Circulating microparticles remain associated with complement activation despite intensive anti-inflammatory therapy in early rheumatoid arthritis

Metabolites as extracellular vesicle cargo in health, cancer, pleural effusion, and cardiovascular diseases: An emerging field of study to diagnostic and therapeutic purposes

Extracellular vesicles (EVs) are highly diverse nanoscale membrane-bound structures released from different cell types into the extracellular environment. They play essential functions in cell signaling by transporting their cargo, such as proteins, RNA, DNA, lipids, metabolites, and small molecules, to recipient cells. It has recently been shown that EVs might modulate carcinogenesis by delivering cargo to recipient cells. Furthermore, recent discoveries revealed that changes in plasma-derived EV levels and cargo in subjects with metabolic diseases were documented by many researchers, suggesting that EVs might be a promising source of disease biomarkers. One of the cargos of EVs that has recently attracted the most attention is metabolites. The metabolome of these vesicles introduces a plethora of disease indicators; hence, examining the metabolomics of EVs detected in human biofluids would be an effective approach. On the other hand, metabolites have various roles in biological systems, including the production of energies, synthesizing macromolecules, and serving as signaling molecules and hormones. Metabolome rewiring in cancer and stromal cells is a characteristic of malignancy, but the current understanding of how this affects the metabolite composition and activity of tumor-derived EVs remains in its infancy. Since new findings and studies in the field of exosome biology and metabolism are constantly being published, it is likely that diagnostic and treatment techniques, including the use of exosome metabolites, will be launched in the coming years. Recent years have seen increased interest in the EV metabolome as a possible source for biomarker development. However, our understanding of the role of these molecules in health and disease is still immature. In this work, we have provided the latest findings regarding the role of metabolites as EV cargoes in the pathophysiology of diseases, including cancer, pleural effusion (PE), and cardiovascular disease (CVD). We also discussed the significance of metabolites as EV cargoes of microbiota and their role in host-microbe interaction. In addition, the latest findings on metabolites in the form of EV cargoes as biomarkers for disease diagnosis and treatment are presented in this study.

Modulation of B cell activation by extracellular vesicles and potential alteration of this pathway in patients with rheumatoid arthritis

Background

Extracellular vesicles are involved in the intercellular communication of the immune system. In rheumatoid arthritis (RA), these structures are considered a source of autoantigens that drive proinflammatory responses of innate immune cells. A high concentration of circulating medium/large size extracellular vesicles (m/lEVs) and m/lEVs forming immune complexes (m/lEV-ICs) have been associated with disease activity and systemic inflammation in patients with RA. B cells are central components of RA immunopathology because of their involvement in the production of autoantibodies, antigen presentation, and cytokine production. However, the effect of m/lEVs on B cell function in the context of RA and other autoimmune diseases remains unknown.

Methods

We evaluated the effect of m/lEVs obtained from healthy donors (HD) and patients with RA on B cell responses in vitro. In addition, we evaluated the effect of pre-exposition of monocyte-derived macrophages (MDM) to m/lEVs on activation of autologous B cells from HD and patients.

Results

The presence of m/lEVs reduced the frequency of CD69⁺ and CD86⁺ B cells from HD activated by an agonist of antigen receptor. This regulation of the B cell activation markers by m/lEVs was partially dependent on phosphatidylserine binging. These m/lEVs also reduced the proliferation, calcium mobilization, and global phosphorylation of tyrosine. Similar responses were observed in B cells from patients with RA. However, the presence of m/lEVs promoted high antibody levels in B cells cultured with T cell-dependent stimuli by 7 days. In addition, despite the direct inhibitory effect of m/lEVs on early B cell responses, when B cells were cocultured with autologous MDM previously exposed to m/lEVs or m/lEV-ICs, an increased frequency of CD69⁺ B cells from patients with RA was observed, albeit not with cells from HD.

Conclusions

These data together suggest that m/lEVs have a direct modulatory effect in early responses of B cells through B cell receptor that can potentially fail in patients with RA because of the impact of these vesicles over cells of the innate immune system. This phenomenon can potentially contribute to the loss of tolerance and disease activity in patients with RA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02837-3.

