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The Fourth Maastricht Consensus Conference on Thrombosis included the following themes. Theme 1: The "coagulome" as a critical driver of cardiovascular disease. Blood coagulation proteins also play divergent roles in biology and pathophysiology, related to specific organs, including brain, heart, bone marrow, and kidney. Four investigators shared their views on these organ-specific topics. Theme 2: Novel mechanisms of thrombosis. Mechanisms linking factor XII to fibrin, including their structural and physical properties, contribute to thrombosis, which is also affected by variation in microbiome status. Virus infection-associated coagulopathies perturb the hemostatic balance resulting in thrombosis and/or bleeding. Theme 3: How to limit bleeding risks: insights from translational studies. This theme included state-of-the-art methodology for exploring the contribution of genetic determinants of a bleeding diathesis; determination of polymorphisms in genes that control the rate of metabolism by the liver of P2Y12 inhibitors, to improve safety of antithrombotic therapy. Novel reversal agents for direct oral anticoagulants are discussed. Theme 4: Hemostasis in extracorporeal systems: the value and limitations of ex vivo models. Perfusion flow chamber and nanotechnology developments are developed for studying bleeding and thrombosis tendencies. Vascularized organoids are utilized for disease modeling and drug development studies. Strategies for tackling extracorporeal membrane oxygenation-associated coagulopathy are discussed. Theme 5: Clinical dilemmas in thrombosis and antithrombotic management. Plenary presentations addressed controversial areas, i.e., thrombophilia testing, thrombosis risk assessment in hemophilia, novel antiplatelet strategies, and clinically tested factor XI(a) inhibitors, both possibly with reduced bleeding risk. Finally, COVID-19-associated coagulopathy is revisited., Competing Interests: None declared., (The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/).)

Cancer-related venous thromboembolism (VTE) is frequent and constitutes the second leading cause of death in patients with cancer. High platelet count is one of independent predictive factors of cancer-associated VTE. Besides the implication of platelets in cancer-associated VTE, recent clinical and experimental evidences support that platelets play several roles in the progression of malignancies and inversely, cancer can also influence platelet count and activity. The objective of this report is to review the current literature regarding the role of platelets in cancer through experimental results and population-based studies. Platelets are implicated in cancer progression and metastasis through proangiogenic factors (growth factors and signaling pathways), antiangiogenic factors (angiostatin, endostatin, thrombospondin-1), and matrix metalloproteinases. In addition, platelets are involved in cancer-associated thrombosis and thus tumor cell-induced platelet activation, through anionic phospholipids on their surface, released soluble factors, such as P-selectin, CD40 ligand, platelet factor 4, thrombospondin-1 or beta-thromboglobulin, tumor cell procoagulant proteins (tissue factor, urokinase-type plasminogen activator, plasminogen activator inhibitor type 1), and microparticles. Due to these different mechanisms, platelets may represent a potential therapeutic target. The main current treatments against platelets are: (1) acetylsalicylic acid (aspirin) and nonsteroidal anti-inflammatory drugs, nonselective cyclo-oxygenase (COX)-1 and COX-2 inhibitors, which are associated with decreased cancer incidence and better overall survival and (2) irreversible inhibitor of P2Y12 subtype which decreases cancer incidence. Platelets are key players in tumor growth, metastasis, and cancer-associated thrombosis. This multifaceted role identifies them as a relevant therapeutic target for prevention of cancer occurrence and treatment of cancer., Competing Interests: Dr. Lacroix reports grants from Stago/BioCytex, during the conduct of the study. In addition, Dr. Lacroix has a patent Microvesicle Plasmin generation licensed to Stago., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Microvesicles (MVs) are small membrane enclosed structures released into the extracellular space by virtually all cell types. Their composition varies according to the cell origin and the stimulus which caused their formation. They harbor functional molecules and participate in intercellular communication. Endothelium, inflammatory cells, and cancer cells produce procoagulant MVs which contribute to cancer-associated thrombosis (CAT) in animal models. The tissue factor (TF) conveyed by these MVs was shown to play a key role in different animal models of experimental CAT. Alternatively, other molecular mechanisms involving polyphosphates or phosphatidylethanolamine could also be involved. In clinical practice, an association between an increase in the number of TF-positive or the procoagulant activity of these MVs and the occurrence of CAT has indeed been demonstrated in pancreatic-biliary cancers, suggesting that they could behave as a biomarker predictive for CAT. However, to date, this association was not confirmed in other types of cancer. Potential causes explaining this limited associated between MVs and CAT are (1) the diversity of mechanisms associating MVs and different types of cancer; (2) a more complex role of MVs in hemostasis integrating their anticoagulant and fibrinolytic activity; and (3) the lack of sensitivity, reproducibility, and standardization of current methodologies permitting measurement of MVs. Each of these hypotheses constitutes an interesting exploration path for a future reassessment of the clinical interest of the MVs in CAT., Competing Interests: R.L. reports grants from Stago/BioCytex, during the conduct of the study; in addition, R.L. has a patent Microvesicle Plasmin generation licensed to Stago. The other authors have no conflict of interest to disclose., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Microvesicles are members of the family of extracellular vesicles shed from the plasma membrane of activated or apoptotic cells. Microvesicles were initially characterised by their pro-coagulant activity and described as "microparticles". There is mounting evidence revealing a role for microvesicles in intercellular communication, with particular relevance to hemostasis and vascular biology. Coupled with this, the potential of microvesicles as meaningful biomarkers is under intense investigation. This Position Paper will summarise the current knowledge on the mechanisms of formation and composition of microvesicles of endothelial, platelet, red blood cell and leukocyte origin. This paper will also review and discuss the different methods used for their analysis and quantification, will underline the potential biological roles of these vesicles with respect to vascular homeostasis and thrombosis and define important themes for future research.

