Cell-derived microparticles in synovial fluid from inflamed arthritic joints support coagulation exclusively via a factor VII-dependent mechanism

HDL interfere with the binding of T cell microparticles to human monocytes to inhibit pro-inflammatory cytokine production

Background

Direct cellular contact with stimulated T cells is a potent mechanism that induces cytokine production in human monocytes in the absence of an infectious agent. This mechanism is likely to be relevant to T cell-mediated inflammatory diseases such as rheumatoid arthritis and multiple sclerosis. Microparticles (MP) generated by stimulated T cells (MP_T) display similar monocyte activating ability to whole T cells, isolated T cell membranes, or solubilized T cell membranes. We previously demonstrated that high-density lipoproteins (HDL) inhibited T cell contact- and MP_T-induced production of IL-1β but not of its natural inhibitor, the secreted form of IL-1 receptor antagonist (sIL-1Ra).

Methodology/Principal Findings

Labeled MP_T were used to assess their interaction with monocytes and T lymphocytes by flow cytometry. Similarly, interactions of labeled HDL with monocytes and MP_T were assessed by flow cytometry. In parallel, the MP_T-induction of IL-1β and sIL-1Ra production in human monocytes and the effect of HDL were assessed in cell cultures. The results show that MP_T, but not MP generated by activated endothelial cells, bond monocytes to trigger cytokine production. MP_T did not bind T cells. The inhibition of IL-1β production by HDL correlated with the inhibition of MP_T binding to monocytes. HDL interacted with MP_T rather than with monocytes suggesting that they bound the activating factor(s) of T cell surface. Furthermore, prototypical pro-inflammatory cytokines and chemokines such as TNF, IL-6, IL-8, CCL3 and CCL4 displayed a pattern of production induced by MP_T and inhibition by HDL similar to IL-1β, whereas the production of CCL2, like that of sIL-1Ra, was not inhibited by HDL.

Conclusions/Significance

HDL inhibit both MP_T binding to monocytes and the MP_T-induced production of some but not all cytokines, shedding new light on the mechanism by which HDL display their anti-inflammatory functions.

Interaction between equally charged membrane surfaces mediated by positively and negatively charged macro-ions

In biological systems, charged membrane surfaces are surrounded by charged molecules such as electrolyte ions and proteins. Our recent experiments in the systems of giant phospholipid vesicles indicated that some of the blood plasma proteins (macro-ions) may promote adhesion between equally charged membrane surfaces. In this work, theory was put forward to describe an IgG antibody-mediated attractive interaction between negatively charged membrane surfaces which was observed in experiments on giant phospholipid vesicles with cardiolipin-containing membranes. The attractive interactions between negatively charged membrane surfaces in the presence of negatively and positively charged spherical macro-ions are explained using functional density theory and Monte Carlo simulations. Both, the rigorous solution of the variational problem within the functional density theory and the Monte Carlo simulations show that spatial and orientational ordering of macro-ions may give rise to an attractive interaction between negatively charged membrane surfaces. It is also shown that the distinctive spatial distribution of the charge within the macro-ions (proteins) is essential in this process.

Proteomic and functional characterisation of platelet microparticle size classes

Activated platelets release large lipid-protein complexes termed microparticles. These platelet microparticles (PMP) are composed of vesicular fragments of the plasma membrane and alpha-granules. PMP facilitate coagulation, promote platelet and leukocyte adhesion to the subendothelial matrix, support angiogenesis and stimulate vascular smooth muscle proliferation.

OBJECTIVES

PMP were separated into 4 size classes to facilitate identification of active protein and lipid components. PMP were obtained from activated human platelets and separated into 4 size classes by gel filtration chromatography. Proteins were identified using 2-dimensional, liquid chromatography tandem mass spectrometry. Functional effects on platelets were determined using the PFA-100 and on endothelial cells by measuring transendothelial cell electrical resistance. PMP size classes differed significantly in their contents of plasma membrane receptors and adhesion molecules, chemokines, growth factors and protease inhibitors. The two smallest size classes (3 and 4) inhibited collagen/adenosine-diphosphate-mediated platelet thrombus formation, while fractions 2 and 4 stimulated barrier formation by endothelial cells. Heat denaturation blocked the effect of fraction 4 on endothelial cell function, but not fraction 2 implying that the active component in fraction 4 is a protein and in fraction 2 is a heat-stable protein or lipid but not sphingosine-1-phosphate. Proteomic and functional analysis of PMP size fractions has shown that PMP can be separated into different size classes that differ in protein components, protein/lipid ratio, and functional effects on platelets and endothelial cells. This analysis will facilitate identification of active components in the PMP and clarify their involvement in diseases such as atherosclerosis and cancer.

The release of microparticles by RAW 264.7 macrophage cells stimulated with TLR ligands

TLR ligands induce microparticle release by macrophages and highlight the importance of nitric oxide.

MPs are small membrane-bound particles that originate from activated and dying cells and mediate intercellular communication. Once released from cells, MPs can serve as novel signaling elements in innate immunity, with levels elevated in immune-mediated diseases. This study tested the hypothesis that TLR stimulation can induce MP release by macrophages. In these experiments, using the RAW 264.7 murine macrophage cell line as a model, LPS, a TLR4 ligand, and poly(I:C), a TLR3 ligand, induced MP release effectively, as measured by flow cytometry; in contrast, a CpG oligonucleotide, which can stimulate TLR9, induced much lower levels of particle release. To determine the role of other mediators in this response, the effects of NO were tested. Thus, MP release from RAW 264.7 cells stimulated by LPS or poly(I:C) correlated with NO production, and treatment with the iNOS inhibitor 1400W decreased particle release and NO production. Furthermore, treatment of RAW 264.7 cells with NO donors induced MP production. As TLR ligands can induce apoptosis, the effect of caspase inhibition on MP release by stimulated cells was assessed. These experiments showed that the pan-caspase inhibitor, ZVAD, although decreasing NO production, increased MP release by stimulated cells. Together, these experiments demonstrate that TLR stimulation of macrophages can lead to MP release, and NO plays a key role in this response.

Increased vitreous shedding of microparticles in proliferative diabetic retinopathy stimulates endothelial proliferation

OBJECTIVE

Diabetic retinopathy is associated with progressive retinal capillary activation and proliferation, leading to vision impairment and blindness. Microparticles are submicron membrane vesicles with biological activities, released following cell activation or apoptosis. We tested the hypothesis that proangiogenic microparticles accumulate in vitreous fluid in diabetic retinopathy.

RESEARCH DESIGN AND METHODS

Levels and cellular origin of vitreous and plasma microparticles from control (n = 26) and diabetic (n = 104) patients were analyzed by flow cytometry, and their proangiogenic activity was assessed by in vitro thymidine incorporation and neovessel formation in subcutaneous Matrigel plugs in mice.

RESULTS

Microparticles of endothelial, platelet, photoreceptor, and microglial origin were identified in vitreous samples. Levels of photoreceptor and microglial microparticles were undetectable in plasmas but were comparable in diabetic and control vitreous samples. Vitreous platelet and endothelial microparticles levels were increased in diabetic patients and decreased following panretinal laser photocoagulation or intravitreal antivascular endothelial growth factor injection in proliferative diabetic retinopathy (PDR). The ratio of vitreous to plasma microparticle levels was calculated to estimate local formation versus potential plasma leakage. In PDR, the endothelial microparticles ratio--but not that for platelet--was greater than 1.0, indicating local formation of endothelial microparticles from retinal vessels and permeation of platelet microparticles from plasma. Isolated vitreous microparticles stimulated by 1.6-fold endothelial proliferation and increased new vessel formation in mice.