The role of extracellular vesicles in rheumatoid arthritis: a systematic review

Rheumatoid arthritis (RA) is a chronic inflammatory disease that carries high social and economic costs and can lead to permanent disability. RA pathogenesis has not been completely elucidated yet. Extracellular vesicles (EVs) are membrane-contained vesicles released by cells playing a role in cell-to-cell communication and they could be involved in different diseases. Evidence on the involvement of EVs in RA is currently inconclusive. Therefore, a systematic review on the role of EVs in RA was performed in order to explore this relationship. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The research was conducted on PubMed, Scopus, and Embase up to March 5, 2020: 41 studies were analyzed out of 674 screened. The total plasmatic and synovial fluid (SF) EV number seems increased in RA as compared with healthy controls. Both RA plasma and SF contained EVs subpopulations of heterogenous origin, especially derived from platelets and immune system cells. No univocal evidence emerged on miRNA expression and EV content profile within RA patients. EVs showed to enhance pro-inflammatory pathways, such as cytokines and chemokine release and TNF blockade seemed to revert this effect. Our work highlights the requirement to standardize study methodologies in order to make results comparable and draw conclusions that remain, at present, unclear.

Increased Expression of Extracellular Vesicles Is Associated With the Procoagulant State in Patients With Established Rheumatoid Arthritis

This study sought to identify different subpopulations of extracellular vesicles (EVs) in plasma from female patients with established rheumatoid arthritis (RA) in relation to the activation of coagulation and fibrin formation in these patients. Forty women were included in the study, 20 patients and 20 age-matched healthy controls. The mean disease duration in patients was 13.0 (5.0-25.0) years, with medium to high disease activity despite ongoing treatment with low-dose prednisolone and methotrexate. There were no differences between the investigated groups regarding the presence of traditional cardiovascular risk factors. The concentration of phosphatidylserine-positive (PS+) EVs; platelet (CD42a+), leucocyte (CD45+), monocyte (CD14+), and endothelial (CD144+)-derived EVs; and EVs-expressing tissue factor (CD142+), P-selectin (CD62P+), and E-selectin (CD62E+) were determined by flow cytometry analysis. Overall hemostasis potential (OHP) was assessed to follow the hemostatic disturbances, including the parameters for overall coagulation potential (OCP) and overall fibrinolytic potential (OFP). Fibrin clot turbidity was measured together with clot lysis time, and scanning electron microscopy was performed. Increased concentrations of PS+, CD42a+, CD142+, CD45+, CD14+, and CD62P+ EVs were found in plasma from patients with RA compared to healthy controls, and the concentrations of PS+, CD42a+, CD14+, and CD62P+ EVs were positively correlated with the inflammatory parameters in RA patients. Positive correlations were also found between the levels of PS+ and CD42a+ EVs and OCP as well as between the levels of PS+, CD42a+, and CD62P+EVs and OHP. The levels of PS+, CD42a+, CD14+, CD62P+, and CD62E+ EVs were negatively correlated with OFP. Elevated levels of circulating EVs of different cell origins were found in patients with established RA, in relation to the inflammatory burden and coagulation activation in the disease.

Extracellular vesicles are associated with C-reactive protein in sepsis

There is increasing evidence that C-reactive protein (CRP) can mediate inflammatory reactions following the transformation of functionally inert pentameric CRP (pCRP) into its structural isoform pCRP* and into monomeric CRP (mCRP). This conversion can occur on the membranes of apoptotic or activated cells or on extracellular vesicles (EVs) shed from the cell surface. Here, we characterized the association of CRP with EVs in plasma from sepsis patients using flow cytometry, and found highly elevated levels of total EV counts and CRP⁺ EVs as compared to healthy individuals. We further assessed the ability of PentraSorb CRP, an extracorporeal device for the adsorption of CRP, to deplete free CRP and CRP⁺ EVs. Treatment of septic plasma with the adsorbent in vitro resulted in almost complete removal of both, free CRP and CRP⁺ EVs, while total EV counts remained largely unaffected, indicating the detachment of CRP from the EV surface. EVs from septic plasma elicited a release of interleukin-8 from cultured human monocytes, which was significantly reduced by adsorbent treatment prior to EV isolation. Our findings provide evidence that CRP⁺ EVs exhibit pro-inflammatory characteristics and can contribute to the spreading of inflammation throughout the circulation on top of their pro-coagulant activity.

