Circulating Apoptotic Microparticles in Systemic Lupus Erythematosus Patients Drive the Activation of Dendritic Cell Subsets and Prime Neutrophils for NETosis

Autoantibody-dependent amplification of inflammation in SLE

Anti-double stranded DNA antibodies (anti-dsDNA) are a hallmark of SLE but their role in disease pathogenesis is not fully resolved. Anti-dsDNA in serum are highly heterogeneous therefore in this study, we aimed to dissect the functional specificities of anti-dsDNA using a panel of human monoclonal antibodies (humAbs) generated from patients with active lupus nephritis. A total of 46 ANA reactive humAbs were isolated and divided into four broad classes based on their reactivity to histones, DNA and Crithidia. Functional analysis indicated that one subclass of antibodies bound strongly to decondensed DNA areas in neutrophil extracellular traps (NETs) and protected NETs from nuclease digestion, similar to the sera from active SLE patients. In addition, these anti-dsDNA antibodies could stimulate type I interferon responses in mononuclear phagocytic cells, or NF-kB activity in endothelial cells, by uptake of NETs-anti-NETs immune complexes and subsequently trigging inflammatory responses in an Fc-gamma receptor (Fcg-R)-dependant manner. Together our data suggest that only a subset of anti-dsDNA antibodies is capable to amplify inflammatory responses by deposit in the nephritic kidney in vivo, protecting NETs digestion as well as uptake of NETs immune complexes into Fcg-R-expressing cells in vitro.

Effects of Cell-Derived Microparticles on Immune Cells and Potential Implications in Clinical Medicine

In the past few years, interest has increased in cell-derived microparticles (MPs), which are defined by their size of from 0.1 to 1 μm, and can be derived from various cell types, including endothelial cells, leukocytes, red blood cells (RBCs), and platelets. These MPs carry negatively charged phosphatidylserine (PS) on their surfaces and proteins packaged from numerous cellular components. MPs that have been shed by the body can play important roles in the pathophysiology of diseases and can affect various biological systems. Among these systems, the immune components have been shown to be modulated by MPs. Therefore, understanding the roles of MPs in the immune system is crucial to developing alternative therapeutic treatments for diseases. This review describes the effects of MPs on various immune cells and provides plausible potential applications of the immune-modulating properties of MPs in clinical medicine.

Neutrophil heterogeneity and fate in inflamed tissues: implications for the resolution of inflammation

Neutrophils are polymorphonuclear leukocytes that play a central role in host defense against infection and tissue injury. They are rapidly recruited to the inflamed site and execute a variety of functions to clear invading pathogens and damaged cells. However, many of their defense mechanisms are capable of inflicting collateral tissue damage. Neutrophil-driven inflammation is a unifying mechanism underlying many common diseases. Efficient removal of neutrophils from inflammatory loci is critical for timely resolution of inflammation and return to homeostasis. Accumulating evidence challenges the classical view that neutrophils represent a homogeneous population and that halting neutrophil influx is sufficient to explain their rapid decline within inflamed loci during the resolution of protective inflammation. Hence, understanding the mechanisms that govern neutrophil functions and their removal from the inflammatory locus is critical for minimizing damage to the surrounding tissue and for return to homeostasis. In this review, we briefly address recent advances in characterizing neutrophil phenotypic and functional heterogeneity and the molecular mechanisms that determine the fate of neutrophils within inflammatory loci and the outcome of the inflammatory response. We also discuss how these mechanisms may be harnessed as potential therapeutic targets to facilitate resolution of inflammation.

Neutrophil Extracellular Traps (NETs) Take the Central Stage in Driving Autoimmune Responses