CONCLUSIONS

The present study demonstrates that vitreous fluid contains shed membrane microparticles of endothelial, platelet, and retinal origin. Vitreous microparticles levels are increased in patients with diabetic retinopathy, where they could contribute to disease progression.

Platelets amplify inflammation in arthritis via collagen-dependent microparticle production

In addition to their pivotal role in thrombosis and wound repair, platelets participate in inflammatory responses. We investigated the role of platelets in the autoimmune disease rheumatoid arthritis. We identified platelet microparticles--submicrometer vesicles elaborated by activated platelets--in joint fluid from patients with rheumatoid arthritis and other forms of inflammatory arthritis, but not in joint fluid from patients with osteoarthritis. Platelet microparticles were proinflammatory, eliciting cytokine responses from synovial fibroblasts via interleukin-1. Consistent with these findings, depletion of platelets attenuated murine inflammatory arthritis. Using both pharmacologic and genetic approaches, we identified the collagen receptor glycoprotein VI as a key trigger for platelet microparticle generation in arthritis pathophysiology. Thus, these findings demonstrate a previously unappreciated role for platelets and their activation-induced microparticles in inflammatory joint diseases.

The role of microparticles in the pathogenesis of rheumatic diseases

Microparticles (MPs) are small membrane-bound vesicles that are emerging as important elements in the pathogenesis of rheumatic diseases owing to their pleiotropic effects on thrombosis, vascular reactivity, angiogenesis and inflammation. Released from cells during activation and apoptosis, MPs carry proteins, lipids and nucleic acids, and serve as platforms for enzymatic processes in thrombosis. Furthermore, MPs can transfer cytokines, receptors, RNA and DNA to modulate the properties of target cells. As MPs appear in the blood in increased numbers during rheumatic disease, they represent novel biomarkers that can be used to assess events in otherwise inaccessible tissues. Future research will define further the pathogenetic role of MPs and explore therapeutic strategies to block their release or signaling properties.

Thrombin-activatable carboxypeptidase B cleavage of osteopontin regulates neutrophil survival and synoviocyte binding in rheumatoid arthritis

OBJECTIVE

Osteopontin (OPN) is a proinflammatory cytokine that plays an important role in the pathogenesis of rheumatoid arthritis (RA). OPN can be cleaved by thrombin, resulting in OPN-R and exposing the cryptic C-terminal alpha4beta1 and alpha9beta1 integrin-binding motif (SVVYGLR). Thrombin-activatable carboxypeptidase B (CPB), also called thrombin-activatable fibrinolysis inhibitor, removes the C-terminal arginine from OPN-R, generating OPN-L and abrogating its enhanced cell binding. We undertook this study to investigate the roles of OPN-R and OPN-L in synoviocyte adhesion, which contributes to the formation of invasive pannus, and in neutrophil survival, which affects inflammatory infiltrates in RA.

METHODS

Using specifically developed enzyme-linked immunosorbent assays, we tested the synovial fluid of patients with RA, osteoarthritis (OA), and psoriatic arthritis (PsA) to determine OPN-R, OPN-L, and full-length OPN (OPN-FL) levels.

RESULTS

Elevated levels of OPN-R and OPN-L were found in synovial fluid samples from RA patients, but not in samples from OA or PsA patients. Increased levels of OPN-R and OPN-L correlated with increased levels of multiple inflammatory cytokines, including tumor necrosis factor alpha and interleukin-6. Immunohistochemical analyses revealed robust expression of OPN-FL, but only minimal expression of OPN-R, in RA synovium, suggesting that cleaved OPN is released into synovial fluid. In cellular assays, OPN-FL, and to a lesser extent OPN-R and OPN-L, had an antiapoptotic effect on neutrophils. OPN-R augmented RA fibroblast-like synoviocyte binding mediated by SVVYGLR binding to alpha4beta1, whereas OPN-L did not.

CONCLUSION

Thrombin activation of OPN (resulting in OPN-R) and its subsequent inactivation by thrombin-activatable CPB (generating OPN-L) occurs locally within inflamed joints in RA. Our data suggest that thrombin-activatable CPB plays a central homeostatic role in RA by regulating neutrophil viability and reducing synoviocyte adhesion.

Increased levels of circulating microparticles in primary Sjögren's syndrome, systemic lupus erythematosus and rheumatoid arthritis and relation with disease activity

INTRODUCTION

Cell stimulation leads to the shedding of phosphatidylserine (PS)-rich microparticles (MPs). Because autoimmune diseases (AIDs) are characterized by cell activation, we investigated level of circulating MPs as a possible biomarker in primary Sjögren's syndrome (pSS), systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA).

METHODS

We measured plasma levels of total, platelet and leukocyte MPs by prothrombinase capture assay and flow cytometry in 43 patients with pSS, 20 with SLE and 24 with RA and in 44 healthy controls (HCs). Secretory phospholipase A2 (sPLA2) activity was assessed by fluorometry. Soluble CD40 ligand (sCD40L) and soluble P-selectin (sCD62P), reflecting platelet activation, were measured by ELISA.

RESULTS

Patients with pSS showed increased plasma level of total MPs (mean +/- SEM 8.49 +/- 1.14 nM PS equivalent (Eq), P < 0.0001), as did patients with RA (7.23 +/- 1.05 n PS Eq, P = 0.004) and SLE (7.3 +/- 1.25 nM PS Eq, P = 0.0004), as compared with HCs (4.13 +/- 0.2 nM PS Eq). Patients with AIDs all showed increased level of platelet MPs (P < 0.0001), but only those with pSS showed increased level of leukocyte MPs (P < 0.0001). Results by capture assay and flow cytometry were correlated. In patients with high disease activity according to extra-glandular complications (pSS), DAS28 (RA) or SLEDAI (SLE) compared with low-activity patients, the MP level was only slightly increased in comparison with those having a low disease activity. Platelet MP level was inversely correlated with anti-DNA antibody level in SLE (r = -0.65; P = 0.003) and serum beta2 microglobulin level in pSS (r = -0.37; P < 0.03). The levels of total and platelet MPs were inversely correlated with sPLA2 activity (r = -0.37, P = 0.0007; r = -0.36, P = 0.002, respectively). sCD40L and sCD62P concentrations were significantly higher in pSS than in HC (P < or = 0.006).

CONCLUSIONS

Plasma MP level is elevated in pSS, as well as in SLE and RA, and could be used as a biomarker reflecting systemic cell activation. Level of leukocyte-derived MPs is increased in pSS only. The MP level is low in case of more severe AID, probably because of high secretory phospholipase A2 (sPLA2) activity, which leads to consumption of MPs. Increase of platelet-derived MPs, sCD40L and sCD62P, highlights platelet activation in pSS.