Chicken-or-egg question: Which came first, extracellular vesicles or autoimmune diseases?

Extracellular vesicles (EVs) have attracted great interest as contributors to autoimmune disease (AD) pathogenesis, owing to their immunomodulatory potential; they may also play a role in triggering tolerance disruption, by delivering auto‐antigens. EVs are released by almost all cell types, and afford paracrine or distal cell communication, functioning as biological carriers of active molecules including lipids, proteins, and nucleic acids. Depending on stimuli from the external microenvironment or on their cargo, EVs can promote or suppress immune responses. ADs are triggered by inappropriate immune‐system activation against the self, but their precise etiology is still poorly understood. Accumulating evidence indicates that lifestyle and diet have a strong impact on their clinical onset and development. However, to date the mechanisms underlying AD pathogenesis are not fully clarified, and reliable markers, which would provide early prediction and disease progression monitoring, are lacking. In this connection, EVs have recently been indicated as a promising source of AD biomarkers. Although EV isolation is currently based on differential centrifugation or density‐gradient ultracentrifugation, the resulting co‐isolation of contaminants (i.e., protein aggregates), and the pooling of all EVs in one sample, limit this approach to abundantly‐expressed EVs. Flow cytometry is one of the most promising methods for detecting EVs as biomarkers, and may have diagnostic applications. Furthermore, very recent findings describe a new method for identifying and sorting EVs by flow cytometry from freshly collected body fluids, based on specific EV surface markers.

Platelets: emerging facilitators of cellular crosstalk in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease in which a variety of circulating pro-inflammatory cells and dysregulated molecules are involved in disease aetiology and progression. Platelets are an important cellular element in the circulation that can bind several dysregulated molecules (such as collagen, thrombin and fibrinogen) that are present both in the synovium and the circulation of patients with RA. Platelets not only respond to dysregulated molecules in their environment but also transport and express their own inflammatory mediators, and serve as regulators at the boundary between haemostasis and immunity. Activated platelets also produce microparticles, which further convey signalling molecules and receptors to the synovium and circulation, thereby positioning these platelet-derived particles as strategic regulators of inflammation. These diverse functions come together to make platelets facilitators of cellular crosstalk in RA. Thus, the receptor functions, ligand binding potential and dysregulated signalling pathways in platelets are becoming increasingly important for treatment in RA. This Review aims to highlight the role of platelets in RA and the need to closely examine platelets as health indicators when designing effective pharmaceutical targets in this disease.

Role of Microparticles in the Pathogenesis of Inflammatory Joint Diseases

Rheumatoid arthritis (RA), juvenile idiopathic arthritis (JIA), ankylosing spondylitis (AS), and psoriatic arthritis (PsA) make up a group of chronic immune-mediated inflammatory diseases (IMIDs). The course of these diseases involves chronic inflammation of joints and enthesopathies, which can result in joint damage and disability. Microparticles (MPs) are a group of small spherical membranous vesicles. The structure and cellular origin of MPs, mechanisms that stimulate their secretion and the place of their production, determine their biological properties, which could become manifest in the pathogenesis of immune-mediated inflammatory diseases. Microparticles can stimulate synovitis with proinflammatory cytokines and chemokines. MPs may also contribute to the pathogenesis of rheumatic diseases by the formation of immune complexes and complement activation, pro-coagulation activity, activation of vascular endothelium cells, and stimulation of metalloproteinase production. It seems that in the future, microparticles can become a modern marker of disease activity, a response to treatment, and, possibly, they can be used in the prognosis of the course of arthritis. The knowledge of the complexity of MPs biology remains incomplete and it requires further comprehensive studies to explain how they affect the development of rheumatic diseases. This review focuses on the immunopathogenic and therapeutic role of MPs in chronic immune-mediated inflammatory joint diseases.

