Abstract Number: PB0250
Meeting: ISTH 2020 Congress
Background: Blood coagulation testing is useful clinically as a screening test for bleeding and hypercoagulable disease states. The activated partial thromboplastin time (aPTT) is one of the most commonly used coagulation tests, performed over 5 billion times annually. The aPTT assay measures the time it takes for recalcified plasma to clot when exposed to substances that activate coagulation factor XII (FXII), a process known as “contact activation”.
Aims: To identify the mechanism of FXII contact activation and establish coagulation diagnostics based on surface-mimicking antibodies that activate FXII.
Methods: Recombinant FXII deletion mutants were used to systematically scan for sequences that are involved in contact activation in vitro and in vivo. Antibodies against the contact activation site on FXII were generated and used for regulatable plasma contact activation.
Results: Reconstitution of FXII-deficient plasma with FXII mutants identified that residues Gln317-Ser339 in the proline-rich domain were essential for foreign- and physiologic surface-driven zymogen FXII activation. FXII deficiency in this 23-residue segment erased surface-triggered thrombin formation and coagulation, however FXII mutants lacking the contact activation site were activatable by proteolysis. A peptide containing Gln317-Ser339 residues interfered with surface-induced coagulation. Thrombus formation was defective in FXII gene-deleted (F12-/-) mice. Reconstitution of F12-/- mice with full length FXII but not with FXII variants lacking the contact activation site restored defective thrombus formation. Based on these studies, we developed antibodies against the contact activation site on FXII. These surface-mimicking antibodies initiated FXII activation, induced thrombin generation and triggered the intrinsic coagulation pathway in a regulatable manner. FXII-activating antibodies enabled us to standardize aPTT reagents and allowed for improved coagulation assays in the absence of particulate surfaces.
Conclusions: The present study adds mechanistic insight into FXII activation in vitro and in vivo and translates the findings to establish antibody-driven controllable aPTT coagulation assays.
To cite this abstract in AMA style:Heestermans M, Naudin C, Klaetschke K, Deppermann C, Pula G, Butler LM, Stavrou EX, Renné T. Coagulation Assays Based on Surface-Mimicking Antibodies against Factor XII [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/coagulation-assays-based-on-surface-mimicking-antibodies-against-factor-xii/. Accessed May 6, 2021.
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