Microparticles (MPs) are submicronic vesicles which are formed by budding of the cellular membrane of virtually any cell type in response to cell activation or apoptosis. Both circulating MPs and MPs generated within tissues harbor molecules with a large repertoire of biological activities and transfer material to target cells. Depending on their cellular origin, the stimuli triggering their formation, or their localization, they may participate in the maintenance of organ or vascular homeostasis as well as inducing dysfunction. MPs have mostly been described as having procoagulant properties. However, the fact that some MP subsets are able to efficiently generate plasmin suggests that the role of MPs in hemostasis is more complex than initially thought. In this review, we summarize key findings showing that MPs provide a heterogeneous catalytic surface for plasmin generation, according to their cellular origin. We further address the specific features of the MP-dependent fibrinolytic system. Potential consequences of this MP-associated fibrinolytic activity in pathology are illustrated in cancer., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Pretreatment with a loading dose (LD) of clopidogrel or ticagrelor before percutaneous coronary intervention (PCI) in acute coronary syndrome (ACS) is supported by the guidelines, but debated following a recent meta-analysis on clopidogrel pretreatment and the ACCOAST trial. In this trial prasugrel pretreatment failed to reduce ischaemic events. The timing of optimal platelet reactivity (PR) inhibition of ticagrelor and prasugrel in non ST-elevation ACS (NSTE ACS) is yet undetermined. In the present study, we aimed to investigate the delay required to reach optimal PR inhibition in NSTE ACS following a LD of ticagrelor or prasugrel. Consecutive patients undergoing PCI for NSTE ACS were randomised in this monocentre study. The Vasodilator-phosphoprotein index (VASP) was used to measure PR before the LD and then at 30 minutes, 1, 2, 4 and 24 hours (h) post-LD. Optimal PR inhibition was defined as a VASP < 50%. We randomised 24 patients to ticagrelor or prasugrel LD. One hour after the LD, 29% of patients had a VASP > 50% (ticagrelor and prasugrel: 25 vs 33%; p=0.7). Optimal PR inhibition was obtained 2 h after the LD in both groups (12/12 with ticagrelor and 11/12 with prasugrel). At that time, the mean VASP index was 19 ± 16% (95%CI: 12-25). Maximal PR inhibition was reached after 4 h: 11 ± 10% (95%CI: 6-15). In NSTE ACS undergoing PCI a LD of ticagrelor or prasugrel given during the procedure provides optimal P2Y12-ADP receptor blockade in 2 h and maximal inhibition within 4 h.