Circulating erythrocyte-derived microparticles are associated with coagulation activation in sickle cell disease

BACKGROUND

Sickle cell disease is characterized by a hypercoagulable state as a result of multiple factors, including chronic hemolysis and circulating cell-derived microparticles. There is still no consensus on the cellular origin of such microparticles and the exact mechanism by which they may enhance coagulation activation in sickle cell disease.

DESIGN AND METHODS

In the present study, we analyzed the origin of circulating microparticles and their procoagulant phenotype during painful crises and steady state in 25 consecutive patients with sickle cell disease.

RESULTS

The majority of microparticles originated from platelets (GPIIIa,CD61) and erythrocytes (glycophorin A,CD235), and their numbers did not differ significantly between crisis and steady state. Erythrocyte-derived microparticles strongly correlated with plasma levels of markers of hemolysis, i.e. hemoglobin (r=-0.58, p<0.001) and lactate dehydrogenase (r=0.59, p<0.001), von Willebrand factor as a marker of platelet/endothelial activation (r=0.44, p<0.001), and D-dimer and prothrombin fragment F1+2 (r=0.52, p<0.001 and r=0.59, p<0.001, respectively) as markers of fibrinolysis and coagulation activation. Thrombin generation depended on the total number of microparticles (r=0.63, p<0.001). Anti-human factor XI inhibited thrombin generation by about 50% (p<0.001), whereas anti-human factor VII was ineffective (p>0.05). The extent of factor XI inhibition was associated with erythrocyte-derived microparticles (r=0.50, p=0.023).

CONCLUSIONS

We conclude that the procoagulant state in sickle cell disease is partially explained by the factor XI-dependent procoagulant properties of circulating erythrocyte-derived microparticles.

Mechanisms for the formation of membranous nanostructures in cell-to-cell communication

Cells interact by exchanging material and information. Two methods of cell-to-cell communication are by means of microvesicles and by means of nanotubes. Both microvesicles and nanotubes derive from the cell membrane and are able to transport the contents of the inner solution. In this review, we describe two physical mechanisms involved in the formation of microvesicles and nanotubes: curvature-mediated lateral redistribution of membrane components with the formation of membrane nanodomains; and plasmamediated attractive forces between membranes. These mechanisms are clinically relevant since they can be affected by drugs. In particular, the underlying mechanism of heparin's role as an anticoagulant and tumor suppressor is the suppression of microvesicluation due to plasma-mediated attractive interaction between membranes.

TRAIL/Apo2L Mediates the Release of Procoagulant Endothelial Microparticles Induced by Thrombin In Vitro

Microparticles are small vesicles playing a crucial role in cell communication by promoting prothrombotic and proinflammatory responses. However, the molecular mechanisms underlying their release are still elusive. We previously established that thrombin promoted the generation of endothelial microparticles (EMPs). In the present study, gene profiling identified TRAIL/Apo2L , a cytokine belonging to the tumor necrosis factor-α superfamily, as a target of thrombin. Thrombin increased the expression of cell-associated and soluble forms of TRAIL (sTRAIL) in HMEC-1 cells and human umbilical vein endothelial cells (HUVECs). Blocking TRAIL by specific antibodies or by small interfering RNA reduced both the number and the procoagulant activity of EMPs released by thrombin. Consistent with an involvement of sTRAIL in thrombin-induced EMP release, we showed that (1) exogenously added sTRAIL generated procoagulant EMPs; (2) supernatants from thrombin-stimulated endothelial cells induced EMP release by HMEC-1 cells and HUVECs, whereas those recovered from TRAIL knockdown endothelial cells displayed no effect. TRAIL/TRAIL-R2 complex mediated EMP release by initiating the recruitment of adaptor proteins and the activation of nuclear factor κB. Moreover, sTRAIL modulated intercellular adhesion molecule-1 and interleukin-8 expression induced by thrombin by a downstream pathway involving nuclear factor κB activation. Our data reveal a novel mechanism controlling EMP release and identify TRAIL as a key partner in the pathway linking coagulation and inflammation elicited by thrombin.

Leukocytapheresis (LCAP) decreases the level of platelet-derived microparticles (MPs) and increases the level of granulocytes-derived MPs: a possible connection with the effect of LCAP on rheumatoid arthritis

Microparticles (MPs) are believed to play an important role in inflammatory diseases such as rheumatoid arthritis (RA). Leukocytapheresis (LCAP) is one of the options available for the treatment of RA. We analyzed the levels of MPs in RA, by flow cytometry, especially in relation to the effect of LCAP. Twenty female patients with RA were recruited into this study. Six of the 20 patients with RA further received LCAP. Plasma levels of platelet-derived MPs were high in patients with RA and are correlated with disease activity. LCAP significantly improved RA in all six patients. The numbers of platelet-derived MPs significantly decreased after the first session of LCAP, which was probably due to direct removal by LCAP. Mean numbers of platelet-derived MPs after four sessions of LCAP markedly decreased. The numbers of granulocyte-derived MPs, which are suggested to have an anti-inflammatory effect, were markedly increased after the first session of LCAP. These data suggest that removal of platelet-derived MPs and increase of granulocyte-derived MPs are novel mechanisms of LCAP as effective treatment in RA.

Microparticle-induced release of B-lymphocyte regulators by rheumatoid synoviocytes

Introduction

In the present study, we investigated the ability of microparticles isolated from synovial fluids from patients with rheumatoid arthritis or osteoarthritis to induce the synthesis and release of key cytokines of B-lymphocyte modulation such as B cell-activating factor, thymic stroma lymphopoietin, and secretory leukocyte protease inhibitor by rheumatoid fibroblast-like synoviocytes.

Methods

Microparticles were analyzed in synovial fluids from patients with rheumatoid arthritis, osteoarthritis, microcristalline arthritis, and reactive arthritis. In addition, microparticle release after activation from various cell lines (CEM lymphocyte and THP-1 cells) was assessed. Microparticles were isolated by differential centrifugation, and quantitative determinations were carried out by prothrombinase assay after capture on immobilized annexin V. B cell-activating factor, thymic stroma lymphopoietin, and secretory leukocyte protease inhibitor release was evaluated by enzyme-linked immunosorbent assay.

Results

Microparticles isolated from synovial fluids obtained from rheumatoid arthritis and osteoarthritis patients or microparticles derived from activated THP-1 cells were able to induce B cell-activating factor, thymic stroma lymphopoietin, and secretory leukocyte protease inhibitor release by rheumatoid arthritis fibroblast-like synoviocytes. Conversely, CEM-lymphocytes-derived microparticles generated by treatment with a combination of PHA, PMA and Adt-D did not promote the release of B cell-activating factor but favored the secretion of thymic stroma lymphopoietin and secretory leukocyte protease inhibitor by rheumatoid arthritis fibrobast-like synoviocytes. However, microparticles isolated from actinomycin D-treated CEM lymphocytes were not able to induce B cell-activating factor, thymic stroma lymphopoietin, or secretory leukocyte protease inhibitor release, indicating that microparticles derived from apoptotic T cells do not function as effectors in B-cell activation.

Conclusions

These results demonstrate that microparticles are signalling structures that may act as specific conveyors in the triggered induction and amplification of autoimmunity. This study also indicates that microparticles have differential effects in the crosstalk between B lymphocytes and target cells of autoimmunity regarding the parental cells from which they derive.

