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Fibronectin‐adherent monocytes express tissue factor and tissue factor pathway inhibitor whereas endotoxin‐stimulated monocytes primarily express tissue factor: physiologic and pathologic implications

Background: Monocytes are critical cells in initiating physiologic and/or pathologic tissue factor (TF)‐induced intravascular and extravascular coagulation. Monocytes constitutively express small amounts of TF and tissue factor pathway inhibitor (TFPI). Non‐adherent lipopolysaccharide (LPS)‐stimulated monocytes express significant amounts of TF; however, increased expression of TFPI by these cells is controversial. Further, whether fibronectin‐adherent monocytes (mimicking conditions in the extravascular space) express sufficient TFPI to inhibit TF‐procoagulant activity (PCA) is unknown.Objective: To compare TF and TFPI expression by fibronectin‐adherent and LPS‐stimulated non‐adherent monocytes.Methods: Monocytes were isolated from normal peripheral blood, adhered to fibronectin or stimulated with lipopolysaccharide (LPS) under non‐adherent conditions and examined for expression of TF and TFPI using quantitative real‐time reverse transcription‐polymerase chain reaction (RT‐PCR), ELISA and factor X (FX) activation.Results: Under LPS‐free conditions, the fibronectin‐adherent monocyte TF mRNA, antigen and activity were markedly upregulated. Notably, cell and microparticle (MP)‐associated TF and alternatively spliced TF (asTF) were all upregulated. TFPI mRNA and antigen were also upregulated in the fibronectin‐adherent monocytes, which significantly inhibited TF‐PCA. TFPI mRNAs for both alpha and beta forms were detected. The peak in TFPI activity occurred in tandem with the peak in TF‐PCA. In contrast, LPS‐stimulated monocytes, which expressed cell and MP‐associated TF and asTF, demonstrated only minimal expression of TFPI as determined by mRNA, antigen or inhibition of TF activity.Conclusion: Both LPS‐stimulated and fibronectin‐adherent monocytes demonstrate a procoagulant phenotype by expressing TF but only fibronectin‐adherent monocytes express significant amounts of TFPI to control thrombin generation and fibrin formation in the context of extravascular space.