A NOVEL BIOLOGICAL EFFECT OF PLATELET-FACTOR-4 (PF4) - ENHANCEMENT OFLPS-INDUCED TISSUE FACTOR ACTIVITY IN MONOCYTES

In a previous study we have shown that granulocytes enhance lipopolysa ccharide (LPS)-induced tissue factor (TF) activity in monocytes in a p latelet-dependent reaction, The present investigation was undertaken t o examine the role of a platelet activation product, platelet factor 4 (PF4), in LPS-induced TF activity in monocytes, Platelet lysate super natant, purified PF4, and the COOH-terminal tridecapeptide of PF4, ter med PF4(58-70), enhanced LPS-induced TF activity in monocytes of whole blood dose dependently, A monoclonal antibody against P-selectin elim inated the enhancing effect of PF4(58-10) on LPS-induced TF activity i n monocytes, and PF4(58-70) was shown to act synergistically with tumo r necrosis factor alpha (TNF-alpha), However, PF4(58-10) did not enhan ce TNF-alpha secretion in LPS-stimulated whole blood, The major effect of PF4(58-10) was granulocyte dependent. Our results suggest that PF4 might play an important role in LPS-stimulated monocyte TF activity o f whole blood.