Tissue factor activity and function in blood coagulation

Tissue factor (TF) is the major physiological initiator of blood coagulation. It exists as an integral membrane protein that upon injury to the blood vessel becomes exposed to the blood stream and initiates a series of enzymatic reactions that cause blood to clot. TF is also found within circulating blood cells, requiring specific signaling events to promote its expression. In this review we will discuss current controversies concerning the structure-activity relationships of TF and contributions of TF to the hemostatic process, the potential roles of intravascular TF, including non-cell-bound TF and cell-expressed TF and the overall relationship between TF function and hemorrhage control.

Common inflammatory mediators orchestrate pathophysiological processes in rheumatoid arthritis and atherosclerosis

RA is characterized by a systemic inflammatory state, in which immune cells and soluble mediators play a crucial role. These inflammatory processes resemble those in other chronic inflammatory diseases, such as atherosclerosis. The chronic systemic inflammation in RA can be considered as an independent risk factor for the development of atherosclerosis, and represents an important field to investigate the reasons of the increase of acute cardiovascular events in RA. In the present review, we focused on several mediators of autoimmunity, inflammation and endothelial dysfunction, which can be considered the most promising targets to prevent atherogenesis in RA. Among several mediators, the pro-inflammatory cytokine TNF-alpha has been shown as a crucial factor to induce atherosclerosis in RA patients.

Protein composition of plasminogen activator inhibitor type 1-derived endothelial microparticles

Endothelial microparticles (EMPs) are small vesicles released from the plasma membrane of endothelial cells in response to cell injury, apoptosis, or activation. Low levels of MPs are shed into the blood from the endothelium, but in some pathologic states, the number of EMPs is elevated. The mechanism of MP formation and the wide-ranging effects of elevated EMPs are poorly understood. Here, we report the protein composition of EMPs derived from human umbilical cord endothelial cells stimulated with plasminogen activator inhibitor type 1 (PAI-1). Two-dimensional gel electrophoresis followed by mass spectrometry identified 58 proteins, of which some were verified by Western blot analysis. Gene Ontology database searches revealed that proteins identified on PAI-1-derived EMPs are highly diverse. Endothelial microparticles are composed of proteins from different cellular components that exhibit multiple molecular functions and are involved in a variety of biological processes. Important insight is provided into the generation and protein composition of PAI-1-derived EMPs.

Comparative proteomic analysis of PAI-1 and TNF-alpha-derived endothelial microparticles

Endothelium-derived microparticles (EMPs) are small vesicles released from endothelial cells in response to cell injury, apoptosis, or activation. Elevated concentrations of EMPs have been associated with many inflammatory and vascular diseases. EMPs also mediate long range signaling and alter downstream cell function. Unfortunately, the molecular and cellular basis of microparticle production and downstream cell function is poorly understood. We hypothesize that EMPs generated by different agonists will produce distinct populations of EMPs with unique protein compositions. To test this hypothesis, different EMP populations were generated from human umbilical vein endothelial cells by stimulation with plasminogen activator inhibitor type 1 (PAI-1) or tumor necrosis factor-alpha (TNF-alpha) and subjected to proteomic analysis by LC/MS. We identified 432 common proteins in all EMP populations studied. Also identified were 231 proteins unique to control EMPs, 104 proteins unique to PAI-1 EMPs and 70 proteins unique to TNF-alpha EMPs. Interestingly, variations in protein abundance were found among many of the common EMP proteins, suggesting that differences exist between EMPs on a relative scale. Finally, gene ontology (GO) and KEGG pathway analysis revealed many functional similarities and few differences between the EMP populations studied. In summary, our results clearly indicate that EMPs generated by PAI-1 and TNF-alpha produce EMPs with overlapping but distinct protein compositions. These observations provide fundamental insight into the mechanisms regulating the production of these particles and their physiological role in numerous diseases.

The role of resident synovial cells in destructive arthritis

Infiltration by inflammatory cells, thickening of the lining layer, and destructive invasion into cartilage and bone are pathognomic features of the synovium in rheumatoid arthritis (RA). However, the most common cell types at the sites of invasion are resident cells of the joint, in particular synovial fibroblasts. These cells differ from healthy synovial fibroblasts in their morphology, their expression of proto-oncogenes and antiapoptotic molecules, and in their lack of certain tumor suppressor genes. Through their production of proinflammatory cytokines and chemokines mediated by signaling via Toll-like receptors, they are not only effector cells but also active parts of the innate immune system attracting inflammatory immune cells to the synovium. Most importantly, by producing matrix-degrading molecules they contribute strongly to the destructive mechanisms operative in RA.

Identification of nanobacteria in human arthritic synovial fluid by method validated in human blood and urine using 200 nm model nanoparticles

Earlier we introduced a biosensor for the identification of nanobacteria in water drops. Here, we generalize its principle and apply it to identify nanobacteria in synovial fluid from a patient with osteoarthritis. Results indicate the prevalence of nanobacteria in the synovial fluid. The identification method is applicable to body fluids such as unfiltered human blood and urine, is independent of culturing procedures, and permits for a rapid detection of nanoparticles in liquid drops. In view of increasing clinical evidence on a contribution of nanobacteria in disease, their reported detection in HIV-infected people in South Africa, laboratory experiments indicating the excretion of viable (i.e., propagating) nanobacteria from humans via urine, the use of human excreta in agricultural irrigation, models predicting an injection of nanoaerosols contained in irrigation water enriched with human excreta into the atmosphere, and the identification of nanobacteria in the terrestrial atmosphere, promote the identification method described in this work to an important tool to monitor nanobacteria in body fluids and environmental samples.

The role of cell death in the pathogenesis of autoimmune disease: HMGB1 and microparticles as intercellular mediators of inflammation

Cell death is critical to normal homeostasis, although this process, when increased aberrantly, can lead to the production of pro-inflammatory mediators promoting autoimmunity. Two novel intercellular mediators of inflammation generated during cell death are high mobility group box 1 (HMGB1) protein and microparticles (MPs). HMGB1 is a nuclear protein that functions in transcription when inside the nucleus but takes on pro-inflammatory properties when released during cell death. Microparticles are small, membrane-bound structures that extrude from cells when they die and contain cell surface proteins and nuclear material from their parent cells. MPs circulate widely throughout the vasculature and mediate long-distance communication between cells. Both MPs and HMGB1 have been implicated in the pathogenesis of a broad spectrum of inflammatory diseases, including the prototypic autoimmune conditions systemic lupus erythematosus and rheumatoid arthritis. Given their range of activity and association with active disease, both structures may prove to be targets for effective therapy in these and other disorders.

