Accelerated uptake of VWF/platelet complexes in macrophages contributes to VWD type 2B–associated thrombocytopenia

C Casari, V Du, YP Wu, A Kauskot… - Blood, The Journal …, 2013 - ashpublications.org
C Casari, V Du, YP Wu, A Kauskot, PG de Groot, OD Christophe, CV Denis, B de Laat…
Blood, The Journal of the American Society of Hematology, 2013ashpublications.org
Von Willebrand disease (VWD) type 2B is characterized by mutations causing enhanced
binding of von Willebrand factor (VWF) to platelets. Bleeding tendency is associated with
heterogeneous clinical manifestations, including moderate to severe thrombocytopenia. The
underlying mechanism of the thrombocytopenia has remained unclear. Here, a mouse
model of VWD type 2B was used to investigate pathways contributing to thrombocytopenia.
Immunohistochemical analysis of blood smears revealed that mutant VWF was exclusively …
Abstract
Von Willebrand disease (VWD) type 2B is characterized by mutations causing enhanced binding of von Willebrand factor (VWF) to platelets. Bleeding tendency is associated with heterogeneous clinical manifestations, including moderate to severe thrombocytopenia. The underlying mechanism of the thrombocytopenia has remained unclear. Here, a mouse model of VWD type 2B was used to investigate pathways contributing to thrombocytopenia. Immunohistochemical analysis of blood smears revealed that mutant VWF was exclusively detected on platelets of thrombocytopenic VWD type 2B mice, suggesting that thrombocytopenic VWD type 2B mice were elevated two- to threefold upon chemical macrophage depletion. Colocalization of platelets with CD68-positive Kupffer cells and CD168-positive marginal macrophages in liver and spleen, respectively, confirmed the involvement of macrophages in the removal of VWF/platelet complexes. Significantly more platelets were found in liver and spleen of VWD type 2B mice compared with control mice. Finally, platelet survival was significantly shorter in VWD type 2B mice compared with control mice, providing a rationale for lower platelet counts in VWD type 2B mice. In conclusion, our data indicate that VWF type 2B binds to platelets and that this is a signal for clearance by macrophages, which could contribute to the thrombocytopenia in patients with VWD type 2B.
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