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Fibrin deposition is an integral feature of the inflammatory response. In response to C-reactive protein (CRP), an acute-phase reactant, blood monocytes synthesize and express tissue factor (TF), the main initiator of blood coagulation. We report the inhibitory effect of interleukin 10 (IL-10) and that of pentoxifylline, a methyl xanthine derivative, on monocyte expression of TF activity, TF protein and TF mRNA in response to CRP. These agents may be of use in diseases where a TF-induced prothrombotic state is detrimental.

Tissue factor (TF) is a transmembrane receptor which, in association with factors VII and VIIa, activates factor IX and X, thereby activating the coagulation protease cascades. In response to bacterial lipopolysaccharide (LPS) monocytes transcribe, synthesize and express TF on their surface. We investigated whether LPS-induced TF in human monocytes is mediated by protein kinase C (PKC) activation. The PKC agonists phorbol 12-myristate 13-acetate (PMA) and phorbol 12, 13 dibutyrate (PdBu) were both potent inducers of TF in human monocytes, whereas 4 alpha-12, 13 didecanoate (4 alpha-Pdd) had no such effect. Both LPS- and PMA-induced TF activity were inhibited, in a concentration dependent manner, by three different PKC inhibitors: H7, staurosporine and calphostin C. TF antigen determination confirmed that LPS-induced cell-surface TF protein levels decreased in parallel to TF functional activity under staurosporine treatment. Moreover, Northern blot analysis of total RNA from LPS- or PMA-stimulated monocytes showed a concentration-dependent decrease in TF mRNA levels in response to H7 and staurosporine. The decay rate of LPS-induced TF mRNA evaluated after the arrest of transcription by actinomycin D was not affected by the addition of staurosporine, suggesting that its inhibitory effect occurred at a transcriptional level. We conclude that LPS-induced production of TF and its mRNA by human monocytes are dependent on PKC activation.

In Gram-negative septic shock, human monocytes synthesize and express on their cytoplasmic membrane tissue factor (TF), a potent activator of the coagulation cascades. The role of TF in triggering disseminated intravascular coagulation (DIC) in these patients appears to be clear. We report the suppressive effect of interleukin-10 (IL-10) on endotoxin-induced TF activity and antigen levels, and on the expression of TF mRNA levels in human monocytes. These results emphasize the potential therapeutic value of this cytokine in septic shock, a condition still associated with a high mortality rate.

Increased expression of tissue factor (TF) procoagulant activity by blood monocytes and tissue macrophages is implicated in a number of thrombotic disorders, as well as in fibrin deposition associated with inflammatory lesions and immunological diseases. We found that interleukin 4 (IL-4), a T lymphocyte-derived cytokine known to regulate a number of monocyte functions, inhibited the production of TF by monocytes in response to endotoxin and phorbol myristate acetate (PMA) in vitro. IL-4 had a concentration-dependent inhibitory effect on functional TF procoagulant activity (PCA) and reduced the binding of an anti-TF antibody, as assessed by flow cytometry analysis. Moreover, IL-4 reduced LPS- and PMA-induced TF mRNA levels. TF mRNA stability was not modified by IL-4 after the arrest of transcription by actinomycin D. We thus conclude that mRNA suppression is mediated by an effect occurring at the transcriptional level. Our results also show that the suppressive effect of IL-4 is independent of an increase in the intracellular concentration of cyclic AMP, another established inhibitor of TF production. Locally produced IL-4 might thus contribute to limiting the consequences of monocyte activation.

Tissue factor (TF) is a transmembrane glycoprotein which, in association with factor VII(a), is the main activator of coagulation. In illnesses such as Gram-negative endotoxemia, circulating monocytes synthesize and express substantial TF activity, resulting in extensive disseminated intravascular coagulation. We investigated the way in which TF is suppressed by pentoxifylline (PTX), and found that PTX down-regulates immunologic TF expression and specific mRNA production in response to LPS. Since TF mRNA stability is not altered, this effect appears to take place at the transcriptional level.

Tissue factor (TF) is a transmembrane receptor that serves as the major cofactor for factor VIIa-catalyzed proteolytic activation of factors IX and X. In response to bacterial lipopolysaccharide (LPS), monocytes transcribe, synthesize, and express TF on their surface, thereby conveying to activated monocytes the ability to initiate the blood coagulation protease cascades. Agents that elevate cellular cyclic AMP (cAMP) inhibit the functional expression of TF by LPS-stimulated monocytes. In this study, we investigated the mechanism of this suppression. Northern blot analysis of total RNA from LPS-stimulated monocytes showed a concentration-dependent decrease in TF messenger RNA (mRNA) levels in response to dibutyryl-cAMP (dBt-cAMP). TF mRNA and procoagulant activity were inhibited as early as 1 hour after the addition of dBt-cAMP and the inhibition persisted through 4 hours. Suppression of specific mRNA abundance was also observed with agents, including forskolin and iso-butyl-methyl-xanthine (IBMX), that increase cAMP levels by independent mechanisms. Flow immunocytometric analysis confirmed that cell-surface TF protein levels declined in parallel with TF functional activity. The rate of decay of TF mRNA after the arrest of transcription by actinomycin D was not altered by the addition of dBt-cAMP, IBMX, or forskolin, thus excluding effects on TF mRNA stability. We conclude that elevated cAMP levels suppress TF mRNA by reducing the rate of TF gene transcription.

Monocytes can play a role in the activation of coagulation via increased procoagulant activity (PCA). We investigated the level of monocyte PCA in 19 patients with systemic lupus erythematosus (SLE), given the high rate of thrombotic events in this condition. Nine of these subjects also presented the lupus anticoagulant (LA). The PCA generated by patient monocytes was significantly higher than control values and was identified as tissue factor-like. Moreover, the number of monocytes with membrane-associated D dimer, a parameter which we have shown to be correlated with the PCA expressed in vitro by endotoxin-activated monocytes, was also significantly increased. Serum from both groups of patients (i.e. SLE and SLE + LA) stimulated the generation of PCA by control monocytes. By contrast, purified IgG from both patient groups had the same effect as control IgG on PCA generation by control monocytes. The nature of the stimulating agent in the serum was not identified. In conclusion, increased monocyte PCA may account for the increased incidence of thrombosis in SLE patients, although other, superimposed, factors would appear to exist in SLE + LA patients, given the higher incidence of thrombosis in this subgroup.

Monocytes can play a role in the activation of coagulation via increased procoagulant activity (PCA). We investigated the level of monocyte PCA in 19 patients with systemic lupus erythematosus (SLE), given the high rate of thrombotic events in this condition. 9 of these subjects also presented the lupus anticoagulant (LA). The PCA generated by patient monocytes was significantly higher than control values and was identified as tissue factor-like. Serum from both groups of patients (i.e. SLE and SLE + LA) stimulated the generation of PCA by control monocytes. By contrast, purified IgG from both patient groups had the same effect as control IgG on PCA generation by control monocytes. The nature of the stimulating agent in the serum was not identified. In conclusion, increased monocyte PCA may account for the increased incidence of thrombosis in SLE patients, although other, superimposed, factors would appear to exist in SLE + LA patients, given the higher incidence of thrombosis in this subgroup.