Optimal P2Y12 receptor blockade is critical to prevent ischaemic recurrence in patients undergoing percutaneous coronary intervention (PCI). We aimed to compare the level of platelet reactivity (PR) inhibition achieved by prasugrel and ticagrelor loading dose (LD) in diabetic acute coronary syndrome (ACS) patients undergoing PCI. We performed a single-center prospective open-label randomised trial. Patients with diabetes mellitus undergoing PCI for an ACS were randomised to receive prasugrel 60 mg or ticagrelor 180 mg. The primary endpoint of the study was the level of platelet reactivity (PR) assessed between 6 and 18 hours post-LD using the VASP index. We randomised 100 diabetic patients undergoing PCI for an ACS. No difference was observed in baseline characteristics between the two groups. In particular, the rate of patient receiving insulin therapy was identical (25 vs 28.6%; p =0.7). Ticagrelor achieved a significantly lower PR compared to prasugrel loading dose (17.3 ± 14.2 vs 27.7 ± 23.3%; p=0.009). In addition the rate of high on-treatment platelet reactivity, defined by a VASP ≥50%, tend to be lower in the ticagrelor group although the difference did not reach statistical significance (6 vs 16%; p=0.2). The rate of low on treatment PR was identical (60 vs 54%; p=0.8). The present study demonstrates that ticagrelor LD is superior to prasugrel LD to reduce PR in ACS patients with diabetes mellitus. Whether the higher potency of ticagrelor could translate into a clinical benefit should be investigated.

Microparticles (MPs) are small vesicles resulting from the shedding of cellular membrane during activation or apoptosis processes. Beyond their well-described procoagulant property, accumulating data show that specific endothelial cell-, leukocyte-, tumor-derived MPs bind plasminogen and vectorize plasminogen activators, leading to an efficient plasmin generation and matrix metalloproteinases activation. This review focuses on the molecular equipment of MPs subpopulations that identify MPs as efficient support for plasmin generation and the potential consequences of this new function. By the combined facts that MPs may disseminate, concentrate active proteolytic molecules and represent a protective environment against soluble inhibitors, MPs behave as an efficient catalytic surface involved in vascular and matrix proteolysis-related biological processes. The existence of this proteolytic MPs in the circulation or in body fluids raises the question about the physiological relevance of this activity. Consequences are suggested in many biological processes such as fibrinolysis, cell survival, matrix remodeling, angiogenesis, and tumor metastasis. However, further studies will be necessary to determine the extent in which in vivo MPs contribute to these pathophysiological mechanisms and how this circulating property of MPs may represent a new biomarker in specific clinical situations., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Optimal platelet reactivity (PR) inhibition is critical to prevent thrombotic events in primary percutaneous coronary intervention (PCI). We aimed to determine the relationship between high on-treatment platelet reactivity (HTPR) and ST-elevation myocardial infarction (STEMI) following a 600 mg loading dose (LD) of clopidogrel. We performed a prospective monocentre study enrolling patients on clopidogrel undergoing PCI. The VASP index was used to assess PR inhibition after clopidogrel LD. HTPR was defined according to the consensus as a VASP index ≥50%. The present study included 833 patients undergoing PCI. Most patients had PCI for an acute coronary syndrome (58.7%). The mean VASP index was 50 ± 23% with a large inter-individual variability (range: 1-94%). Patients with a VASP index ≥50% were significantly older (p= 0.03), with a higher body mass index (BMI) (p<0.001), more often diabetic (p=0.03), taking omeprazole (p=0.03), admitted for an acute coronary syndrome (ACS) and with a high fibrinogen level compared to good responders (VASP <50%). In multivariate analysis BMI, omeprazole use, ACS and high fibrinogen level (p<0.001) remained significantly associated with HTPR. Of importance, in this analysis STEMI was independently associated with HTPR when compared with the other forms of ACS (NSTEMI and unstable angina) with an odd ratio of 2.14 (95% CI: 1.3 -3.5; p=0.003). In conclusion, STEMI is associated with high on-treatment platelet reactivity following 600 mg of clopidogrel. The present results suggest that 600 mg of clopidogrel may not be able to achieve an optimal PR inhibition in STEMI patients undergoing PCI and more potent drugs may be preferred.

