title: Antibodies associated with heparin-induced thrombocytopenia (HIT) inhibit activated protein C generation: new insights into the prothrombotic nature of HIT.
abstract: Heparin-induced thrombocytopenia (HIT) is caused by antibodies that recognize complexes between platelet factor 4 (PF4) and heparin or glycosaminoglycan side chains. These antibodies can lead to a limb- and life-threatening prothrombotic state. We now show that HIT antibodies are able to inhibit generation of activated protein C (aPC) by thrombin/thrombomodulin (IIa/TM) in the presence of PF4. Tetrameric PF4 potentiates aPC generation by formation of complexes with chondroitin sulfate (CS) on TM. Formation of these complexes occurs at a specific molar ratio of PF4 to glycosaminoglycan. This observation and the finding that the effect of heparin on aPC generation depends on the concentration of PF4 suggest similarity between PF4/CS complexes and those that bind HIT antibodies. HIT antibodies reduced the ability of PF4 to augment aPC formation. Cationic protamine sulfate, which forms similar complexes with heparin, also enhanced aPC generation, but its activity was not blocked by HIT antibodies. Our studies provide evidence that complexes formed between PF4 and TM's CS may play a physiologic role in potentiating aPC generation. Recognition of these complexes by HIT antibodies reverses the PF4-dependent enhancement in aPC generation and may contribute to the prothrombotic nature of HIT.
authors.affiliation: Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA. kowalska@email.chop.edu
authors.forename: M Anna
authors.initials: MA
authors.lastname: Kowalska
authors.forename: Sriram
authors.initials: S
authors.lastname: Krishnaswamy
authors.forename: Lubica
authors.initials: L
authors.lastname: Rauova
authors.forename: Li
authors.initials: L
authors.lastname: Zhai
authors.forename: Vincent
authors.initials: V
authors.lastname: Hayes
authors.forename: Karine
authors.initials: K
authors.lastname: Amirikian
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Esko
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Bougie
authors.forename: Richard H
authors.initials: RH
authors.lastname: Aster
authors.forename: Douglas B
authors.initials: DB
authors.lastname: Cines
authors.forename: Mortimer
authors.initials: M
authors.lastname: Poncz
mesh_terms: D000328:Adult; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D000925:Anticoagulants / Q000009:adverse effects; D002478:Cells, Cultured; D006025:Glycosaminoglycans / Q000378:metabolism; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D019426:Integrases / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010978:Platelet Factor 4 / Q000502:physiology; D011486:Protein C / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D018046:Protein C Inhibitor / Q000494:pharmacology*; D055503:Protein Multimerization; D011516:Prothrombin / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013917:Thrombin / Q000378:metabolism; D013921:Thrombocytopenia / Q000139:chemically induced* / Q000276:immunology / Q000378:metabolism*; D018180:Thrombomodulin / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D000925:Anticoagulants; D006025:Glycosaminoglycans; D011486:Protein C; D018046:Protein C Inhibitor; D011994:Recombinant Proteins; D018180:Thrombomodulin; D010978:Platelet Factor 4; D011516:Prothrombin; D006493:Heparin; C045073:Cre recombinase; D019426:Integrases; D013917:Thrombin