title: Endothelial antigen assembly leads to thrombotic complications in heparin-induced thrombocytopenia.
abstract: Heparin-induced thrombocytopenia (HIT) is a prothrombotic disorder initiated by antibodies against complexes between human platelet factor 4 (hPF4) and heparin. A better understanding of the events that initiate the prothrombotic state may improve approaches to antithrombotic management. Here, we visualized thrombus formation in an in vivo murine model and an endothelialized microfluidic system that simulate the pathogenesis of HIT. hPF4 released from platelets predominantly bound to peri-injury endothelium and formed HIT antigenic complexes that were dissociated by heparin. In mice expressing both hPF4+ and human platelet IgG Fc receptor IIA (FcγRIIA), infusion of the HIT-like monoclonal antibody KKO increased fibrin and platelet deposition at sites of injury, followed immediately by antigen formation on proximate endothelial cells. After a few minutes, HIT antigen was detected within the thrombus itself at the interface between the platelet core and the surrounding shell. We observed similar results in the humanized, endothelialized microfluidic system. hPF4 and KKO selectively bound to photochemically injured endothelium at sites where surface glycocalyx was reduced. These studies support the concept that the perithrombus endothelium is the predominant site of HIT antigen assembly. This suggests that disrupting antigen formation along the endothelium or protecting the endothelium may provide a therapeutic opportunity to prevent thrombotic complications of HIT, while sparing systemic hemostatic pathways.
authors.forename: Vincent
authors.initials: V
authors.lastname: Hayes
authors.forename: Ian
authors.initials: I
authors.lastname: Johnston
authors.forename: Gowthami M
authors.initials: GM
authors.lastname: Arepally
authors.forename: Steven E
authors.initials: SE
authors.lastname: McKenzie
authors.forename: Douglas B
authors.initials: DB
authors.lastname: Cines
authors.forename: Lubica
authors.initials: L
authors.lastname: Rauova
authors.forename: Mortimer
authors.initials: M
authors.lastname: Poncz
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism* / Q000473:pathology; D004195:Disease Models, Animal; D005260:Female; D005337:Fibrin / Q000235:genetics / Q000378:metabolism; D019276:Glycocalyx / Q000235:genetics / Q000378:metabolism; D006493:Heparin / Q000009:adverse effects* / Q000494:pharmacology; D006801:Humans; D008297:Male; D018345:Mice, Knockout; D010978:Platelet Factor 4 / Q000235:genetics / Q000378:metabolism*; D017452:Receptors, IgG / Q000235:genetics / Q000378:metabolism*; D013921:Thrombocytopenia / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D013927:Thrombosis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism*
chemical_list: C445323:FCGR2A protein, human; D017452:Receptors, IgG; D010978:Platelet Factor 4; D005337:Fibrin; D006493:Heparin