In spite of these remaining questions, the study by Noubouossie et al provides significant insight about the potential of cell-derived MVs to elicit thrombotic and immunomodulatory responses. In the past 15 years, there has been a revival of interest in the contact system as more biologic substances have been recognized to support FXII activation in vivo, as novel FXII functions have emerged, and as animal and human studies have shown that the contact system is dispensable for hemostasis but contributes to thrombosis. 9, 10 The study by Noubouossie et al adds to the growing list of potentially relevant FXII activators and sets the stage for future experimental studies to address the therapeutic potential of inhibiting the contact system as a strategy for preventing and managing complications for recipients of RBC transfusions.