Circulating microparticles are submicron vesicles released from cell membranes in response to activation or apoptosis. Acknowledgment of their role both as markers and pathogenic effectors in thrombosis, inflammation, and the spread of cancer has increased the interest of their measurement in clinical practice. However, assessment of their clinical use is impeded by technological issues. Among the different methodologies available, flow cytometry is the most commonly used technique. This review addresses flow cytometry limitations in microparticle measurement that may be subdivided into three domains: sizing, probing, and counting. This article also covers the various standardization strategies and technological improvements that have been proposed to overcome these limitations. New tools using size-calibrated beads and recent progress in instrumentation have opened new avenues to improve detection of microparticle populations of smaller sizes. Significant optimization in microparticle detection is also expected from the use of new fluorescent dyes and the establishment of practical recommendations. Finally, absolute counting of microparticles will also benefit from adapted bead-based strategies or, alternatively, from the generalized availability of volumetric systems. Overall, recent technological improvements maintain flow cytometry as a highly competitive analytical method to measure microparticles. Challenging these evolutions in pathological situations is a mandatory step to validate their real impact in clinical practice., (© Thieme Medical Publishers.)

Endothelial microparticles (EMP) are complex vesicular structures that can be shed by activated or apoptotic endothelial cells. EMP are composed of a phospholipid bilayer that exposes transmembrane proteins and receptors and encloses cytosolic components such as enzymes, transcription factors and mRNA derived from their parent cells. Thus, EMP behave as biological conveyors playing a key role in the tuning of vascular homeostasis. This review focuses on the multifaceted roles of EMP, notably in coagulation, inflammation and angiogenesis and also on the mechanisms that trigger their formation. In this context, EMP could compromise vascular homeostasis and then represent key players in the pathogenesis of several inflammatory and thrombotic diseases. Consequently, elucidating their role and their mechanisms of formation will bring new insights into the understanding of endothelial-associated diseases. Moreover, in the future, it can open novel therapeutic perspectives based on the inhibition of EMP release.

Endothelial progenitor cells (EPC) display a unique ability to repair vascular injury and promote neovascularization although the underlying molecular mechanisms remain poorly understood. Urokinase-type plasminogen activator (uPA) and its receptor (uPAR) play a critical role in cell migration and angiogenesis by facilitating proteolysis of extracellular matrix. The aim of the present study was to characterize the uPA/uPAR-dependent proteolytic potential of EPC outgrown from human umbilical cord blood and to analyze its contribution to their angiogenic properties in vitro. Cells derived from EPC (EPDC), presenting typical features of late outgrowth endothelial cells, were compared to mature endothelial cells, represented by human umbilical vein endothelial cells (HUVEC). Using quantitative flow cytometry, enzyme-linked immunosorbent assays and zymography, we demonstrated that EPDC displayed higher levels of uPA and uPAR. In conditioned culture media, uPA-dependent proteolytic activity was also found to be significantly increased in EPDC. This activity was paralleled by a higher secretion of pro-metalloproteinase-2 (pro-MMP-2). Inhibition of EPDC-associated uPA by monoclonal antibodies that block either uPA activity or receptor binding, significantly reduced proliferation, migration and capillary like tube formation. Moreover, tumor necrosis factor-alpha and vascular endothelial growth factor, known to be locally secreted in ischemic areas, further increased the proteolytic potential of EPDC by up-regulating uPA and uPAR expression respectively. The EPDC response to these factors was found to be more pronounced than that of HUVEC. In conclusion, these findings indicated that EPDC are characterized by high intrinsic uPA/uPAR-dependent proteolytic potential that could contribute to their invasive and angiogenic behaviour.

The mechanisms responsible for pregnancy loss have not all been elucidated. CD146 is a cell adhesion molecule involved in the control of both endothelium integrity and intermediate trophoblast invasiveness, two potential key features in the pathogenesis of pregnancy loss. As CD146 is detectable as a soluble form in the plasma (sCD146), we investigated sCD146 plasma levels in women with a history of pregnancy loss. We conducted a paired case-control study to compare sCD146 plasma levels in 100 women with unexplained pregnancy losses (2 or more consecutive losses at or before 21 weeks of gestation, or at least one later loss) and in 100 age-matched control women (no pregnancy loss and at least one living child). The sCD146 concentrations were determined at least 2 months after the last obstetrical event. Patients and controls were comparable regarding thrombophilia. Among the patients, 83 women experienced early pregnancy losses (average of 3 losses, mean gestation of 6.6 weeks) and 22 women suffered at least one late pregnancy loss. We found significantly higher sCD146 plasma levels in the 100 patients compared to age matched control women (p < 0.001). The sCD146 plasma levels did not correlate with the number of pregnancy losses nor with the mean gestation time. Alterations in sCD 146 plasma levels could be related to endothelial dysfunction associated to defective endovascular trophoblast invasiveness. Additional studies should explore whether sCD146 assessment could provide diagnostic and prognostic information with a view to screening and thus managing women with unexplained pregnancy loss.