Endothelial activation and injury by microparticles in patients with systemic lupus erythematosus and rheumatoid arthritis

BACKGROUND

Endothelial activation and damage is commonly observed in patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) and is related to development of atherosclerosis and cardiovascular diseases. Different components of the immune system seem to participate in the endothelial injury, such as generation of autoantibodies and formation of immune complexes (ICs). Microparticles (MPs) and their immune complexes (MPs-ICs) are increased in the circulation of patients with SLE and RA; therefore, we propose these extracellular vesicles could interact and modulate the function of endothelial cells. Hence, the effect of MPs and MPs-ICs from patients with SLE and RA in endothelial cells was evaluated.

METHODS

Macrovascular and microvascular endothelial cells were exposed to MPs and MPs-ICs from healthy donors and patients with SLE and RA. Vesicles uptake/binding, expression of adhesion molecules, cytokine and chemokine production, monocyte adherence, and alterations of endothelial monolayer were evaluated by flow cytometry and fluorescence microscopy.

RESULTS

Endothelial cells internalized MPs and MPs-ICs and increased CD54 and CD102 expression and CCL2, CCL5, and IL-6 production after the treatment with these extracellular vesicles, which led to an increase in the adherence of classic monocytes. These vesicles also induced low expression of VE-cadherin in membrane, depolymerization of actin filaments, and formation of intercellular spaces, which led to endothelial death and increased permeability after MPs and MPs-ICs exposure.

CONCLUSIONS

MPs and MPs-ICs from patients with SLE and RA increase adhesion molecules expression, chemokine production, and structural alterations in macrovascular and microvascular endothelial cells. Therefore, high counts of these vesicles in patients would promote endothelial alterations and secondary tissue leukocyte infiltration.

Extracellular vesicles: A new therapeutic strategy for joint conditions

Extracellular vesicles (EVs) are attracting increasing interest since they might represent a more convenient therapeutic tool with respect to their cells of origin. In the last years much time and effort have been expended to determine the biological properties of EVs from mesenchymal stem cells (MSCs) and other sources. The immunoregulatory, anti-inflammatory and regenerative properties of MSC EVs have been demonstrated in in vitro studies and animal models of rheumatoid arthritis or osteoarthritis. This cell-free approach has been proposed as a possible better alternative to MSC therapy in autoimmune conditions and tissue regeneration. In addition, EVs show great potential as biomarkers of disease or delivery systems for active molecules. The standardization of isolation and characterization methods is a key step for the development of EV research. A better understanding of EV mechanisms of action and efficacy is required to establish the potential therapeutic applications of this new approach in joint conditions.

Circulating LL37 targets plasma extracellular vesicles to immune cells and intensifies Behçet's disease severity

Behçet's disease (BD) activity is characterised by sustained, over-exuberant immune activation, yet the underlying mechanisms leading to active BD state are poorly defined. Herein, we show that the human cathelicidin derived antimicrobial peptide LL37 associates with and directs plasma extracellular vesicles (EV) to immune cells, thereby leading to enhanced immune activation aggravating BD pathology. Notably, disease activity was correlated with elevated levels of circulating LL37 and EV plasma concentration. Stimulation of healthy PBMC with active BD patient EVs induced heightened IL1β, IFNα, IL6 and IP10 secretion compared to healthy and inactive BD EVs. Remarkably, when mixed with LL37, healthy plasma-EVs triggered a robust immune activation replicating the pathology inducing properties of BD EVs. The findings of this study could be of clinical interest in the management of BD, implicating LL37/EV association as one of the major contributors of BD pathogenesis. Abbreviations: BD: Behçet's disease; EV: extracellular vesicle; BB: binding buffer; AnV: annexin V; autologEV: autologous extracellular vesicles; alloEV: allogeneic extracellular vesicles.

Identification of potential saliva and tear biomarkers in primary Sjögren's syndrome, utilising the extraction of extracellular vesicles and proteomics analysis

Background

There is a long-lasting need for non-invasive, more accurate diagnostic techniques when evaluating primary Sjögren’s syndrome (pSS) patients. Incorporation of additional diagnostics involving screening for disease-specific biomarkers in biological fluid is a promising concept that requires further investigation. In the current study we aimed to explore novel disease biomarkers in saliva and tears from pSS patients.

