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Blood, 1 September 2008, Vol. 112, No. 5, pp. 1704-1712. Prepublished online as a Blood First Edition Paper on June 16, 2008; DOI 10.1182/blood-2008-01-133181.
HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY Macrophages contribute to the cellular uptake of von Willebrand factor and factor VIII in vivo1 Department of Clinical Chemistry and Haematology, University Medical Center Utrecht, Utrecht, The Netherlands; 2 Inserm U.770 and University Paris-Sud, 94276, Le Kremlin-Bicêtre, France; 3 Van Creveld Clinic, University Medical Center Utrecht, Utrecht, The Netherlands; and 4 Department of Protein Discovery, Crucell Holland BV, Leiden, The Netherlands 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 VWF-deficient 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 VWF-null mice, and of VWF levels in wild-type mice. Moreover, the survival of infused VWF was prolonged almost 2-fold in VWF-deficient 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 dose-dependent, 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 VWF–green fluorescent protein fusion protein. In conclusion, our data strongly indicate that macrophages play a prominent role in the clearance of the VWF/FVIII complex.
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