International Immunology, Vol. 14, No. 2, 121-129,
February 2002
© 2002 Japanese Society for Immunology
Anti-platelet factor 4/heparin antibodies from patients with heparin-induced thrombocytopenia provoke direct activation of microvascular endothelial cells
Research Unit of Autoimmune Diseases and Department of Medicine B, Sheba Medical Center, Tel-Hashomer, Israel
1 Institute of Hematology, Tel-Aviv Sourasky Medical Center, Tel-Aviv, Israel
2 Department of Rheumatology, University Medical Centre, Vadnikova 62 1000, Ljubljana, Slovenia
3 INSERM U353, Hopital Saint-Louis, 13-75651 Paris, France
4 Department of Medicine, Weill Medical College of Cornell University, New York, NY 10021, USA
5 Cardiovascular Institute, Loyola University Medical Center, Maywood, IL 60153, USA
6 Hyphen Biomed, Conflans St Honorine, France
Correspondence to: Y.Shoenfeld; E-mail: shoenfel{at}post.tau.ac.il
Heparin-induced thrombocytopenia (HIT) is a serious complication that occurs in ~1–5% of patients treated with heparin and may be associated with severe thrombotic events. HIT is mediated by antibodies directed mostly to epitope(s) formed by complexes between heparin or other anionic mucopolysaccharides and platelet factor 4 (PF4). Anti-PF4/heparin IgG antibodies from six patients with HIT were affinity purified and assessed for interaction with human microvascular and macrovascular endothelial cells (EC). The antibodies directly activated primary cultures of human bone marrow microvascular EC (HBMEC) and SV40 immortalized HBMEC (TrHBMEC) only in the presence of PF4, but did not activate macrovascular human umbilical vein EC (HUVEC) under the same conditions. These antibodies were found to bind to TrHBMEC through the F(ab)2 portion of the anti-PF4/heparin IgG. TrHBMEC activation was characterized by an augmented release of IL-6, von Willebrand factor, soluble thrombomodulin, and by an elevated expression of the adhesion molecules P-selectin, E-selectin and vascular cellular endothelial molecule-I to different degrees. Enhanced monocyte adhesion to PF4/heparin antibody-treated TrHBMEC (33–72% adhesion) was also observed. None of these effects occurred with unstimulated HUVEC. However, pre-treatment of HUVEC with tumor necrosis factor-
resulted in the same changes observed with microvascular EC exposed to the HIT antibodies. Our findings indicate that anti-PF4/heparin antibodies directly activate microvascular EC while interaction with macrovascular EC requires pre-activation. These results may explain some of the specific clinical manifestations in HIT.
Keywords: anti-platelet factor 4, heparin, microvascular endothelial cells, thrombocytopenia
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