Thrombotic occlusion of blood vessels, which leads to myocardial infarctions, strokes and venous thromboembolisms, is the major cause of death in the western hemisphere. Therefore, it is of critical importance to understand mechanisms preventing thrombus formation. A new study by the research group of Christoph Binder, Principal Investigator at the CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences and Professor at the Medical University of Vienna, now explains the important role of immunoglobulin-M (IgM) antibodies in preventing thrombosis. The study published in the journal Blood shows that these antibodies recognize microvesicles, which are membrane blebs shed by cells and recognized for their critical role in thrombosis, and therefore prevent their pro-thrombotic effects. These results provide a novel approach to reduce the risk of thrombosis by using IgM antibodies.