CD146 is an adhesion molecule present on endothelial cells throughout the vascular tree. CD146 is also expressed by circulating endothelial cells (CECs) widely considered to be mature endothelial cells detached from injured vessels. The discovery of circulating endothelial progenitor cells (EPCs) originating from bone marrow prompted us to investigate whether CD146 circulating cells could also contains EPCs. We tested this hypothesis using an approach combining elimination of CECs by an adhesion step, followed by immunomagnetic sorting of remaining CD146+ cells from the non adherent fraction of cord blood mononuclear cells. When cultured under endothelial-promoting conditions, these cells differentiated as late outgrowth endothelial colonies: they grew as a cobblestone monolayer, were uniformly positive for endothelial markers and did not express leukocyte antigens. They highly proliferated and were expanded in long-term culture without alterations of their phenotypic and functional properties (Dil-ac-LDL uptake, wound repair, capillary-like network formation, and TNFalpha response). Moreover, these cells colonized a Matrigel plug in immunodeficient mice (NOD/SCID). Finally, using 4-color flow cytometry analysis of purified CD34+ cells, we clearly discriminated, CD146+ EPCs (CD146+ CD34+ CD45+ CD133+ or CD117+), and CD146+ CECs (CD146+ CD34+, CD45- CD133- or CD117-), both in cord and adult peripheral blood.The relative proportions of the two CD146+ subsets varied in patients with myocardial infarction as compared to healthy subjects. Our study establishes that, beside CECs, CD146+ circulating cells contain a subpopulation of EPCs with potential use in proangiogenic therapy. In addition, the dual measurement of CD146+ CECs and CD146+ EPCs offers a promising tool for monitoring vascular injury/regeneration processes in clinical situations.

Recent research has recognised new populations of non-hematopoietic cells in the blood. One of these, circulating endothelial cells (CECs), often defined by the expression of membrane glycoprotein CD146, are rarely found in the blood in health, but raised numbers are present in a wide variety of human conditions, including inflammatory, immune, infectious, neoplastic and cardiovascular disease, and seem likely to be evidence of profound vascular insult. An additional population are endothelial progenitor cells, defined by the co-expression of endothelial and immaturity cell surface molecules and also by the ability to form colonies in vitro. Although increased numbers of CECs correlate with other markers of vascular disease, questions remain regarding the precise definition, cell biology and origin of CECs. For example, they may be damaged, necrotic or apopototic, or alive, and could possess procoagulant and/or proinflammatory properties. However, since these cells seem to be representative of in situ endothelium, their phenotype may provide useful information. Indeed, whatever their phenotype, there is growing evidence that CECs may well be a novel biomarker, the measurement of which will have utility in various clinical settings related to vascular injury. Despite this promise, progress is impeded by the diversity of methodologies used to detect these cells. Accordingly, results are sometimes inconclusive and even conflicting. Nevertheless, increased CECs predict adverse cardiovascular events in acute coronary syndromes, suggesting they may move from being simply a research index to having a role in the clinic. The objective of the present communication is to condense existing data on CECs, briefly compare them with progenitor cells, and summarise possible mechanism(s) by which they may contribute to vascular pathology.

The aim of this study was to evaluate the heterogeneity of IgGanti-beta2-glycoprotein I antibodies (IgG-abeta2GPI) as regarding their reactivity pattern against different sources of human beta2 GPI, their avidity and their association with clinical events of antiphospholipid syndrome (APS). Three thousand six hundred and eighty-four consecutive patient sera were routinely tested for IgGabeta2 GPI over 1 year using an in-house ELISA with 2 different commercial preparations of human purified beta2GPI. Of the 340 sera found positive, all those clinically documented were included in this study; 61 were positive with only one preparation (S1) and 59 with both (S2). The results of ELISA were confirmed by Western blot. Heterogeneity was stressed by testing sera with a human recombinant protein and 3 beta2GPI-related peptides. No contribution of glycosylation in the binding to beta2GPI was found. The avidity indices for each protein were significantly higher in S1 than in S2 (p=0.0021). S2 were more associated with antiphospholipid antibodies than S1 (75% versus 21% ; p<0.0001). A similar frequency of the main clinical features of APS was found in S1 and S2 sera (69% and 71%, respectively). In conclusion, our data show a heterogeneity in the antigenic reactivity pattern of IgG- abeta2 GPI and a relationship between a binding profile and antibody avidity. This heterogeneity could represent a crucial factor of variability in test results and underlines the difficulty of getting standardisation.

