| Abstract: | Human recombinant tumor necrosis factor (rTNF) was found to act directly on cultured human vascular endothelium to induce a tissue factor-like procoagulant activity (PCA). After a 4-hr incubation in rTNF (100 units/ml), serially passaged endothelial cells isolated from umbilical veins, saphenous veins, iliac arteries, and thoracic aortae demonstrated a dramatic increase (4- to 15-fold, 21 experiments) in total cellular PCA as measured with a one-stage clotting assay. rTNF-induced PCA was also expressed at the surface of intact viable endothelial monolayers. Induction of PCA by rTNF was concentration dependent (maximum, 500 units/ml), time dependent, reversible, and blocked by cycloheximide and actinomycin D, and it occurred without detectable endothelial cell damage. Actions of rTNF were compared with those of natural human interleukin 1 (IL-1) derived from stimulated monocytes and two distinct species of recombinant IL-1, each of which also induced endothelial PCA. The use of recombinant polypeptides and specific neutralizing antisera established the distinct natures of the mediators. The kinetics of the endothelial PCA responses to TNF and IL-1 were similar, demonstrating a rapid rise to peak activity at approximately equal to 4 hr, and a decline toward basal levels by 24 hr. This characteristic decline in PCA after prolonged incubation with TNF or IL-1 was accompanied by selective endothelial hyporesponsiveness to the initially stimulating monokine. Interestingly, the effects of TNF and IL-1 were found to be additive even at apparent maximal doses of the individual monokines. Endothelial-directed actions of TNF, alone or in combination with other monokines, may be important in the initiation of coagulation and inflammatory responses in vivo. |