Methods

Liquid chromatography-mass spectrometry (LC-MS) was performed on stimulated whole saliva and tears from 27 pSS patients and 32 healthy controls, and salivary and tear proteomic biomarker profiles were generated. LC-MS was also combined with size exclusion chromatography to isolate extracellular vesicles (EVs) from both fluids. Nanoparticle tracking analysis was conducted on joint fractions from the saliva and tears to determine size distribution and concentration of EVs. Further EV characterisation was performed by immunoaffinity capture of CD9-positive EVs using magnetic beads, detected by flow cytometry. The LC-MS data were analysed for quantitative differences between patient and control groups using Scaffold, and the proteins were further analysed using the Database for Annotation, Visualization and Integrated Discovery (DAVID), for gene ontology overrepresentation, and the Search Tool for the Retrieval of Interacting Genes/Proteins for protein-protein interaction network analysis.

Results

Upregulation of proteins involved in innate immunity (LCN2), cell signalling (CALM) and wound repair (GRN and CALML5) were detected in saliva in pSS. Saliva EVs also displayed biomarkers critical for activation of the innate immune system (SIRPA and LSP1) and adipocyte differentiation (APMAP). Tear analysis indicated overexpression of proteins involved in TNF-α signalling (CPNE1) and B cell survival (PRDX3). Moreover, neutrophil gelatinase-associated lipocalin was upregulated in saliva and tears in pSS. Consistently, DAVID analysis demonstrated pathways of the adaptive immune response in saliva, of cellular component assembly for saliva EVs, and of metabolism and protein folding in tears in pSS patients.

Conclusions

LC-MS of saliva and tears from pSS patients, solely and in combination with size-exclusion chromatography allowed screening for possible novel biomarkers encompassing both salivary and lacrimal disease target organs. This approach could provide additional diagnostic accuracy in pSS, and could possibly also be applied for staging and monitoring the disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1228-x) contains supplementary material, which is available to authorized users.

Major involvement of bacterial components in rheumatoid arthritis and its accompanying oxidative stress, systemic inflammation and hypercoagulability

We review the evidence that infectious agents, including those that become dormant within the host, have a major role to play in much of the etiology of rheumatoid arthritis and the inflammation that is its hallmark. This occurs in particular because they can produce cross-reactive (auto-)antigens, as well as potent inflammagens such as lipopolysaccharide that can themselves catalyze further inflammagenesis, including via β-amyloid formation. A series of observables coexist in many chronic, inflammatory diseases as well as rheumatoid arthritis. They include iron dysregulation, hypercoagulability, anomalous morphologies of host erythrocytes, and microparticle formation. Iron dysregulation may be responsible for the periodic regrowth and resuscitation of the dormant bacteria, with concomitant inflammagen production. The present systems biology analysis benefits from the philosophical idea of "coherence," that reflects the principle that if a series of ostensibly unrelated findings are brought together into a self-consistent narrative, that narrative is thereby strengthened. As such, we provide a coherent and testable narrative for the major involvement of (often dormant) bacteria in rheumatoid arthritis.

Toll-like receptor 4 senses oxidative stress mediated by the oxidation of phospholipids in extracellular vesicles

Oxidative stress produced in response to infection or sterile injury activates the innate immune response. We found that extracellular vesicles (EVs) isolated from the plasma of patients with rheumatoid arthritis or secreted from cells subjected to oxidative stress contained oxidized phospholipids that stimulated cells expressing Toll-like receptor 4 (TLR4) in a manner dependent on its co-receptor MD-2. EVs from healthy subjects or reconstituted synthetic EVs subjected to limited oxidation gained the ability to stimulate TLR4-expressing cells, whereas prolonged oxidation abrogated this property. Furthermore, we found that 15-lipoxygenase generated hydro(pero)xylated phospholipids that stimulated TLR4-expressing cells. Molecular modeling suggested that the mechanism of activation of TLR4 by oxidized phospholipids in EVs was structurally similar to that of the TLR4 ligand lipopolysaccharide (LPS). This was supported by experiments showing that EV-mediated stimulation of cells required MD-2, that mutations that block LPS binding to TLR4 abrogated the stimulatory effect of EVs, and that EVs induced TLR4 dimerization. On the other hand, analysis of gene expression profiles showed that genes encoding factors that resolve inflammation were more abundantly expressed in responses to EVs than in response to LPS. Together, these data suggest that EVs act as an oxidative stress-induced endogenous danger signal that underlies the pervasive role of TLR4 in inflammatory diseases.

