The von Willebrand factor A1 domain mediates thromboinflammation, aggravating ischemic stroke outcome in mice

_V ^on stroke. _gression^Willebrand However, _{of ischemic}^factor the exact _stroke^(VWF) mechanism _brain^plays_damage^an by ^important which _{is not} VWF _completely^role mediates ^{in ischemic}_under- pro-stood. Using flow cytometric analysis of single cell suspensions prepared from brain tissue and immunohistochemistry, we investigated the potential inflammatory mechanisms by which VWF contributes to ischemic stroke brain damage in a mouse model of cerebral ischemia/reperfusion injury. Twenty-four hours after stroke, flow cytometric analysis of brain tissue revealed that overall white blood cell recruitment in the ipsilesional brain hemisphere of VWF knockout mice was two times lower than that in wild-type mice. More detailed analysis showed a specific reduction of proinflammatory monocytes, neutrophils and T cells in the ischemic brain of VWF knockout mice compared to wild-type mice. Interestingly, histological analysis revealed a substantial number of neutrophils and T cells still within the microcirculation of the stroke brain, potentially contributing to the no-reflow phenomenon. Specific therapeutic targeting of the VWF A1 domain in the wild-type mice resulted in reduced numbers of immune cells in the affected brain and protected mice from ischemic stroke brain damage. More specifically, recruitment of proinflammatory monocytes was reduced two-fold, neutrophil recruitment was reduced five-fold and T-cell recruitment was reduced two-fold in mice treated with a VWF A1-targeting nanobody compared to the recruitment in mice receiving a control nanobody. In conclusion, our data identify a potential role for VWF in the recruitment of proinflammatory monocytes, neutrophils and T cells to the ischemic brain through a mechanism that is mediated by its A1 domain.