Platelet factor 4 inhibits ADAMTS13 activity and regulates the multimeric distribution of von Willebrand factor

Summary The efficiency of von Willebrand factor (VWF) in thrombus formation is related to its multimeric size, which is controlled by the protease ADAMTS13. However, it is not clear what regulates ADAMTS13 activity. In this study, we investigated whether PF4 could bind to VWF and inhibit ADAMTS13 activity. We found that PF4 binds to VWF and protects against ADAMTS13 activity. We also found that VWF‐PF4 complexes circulate in patients with thrombotic thrombocytopenic purpura (TTP). Our data provides the first evidence that PF4 may have a novel role in regulating VWF multimers during primary haemostasis and thrombosis.