IN-VITRO EXPRESSION AND INHIBITION OF PROCOAGULANT ACTIVITY PRODUCED BY BOVINE ALVEOLAR MACROPHAGES AND PERIPHERAL-BLOOD CELLS

Local and systemic activation of coagulation is frequently associated with bacterial sepsis. The coagulopathy is due, at least in part, to e xpression of tissue factor (TF) by monocytes and macrophages. The purp ose of this study was to evaluate the expression of procoagulant activ ity by bovine alveolar macrophages, leukocytes and platelets, and to d etermine the relative potency of three chemical inhibitors of TF expre ssion (pentoxifylline, retinoic acid, and cyclosporin A). Bovine alveo lar macrophages were stimulated with lipopolysaccharide (LPS) derived from Pasteurella haemolytica or recombinant bovine tumour nervous fact or (TNF) and dose- and time-dependent effects on TF expression were st udied. LPS and TNF induced TF expression in alveolar macrophages and L PS treatment of whole blood induced TF expression in mononuclear cells . Neutrophils and platelets also expressed procoagulant activity, but this activity was not inhibited by anti-bovine TF monoclonal antibody. Pentoxifylline (40 mu mol/L), retinoic acid (0.01 mmol/L) and cyclosp orin A (0.08 mu mol/L) inhibited TF expression when added concurrently with LPS or TNF, but not when added 4 h after stimulation. TF mRNA wa s not detected in unstimulated alveolar macrophages by Northern blot a nalysis. In contrast, exposure to LPS or TNF for 6 h induced marked ex pression of TF mRNA, which was inhibited by treatment with pentoxifyll ine, retinoic acid and cyclosporin A. Expression of TNF by alveolar ma crophages stimulated with LPS was also inhibited by these compounds. O ur results indicate that procoagulant activity expressed by alveolar m acrophages and monocytes is associated with expression of TF, whereas procoagulant activity expressed by neutrophils and platelets is not. T he concentrations of pentoxifylline and retinoic acid necessary for in hibition of TF expression in vitro. may not be achievable in vivo owin g to their toxic effects. However, the in vitro concentration of cyclo sporin A that inhibited TF expression did not exceed the plasma concen tration observed in humans, and therefore may be useful for inhibition of TF expression in vivo.