Complement proteins participate in venous thrombosis after ligation of the IVC. C3 has a role in activation of platelets. C5 has a role in activation of TF on leukocytes. The effect of C5 on TF activation depends on the assembly of C5b-7, expression of phosphatidylserine (PS), and activity of protein disulfide isomerase (PDI) on the cell membrane. Illustration by The University of Texas MD Anderson Cancer Center.