High tissue factor-expressing human monocytes carry low surface CD36: application to intersubject variability

Cellular regulation of blood coagulation: a model for venous stasis

We have adapted the corn-trypsin inhibitor whole-blood model to include EA.hy926 as an endothelium surrogate to evaluate the vascular modulation of blood coagulation initiated by relipidated recombinant tissue factor (rTf) and a cellular Tf surrogate, lipopolysaccharide (LPS)-stimulated THP1 cells (LPS-THP-1). Compared with bare tubes, EA.hy926 with rTf decreased the rate of thrombin formation, ITS accumulation, and the production of fibrinopeptide A. These phenomena occurred with increased rates of factor Va (fVa) inactivation by cleavages at R(506) and R(306). Thus, EA.hy926 provides thrombin-dependent protein C activation and APC fVa inactivation. Comparisons of rTf with LPS-THP-1 showed that the latter gave reduced rates for TAT formation but equivalent fibrinopeptide A, and fV activation/inactivation. In the presence of EA.hy926, the reverse was obtained; with the surrogate endothelium and LPS-THP-1 the rates of TAT generation, fibrinopeptide release, and fV activation were almost doubled, whereas cleavage at R(306) was equivalent. These observations suggest cooperativity between the 2 cell surrogates. These data suggest that the use of these 2 cell lines provides a reproducible quasi-endothelial quasi-inflammatory cytokine-stimulated monocyte system that provides a method to evaluate the variations in blood phenotype against the background of stable inflammatory cell activator and a stable vascular endothelial surrogate.

Development of a continuous assay for the measurement of tissue factor procoagulant activity on intact cells

Tissue factor (TF) is the major physiological initiator of the coagulation cascade and has an important function in the morbidity and mortality associated with many disease states, including cancer-associated thrombosis and atherosclerosis. TF normally exists in a partially encrypted state and its de-encryption on circulating monocytes, platelets or endothelial cells by inflammatory mediators can lead to thrombosis. Furthermore, many cancer cells express large amounts of TF and these cells communicate readily with the circulation through the fenestrated tumor endothelium. To assess agents or conditions that modulate the encryption state of TF, we developed a continuous assay for the determination of TF procoagulant activity (PCA) in a cell-based system. We have shown the use of this assay at detecting agents that de-encrypt TF thereby leading to an increase in TF PCA in three cancer cell lines, namely, T24/83 bladder carcinoma cells and PC-3 and DU145 prostate cancer cells. Further, through use of this assay, we have shown that the endoplasmic reticulum calcium pump inhibitor, thapsigargin, stimulates the de-encryption of TF. The continuous assay for the determination of TF PCA proved to have inherently less intra- and inter-assay variability than the widely used discontinuous assay and is considerably less labor intensive. Further, the continuous assay produced progress curves that were compatible with curve fitting to allow for the determination of the nature of reaction as well as rate constants for the underlying enzymes, TF/FVIIa and FXa. The continuous assay for the assessment of TF PCA on intact cells is applicable for high-throughput screening to allow for the determination of compounds that modulate TF PCA.

No evidence for the presence of tissue factor in high-purity preparations of immunologically isolated eosinophils

BACKGROUND

To date, there is no unequivocal opinion on whether human eosinophils express tissue factor (TF). Therefore, we studied the expression of TF protein and activity in resting or stimulated immunologically purified human eosinophils.

METHODS AND RESULTS

By use of immunologic isolation, we achieved over 96% purity of eosinophil preparations, and contamination by CD14-positive cells was below 0.3%. Flow cytometric [fluorescence-activated cell sorting (FACS)] analysis of eosinophils revealed no surface expression of TF antigen in resting or stimulated eosinophils. Immunoblotting of eosinophil lysates did not show any TF protein under resting or stimulated conditions. The lysates of resting or stimulated eosinophils contained no detectable levels of TF procoagulant activity. In contrast, monocytes, stimulated in plasma or medium, possessed readily detectable TF levels on the cell surface and in cell lysates as detected by FACS and immunoblotting. This was active TF antigen, as confirmed by TF activity assay (19.2 +/- 4.2 and 28.6 +/- 3.1 mU per 10(6) cells, stimulated in medium or plasma, respectively). We found no detectable TF mRNA levels in resting or stimulated eosinophils by real-time polymerase chain reaction (PCR), whereas in monocytes TF mRNA levels were significantly increased after stimulation.

CONCLUSIONS

Our data indicate that there is no evidence for TF expression in high-purity preparations of immunologically isolated eosinophils.