ADAMTS13 and thrombotic thrombocytopenic purpura: In other words, in human endothelial cells the viral S protein evokes a disbalance in the vWF:ADAMTS-13 ratio which may favor thrombi formation, similar to that observed in certain pro-coagulant and pro-thrombotic conditions such as thrombotic thrombocytopenic purpura or stroke [50, 51].