Microvesicles from platelets: novel drivers of vascular inflammation

Microvesicles are receiving increased attention not only as biomarkers but also as mediators of cell communication and as integral effectors of disease. Platelets present a major source of microvesicles and release these microvesicles either spontaneously or upon activation. Platelet-derived microvesicles retain many features of their parent cells and have been shown to exert modulatory effects on vascular and immune cells. Accordingly, microvesicles from platelets can be measured at increased levels in patients with cardiovascular disease or individuals at risk. In addition, isolated microvesicles from platelets were shown to exert immunomodulatory actions on various cell types. In this review the various aspects of platelet-derived microvesicles including release, clearance, measurement, occurrence during disease and relevance for the pathophysiology of vascular inflammation will be discussed.

Proportions of several types of plasma and urine microparticles are increased in patients with rheumatoid arthritis with active disease

We analysed the proportions of different microparticles (MPs) in plasma from patients with rheumatoid arthritis (RA), and assessed their relationship with disease activity/therapy and their in-vitro effect on proinflammatory cytokine release. Blood and urine samples were obtained from 55 patients with RA (24 untreated and 31 under conventional therapy) and 20 healthy subjects. Fourteen patients with systemic lupus erythematosus (SLE) were also studied. The proportions of CD3(+) , CD14(+) , CD19(+) , CD41(+) and CD62E(+) MPs were determined by flow cytometry analysis. The in-vitro effect of plasma MPs on the release of interleukin (IL)-1, IL-6, IL-17 and tumour necrosis factor (TNF)-α was also analysed. We detected that the proportions of different types of annexin-V(+) MPs were enhanced in plasma (CD3(+) , CD14(+) , CD19(+) , CD41(+) and CD62E(+) MPs) and urine (CD14(+) , CD3(+) and CD19(+) MPs) from RA patients with high disease activity (DAS28 index > 5·1). Accordingly, a significant positive correlation was observed between the levels of MPs and DAS28 score, and these levels diminished significantly at week 4 of immunosuppressive therapy. Finally, MPs isolated from patients with high disease activity induced, in vitro, an enhanced release of IL-1, IL-17 and TNF-α. In SLE, enhanced levels of different types of plasma MPs were also detected, with a tight correlation with disease activity. Our data further support that MPs have a relevant role in the pathogenesis of RA and suggest that the analysis of the proportions of these microvesicles in plasma could be useful to monitor disease activity and therapy response in patients with RA.

Are microparticles the missing link between thrombosis and autoimmune diseases? Involvement in selected rheumatologic diseases

Microparticles (MPs) are membrane-bound vesicles with important physiologic effects. MPs exchange information intercellularly, with each kind of MP carrying antigens and receptors of the cells from which they originated. They are biologic effectors in inflammation, angiogenesis, vascular injury, and thrombosis. Thrombosis is generally caused by abnormalities in blood flow, blood composition, and/or properties of the vessel wall. Thrombosis is a well-described feature of cardiovascular disease and cerebrovascular disease. Accumulating evidence suggests that increased risk of thrombosis is also characteristic of autoimmune disorders and immune-mediated diseases affecting all age groups, although the older adults are most vulnerable. Current research has also implicated MPs as a source of autoantigenic nuclear material that can form immune complexes, activate the innate immune system, and may lead to autoimmunity. This review focuses on the contribution of MPs to both the pathogenesis of autoimmune diseases and, as the immune and coagulation systems are tightly linked, their role in hypercoagulability in the setting of autoimmunity in an aging population.

