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Abstract Background Monocytes play a prominent role in inflammation, coagulation and atherosclerosis by their ability to produce tissue factor (TF) and cytokines. The aim of the present study was to establish whether virus-infected monocytes initiate coagulation. In addition, the production of cytokines by monocytes may accelerate the chronic process of atherosclerosis and may contribute to coronary syndromes by eliciting plaque instability. Materials and methods Monocytes were isolated by Vacutainer® , BD Biosciences, Alphen aan den Rijn, Netherlands and subsequent magnetic cell sorting (MACS® , Milteny Biotec, Bergish Gladbach, Germany). Coagulation times in normal pooled plasma and Factor VII-deficient plasma were measured after infection with cytomegalovirus (CMV), Chlamydia pneumoniae (Cp) and influenza A\H1N1. Anti-TF antibodies were added to neutralize TF expressed on monocytes. Interleukins (IL) 6, 8 and 10 were measured in the supernatants. Results Chlamydia pneumoniae- and CMV-infected monocytes decreased the clotting time by 60%, and influenza-infected monocytes by 19%, as compared to uninfected monocytes. Procoagulant activity was absent when Factor VII-deficient plasma or anti-TF antibodies were used. Monocytes produced both IL-6 and IL-8 after infection with CMV (317 pg mL-1 and 250 pg mL-1 ) or Cp (733 pg mL-1 and 268 pg mL-1 ). Similar results were obtained for influenza virus-infected monocytes, but the levels of both cytokines were 3–5-fold higher (1797 pg mL-1 and 725 pg mL-1 ). Interleukin-10 was not produced by infected monocytes. Conclusion The procoagulant activity of virus-infected monocytes is TF-dependent. Although influenza infection did not generate a significant reduction in clotting time, the pronounced expression of IL-6 and IL-8 may induce local and/or systemic inflammatory reactions, which may be associated with plaque rupture... [ABSTRACT FROM AUTHOR]

Abstract Background Chronic low-grade inflammation is associated with increased risk of vascular diseases. The source of inflammation is unknown but may well be chronic and/or repetitive infections with microorganisms. Direct infection of endothelial cells (ECs) may also be a starting point for atherogenesis by initiating endothelial procoagulant activity, increased monocyte adherence and increased cytokine production. We hypothesized that iron-mediated intracellular hydroxyl radical formation after infection is a key event in triggering the production of interleukin-6 (IL-6) by ECs in vitro . Methods Cultured ECs were incubated with Fe(II) and Fe(III) or infected with Chlamydia pneumoniae or influenza A/H1N1/Taiwan/1/81 for 48 and 24 h, respectively. To determine the role of iron and reactive oxygen species, cells were coincubated with the H2 O2 scavenger N -acetyl-l -cysteine, with the iron chelator deferoxamine (DFO) or with the intracellular hydroxyl radical scavenger dimethylthiourea (DMTU). After the incubation periods, supernatants were harvested for IL-6 determination. Results Incubating ECs with Fe(II) and Fe(III) resulted in increased IL-6 production. Similarly, infection with C. pneumoniae and influenza A also induced an IL-6 response. Coincubating ECs with DFO or DMTU blocked this response. Nuclear factor-κB activity was increased after infection and blocked by coincubation with DFO or DMTU. Conclusion Cultured ECs respond to infection and iron incubation with increased production of IL-6. Iron, the generation of intracellular hydroxyl radical and NF-κB activity are essential in cellular activation, suggesting that reactive oxygen species generated in the Haber–Weiss reaction are essential in invoking an immunological response to infection by ECs. [ABSTRACT FROM AUTHOR]