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Amsterdam-Zuidoost, Netherlands

Schaller M.,University of Bern | Studt J.-D.,University of Zurich | Voorberg J.,Sanquin AMC Landsteiner Laboratory | Kremer Hovinga J.A.,University of Bern
Hamostaseologie | Year: 2013

The von Willebrand factor (VWF)-cleaving metalloprotease, ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motifs-13) is the only known target of the dysregulated immune response in acquired TTP. Autoantibodies to ADAMTS13 either neutralize its activity or accelerate its clearance, thereby causing a severe deficiency of ADAMTS13 in plasma. As a consequence, size regulation of VWF is impaired and the persistence of ultra-large VWF (ULVWF) multimers facilitates micro vascular platelet aggregation causing microangiopathic haemolytic anaemia and ischaemic organ damage. Autoimmune TTP although a rare disease with an annual incidence of 1.72 cases has a mortality rate of 20% even with adequate therapy. We describe the mechanisms involved in ADAMTS13 autoimmunity with a focus on the role of B- and T-cells in the pathogenesis of this disorder. We discuss the potential translation of recent experimental findings into future therapeutic concepts for the treatment of acquired TTP. © Schattauer 2013. Source

Vergouwen M.D.I.,University Utrecht | Vergouwen M.D.I.,University of Amsterdam | Knaup V.L.,University of Amsterdam | Roelofs J.J.T.H.,University of Amsterdam | And 3 more authors.
Journal of Thrombosis and Haemostasis | Year: 2014

Summary: Background: A common complication after aneurysmal subarachnoid hemorrhage (SAH) is delayed cerebral ischemia (DCI), which is associated with vasospasm and other mechanisms such as microthrombosis. ADAMTS-13 activity plays a role in the prevention of thrombus formation in the cerebral microvasculature. Previously, we observed that patients with DCI have lower levels of ADAMTS-13. Objectives: To examine whether recombinant human ADAMTS-13 (rADAMTS-13) reduces cerebral microthrombus formation and brain injury in an experimental mouse model of SAH including wild-type and ADAMTS-13-/- mice. Methods: Experimental SAH was induced with the prechiasmatic blood injection model. The following experimental groups were investigated: (i) C57BL/6J mice (n = 10); (ii) C57BL/6J mice (n = 10) treated with rADAMTS-13 20 min after SAH; (iii) ADAMTS-13-/- mice (n = 10); and (iv) ADAMTS-13-/- mice (n = 10) treated with rADAMTS-13 20 min after SAH. Mice were killed at 48 h. Results are presented as means with standard errors of the mean. Results: Infusion with rADAMTS-13 reduced the extent of microthrombosis by ~ 50% in both wild-type mice (mean fibrinogen area: 0.28% ± 0.09% vs. 0.15% ± 0.04%; P = 0.20) and ADAMTS-13-/- mice (mean fibrinogen area: 0.32% ± 0.05% vs. 0.16% ± 0.03%; P = 0.016). In addition, rADAMTS-13 reduced brain injury by > 60% in both wild-type mice (mean microglia area: 0.65% ± 0.18% vs. 0.18% ± 0.04%; P = 0.013) and ADAMTS-13-/- mice (mean microglia area: 1.24% ± 0.36% vs. 0.42% ± 0.13%; P = 0.077). Conclusions: Our results support the further study of rADAMTS-13 as a treatment option for the prevention of microthrombosis and brain injury after SAH. © 2014 International Society on Thrombosis and Haemostasis. Source

Mourik M.J.,Leiden University | Valentijn J.A.,Leiden University | Voorberg J.,Sanquin AMC Landsteiner Laboratory | Koster A.J.,Leiden University | And 2 more authors.
Journal of Thrombosis and Haemostasis | Year: 2013

