Complement mediates binding and procoagulant effects of ultralarge HIT immune complexes.

Journal Article (Journal Article)

Heparin-induced thrombocytopenia (HIT) is a prothrombotic disorder mediated by ultra-large immune complexes (ULICs) containing immunoglobulin G (IgG) antibodies to a multivalent antigen composed of platelet factor 4 and heparin. The limitations of current antithrombotic therapy in HIT supports the need to identify additional pathways that may be targets for therapy. Activation of FcγRIIA by HIT ULICs initiates diverse procoagulant cellular effector functions. HIT ULICs are also known to activate complement, but the contribution of this pathway to the pathogenesis of HIT has not been studied in detail. We observed that HIT ULICs physically interact with C1q in buffer and plasma, activate complement via the classical pathway, promote codeposition of IgG and C3 complement fragments (C3c) on neutrophil and monocyte cell surfaces. Complement activation by ULICs, in turn, facilitates FcγR-independent monocyte tissue factor expression, enhances IgG binding to the cell surface FcγRs, and promotes platelet adhesion to injured endothelium. Inhibition of the proximal, but not terminal, steps in the complement pathway abrogates monocyte tissue factor expression by HIT ULICs. Together, these studies suggest a major role for complement activation in regulating Fc-dependent effector functions of HIT ULICs, identify potential non-anticoagulant targets for therapy, and provide insights into the broader roles of complement in immune complex-mediated thrombotic disorders.

Full Text

Duke Authors

Cited Authors

  • Khandelwal, S; Barnes, A; Rauova, L; Sarkar, A; Rux, AH; Yarovoi, SV; Zaitsev, SS; Lambris, JD; Myoung, SS; Johnson, A; Lee, GM; Duarte, M; Poncz, M; Arepally, GM; Cines, DB

Published Date

  • November 25, 2021

Published In

Volume / Issue

  • 138 / 21

Start / End Page

  • 2106 - 2116

PubMed ID

  • 34189574

Pubmed Central ID

  • PMC8617432

Electronic International Standard Serial Number (EISSN)

  • 1528-0020

Digital Object Identifier (DOI)

  • 10.1182/blood.2020009487


  • eng

Conference Location

  • United States