Co-isolation of extracellular vesicles and high-density lipoproteins using density gradient ultracentrifugation

Extracellular vesicles (EVs) facilitate intercellular communication by carrying bioactive molecules such as proteins, messenger RNA, and micro (mi)RNAs. Recently, high-density lipoproteins (HDL) isolated from human plasma were also reported to transport miRNA to other cells. HDL, when isolated from human plasma, ranges in density between 1.063 and 1.21 g/mL, which grossly overlap with the reported density of EVs. Consequently, HDL and EV will be co-isolated when using density gradient ultracentrifugation. Thus, more stringent isolation/separation procedures of EV and HDL are essential to know their relative contribution to the pool of circulating bioactive molecules.

Microparticles: biomarkers and beyond

Membrane microparticles are submicron fragments of membrane shed into extracellular space from cells under conditions of stress/injury. They may be distinguished from other classes of extracellular vesicles (i.e. exosomes) on the basis of size, content and mechanism of formation. Microparticles are found in plasma and other biological fluids from healthy individuals and their levels are altered in various diseases, including diabetes, chronic kidney disease, pre-eclampsia and hypertension among others. Accordingly, they have been considered biomarkers of vascular injury and pro-thrombotic or pro-inflammatory conditions. In addition to this, emerging evidence suggests that microparticles are not simply a consequence of disease, but that they themselves may contribute to pathological processes. Thus microparticles appear to serve as both markers and mediators of pathology. The present review examines the evidence for microparticles as both biomarkers of, and contributors to, the progression of disease. Approaches for the detection of microparticles are summarized and novel concepts relating to the formation of microparticles and their biological effects are examined.

Light and electron microscopic features of synovium in patients with psoriatic arthritis

INTRODUCTION

Few ultrastructural studies have been reported in psoriatic arthritis (PsA). The authors report a series of synovial biopsies with emphasis on patients with early disease to look for distinctive light (LM) and electron microscopic (EM) features of possible importance.

METHODS

The authors examined synovial biopsies obtained primarily by needle biopsy from 13 PsA patients using LM and/or EM. Sections from 12 patients were evaluated by LM for vascularity, synovial lining thickness, fibrin deposition, and inflammation via a semi-quantitative scale. Nine EM specimens were descriptively analyzed. Clinical, synovial fluid (SF), and radiographic characteristics were recorded.

RESULTS

Patients were mostly male, with mean disease duration before biopsy of 2.19 ± 2.60 years; 7 patients had arthritis for less than 1 year. All patients had peripheral arthritis, 2 had axial involvement. SFs disclosed predominance of polymorphonuclear leukocytes. LM demonstrated proliferation of synovial lining cells, lymphocyte and plasma cell infiltration, as well as dramatic clusters of small vessels in the superficial synovium. EMs showed more detailed vascular changes, including small, subendothelial, electron-dense deposits and scattered microparticles in vessel lumens and walls.

CONCLUSIONS

Prominent vascularity is confirmed as an important feature of some PsA. Vascular changes and other features, including the first EM demonstration of microparticles in PsA (identified as potent factors in other inflammatory joint diseases), are potential targets for therapy.

The exposure of autoantigens by microparticles underlies the formation of potent inflammatory components: the microparticle-associated immune complexes

Immunoglobulins, antigens and complement can assemble to form immune complexes (IC). ICs can be detrimental as they propagate inflammation in autoimmune diseases. Like ICs, submicron extracellular vesicles termed microparticles (MP) are present in the synovial fluid from patients affected with autoimmune arthritis. We examined MPs in rheumatoid arthritis (RA) using high sensitivity flow cytometry and electron microscopy. We find that the MPs in RA synovial fluid are highly heterogeneous in size. The observed larger MPs were in fact MP-containing ICs (mpICs) and account for the majority of the detectable ICs. These mpICs frequently express the integrin CD41, consistent with platelet origin. Despite expression of the Fc receptor FcγRIIa by platelet-derived MPs, we find that the mpICs form independently of this receptor. Rather, mpICs display autoantigens vimentin and fibrinogen, and recognition of these targets by anti-citrullinated peptide antibodies contributes to the production of mpICs. Functionally, platelet mpICs are highly pro-inflammatory, eliciting leukotriene production by neutrophils. Taken together, our data suggest a unique role for platelet MPs as autoantigen-expressing elements capable of perpetuating formation of inflammatory ICs.