Following fifteen years of research, neutrophil extracellular traps (NETs) are widely reported in a large range of inflammatory infectious and non-infectious diseases. Cumulating evidences from in vitro, in vivo and clinical diagnostics suggest that NETs may play a crucial role in inflammation and autoimmunity in a variety of autoimmune diseases, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV). Most likely, NETs contribute to breaking self-tolerance in autoimmune diseases in several ways. During this review, we discuss the current knowledge on how NETs could drive autoimmune responses. NETs can break self-tolerance by being a source of autoantigens for autoantibodies found in autoimmune diseases, such as anti-citrullinated protein antibodies (ACPAs) in RA, anti-dsDNA in SLE and anti-myeloperoxidase and anti-protein 3 in AAV. Moreover, NET components could accelerate the inflammatory response by mediating complement activation, acting as danger-associated molecular patterns (DAMPs) and inflammasome activators, for example. NETs also can activate other immune cells, such as B cells, antigen-presenting cells and T cells. Additionally, impaired clearance of NETs in autoimmune diseases prolongs the presence of active NETs and their components and, in this way, accelerate immune responses. NETs have not only been implicated as drivers of inflammation, but also are linked to resolution of inflammation. Therefore, NETs may be central regulators of inflammation and autoimmunity, serve as biomarkers, as well as promising targets for future therapeutics of inflammatory autoimmune diseases.

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.

Lupus nephritis

Lupus nephritis (LN) is a form of glomerulonephritis that constitutes one of the most severe organ manifestations of the autoimmune disease systemic lupus erythematosus (SLE). Most patients with SLE who develop LN do so within 5 years of an SLE diagnosis and, in many cases, LN is the presenting manifestation resulting in the diagnosis of SLE. Understanding of the genetic and pathogenetic basis of LN has improved substantially over the past few decades. Treatment of LN usually involves immunosuppressive therapy, typically with mycophenolate mofetil or cyclophosphamide and with glucocorticoids, although these treatments are not uniformly effective. Despite increased knowledge of disease pathogenesis and improved treatment options, LN remains a substantial cause of morbidity and death among patients with SLE. Within 10 years of an initial SLE diagnosis, 5-20% of patients with LN develop end-stage kidney disease, and the multiple comorbidities associated with immunosuppressive treatment, including infections, osteoporosis and cardiovascular and reproductive effects, remain a concern. Clearly, early and accurate diagnosis of LN and prompt initiation of therapy are of vital importance to improve outcomes in patients with SLE.

Apoptotic cell-derived exosomes: messages from dying cells

Apoptosis, a type of programmed cell death that plays a key role in both healthy and pathological conditions, releases extracellular vesicles such as apoptotic bodies and microvesicles, but exosome release due to apoptosis is not yet commonly accepted. Here, the reports demonstrating the presence of apoptotic exosomes and their roles in inflammation and immune responses are summarized, together with a general summary of apoptosis and extracellular vesicles. In conclusion, apoptosis is not just a 'silent' type of cell death but an active form of communication from dying cells to live cells through exosomes.

LTB4 and 5-oxo-ETE from extracellular vesicles stimulate neutrophils in granulomatosis with polyangiitis

Activation of neutrophils is an important mechanism in the pathology of granulomatosis with polyangiitis (GPA). In this study, we evaluated whether extracellular vesicles (EVs) circulating in the plasma of GPA patients could contribute to this process. EVs from the plasma of GPA patients in the active stage of the disease (n = 10) and healthy controls (n = 10) were isolated by ultracentrifugation and characterized by flow cytometry (CD63, CD8) and nanoparticle tracking analysis. Targeted oxylipin lipidomics of EVs was performed by HPLC-MS/MS. EV/oxylipin-induced neutrophil extracellular traps (NETs) were analyzed by confocal microscopy, and released double-stranded DNA (dsDNA) was quantified by PicoGreen fluorescent dye. Reactive oxygen species (ROS) production and neutrophils' EV binding/uptake were evaluated by flow cytometry. Brief priming with granulocyte-macrophage colony-stimulating factor was required for EV-mediated ROS production and dsDNA release. It was observed that priming also increased EV binding/uptake by neutrophils only for EVs from GPA patients. EVs from GPA patients had higher concentrations of leukotriene (LT)B4 and 5-oxo-eicosatetraenoic acid (5-oxo-ETE) as compared with EVs from healthy controls. Moreover, neutrophils stimulated with LTB4 or 5-oxo-ETE produced ROS and released dsDNA in a concentration-dependent manner. These results reveal the potential role of EVs containing oxylipin cargo on ROS production and NET formation by activated neutrophils.

