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Heestermans M.,Leiden University | Salloum-Asfar S.,Leiden University | Salvatori D.,Leiden University | Laghmani E.H.,Leiden University | And 7 more authors.

Recently, platelets, neutrophils, and factor XII (FXII) have been implicated as important players in the pathophysiology of venous thrombosis. Their role became evident in mouse models in which surgical handling was used to provoke thrombosis. Inhibiting anticoagulation in mice by using small interfering RNA (siRNA) targeting Serpinc1 and Proc also results in a thrombotic phenotype, which is spontaneous (no additional triggers) and reproducibly results in clots in the large veins of the head and fibrin deposition in the liver. This thrombotic phenotype is fatal but can be fully rescued by thrombin inhibition. The mouse model was used in this study to investigate the role of platelets, neutrophils, and FXII. After administration of siRNAs targeting Serpinc1 and Proc, antibody-mediated depletion of platelets fully abrogated the clinical features as well as microscopic aspects in the head. This was corroborated by strongly reduced fibrin deposition in the liver. Whereas neutrophils were abundant in siRNA-triggered thrombotic lesions, antibody-mediated depletion of circulating Ly6G-positive neutrophils did not affect onset, severity, or thrombus morphology. In addition, absence of circulating neutrophils did not affect quantitative liver fibrin deposition. Remarkably, siRNA-mediated depletion of plasma FXII accelerated the onset of the clinical phenotype; mice were affected with more severe thrombotic lesions. To summarize, in this study, onset and severity of the thrombotic phenotype are dependent on the presence of platelets but not circulating neutrophils. Unexpectedly, FXII has a protective effect. This study challenges the proposed roles of neutrophils and FXII in venous thrombosis pathophysiology. © 2016 by The American Society of Hematology. Source

Sorvillo N.,Sanquin Academic Medical Center Landsteiner Laboratory | Pos W.,Sanquin Academic Medical Center Landsteiner Laboratory | Van Den Berg L.M.,University of Amsterdam | Fijnheer R.,University Utrecht | And 4 more authors.

ADAMTS13 is a plasma metalloproteinase that regulates platelet adhesion and aggregation by cleaving ultra-large VWF multimers on the surfaces of endothelial cells. Autoantibodies directed against ADAMTS13 prohibit the processing of VWF multimers, initiating a rare and life-threatening disorder called acquired thrombotic thrombocytopenic purpura. The formation of autoantibodies depends on the activation of CD4 + T cells. This process requires immune recognition, endocytosis, and subsequent processing of ADAMTS13 into peptides that are presented on MHC class II molecules to CD4 + T cells by dendritic cells (DCs). In the present study, we investigated endocytosis of recombinant ADAMTS13 by immature monocyte-derived DCs using flow cytometry and confocal microscopy. After incubation of fluorescently labeled ADAMTS13 with DCs, significant uptake of ADAMTS13 was observed. Endocytosis of ADAMTS13 was completely blocked by the addition of EGTA and mannan. ADAMTS13 endocytosis was decreased in the presence of a blocking mAb directed toward the macrophage mannose receptor (MR). Furthermore, siRNA silencing of MR reduced the uptake of ADAMTS13 by DCs. In addition, in vitro binding studies confirmed the interaction of ADAMTS13 with the carbohydrate recognition domains of MR. The results of the present study indicate that sugar moieties on ADAMTS13 interact with MR, thereby promoting its endocytosis by APCs. © 2012 by The American Society of Hematology. Source

Verbij F.C.,Sanquin Research | Turksma A.W.,Sanquin Academic Medical Center Landsteiner Laboratory | De Heij F.,Sanquin Research | Kaijen P.,Sanquin Research | And 5 more authors.

Acquired thrombotic thrombocytopenic purpura (TTP) is a life-threatening disorder resulting from the development of autoantibodies against ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). HLA-DRB1∗11 provides a risk factor for developing acquired TTP. Pulsing of antigen-presenting cells from HLA-DRB1∗11- and HLA-DRB1∗03-positive individuals with ADAMTS13 resulted in presentation of peptides derived from the CUB2 domain of ADAMTS13 with core sequences FINVAPHAR or ASYILIRD. Here, we assessed whether FINVAPHAR- or ASYILIRD-reactive CD4+ T cells are present in peripheral blood mononuclear cells from HLA-DRB1∗11 and HLA-DRB1∗03-positive subjects with acquired TTP. The presence of ADAMTS13-reactive CD4+ T cells was addressed by flow cytometry and the expression of activation marker CD40 ligand by CD4+ T cells. FINVAPHAR-reactive CD4+ T cells were identified in an HLA-DRB1∗11-positive patient during the acute phase of the disease whereas ASYILIRD-positive CD4+ T cells were identified in a DRB1∗03-positive patient with acquired TTP. Frequencies of CUB2 domain-reactive CD4+ T cells ranged from 3.3% to 4.5%. Control peptides in which the anchor residues were modified did not induce activation of CD4+ T cells. Taken together, our data provide evidence for the involvement of CUB2 domain-reactive CD4+ T cells in the etiology of acquired TTP. © 2016 by The American Society of Hematology. Source

Nicolaes G.A.F.,Maastricht University | Kulharia M.,Maastricht University | Voorberg J.,Sanquin Academic Medical Center Landsteiner Laboratory | Kaijen P.H.,Sanquin Academic Medical Center Landsteiner Laboratory | And 5 more authors.

The C domains of coagulation factors V (FV) and VIII (FVIII) are structurally conserved domains and share a common and essential function in membrane binding. In vivo regulation of thrombin formation strongly depends on the expression and regulation of the cofactor activities of FVIII and FV. With this study, we explored the possibility of inhibition of thrombin formation in full blood with small druglike molecules. Such compounds may serve as lead molecules for the development of a new type of orally available coagulation inhibitors that act by blocking the interaction between the C domains of FVIII and the membrane surface. We identified 9 novel molecules that are able to inhibit binding of the FVIII C2 domain to a model membrane by application of a combined ligand-based and target structure-based virtual screening approach that took into account the knowledge of a set of previously identified low-molecular-weight FVIII binders that were, however, not active in full blood. The half-maximal inhibitory concentration values of our newly identified compounds varied from 2.1 to 19.9 mM, of which 7 of 9 molecules did not appreciably inhibit FV membrane binding and were thus specific for FVIII. The most active bioactive compound showed activity in both plasma and in full blood. © 2014 by The American Society of Hematology. Source

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