We have demonstrated in several experimental systems that tissue factor activity has a close link with the life cycle of the monocyte/macrophage and its participation in inflammation. Increased amounts of this factor VII activator become available in hematogenous leukocytes in the Schwartzman reaction as a result of marrow-blood-spleen cell stimulation by endotoxin. This effect may induce intravascular coagulation. In other studies, we found that alveolar macrophages, extravascular cells vital to lung defense, gain in tissue factor activity during physiologic maturation from monocytes, and shed the procoagulant on membranes at high specific activity into bronchoalveolar lavage fluids. In addition, the cells generate factor V activity in a process dependent on protein synthesis and maturation, and serve as prothrombinase assembly sites. We also found that mature alveolar macrophages with large amounts of tissue factor activity accumulate in the lung during granulomatous pneumonitis, a delayed pulmonary hypersensitivity reaction. Further evidence of the importance of macrophage tissue factor activity is indicated by our experiments with models of allogeneic reactions and kidney rejection, and of tissue factor activity stimulation due to immune complexes. To more definitively characterize monocyte procoagulants, we now propose to investigate synthesis of monocyte/macrophage generated extrinsic pathway factors, with emphasis on tissue factor (and factor V in the alveolar macrophage). We are using human tissue factor apoprotein and other clotting factors (purified to homogeneity) to develop monoclonal and polyclonal antibody reagents for immunoprecipitation of antigen in the synthesis studies. These highly purified reagents will also be used in flow cytometric and electron microscopic investigation of tissue factor distribution on individual monocytes and macrophages relative to factor VII and X binding sites. In addition, kinetics of prothrombinase and tissue factor - VII complex assembly on surfaces of alveolar macrophages will be studied. This series of studies will be extended from healthy controls to SLE and kidney allograft rejection in humans, and to granulomatous pneumonitis and endotoxemia in rabbits.
