Hemostasis: old system, new players, new directions.

Initiation of clotting cascade by tissue factor (TF): Factor VII (FVII) complex is essential for hemostasis however pathologic expression of TF leads to thrombosis. In contrast, the contact pathway factor XII, and to the smaller extent FXI are dispensable for normal hemostasis but still contribute to pathologic thrombosis. New data suggest that not only platelets but also leukocytes and red blood cells can actively participate to thrombosis. Growing evidence demonstrates that coagulation proteases not only regulate hemostasis and thrombosis but also contribute to the many cellular responses via activation of protease activated receptors (PARs). The reviews in this supplement summarize the latest findings related to TF and coagulation proteases, including novel models of hemostasis and thrombosis, new insights into mechanism of thrombosis and trauma induced coagulopathy, interplay between coagulation and innate immune system and pathophysiology of contact activation pathway.