INDUCTION OF TISSUE FACTOR EXPRESSION IN HUMAN MONOCYTE ENDOTHELIUM COCULTURES/

Induction of tissue factor (TF) expression on monocyctes and endotheli al cells is central to the development of septic coagulopathy, Serum c oncentrations of endotoxin in septic patients who develop disseminated intravascular coagulation (DIG) do not, however, reach the levels tha t would directly stimulate TF expression on either monocytes or endoth elium. We show, using an in vitro coculture system, that the interacti on of monocytes with endothelium induces the expression of significant levels of TF, Unstimulated cocultures of monocytes (2 x 10(4)/well) a nd endothelial cells (2 x 10(4)/well) produced 35.3+/-8.5 mU of PCA/we ll, representing a 5-fold increase over the combined PCA of each cell type cultured alone (7.1+/-1.5 mU, n = 6, P < 0.001), Significant enha ncement was also found in the presence of low concentrations of LPS, I nduction of TF protein was confirmed by Western blotting, Fixation of monocytes with paraformaldehyde completely abolished TF induction in c ocultures, whereas fixation of endothelium had no effect, suggesting t hat TF induction occurred in monocytes rather than endothelial cells. Induction of TF in cocultures could be further augmented by preincubat ing the endothelial cells with IFN-gamma. When endothelium was prestim ulated with 500 U/ml IFN-gamma there was 142+/-11% increase over unsti mulated cocultures (n = 5, P < 0.01). TF induction was inhibited by 32 +/-6% in the presence of anti-ICAM-1 mAb (n = 5, P < 0.01). Our result s suggest that monocyte interactions with vascular endothelium, regula ted by inflammatory cytokines, and mediated by adhesive ligand binding , leads to the induction of functional monocyte TF protein, which may be responsible for the initiation of DIC in sepsis.