Intracellular and Surface Distribution of Monocyte Tissue Factor

Abstract

Objective— The high and low responder phenomenon describes individual differences in lipopolysaccharide (LPS)-induced monocyte tissue factor (TF) activity. We characterized patterns of intracellular accumulation, externalization, and shedding of TF in response to LPS in mononuclear cells (MNCs) from high responders (HRs) and low responders (LRs). Methods and Results— After 2 hours of LPS stimulation of whole blood, flow cytometry analyses revealed a larger population of TF-positive monocytes in HRs (32.0±3.5%) versus LRs (11.2±1.2%; P ≤0.05), along with a stronger mean fluorescence intensity of TF signal in HRs (7.1±0.5 arbitrary units [AU]) compared with LRs (5.4±0.4 AU; P ≤0.05). The LPS-treated blood of the HR group contained 2-fold more TF-positive microparticles than LRs. In-cell Western assay demonstrated higher intracellular accumulation of TF in mononuclear cells (MNCs) from LRs because LPS induced a 3.7-fold increase of total TF levels in LRs versus a 1.5-fold increase in HRs. In contrast, in response to LPS stimulation, MNCs from HRs exhibited a 4-fold induction of surface TF, whereas MNCs from LRs only had a minor increase in surface TF levels. Conclusions— The higher availability of surface TF antigen on MNCs from HRs and TF-containing microparticles might make these individuals more susceptible to hypercoagulation. In the present ex vivo study, we report several novel observations characterizing the distribution of TF antigen between the interior and the surface of MNCs from HRs and LRs. MNCs from HRs and LRs exhibit distinct patterns of intracellular accumulation, externalization and shedding of TF in LPS-stimulated conditions.