The role of cellular cooperation in thromboplastin synthesis

Increasing evidence [1, 2, 3] demonstrates the clinical importance of monocyte thromboplastin synthesis in the pathogenesis of thrombosis and disseminated intravascular coagulation. Among the first to describe this was the group of the late F Josso [4, 5]. In addition, monocytes and macrophages appear to contribute to fibrin deposition in inflammatory lesions [6, 7]. Several procoagulant substances have been reported to appear in monocyte cultures. Among these, thromboplastin is the most potent and probably also the most important and well studied. Based as it is on our own work, this brief review will deal only with thromboplastin. It is a phospholipid-protein complex, consisting in human material of one species of protein (apoprotein III) mol. wt. approximately 52,000 surrounded by phospholipids [8] in an optimal molecular ratio of apoprotein:phospholipids of approximately 1:80 [9]. Apoprotein III is an integral membrane glycoprotein which apparently is located mainly on the outside of the plasma membrane. The molecular weight has recently been confirmed in our laboratory by Western blotting, using a monoclonal antibody to apoprotein III developed here (Johnsen, unpublished).