The nature of the stable blood clot procoagulant activities

The function of tissue factor (Tf)-initiated coagulation is hemorrhage control through the formation and maintenance of an impermeable platelet-fibrin barrier. The catalytic processes involved in the clot maintenance function are not well defined, although the rebleeding problems characteristic of individuals with hemophilias A and B suggest a link between specific defects in the Tf-initiated process and defects in the maintenance function. We have previously demonstrated, using a methodology of "flow replacement" (or resupply) of ongoing Tf-initiated reactions with fresh reactants, that procoagulant complexes are produced during Tf-initiated coagulation, which are capable of reinitiating coagulation without input from extrinsic factor Xase activity (Orfeo, T., Butenas, S., Brummel-Ziedins, K. E., and Mann, K. G. (2005) J. Biol. Chem. 280, 42887-42896). Here we used Tf-initiated reactions in normal and hemophilia blood or in their corresponding proteome mixtures as sources of procoagulant end products and then varied the resupplying material to determine the identity of the catalysts that drive the new cycle of thrombin formation. The central findings are as follows: 1) the prothrombinase complex (fVa-fXa-Ca(2+)-membrane) accumulated during the episode of Tf-initiated coagulation is the primary catalyst responsible for the observed pattern of prothrombin activation after resupply; 2) impairments in intrinsic factor Xase function, i.e. hemophilias A and B, result in an impaired capacity to mount a resupply response; and 3) in normal hemostasis the intrinsic factor Xase function contributes to the durability of the resupply response.

Gender-specific and menstrual cycle dependent differences in circulating microparticles

In comparison to age-matched men, young women are at increased risk to suffer from venous thromboembolism (VTE). Some risk factors of inherited and acquired thrombophilia are known, but approximately 30% of the overall risk remains unexplained. Recently, a role for microparticles (MP) in coagulation has been suggested. We investigated, if gender- and menstrual cycle-specific differences in circulating MP exist. Platelet- and endothelial cell-derived microparticles (PMP, EMP) and subpopulations thereof were evaluated flow-cytometrically in healthy women (n = 27) in different phases of their menstrual cycles (follicular phase: n = 14, luteal phase: n = 13) and in healthy men (n = 18). Additionally, D-dimer levels were determined. Compared to men, women had elevated numbers of annexin V-binding MP (p = 0.007), PMP (CD61; p = 0.013), P-selectin-exposing PMP (p = 0.002) and E-selectin-exposing EMP (p = 0.009). During the luteal phase, women had strongly elevated concentrations of MP, PMP, P-selectin- and CD63-exposing PMP as well as E-selectin-exposing EMP (p = 0.001, p < 0.001, p = 0.004, p = 0.003, and p < 0.001, respectively), and the ratio of P-selectin-exposing PMP/platelet increased more than three-fold as compared to men (p = 0.01). When different phases of the menstrual cycle were analysed, MP (annexin V; p = 0.025), PMP (CD61: p < 0.001; CD63: p = 0.015) and E-Selectin-positive EMP (p = 0.006) were all increased in the luteal phase. Although D-dimer concentrations in women were increased compared to men (p = 0 = 0.006), no menstrual cycle-specific differences were observed. In summary, circulating MP and subpopulations thereof are increased in women when compared to men, and this increase seems to be modulated by the menstrual cycle. Therefore, circulating MP may be an additional risk factor contributing to the hitherto unexplained procoagulatory state of young women.

Phospholipid composition of in vitro endothelial microparticles and their in vivo thrombogenic properties

INTRODUCTION

Microparticles from activated endothelial cells (EMP) are well known to expose tissue factor (TF) and initiate coagulation in vitro. TF coagulant activity is critically dependent on the presence of aminophospholipids, such as phosphatidylserine (PS) and phosphatidylethanolamine (PE), but it is unknown whether or not TF-exposing EMP are enriched in such aminophospholipids. Furthermore, despite the fact that EMP have been reported in several pathological conditions, direct evidence for their (putative) coagulant properties in vivo is still lacking. We investigated the phospholipid composition of endothelial MP (EMP) and their thrombogenic properties in vivo.

MATERIALS AND METHODS

Human umbilical vein endothelial cells (HUVEC; n=3) were incubated with or without interleukin (IL)-1alpha (5 ng/mL; 0-72 h). Phospholipid composition of EMP was determined by high-performance thin layer chromatography. The association between EMP, TF antigen and activity was confirmed in vitro (ELISA, Western blot and thrombin generation). Thrombogenic activity of EMP in vivo was determined in a rat venous stasis model.

RESULTS

Levels of TF antigen increased 3-fold in culture medium of IL-1alpha-treated cells (P<0.0001). This TF antigen was associated with EMP and appeared as a 45-47 kDa protein on Western blot. In addition, EMP from activated cells were enriched in both PS (P<0.0001) and PE (P<0.0001), and triggered TF-dependent thrombin formation in vitro and thrombus formation in vivo. In contrast, EMP from control cells neither initiated coagulation in vitro nor thrombus formation in vivo.

CONCLUSIONS

EMP from activated endothelial cells expose coagulant tissue factor and are enriched in its cofactors PS and PE.

Microparticles stimulate the synthesis of prostaglandin E(2) via induction of cyclooxygenase 2 and microsomal prostaglandin E synthase 1

OBJECTIVE

Microparticles are small vesicles that are released from activated or dying cells and that occur abundantly in the synovial fluid of patients with rheumatoid arthritis (RA). The goal of these studies was to elucidate the mechanisms by which microparticles activate synovial fibroblasts to express a proinflammatory phenotype.

METHODS

Microparticles from monocytes and T cells were isolated by differential centrifugation. Synovial fibroblasts were cocultured with increasing numbers of microparticles. Gene expression was analyzed by real-time polymerase chain reaction and confirmed by Western blotting and enzyme immunoassay. Arachidonic acid labeled with tritium was used to study the transport of biologically active lipids by microparticles. The roles of NF-kappaB and activator protein 1 (AP-1) signaling were analyzed with electrophoretic mobility shift assay and transfection with small interfering RNA and IkappaB expression vectors.

RESULTS

Microparticles strongly induced the synthesis of cyclooxygenase 2 (COX-2), microsomal prostaglandin E synthase 1 (mPGES-1), and prostaglandin E(2) (PGE(2)). In contrast, no up-regulation of COX-1, mPGES-2, cytosolic PGES, or phospholipase A(2) was observed. The induction of PGE(2) was blocked by selective inhibition of COX-2. Microparticles activated NF-kappaB, AP-1, p38, and JNK signaling in synovial fibroblasts. Inhibition of NF-kappaB, AP-1, and JNK signaling reduced the stimulatory effects. Arachidonic acid was transported from leukocytes to fibroblasts by microparticles. Arachidonic acid derived from microparticles was converted to PGE(2) by synovial fibroblasts.

CONCLUSION

These results demonstrate that microparticles up-regulate the production of PGE(2) in synovial fibroblasts by inducing COX-2 and mPGES-1. These data provide evidence for a novel mechanism by which microparticles may contribute to inflammation and pain in RA.

Tissue factor in thrombosis and hemorrhage

The research aims of our laboratory are to provide a realistic description of biologic processes involved in protection from hemorrhage and the evolution of thrombosis. To evaluate these processes, we use 4 models of coagulation ranging from 1) studies of blood exiting from microvascular wounds in humans through 2) minimally altered whole blood induced to clot by tissue factor (TF) to 3) reconstitution of the blood coagulation proteome with purified components and to 4) mathematical descriptions of the chemical processes and dynamics that occur. The integration of these 4 models permits comprehensive analyses of the blood coagulation system and predictions of its behavior under normal and pathologic conditions. Data accumulated thus far have led to advances in our understanding of 1) the processes occurring during the initiation and propagation phases of thrombin generation, 2) the roles for individual proteins involved in blood coagulation and its regulation, 3) defects in thrombin generation and clot formation in hemophilia, 4) actions and limitations of pharmacologic agents used to control hemorrhage, thrombosis, and chronic cardiovascular disease, and 5) the relationship between genotypic and phenotypic features of an individual's plasma proteome and his/her immediate and long-term thrombotic risk.

