Summary
Pleural fibrin deposition that promotes loculation and fibrosis after pleural injury
is initiated by tissue factor (TF). In this study, we sought to determine if tissue
factor pathway inhibitor (TFPI), an inhibitor of the TF-factor VIIa complex, was likewise
expressed in tetracycline (TCN)-induced pleural injury and, if so, whether TFPI was
locally elaborated. Pleural fluid TFPI activity approximated that of plasma by 24
h and doubled by 3 days after intrapleural TCN. By contrast, pleural fluid coagulation
factors VII and V remained below plasma concentrations at these intervals. Immunohistochemical
studies demonstrated TF, TFPI and fibrin localized in pleural and subpleural tissues
and within intrapleural adhesions. TFPI activity and mRNA were also elaborated by
rabbit pleural mesothelial cells and lung fibroblasts. TFPI is locally expressed and
pleural fluid TFPI exceeds plasma levels during TCN-induced pleural injury. Resident
cells as well as extravasation likely contribute to intrapleural TFPI. TFPI expression
temporally and anatomically approximates that of TF and may limit TF-induced fibrin
deposition in evolving TCN-induced pleuritis.