Patients with chronic renal failure (CRF) exhibit endothelial dysfunction, which may involve uremic retention solutes that accumulate in blood and tissues. In this study, we investigated the in vitro effect of the uremic retention solute p-cresol on the barrier function of endothelial cells (HUVEC). P-cresol was tested at concentrations found in CRF patients, and since p-cresol is protein-bound, experiments were performed with and without physiological concentration of human albumin (4 g/dl). With albumin, we showed that p-cresol caused a strong increase in endothelial permeability after a 24-hour exposure. Concomitant with this increase in endothelial permeability, p-cresol induced a reorganization of the actin cytoskeleton and an alteration of adherens junctions. These molecular events were demonstrated by the decreased staining of cortical actin, associated with the formation of stress fibers across the cell, and by the decreased staining of junctional VE-cadherin. This decrease in junctional VE-cadherin staining was not associated with a reduction of membrane expression. Without albumin, the effects of p-cresol were more pronounced. The specific Rho kinase inhibitor, Y-27632, inhibited the effects of p-cresol, indicating that p-cresol mediates the increase in endothelial permeability in a Rho kinase-dependent way. In conclusion, these results show that p-cresol causes a severe dysfunction of endothelial barrier function in vitro and suggest this uremic retention solute may participate in the endothelium dysfunction observed in CRF patients.

The antiphospholipid syndrome (APS) refers to persistent anti-phospholipid antibodies (aPL) associated with thrombotic and/or obstetrical complications. The endothelial cell is a target of aPL which can induce a procoagulant and proinflammatory endothelial phenotype, as reported both in vivo and in vitro. Microparticle production is a hallmark of cell activation. In the present study, the presence of endothelial microparticles (EMP) in the plasma of APS patients was investigated. To determine if there is a correlation with certain biological and clinical features, EMP levels were measured in thrombosis-free patients with systemic lupus erythematosus (SLE) patients, with and without aPL, in patients with non aPL-related thrombosis, as well as in healthy controls. Compared to healthy subjects, elevated plasma levels of EMP were found in patients with APS and in SLE patients with aPL, but not in SLE patients without aPL or in non aPL-related thrombosis. EMP levels were also associated with Lupus Anticoagulant (LA) detected by a positive Dilute Russell's Viper Venom time (DRVVT). In parallel, we analyzed the capacity of these plasma to induce vesiculation of cultured endothelial cells. We demonstrated an increase of EMP generated in response to plasma from patients with auto-immune diseases. Interestingly, only APS plasma induced the release of EMP with procoagulant activity. These ex vivo and in vitro observations indicate that generation of EMP in APS and SLE patients results from an autoimmune process involving aPL. Production of procoagulant microparticles in APS patients may represent a new pathogenic mechanism for the thrombotic complications of this disease.

CD146, a novel cell adhesion molecule localized at the endothelial junction, is involved in the control of cell-cell cohesion. It is found as a soluble form in conditioned medium of cultured endothelial cells. We developed an ELISA and report for the first time the presence of a soluble form of CD146 (sCD146) in the plasma of healthy subjects. Mean sCD146 values (260 +/- 60 ng/ml) were higher in subjects over 50 years and in men. We therefore investigated sCD146 values in patients with chronic renal failure (CRF), a clinical setting associated with junctional alterations. A significant increase in sCD146 was found in patients with CRF matched with controls (457 +/- 181 ng/ml versus 288 +/- 82 ng/ml respectively, p<0.0001). This increase was corroborated by increased endothelial expression of CD146 on kidney biopsies from patients with CRF. In contrast, in patients with CRF no modulation was observed for the soluble and cell-associated form of CD31, another junctional molecule. Together these data indicate that sCD146 circulates in the plasma of healthy subjects. Modifications of its basal levels could reflect alterations of junctional functions such as vascular permeability.