The release of microparticles by apoptotic cells and their effects on macrophages

Microparticles are small membrane vesicles released from the cell membrane by exogenous budding. To elucidate the interactions of microparticles with macrophages, the effect of microparticles released from Jurkat T cells on RAW 264.7 cells was determined. Microparticles were isolated by differential centrifugation, using FACS analysis with annexin V and cell surface markers for identification. Various inducers of apoptosis increased the release of microparticles from Jurkat cells up to 5-fold. The released microparticles were then cultured with RAW 264.7 cells. As shown by confocal microscopy and FACS analysis, RAW 264.7 macrophages cleared microparticles by phagocytosis. In addition, microparticles induced apoptosis in RAW 264.7 cells in a dose-dependent manner with up to a 5-fold increase of annexin V positive cells and 9-fold increase in caspase 3 activity. Cell proliferation as determined by the MTT test was also reduced. Furthermore, microparticles stimulated the release of microparticles from macrophages. These effects were specific for macrophages, since no apoptosis was observed in NIH 3T3 and L929 cells. These findings indicate that microparticles can induce macrophages to undergo apoptosis, in turn resulting in a further increase of microparticles. The release of microparticles from apoptotic cells may therefore represent a novel amplification loop of cell death.

Developments in the synovial biology field 2006

Synovial pathophysiology is a complex and synergistic interplay of different cell populations with tissue components, mediated by a variety of signaling mechanisms. All of these mechanisms drive the affected joint into inflammation and drive the subsequent destruction of cartilage and bone. Each cell type contributes significantly to the initiation and perpetuation of this deleterious concert, especially in rheumatoid arthritis. Rheumatoid arthritis synovial fibroblasts and macrophages, both cell types with pivotal roles in inflammation and destruction, but also T cells and B cells are crucial for complex network in the inflamed synovium. An even more complex cellular crosstalk between these key players maintains a process of chronic inflammation. As outlined in the present review, in the past year substantial progress has been made to elucidate further details of the rich pathophysiology of rheumatoid arthritis, which may also facilitate the identification of novel targets for future therapeutic strategies.

The Role of Microparticles in Inflammation and Thrombosis

Microparticles (MP) are small membrane-bound vesicles that circulate in the peripheral blood and play active roles in thrombosis, inflammation and vascular reactivity. While MP can be released from nearly every cell type, most investigation has focused on MP of platelet, leucocyte and endothelial cell origin. Cells can release MP during activation or death. Flow cytometry is the usual method to quantify MP; the small size of these structures and lack of standardization in methodology complicate measurement. As MP contain surface and cytoplasmic contents of the parent cells and bear phosphatidylserine, antibodies to specific cell surface markers and annexin V can be used for identification. Through various mechanisms, MP participate in haemostasis and have procoagulant potential in disease. MP contribute to inflammation via their influence on cell-cell interactions and cytokine release, and MP also function in mediating vascular tone. In several disease states characterized by inflammation and vascular dysfunction, MP subpopulations are elevated, correlate with clinical events, and may have important roles in pathogenesis. In the rheumatic conditions such as rheumatoid arthritis and systemic lupus erythematosus, MP are potentially important markers of disease activity and have an increasingly recognized role in immunopathogenesis. It is clear that MP play an important role in atherosclerosis, and study of these structures may provide insight into the link between chronic inflammatory conditions and accelerated atherosclerosis. As biomarkers, MP allow access to usually inaccessible tissues such as the endothelium. Further research will hopefully lead to interventions targeting MP release and function.

Activated complement components and complement activator molecules on the surface of cell-derived microparticles in patients with rheumatoid arthritis and healthy individuals

OBJECTIVES

In vitro, microparticles can activate complement via the classical pathway. If demonstrable ex vivo, this mechanism may contribute to the pathogenesis of rheumatoid arthritis (RA). We therefore investigated the presence of activated complement components and complement activator molecules on the surface of cell-derived microparticles of RA patients and healthy individuals.

METHODS

Microparticles from synovial fluid (n = 8) and plasma (n = 9) of 10 RA patients and plasma of sex- and age-matched healthy individuals (n = 10) were analysed by flow cytometry for bound complement components (C1q, C4, C3) and complement activator molecules (C-reactive protein (CRP), serum amyloid P component (SAP), immunoglobulin (Ig) M, IgG).

RESULTS

Microparticles with bound C1q, C4, and/or C3 were abundant in RA synovial fluid, while in RA and control plasma much lower levels were present. Microparticles with bound C1q correlated with those with bound C3 in synovial fluid (r = 0.961, p = 0.0001), and with those with bound C4 in plasma (RA: r = 0.908, p = 0.0007; control: r = 0.632, p = 0.0498), indicating classical pathway activation. In synovial fluid, microparticles with IgM and IgG correlated with those with C1q (r = 0.728, p = 0.0408; r = 0.952, p = 0.0003, respectively), and in plasma, microparticles with CRP correlated with those with C1q (RA: r = 0.903, p = 0.0021; control: r = 0.683, p = 0.0296), implicating IgG and IgM in the classical pathway activation in RA synovial fluid, and CRP in the low level classical pathway activation in plasma.

CONCLUSIONS

This study demonstrates the presence of bound complement components and activator molecules on microparticles ex vivo, and supports their role in low grade complement activation in plasma and increased complement activation in RA synovial fluid.

The role of membrane lipids in the induction of macrophage apoptosis by microparticles

Microparticles are membrane-derived vesicles that are released from cells during activation or cell death. These particles can serve as mediators of intercellular cross-talk and induce a variety of cellular responses. Previous studies have shown that macrophages undergo apoptosis after phagocytosing microparticles. Here, we have addressed the hypothesis that microparticles trigger this process via lipid pathways. In these experiments, microparticles induced apoptosis in primary macrophage cells or cell lines (RAW 264.7 or U937) with up to a 5-fold increase. Preincubation of macrophages with phosphatidylinositol-3,5-bisphosphate (PtdIns(3,5)BP) reduced the microparticle-induced apoptosis in a dose-dependent manner. PtdIns(3,5)BP is a specific inhibitor of the acid sphingomyelinase and thus can block the generation of pro-apoptotic ceramides. Similarly, the pre-incubation of macrophages with PtdIns(3,5)BP prevented microparticle-induced upregulation of caspase 8, which is a major target molecule of ceramide action in the apoptosis pathway. PtdIns(3,5)BP, however, had no effect on the spontaneous rate of apoptosis. To evaluate further signaling pathways induced by microparticles, the extracellular signal regulated kinase (ERK-) 1 was investigated. This kinase plays a role in activating phospholipases A2 which cleaves membrane phospholipids into arachidonic acid; microparticles have been suggested to be a preferred substrate for phospholipases A2. As shown in our experiments, microparticles strongly increased the amount of phosphorylated ERK1/2 in RAW 264.7 macrophages in a time-dependent manner, peaking 15 min after co-incubation. Addition of PD98059, a specific inhibitor of ERK1, prevented the increase in apoptosis of RAW 264.7 macrophages. Together, these data suggest that microparticles perturb lipid homeostasis of macrophages and thereby induce apoptosis. These results emphasize the importance of biolipids in the cellular cross-talk of immune cells. Based on the fact that in clinical situations with excessive cell death such as malignancies, autoimmune diseases and following chemotherapies high levels of circulating microparticles might modulate phagocytosing cells, a suppression of the immune response might occur due to loss of macrophages.

