Oxidized Low-Density Lipoproteins Induce Tissue Factor Expression in T-Lymphocytes via activation of Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1.

BACKGROUND: T-lymphocytes plays an important role in the pathophysiology of acute coronary syndromes (ACS). T-cell activation in vitro by pro-inflammatory cytokines may lead to functional Tissue Factor (TF) expression, indicating a possible contribution of immunity to thrombosis. Oxidized low-density lipoproteins (oxLDLs) are found abundantly in atherosclerotic plaques. We aimed at evaluating the effects of oxLDLs on TF expression in T-cells and the role of the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1). METHODS AND RESULTS: CD3+ cells were isolated from healthy volunteers. Gene, protein, and surface expression of TF, as well as of LOX-1, was assessed at different time-points after oxLDL stimulation. To determine whether oxLDL-induced TF was LOX-1 dependent, T-cells were preincubated with a LOX-1 inhibiting peptide (L-RBP) or with an anti-LOX-1 blocking antibody. To exclude that TF expression was mediated by reactive oxygen species (ROS) generation, oxLDL-stimulated T-cells were preincubated with superoxide dismutase (SOD) + catalase or with 4-Hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol), an intracellular free radical scavenger. Finally, to determine if the observed findings in vitro may have a biological relevance, the presence of CD3+/TF+/LOX-1+ cells was evaluated by immunofluorescence in human carotid atherosclerotic lesions.OxLDLs induced functionally active TF expression in T-cells in a dose and time-dependent manner, independently on ROS generation. No effect was observed in native LDL-treated T-cells. LOX-1 expression was also induced by oxLDLs in a time- and dose-dependent manner. Pre-incubation with L-RBP or anti LOX-1 antibody almost completely inhibited oxLDL-mediated TF expression. Interestingly, human carotid plaques showed significant infiltration of CD3+ cells (mainly CD8+ cells), some of which were positive for both TF and LOX-1. CONCLUSIONS: oxLDLs induce functional TF expression in T-lymphocytes in vitro via interaction of oxLDLs with LOX-1. Human carotid atherosclerotic plaques contain CD3+/CD8+cells that express both TF and LOX-1, indicating that also in patients these mechanisms may play an important role. TRANSLATIONAL PERSPECTIVES: Despite significant advancements have been made in antithrombotic therapy, current strategies still fail to prevent acute thrombotic coronary events in a substantial number of patients, indicating that the complex mechanisms underlying the pathophysiology of ACS are not fully elucidated. The present study demonstrates, for the first time, that T-lymphocytes may express functional TF in response to oxLDLs via mechanisms other than the "classical" activation of the T-cell receptor, namely via interaction with LOX-1. Further studies aimed at interfering with LOX-1 in T-lymphocytes might offer innovative and additional therapeutical approaches for ACS patients.