Evaluation of Circulating Endothelial and Platelet Microparticles in Men with Ankylosing Spondylitis

Objective.

To evaluate the profiles of endothelial microparticles (EMP) and platelet microparticles (PMP) in men with ankylosing spondylitis (AS) and healthy subjects. We also aimed to determine whether microparticles (MP) correlate with disease activity, function, and spinal mobility indices.

Methods.

There were 82 men with AS and 53 healthy controls. Subjects with a history of chronic diseases including coronary artery disease, hypertension, diabetes mellitus, and dyslipidemia were excluded. MP were stained with monoclonal antibodies against platelets and endothelial cells and quantified using flow cytometry. MP that were positive for both CD42a+/CD31+ and total CD42a+ were identified as PMP; and MP consisting of CD42a–/CD31+ and total CD144+ were considered EMP.

Results.

EMP and PMP were similar between the patient and control groups (p > 0.05). Comparison of patients with AS in the active disease state (BASDAI ≥ 4) and in the inactive state showed that EMP and PMP were not different between the groups (p > 0.05). Correlation analysis revealed no correlation with Bath Ankylosing Spondylitis Disease Activity Index, Bath Ankylosing Spondylitis Functional Index, or Bath Ankylosing Spondylitis Metrology Index. C-reactive protein was significantly correlated with PMP and CD42a–/CD31+ EMP (p < 0.05). Comparison of patients with AS treated with anti-tumor necrosis factor (anti-TNF) drugs, subjects treated conventionally, and healthy controls revealed that PMP and CD42a–/CD31+ EMP were significantly downregulated in patients receiving biological agents.

Conclusion.

Circulating EMP and PMP, known to be indicators and mediators of vascular injury, were not significantly altered in men with AS who did not have classical cardiovascular risk factors. Significantly downregulated MP in patients receiving biological agents suggested that anti-TNF treatment may have a beneficial effect on vascular function in AS.

Increased IgG on cell-derived plasma microparticles in systemic lupus erythematosus is associated with autoantibodies and complement activation

OBJECTIVE

To quantify immunoglobulin and C1q on circulating cell-derived microparticles (MPs) in patients with systemic lupus erythematosus (SLE) and to determine whether immunoglobulin and C1q levels are correlated with clinical and serologic parameters.

METHODS

Sixty-eight clinically well-characterized SLE patients, 38 healthy controls, 6 patients with systemic sclerosis (SSc), and 6 patients with rheumatoid arthritis (RA) were included. The numbers of annexin V-binding MPs displaying IgG, IgM, or C1q were enumerated by flow cytometry. MP protein levels were determined by mass spectrometry in clinically defined subsets of SLE patients and controls. The MP IgG load was determined by flow cytometric analysis of all samples from SLE patients and healthy controls.

RESULTS

SLE patients had significantly increased total and relative numbers of IgG-positive MPs (P = 0.0004), with a much higher average IgG load per MP (P < 0.0001) than healthy controls. Quantitative mass spectrometry of purified MPs verified significantly increased IgG, IgM, and C1q levels in SLE patients. In RA and SSc patients, the average IgG load per MP was significantly lower than in SLE patients (P = 0.006 and P = 0.05, respectively). Also, the IgM load and C1q load per MP were significantly higher in SLE patients than in the control groups (P < 0.05), except for IgM in the RA group. IgG-positive MPs were significantly associated with the presence of anti-double-stranded DNA, anti-extractable nuclear antigen, and antihistone antibodies, with total IgG, and with decreased leukocyte counts. Average IgG load per MP was associated with lower concentrations of MPs, the presence of anti-C1q antibodies, and complement consumption.

CONCLUSION

Our findings indicate that circulating cell-derived MPs in SLE patients carry increased loads of IgG, IgM, and C1q and that IgG MPs are associated with autoantibodies and complement activation. The findings link immunologic reactions on MPs with the etiology of SLE.