Induction of tissue factor expression in whole blood: Lack of evidence forthe presence of tissue factor expression in granulocytes

The present investigation was undertaken to explore the effect of platelets , tumor necrosis factor (TNF) and phorbel ester [phorbol 12-myristate 13-ac etate (PMA)] on lipopolysaccharide (LPS)-induced tissue factor (TF) activit y and TF antigen by using Western blot and ELISA-techniques. LPS was found to induce correlating levels of TF antigen and the activity in monocytes. T NF and PMA, when used alone, failed to induce TF activity and the antigen i n monocytes, but enhanced the LPS-induced TF activity and the antigen by 2 to 3-fold. Addition of platelet rich plasma to isolated blood cells enhance d the LPS-induced TF activity but not the antigen levels in monocytes. In c ontrast to whole platelets, platelet lysates enhanced both LPS-in- duced TF activity and the antigen. Granulocytes isolated from heparinized plasma in cubated for 2 or 24 h with LPS alone or together with PMA, failed to genera te TF antigen or the activity. Although granulocyte preparations isolated f rom whole blood that was incubated for 24 h with LPS and PMA apparently pos sessed a significant amount of TF activity and the antigen, this could be a ccounted for by trace levels of contaminating monocytes. Upregulation of LP S-induced TF activity but not the antigen by platelets in the presence of g ranulocytes suggests that the increased TF activity could be the result of PS enrichment of monocytes by fusion or platelets with activated monocytes.