In the present study, we explored the microparticles involved in the control of hemostatic equilibrium, i.e microparticles originating from platelet, endothelial cells and total MP defined as annexin V positive microparticles. Our aim was to analyze the level and procoagulant activity of these microparticles in normal pregnancy and pregnancies complicated with preeclampsia or isolated intrauterine growth restriction. We reported increased levels of platelet and endothelial microparticles in normal pregnancy compared to non pregnant healthy women. Number of annexin V microparticles was significantly increased together with their procoagulant activity. In pathological pregnancies, significant reduction in platelet microparticle number was found in preeclampsia. The procoagulant activity generated by the total annexin V MP was unchanged, suggesting that the microparticles remaining in the circulation were procoagulant. This study evidenced that microparticles constitute a cellular marker of a proinflammatory and procoagulant responses in normal pregnancy. In pregnancies with vascular complications, circulating MP with procoagulant potential may be part of the exacerbation of these responses.

Adhesion of platelets to endothelium has been shown to induce important changes in endothelial properties. In this study, we examined the effect of platelet-endothelial cell interactions on the expression of urokinase-type plasminogen activator (u-PA) by human microvascular endothelial cells. After incubation of endothelial cells with platelets, a dose-dependent increase in the expression of u-PA Ag was observed and reached a plateau for a ratio of 300 platelets per endothelial cells. The u-PA Ag upregulation resulted from an increase in u-PA mRNA that originated from a synthesis by endothelial cells since no u-PA mRNA was detected in platelets. The platelet-induced u-PA synthesis was inhibited when the endothelial cells were pre-treated with phospholipase C to remove the u-PA receptor, or when the platelets were incubated with an antibody that blocks the binding of u-PA to u-PAR. Taken together, these data indicate that u-PA present on the platelet surface interacts with u-PAR on the endothelial cells and induces the u-PA synthesis. This mechanism may represent a physiological control of platelet-mediated intravascular fibrin deposition.

In the present study, we investigated the plasma levels of soluble adhesion molecules E-selectin, P-selectin, intercellular adhesion molecule- (ICAM- ) and vascular cell adhesion molecule-1(VCAM-1) in 24 patients with Mediterranean spotted fever (MSF), 6 of whom with a malignant form. Measurements were performed on blood samples collected before treatment (T1), then twice during treatment (T2 and T3). Before treatment, MSF patients taken as a whole presented elevated levels of sICAM-1 and sVCAM-1 and normal levels of sE-selectin and sP-selectin compared to healthy controls. We found that sICAM-1 was elevated both in mild and malignant MSF. sE-selectin and sVCAM-1 were elevated only in patients with the malignant form and allowed to discriminate the two clinical subgroups. Their levels decreased after treatment with sE-selectin reaching control values at T2 whereas sVCAM-1 remained higher over the course of the malignant form. In patients with mild MSF, sP-selectin steadily increased after treatment, whereas it did not present any modification at any of the two sampling times in patients with the malignant form. Raised plasma levels of sE-selectin and sVCAM-1 reflect endothelial activation in malignant rickettsial disease and may be sufficiently early markers to influence the therapeutic decision.

Endothelial cells (ECs) in culture synthesize and secrete urokinase-type plasminogen activator (u-PA), but the normal vascular endothelium is believed to synthesize only tissue plasminogen activator (t-PA), which is thought to be responsible for intravascular fibrinolysis. More recently, animal studies have shown that the biological role of u-PA in fibrinolysis has been underestimated, prompting a re-examination of its synthesis by the endothelium. In this study, we investigated whether u-PA was synthesized by non-atherosclerotic endothelial cells in vivo by testing ECs dislodged by venipuncture from 12 normal volunteers and 17 patients admitted for plasmapheresis. The ECs were isolated with an anti-endothelial monoclonal antibody coupled to immunomagnetic beads and characterized by morphology and by labelling for vWF, CD31, and UEA-1 binding. U-PA antigen was found in 50% of the ECs from the normal subjects and in 60% of those from patients. U-PA enzymatic activity on zymograms was detected in 50% of the normal samples and 60% of the patient samples, with the latter being more frequently and more strongly positive. U-PA mRNA was found in all the normal and patient samples tested. The results indicate that u-PA is synthesized by the venous endothelium in vivo but that its expression is highly variable.