Abstract
Normal human monocytes and macrophages generate potent procoagulant activity (PCA) resembling tissue factor (TF) in response to various stimuli. In this study we show that tuftsin, a natural stimulator of many functions of monocytes and macrophages, also stimulates a potent PCA in mixed mononuclear cells and monocytes, and a mild PCA in lymphocytes and cell lines of monocytic origin (U937 and THP). No activity was generated by several lymphoid cell lines and HL-60 cells. The PCA resembled TF in that it accelerated clotting through the extrinsic coagulation pathway and was inhibited by concanavalin-A and by monoclonal anti-TF antibodies. The induction of TF-like activity by tuftsin was dose- and time-dependent. It was located in the cell membrane and did not require T cells for expression. Generation of TF- like activity was prevented by actinomycin D, while cytarabine had no effect on this process, suggesting that expression of the activity depends on protein synthesis. Studies with various tuftsin analogs suggest that tuftsin stimulates generation of TF-like activity, as well as other functions of monocytes via the same receptors. The results with the monocytic cell lines show that tuftsin affects mainly mature cells. The induction of TF-like activity in mononuclear cells by tuftsin constitutes an important link between mononuclear cells and the immune and coagulation systems. It may play a major role in the pathogenesis of thromboembolism and fibrin deposition in various inflammatory and immunologic disorders.