Summary: Background: In vascular endothelial cells, high molecular weight multimers of von Willebrand factor (VWF) are folded into tubular structures for storage in Weibel-Palade bodies. On stimulation, VWF is secreted and forms strings to induce primary hemostasis. The structural changes composing the transition of stored tubular VWF into secreted unfurled VWF strings are still unresolved even though they are vital for normal hemostasis. The secretory pod is a novel structure that we previously described in endothelial cells. It is formed on stimulation and has been postulated to function as a VWF release site. In this study, we investigated the actual formation of secretory pods and the subsequent remodeling of VWF into strings. Methods: Human umbilical vein endothelial cells were stimulated and studied using various imaging techniques such as live-cell imaging and correlative light and electron microscopy. Results: We found by using live-cell imaging that secretory pods are formed through the coalescence of multiple Weibel-Palade bodies without involvement of other large structures. Secreted VWF expelled from secretory pods was found to adopt a globular conformation. We visualized that VWF strings derive from those globular masses of VWF. Flow experiments showed that, on secretion, the globular masses of VWF move to the edge of the cell, where they anchor and generate VWF strings. Conclusion: On secretion, VWF adopts a globular conformation that remodels into strings after translocation and anchoring at the edge of the cell. This finding reveals new pathophysiological mechanisms that could be affected in patients with von Willebrand disease. © 2013 International Society on Thrombosis and Haemostasis. Source

Verbij F.C.,Sanquin AMC Landsteiner Laboratory | Fijnheer R.,University Utrecht | Voorberg J.,Sanquin AMC Landsteiner Laboratory | Sorvillo N.,Sanquin AMC Landsteiner Laboratory
Blood Reviews | Year: 2014

The majority of the patients affected by acquired thrombotic thrombocytopenic purpura (TTP) develop autoantibodies directed towards ADAMTS13 that interfere with its von Willebrand Factor (VWF) processing activity. B cell responses have been shown to primarily target the spacer domain of ADAMTS13 thereby prohibiting the binding of ADAMTS13 to the VWF A2 domain. In this review we summarize recent knowledge gained on the immune recognition and processing of ADAMTS13 by antigen-presenting cells (APCs). HLA-DRB1*11 has been identified as a risk factor for acquired TTP. Analysis of MHC class II/peptide complexes of ADAMTS13 pulsed dendritic cells have shown that the CUB2 domain derived peptide FINVAPHAR is preferentially presented on HLA-DRB1*11. Based on these findings we propose a model for the initiation of the autoimmune reactivity against ADAMTS13 in previously healthy individuals. We hypothesize that mimicry between a pathogen-derived peptide and the CUB2 derived FINVAPHAR-peptide might contribute to the onset of acquired TTP. © 2014 Elsevier Ltd. Source

Pos W.,Sanquin AMC Landsteiner Laboratory | Sorvillo N.,Sanquin AMC Landsteiner Laboratory | Fijnheer R.,University Utrecht | Feys H.B.,Catholic University of Leuven | And 3 more authors.
Haematologica | Year: 2011

Background: The majority of patients diagnosed with thrombotic thrombocytopenic purpura have autoantibodies directed towards the spacer domain of ADAMTS13. Design and Methods: In this study we explored the epitope specificity and immunoglobulin class and immunoglobulin G subclass distribution of anti-ADAMTS13 antibodies. The epitope specificity of antispacer domain antibodies was examined using plasma from 48 patients with acute acquired thrombotic thrombocytopenic purpura by means of immunoprecipitation of ADAMTS13 variants containing single or multiple alanine substitutions. Using similar methods, we also determined the presence of anti-TSP2-8 and CUB1-2 domain antibodies in this cohort of patients. Results: Antibody profiling revealed that anti-ADAMTS13 immunoglobulin G1 and immunoglobulin G4 predominate in plasma of patients with acquired thrombotic thrombocytopenic purpura. Analysis of anti-spacer domain antibodies revealed that Arg568 and Phe592, in addition to residues Arg660, Tyr661, and Tyr665, also contribute to an antigenic surface in the spacer domain. The majority of patients (90%) lost reactivity towards the spacer domain following introduction of multiple alanine substitutions at Arg568, Phe592, Arg660, Tyr661 and Tyr665. Anti-TSP2-8 and anti-CUB1-2 domain-directed antibodies were present in, respectively, 17% and 35% of the patients' samples analyzed. Conclusions: Immunoglobulin G directed towards a single antigenic surface comprising residues Arg568, Phe592, Arg660, Tyr661 and Tyr665 predominates in the plasma of patients with acquired thrombotic thrombocytopenic purpura. ©2011 Ferrata Storti Foundation. Source

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