Emerging targets of biologic therapies for rheumatoid arthritis

Advances in molecular biology and the clinical success of strategies that target tumor necrosis factor (TNF) have led to further research into the pathophysiology of human rheumatoid arthritis. Several novel therapeutic targets have emerged from these efforts, including not only molecules that regulate TNF (e.g. TNF-alpha converting enzyme), the complex cytokine network (e.g. interleukin [IL]-6, IL-15, IL-17) and several adipokines, but also targets that originate from cellular and subcellular components of the disease. Strategies that aim at cellular targets include antibodies to CD20 or BLyS (also known as TNF ligand family member 13b), which deplete or inhibit B cells, as well as approaches that interfere with membrane-derived microparticles. Components of subcellular pathways, which are predominantly upstream of the central regulator of transcription nuclear factor kappaB, have also been studied. Of these, strategies that target mitogen-activated protein kinases have a leading role and are on the verge of clinical use; approaches that target specific molecules such as Janus kinases, signal transducer and activator of transcription proteins, and suppressor of cytokine signaling proteins also seem to show promise and might have a clinical application in the future.

Microparticles as mediators of cellular cross-talk in inflammatory disease

Microparticles are a heterogeneous population of membrane-coated vesicles which can be released from virtually all cell types during activation or apoptosis. Release occurs from the cell surface in an exogenous budding process involving local rearrangement of the cytoskeleton. Given their origin, these particles can be identified by staining for cell surface markers and annexin V. As shown in in vitro studies, microparticles may represent a novel subcellular element for intercellular communication in inflammation. Thus, microparticles can transfer chemokine receptors and arachidonic acid between cells, activate complement, promote leukocyte rolling and stimulate the release of pro-inflammatory mediators. Under certain conditions, however, microparticles may also exert anti-inflammatory properties by inducing immune cell apoptosis and the production of anti-inflammatory mediators. Microparticles may play an important role in the pathogenesis of rheumatologic diseases as evidenced by their elevation in diseases such as systemic sclerosis (SSc), systemic vasculitis and antiphospholipid antibody syndrome and correlation with clinical events. A role in inflammatory arthritis is suggested by the finding that leukocyte-derived microparticles induce the production of matrix metalloproteinases and cytokines by synovial fibroblasts. Together, these findings point to novel signaling pathways of cellular cross-talk that may operate along the spectrum of soluble cytokines and mediators of direct cell-cell contact.

Rheumatoid arthritis and the complement system

Complement activation contributes to a pathological process in a number of autoimmune and inflammatory diseases, including rheumatoid arthritis (RA). In this review we summarize current knowledge of complement contribution to RA, based on clinical observations in patients and in vivo animal models, as well as on experiments in vitro aiming at elucidation of underlying molecular mechanisms. There is strong evidence that both the classical and the alternative pathways of complement are pathologically activated during RA as well as in animal models for RA. The classical pathway can be initiated by several triggers present in the inflamed joint such as deposited autoantibodies, dying cells, and exposed cartilage proteins such as fibromodulin. B cells producing autoantibodies, which in turn form immune complexes, contribute to RA pathogenesis partly via activation of complement. It appears that anaphylatoxin C5a is the main product of complement activation responsible for tissue damage in RA although deposition of membrane attack complex as well as opsonization with fragments of C3b are also important. Success of complement inhibition in the experimental models described so far encourages novel therapeutic approaches to the treatment of human RA.

Monocyte/Macrophage-Derived Microparticles Up-Regulate Inflammatory Mediator Synthesis by Human Airway Epithelial Cells

Cell-derived microparticles (MP) are membrane fragments shed by virtually all eukaryotic cells upon activation or during apoptosis that play a significant role in physiologically relevant processes, including coagulation and inflammation. We investigated whether MP derived from monocytes/macrophages have the potential to modulate human airway epithelial cell activation. Monocytes/macrophages were isolated from the buffy coats of blood donors by Ficoll gradient centrifugation, followed by overnight culture of the mononuclear cell fraction. Adherent cells were washed and incubated with the calcium ionophore, A23187, or with histamine. The MP-containing supernatant was incubated with cells of the human bronchial epithelial line BEAS-2B and of the human alveolar line A549. IL-8, MCP-1, and ICAM-1 production was assessed by ELISA and by RT-PCR. In some experiments, monocytes/macrophages were stained with the fluorescent lipid intercalating dye PKH67, and the supernatant was analyzed by FACS. Stimulation of monocytes/macrophages with A23187 caused the release of particles that retain their fluorescent lipid intercalating label, indicating that they are derived from cell membranes. Incubation with A549 and BEAS-2B cells up-regulate IL-8 synthesis. Ultrafiltration and ultracentrifugation of the material abolished the effect, indicating that particulate matter, rather than soluble molecules, is responsible for it. Up-regulation of MCP-1 and ICAM-1 was also demonstrated in A549 cells. Similar results were obtained with histamine. Our data show that human monocytes/macrophages release MP that have the potential to sustain the innate immunity of the airway epithelium, as well as to contribute to the pathogenesis of inflammatory diseases of the lungs through up-regulation of proinflammatory mediators.

Cell vesiculation and immunopathology: implications in cerebral malaria

Microparticles are plasma membrane fragments that are generated and released under physiological conditions. They are also released when tissue and/or systemic homeostasis is disrupted. These microparticles display different physiological features of the cells from which they originate. They are detected in some pathological conditions, but rarely suspected of participating in the disease's pathogenesis. In the present review, we summarise data about the production of the microparticles, their biological significance and potential role during microorganism-driven processes, especially in cerebral malaria.

Pathogenesis of hemophilic arthropathy

Intra-articular bleeding is the most common clinical manifestation of hemophilia, and can adversely affect joints and lead to arthropathy. Affected joints are associated with changes to the synovium, bone, cartilage and blood vessels. Iron plays a critical role in the pathogenesis of this condition, and may exert its effects through a variety of different mechanisms. Hemophilic arthropathy shares some injury characteristics with rheumatoid arthritis, although the degree of analogy is a matter of some debate. The influences of the mechanisms underlying joint inflammation are better understood for rheumatoid arthritis than for hemophilia, and it is hoped that this knowledge can be used to provide a more comprehensive knowledge of the pathological process of hemophilic arthropathy. This, in turn, may enable novel targets for therapeutic intervention to be identified.

