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Summary.  Background: Diagnosis of acquired von Willebrand syndrome (AVWS) remains challenging. Diagnostic algorithms suggest the use of factor VIII (FVIII:C), von Willebrand factor antigen (VWF:Ag), ristocetin cofactor (VWF:RCo), and collagen‐binding capacity (VWF:CB), but the sensitivity of these and other laboratory tests for the diagnosis of AVWS is unknown. Objectives: To analyze the capacity of laboratory tests, including point‐of‐care testing (POCT), for the identification of patients with AVWS. Patients/methods: Thirty‐five consecutive patients were enrolled with AVWS diagnosed because of a history of recent onset of bleeding, a negative family history of von Willebrand disease, and abnormal plasma VWF multimers. Results: According to our inclusion criteria, all patients had bleeding symptoms, and the VWF high molecular weight multimers were either decreased or absent. Regarding POCT, PFA‐100 was inconclusive, due to anemia or thrombocytopenia, in 29%; the sensitivity was 80% in the remaining patients. The sensitivity of VWF:Ag (23%), VWF:RCo/Ag ratio < 0.7 (26%), VWF:CB/Ag ratio < 0.7 (46%), anti‐VWF antibodies (15%) and VWF propeptide/Ag ratio (22%) was too low to rule out the disease. A combination of VWF:Ag < 50 IU dL−1, VWF:RCo/Ag ratio < 0.7 and VWF:CB/Ag ratio < 0.8 yielded a sensitivity of 86%. Patients diagnosed only because of abnormal VWF multimers showed similar clinical characteristics as other patients. Conclusions: Early diagnosis of AVWS is difficult, due to lack of sensitivity of the tests used. A substantial number of patients present with normal or increased test results, emphasizing the importance of multimer analysis in all patients with suspected AVWS.

Von Willebrand factor (VWF) and factor VIII (FVIII) circulate in a tight noncovalent complex. At present, the cells that contribute to the removal of FVIII and VWF are of unknown identity. Here, we analyzed spleen and liver tissue sections of VWFdeficient mice infused with recombinant VWF or recombinant FVIII. This analysis revealed that both proteins were targeted to cells of macrophage origin. When applied as a complex, both proteins were codirected to the same macrophages.Chemical inactivation of macrophages using gadolinium chloride resulted in doubling of endogenous FVIII levels in VWFnull mice, and of VWF levels in wild-type mice. Moreover, the survival of infused VWF was prolonged almost 2-fold in VWFdeficient mice after gadolinium chloride treatment. VWF and FVIII also bound to primary human macrophages in in vitro tests. In addition, radiolabeled VWF bound to human THP1 macrophages in a dosedependent, specific, and saturable manner (half-maximal binding at 0.014 mg/mL). Binding to macrophages was followed by a rapid uptake and subsequent degradation of the internalized protein. This process was also visualized using a VWFgreen fluorescent protein fusion protein.In conclusion, our data strongly indicate that macrophages play a prominent role in the clearance of the VWF/FVIII complex. (Blood. 2008;112:1704-1712)

Our data demonstrate a critical role for complement in the acute induction of EndMT via the Akt pathway. Therapeutic inhibition of these systems may be essential to prevent vascular damage and tissue fibrosis in transplanted kidney.

Objective-Although von Willebrand factor (VWF) is a heavily glycosylated protein, its potential to associate with glycan-binding proteins is poorly investigated. Here, we explored its interaction with the glycan-binding proteins galectin-1 and galectin-3. Methods and Results-Immunofluorescence analysis using Duolink proximity ligation assays revealed that VWF colocalizes with galectin-1 and galectin-3 in endothelial cells, both before and after stimulation of endothelial cells. Moreover, galectin-1 was found along the typical VWF bundles that are released by endothelial cells. Galectin-1 and galectin-3 could be coprecipitated with VWF from plasma in immunoprecipitation assays, whereas plasma levels of galectin-1 and galectin-3 were significantly reduced in VWF-deficient mice. Binding studies using purified proteins confirmed that VWF could directly interact with both galectins, predominantly via its N-linked glycans. In search of the physiological relevance of the VWF-galectin interaction, we found that inhibition of galectins in in vitro perfusion assays was associated with increased VWF-platelet string formation, a phenomenon that was reproduced in galectin-1/galectin-3 double-deficient mice. These mice were also characterized by a more rapid formation of initial thrombi following ferric chloride-induced injury. Key Words: endothelium Ⅲ hemostasis Ⅲ platelets Ⅲ galectin Ⅲ von Willebrand factor V on Willebrand factor (VWF) is an adhesive protein that is critical to the recruitment of platelets in response to vessel injury. The majority of the circulating VWF molecules are produced in the endothelial cells, where VWF is synthesized as a single prepropolypeptide chain. Following signal peptide removal, the polypeptides are assembled into C-terminal linked pro-VWF dimers. Further processing includes proteolytic removal of the propeptide and multimerization of the molecule by intermolecular N-terminal cystine bonding, generating a pool of differentially sized multimers that may contain more than 50 subunits. An important portion of the newly synthesized VWF multimers is directed to endothelial storage organelles, Weibel-Palade (WP) bodies. Conclusion-We1,2 VWF is obligatory for the formation of WP bodies, which are indeed absent in endothelial cells isolated from VWF-deficient mice or dogs.3,4 These storage organelles also contain other proteins besides VWF, including P-selectin, osteoprotegerin, CD63, and interleukin-8. 5 Some of these proteins directly interact with VWF, which may facilitate their uptake into the WP bodies. 6,7 For other residents of the storage granules, the uptake may be the result of a more random inclusion process. 8 Following endothelial stimulation, the content of the WP bodies is released into the circulation, allowing the first encounter between VWF and circulating platelets. Indeed, VWF multimers assemble into twisted bundles and networks that form long strings along the endothelial surface. 9 These VWF strings are able to catch platelets, and these platelet-decorated strings can be vis...