title: A novel nanobody that detects the gain-of-function phenotype of von Willebrand factor in ADAMTS13 deficiency and von Willebrand disease type 2B.
abstract: Von Willebrand factor (VWF) is unable to interact spontaneously with platelets because this interaction requires a conversion of the VWF A1 domain into a glycoprotein Ibalpha (GpIbalpha) binding conformation. Here, we discuss a llama-derived antibody fragment (AU/VWFa-11) that specifically recognizes the GpIbalpha-binding conformation. AU/VWFa-11 is unable to bind VWF in solution, but efficiently interacts with ristocetin- or botrocetin-activated VWF, VWF comprising type 2B mutation R1306Q, or immobilized VWF. These unique properties allowed us to use AU/VWFa-11 for the detection of activated VWF in plasma of patients characterized by spontaneous VWF-platelet interactions: von Willebrand disease (VWD) type 2B and thrombotic thrombocytopenic purpura (TTP). For VWD type 2B, levels of activated VWF were increased 12-fold (P < .001) compared to levels in healthy volunteers. An inverse correlation between activated VWF levels and platelet count was observed (R2 = 0.74; P < .003). With regard to TTP, a 2-fold (P < .001) increase in activated VWF levels was found in plasma of patients with acquired TTP, whereas an 8-fold increase (P < .003) was found in congenital TTP. No overlap in levels of activated VWF could be detected between acquired and congenital TTP, suggesting that AU/VWFa-11 could be used to distinguish between both disorders. Furthermore, it could provide a tool to investigate the role of VWF in the development of thrombocytopenia in various diseases.
authors: Laboratory for Thrombosis and Haemostasis, Department of Haematology, G03.647, University Medical Center Utrecht, PO Box 85500, 3584 CX Utrecht, The Netherlands.
authors: Janine J J
authors: JJ
authors: Hulstein
authors: Philip G
authors: PG
authors: de Groot
authors: Karen
authors: K
authors: Silence
authors: Agnès
authors: A
authors: Veyradier
authors: Rob
authors: R
authors: Fijnheer
authors: Peter J
authors: PJ
authors: Lenting
mesh_terms: D051722:ADAM Proteins / Q000172:deficiency* / Q000378:metabolism; D000071120:ADAMTS13 Protein; D000818:Animals; D000906:Antibodies / Q000276:immunology*; D001792:Blood Platelets / Q000378:metabolism; D002161:Camelids, New World; D006801:Humans; D050997:Nanomedicine; D010641:Phenotype; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism; D011697:Purpura, Thrombotic Thrombocytopenic / Q000378:metabolism; D012996:Solutions; D014842:von Willebrand Diseases / Q000378:metabolism*; D014841:von Willebrand Factor / Q000276:immunology / Q000378:metabolism*
chemical_list: D000906:Antibodies; D019038:Platelet Glycoprotein GPIb-IX Complex; D012996:Solutions; D014841:von Willebrand Factor; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human