Synovial fibroblasts: key players in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune-disease of unknown origin that primarily affects the joints and ultimately leads to their destruction. The involvement of immune cells is a general hallmark of autoimmune-related disorders. In this regard, macrophages, T cells and their respective cytokines play a pivotal role in RA. However, the notion that RA is a primarily T-cell-dependent disease has been strongly challenged during recent years. Rather, it has been understood that resident, fibroblast-like cells contribute significantly to the perpetuation of disease, and that they may even play a role in its initiation. These rheumatoid arthritis synovial fibroblasts (RASFs) constitute a quite unique cell type that distinguishes RA from other inflammatory conditions of the joints. A number of studies have demonstrated that RASFs show alterations in morphology and behaviour, including molecular changes in signalling cascades, apoptosis responses and in the expression of adhesion molecules as well as matrix-degrading enzymes. These changes appear to reflect a stable activation of RASFs, which occurs independently of continuous exogenous stimulation. As a consequence, RASFs are no longer considered passive bystanders but active players in the complex intercellular network of RA.

Les microparticules circulantes : rôles physiologiques et implications dans les maladies inflammatoires et thrombotiques

BACKGROUND

In multicellular organisms, apoptosis and subsequent microparticle shedding play a key role in homeostasis. Having long been considered as << cellular dust >>, microparticles released in biological fluids upon cell activation or apoptosis appear as multifunctional bioeffectors involved in the modulation of key functions including immunity, inflammation, hemostasis and thrombosis, angiogenesis. MP constitute reliable markers of vascular damage, accessible to biological detection whilst the cells they originate from remain sequestered in tissues or are promptly submitted to phagocytosis.

RECENT FINDINGS

MP modulate biological functions of target cells through the transfer of cytoplasmic content, lipids and membrane receptors. The pharmacological modulation of circulating levels of microparticles could be of particular interest in thrombotic or inflammatory diseases, cancer or hemophilia.

CONCLUSION

MP can now be viewed not only as a hallmark of cell damage but also as a true biological tool.

[Cardiovascular manifestations in rheumatoid arthritis]

Rheumatoid arthritis (RA) is a chronic inflammatory disease, characterized by a polyarticular joint inflammation which eventually leads to joint destruction and general disability. Besides these polyarticular manifestations, several systemic immune phenomena have been described. An increased mortality in RA patients is evident and is mainly caused by an increased cardiovascular risk. The correlation between disease activity and mortality highlighted the important role of the systemic inflammatory reaction in induction and progression of vascular damaging processes. Endothelial dysfunction and vascular inflammation are important, mechanisms in atherosclerosis and induced by conventional risk factors and systemic inflammation. It has been shown that the deleterious influence of conventional risk factors is aggravated by inflammatory mediators, mainly by pro-inflammatory cytokines. In addition, certain inflammatory mediators exert damaging effects to blood vessels. Especially CRP, merely considered as a risk indicating parameter in the past, has attracted remarkable attention. Also certain RA specific immune phenomena are of considerable proatherosclerotic potential. At least in part, they could be responsible for the excess mortality in RA patients. The newer TNFalpha blocking agents interfere with different mechanisms responsible for induction and perpetuation of atherosclerotic processes. Time will show whether they make a remarkable impact on the cardiovascular mortality in RA patients.

Synovial microparticles from arthritic patients modulate chemokine and cytokine release by synoviocytes

Synovial fluid from patients with various arthritides contains procoagulant, cell-derived microparticles. Here we studied whether synovial microparticles modulate the release of chemokines and cytokines by fibroblast-like synoviocytes (FLS). Microparticles, isolated from the synovial fluid of rheumatoid arthritis (RA) and arthritis control (AC) patients (n = 8 and n = 3, respectively), were identified and quantified by flow cytometry. Simultaneously, arthroscopically guided synovial biopsies were taken from the same knee joint as the synovial fluid. FLS were isolated, cultured, and incubated for 24 hours in the absence or presence of autologous microparticles. Subsequently, cell-free culture supernatants were collected and concentrations of monocyte chemoattractant protein-1 (MCP-1), IL-6, IL-8, granulocyte/macrophage colony-stimulating factor (GM-CSF), vascular endothelial growth factor (VEGF) and intracellular adhesion molecule-1 (ICAM-1) were determined. Results were consistent with previous observations: synovial fluid from all RA as well as AC patients contained microparticles of monocytic and granulocytic origin. Incubation with autologous microparticles increased the levels of MCP-1, IL-8 and RANTES in 6 of 11 cultures of FLS, and IL-6, ICAM-1 and VEGF in 10 cultures. Total numbers of microparticles were correlated with the IL-8 (r = 0.91, P < 0.0001) and MCP-1 concentrations (r = 0.81, P < 0.0001), as did the numbers of granulocyte-derived microparticles (r = 0.89, P < 0.0001 and r = 0.93, P < 0.0001, respectively). In contrast, GM-CSF levels were decreased. These results demonstrate that microparticles might modulate the release of chemokines and cytokines by FLS and might therefore have a function in synovial inflammation and angiogenesis.

The induction of matrix metalloproteinase and cytokine expression in synovial fibroblasts stimulated with immune cell microparticles

Rheumatoid arthritis is a chronic inflammatory disease characterized by destruction of cartilage and bone that is mediated by synovial fibroblasts. To determine the mechanisms by which these cells are activated to produce matrix metalloproteinases (MMPs), the effects of microparticles were investigated. Microparticles are small membrane-bound vesicles whose release from immune cells is increased during activation and apoptosis. Because microparticles occur abundantly in the synovial fluid in rheumatoid arthritis, they could represent novel stimulatory agents. Microparticles derived from T cells and monocytes strongly induced the synthesis of MMP-1, MMP-3, MMP-9, and MMP-13 in fibroblasts. The induction was time-dependent, with effects primarily observed after 36 h; under these conditions, MMP-2, MMP-14, and tissue inhibitor of MMP-1 (TIMP-1), TIMP-2, and TIMP-3 were not induced. Microparticles also increased the synthesis of inflammatory mediators including IL-6, IL-8, monocyte chemoattractant protein 1 (MCP-1), and MCP-2. In Ikappa-B-transfected synovial fibroblasts, MMPs were less inducible by microparticles compared with wild-type fibroblasts. Blocking of TNFalpha and IL-1beta with antibodies against TNFalpha and with IL-1 receptor antagonist did not abrogate stimulation by microparticles. These data provide evidence for a novel mechanism by which vesicles derived from activated or apoptotic immune cells can promote the destructive activity of synovial fibroblasts in rheumatoid arthritis.

Tissue factor activity in whole blood

Tissue factor (TF) is an integral membrane protein essential for hemostasis. During the past several years, a number of studies have suggested that physiologically active TF circulates in blood at concentrations greater than 30 pM either as a component of blood cells and microparticles or as a soluble plasma protein. In our studies using contact pathway-inhibited blood or plasma containing activated platelets, typically no clot is observed for 20 minutes in the absence of exogenous TF. An inhibitory anti-TF antibody also has no effect on the clotting time in the absence of exogenous TF. The addition of TF to whole blood at a concentration as low as 16 to 20 fM results in pronounced acceleration of clot formation. The presence of potential platelet TF activity was evaluated using ionophore-treated platelets and employing functional and immunoassays. No detectable TF activity or antigen was observed on quiescent or ionophore-stimulated platelets. Similarly, no TF antigen was detected on mononuclear cells in nonstimulated whole blood, whereas in lipopolysaccharide (LPS)-stimulated blood a significant fraction of monocytes express TF. Our data indicate that the concentration of physiologically active TF in non-cytokine-stimulated blood from healthy individuals cannot exceed and is probably lower than 20 fM.