Human allogeneic lymphocytes trigger endothelial cell tissue factor expression by a tumor necrosis factor-dependent pathway

Lymphocyte adhesion to endothelial cells and the extravascular deposition o f fibrin are 2 important processes during pathologic situations such as all ograft rejection. Tissue factor (TF) expression was therefore measured on h uman umbilical vein endothelial cells (HUVECs) after coculture with allogen eic lymphocytes (PBLs) by a factor Xa generation assay. When cocultured wit h PBLs, HUVECs expressed strong procoagulant activity related to the TF/fac tor VII-dependent pathway, which was enhanced when endothelial cells were t reated with interferon-gamma (IFN- gamma). The highest TF activity was meas ured when 10(5) lymphocytes were incubated with 10(4) HUVECs (ratio 10:1) f or 4 hours, a time-dependent course similar to that obtained with tumor nec rosis factor-alpha (TNF-alpha), and direct contact between the 2 cell types was necessary. PBL-induced TF activity was inhibited by cycloheximide or a ctinomycin D, indicating active protein synthesis that was confirmed by the increase in TF mRNA detected by reverse transcription-polymerase chain rea ction. It was then demonstrated that 1 of the primary signaling pathways le ading to endothelial cell TF expression was a rapid initial interaction bet ween membrane TNF expressed on PBLs and the 75-kd TNF receptor, with subseq uent involvement of platelet-activating factor and P-selectin, Finally, we showed that the transduction of external signals involving the activation o f protein kinase C and protein tyrosine kinases also contributed to the reg ulation of TF expression.