascular Research), partner site Greifswald, Germany
,
Andreas Greinacher
1  Institute for Immunology and Transfusion Medicine, University Medicine Greifswald, Greifswald, Germany
› Author Affiliations
Further Information

Publication History

Received: 01 April 2016

Accepted after major revision: 07 September 2016

Publication Date:
30 November 2017 (online)

Summary

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.