BackgroundActivated platelets exert a pro-inflammatory action that can be largely ascribed to their ability to interact with leukocytes and modulate their activity. We hypothesized that platelet activation and consequent formation of monocyte-platelet aggregates (MPA) induces a pro-inflammatory phenotype in circulating monocytes.Methodology/Principal FindingsCD62P+ platelets and MPA were measured, and monocytes characterized, by whole blood flow cytometry in healthy subjects, before and two days after receiving influenza immunization. Three monocytic subsets were identified: CD14+CD16−, CD14highCD16+and CD14lowCD16+. The increase in high sensitivity C-reactive protein post-immunization was accompanied by increased platelet activation and MPA formation (25.02±12.57 vs 41.48±16.81; p = 0.01), along with enhancement of circulating CD14highCD16+ cells (4.7±3.6 vs 10.4±4.8; p = 0.003), their percentage being linearly related to levels of CD62P+-platelets (r2 = 0.4347; p = 0.0008). In separate in vitro experiments, co-incubation of CD14+CD16− cells, isolated from healthy donor subjects, with autologous platelets gave rise to up-regulation of CD16 on monocytes as compared with those maintained in medium alone (% change in CD14+CD16+ cells following 48 h co-incubation of monocytes with platelets was +106±51% vs monocytes in medium alone; p<0.001). This effect correlated directly with degree of MPA formation (r2 = 0.7731; p<0.0001) and was associated with increased monocyte adhesion to endothelial cells. P-selectin glycoprotein ligand-1 (PSGL-1) blocking antibody, which abrogates MPA formation, abolished these effects, as did the cyclooxygenase (COX)-2 selective inhibitor NS-398, aspirin and the EP1/EP2-selective antagonist AH6809.Conclusions/SignificanceThese data suggest that MPA formation, as occurs in the blood under pro-inflammatory conditions, expands the pool of circulating CD14highCD16+ monocytes in a COX-2 dependent manner, and these monocytes exhibit increased adhesion to endothelium. Our findings delineate a novel mechanism underlying the pro-inflammatory effect of platelet activation.

Objective: To determine the effects of primary antiphospholipid syndrome (PAPS)-derived anti-b 2 GPI antibodies on gene expression in human umbilical vein endothelial cells (HUVEC) by gene profiling using microarrays. Methods: Anti-b 2 GPI antibodies purified from sera of patients with PAPS or control IgG isolated from normal subjects were incubated with HUVEC for 4 h before isolation of RNA and processing for hybridisation to Affymetrix Human Genome U133A-2.0 arrays. Data were analysed using a combination of the MAS 5.0 (Affymetrix) and GeneSpring (Agilent) software programmes. For selected genes microarray data were confirmed by real-time PCR analysis or at the protein level by ELISA. Results: A total of 101 genes were found to be upregulated and 14 genes were downregulated twofold or more in response to anti-b 2 GPI antibodies. A number of novel genes not previously associated with APS were induced, including chemokines CCL20, CXCL3, CX3CL1, CXCL5, CXCL2 and CXCL1, the receptors Tenascin C, OLR1, IL-18 receptor 1, and growth factors CSF2, CSF3 IL-6, IL1b and FGF18. The majority of downregulated genes were transcription factors/signalling molecules including ID2. Quantitative real-time RT-PCR analysis confirmed the microarray results for selected genes (CSF3, CX3CL1, FGF18, ID2, SOD2, Tenascin C). Conclusions: This study reveals a complex gene expression response in HUVEC to anti-b 2 GPI antibodies with multiple chemokines, pro-inflammatory cytokines, pro-thrombotic and pro-adhesive genes regulated by these antibodies in vitro. Some of these newly identified anti-b 2 GPI antibody-regulated genes could contribute to the vasculopathy associated with this disease.

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This study investigated the effects of ponesimod, a selective S1P1 receptor modulator, on T lymphocyte subsets in 16 healthy subjects. Lymphocyte subset proportions and absolute numbers were determined at baseline and on Day 10, after once-daily administration of ponesimod (10 mg, 20 mg, and 40 mg each consecutively for 3 days) or placebo (ratio 3:1). The overall change from baseline in lymphocyte count was −1,292±340×106 cells/L and 275±486×106 cells/L in ponesimod- and placebo-treated subjects, respectively. This included a decrease in both T and B lymphocytes following ponesimod treatment. A decrease in naïve CD4+ T cells (CD45RA+CCR7+) from baseline was observed only after ponesimod treatment (−113±98×106 cells/L, placebo: 0±18×106 cells/L). The number of T-cytotoxic (CD3+CD8+) and T-helper (CD3+CD4+) cells was significantly altered following ponesimod treatment compared with placebo. Furthermore, ponesimod treatment resulted in marked decreases in CD4+ T-central memory (CD45RA−CCR7+) cells (−437±164×106 cells/L) and CD4+ T-effector memory (CD45RA−CCR7−) cells (−131±57×106 cells/L). In addition, ponesimod treatment led to a decrease of −228±90×106 cells/L of gut-homing T cells (CLA−integrin β7+). In contrast, when compared with placebo, CD8+ T-effector memory and natural killer (NK) cells were not significantly reduced following multiple-dose administration of ponesimod. In summary, ponesimod treatment led to a marked reduction in overall T and B cells. Further investigations revealed that the number of CD4+ cells was dramatically reduced, whereas CD8+ and NK cells were less affected, allowing the body to preserve critical viral-clearing functions.