TISSUE FACTOR EXPRESSION IN MESOTHELIAL CELLS - INDUCTION BOTH IN-VIVO AND IN-VITRO

Exudative pleural effusions are characterized by a high protein conten t and frequently progress to loculation and fibrosis. To test the hypo thesis that tissue factor (TF) plays an integral role in this process, we in vestigated the expression of TF by human mesothelial cells (HMC ) both in vivo and bl vitro, and measured the effect of serum on HMC e xpression of TF in vitro, In vitro TF expression was not detected in H MC of normal pleura, but was detected in HMC of pleura overlying infla med lung. In vitro, quiescent HMC demonstrated negligible levels of: T F expression; however, upon serum stimulation there was a marked induc tion in both TF protein level and activity, peaking at 8-9 h. In contr ast, treating quiescent HMC with plasma resulted in a further small, b ut significant, decrease in TF expression. This serum-induced rise in TF was also reflected in TF mRNA levels and did not require de novo pr otein synthesis, These results suggest that induction of HMC TF expres sion may be important in triggering both the intrapleural activation o f prothrombin and the deposition of fibrin characteristic of inflammat ory effusions.