VWF and Thrombocytopenia: Because alpha-toxin, a key virulence factor secreted by almost all strains of S. aureus, binds directly to platelets and causes aberrant aggregation in the microvasculature, microthombi in the microvasculature, endothelial cell activation, and von Willebrand factor release [5, 8], it is likely that thrombocytopenia is a marker indicative of the pathogen-mediated immunothrombotic event that predisposes patients to the development of endocarditis.