Programmed Cell Death Pathways in the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease characterized by excessive inflammatory and immune responses and tissue damage. Increasing evidence has demonstrated the important role of programmed cell death in SLE pathogenesis. When apoptosis encounters with defective clearance, accumulated apoptotic cells lead to secondary necrosis. Different forms of lytic cell death, including secondary necrosis after apoptosis, NETosis, necroptosis, and pyroptosis, contribute to the release of damage-associated molecular patterns (DAMPs) and autoantigens, resulting in triggering immunity and tissue damage in SLE. However, the role of autophagy in SLE pathogenesis is in dispute. This review briefly discusses different forms of programmed cell death pathways and lay particular emphasis on inflammatory cell death pathways such as NETosis, pyroptosis, and necroptosis and their roles in the inflammatory and immune responses in SLE.

The Role of NETosis in Systemic Lupus Erythematosus

Systemic lupus erythematosus is an autoimmune disease affecting multiple organs with devastating pathological consequences. Current treatment regimens largely rely on immunosuppressants and corticosteroids to attenuate autoimmune activity. However, such treatments have toxic side effects, often lacks efficacy, and inherently leaves the patient prone to infections, making the discovery of novel biomarkers and therapeutic targets an urgent need. Neutrophil extracellular traps (NETs) that participate in host defense are generated by neutrophils by a process called NETosis. NETs play an important role in the pathogenesis of SLE. In this review, we discuss the current literature regarding the role of NETs in SLE while entertaining the possibility that NETosis could serve as therapeutic targets thereby rendering the treatment more specific and effective in comparison to the current lupus therapy.

Circulating biomarkers of cell death

Numerous disease states are associated with cell death. For many decades, apoptosis and accidental necrosis have been assumed to be the two ways how a cell can die. The recent discovery of additional cell death processes such as necroptosis, ferroptosis or pyroptosis revealed a complex interplay between cell death mechanisms and diseases. Depending on the particular cell death pathway, cells secrete distinct molecular patterns, which differ between cell death types. This review focusses on released molecules, detectable in the blood flow, and their potential role as circulating biomarkers of cell death. We elucidate the molecular background of different biomarkers and give an overview on their correlation with disease stage, therapy response and prognosis in patients.

Lymphopenia and neutropenia are associated with subsequent incident proteinuria in Danish patients with systemic lupus erythematosus

Objective: The aim of this study was to investigate whether incident proteinuria in patients with systemic lupus erythematosus (SLE) was preceded by changes in blood lymphocytes and neutrophil counts and/or neutrophil-lymphocyte ratio (NLR).Method: SLE patients with no proteinuria before or at the time of classification were included. Longitudinal data on SLE manifestations, vital status, and SLE-associated medications were collected during clinical visits and chart review. Laboratory data were collected through a nationwide database. Lymphopenia, severe lymphopenia, and neutropenia were defined as values below 0.8 × 10⁹, 0.5 × 10⁹, and 2.0 × 10⁹ cells/L, respectively. High NLR was defined as values above the median. Proteinuria was defined by at least two measurements of elevated urine protein excretion (> 0.5 g/day). Hazard ratios (HRs) were calculated by Cox modelling using time-dependent continuous and binary covariates based on multiple laboratory measurements adjusted for use of immunosuppressants.Results: In total, 260 SLE patients were available for the analysis, of whom 30 (12%) developed incident proteinuria following the diagnosis of SLE. Median follow-up time was 73.5 months. Lymphocyte and neutrophil counts, but not NLR, were associated with incident proteinuria. HRs for incident proteinuria were 2.71 for lymphopenia [95% confidence interval (CI) 1.20-6.11], 4.73 for severe lymphopenia (95% CI 1.93-11.59), and 2.54 for neutropenia (95% CI 1.14-5.65).Conclusion: Lymphopenia and neutropenia predicted the risk of first-time proteinuria independently of immunosuppressants.

Therapeutic potential of aryl hydrocarbon receptor in autoimmunity

Aryl hydrocarbon receptor (AhR), a type of transcriptional factor, is widely expressed in immune cells. The activation of AhR signaling pathway depends on its ligands, which exist in environment and can also be produced by metabolism. Normal expressions of AhR and AhR-mediated signaling may be essential for immune responses, and effects of AhR signaling on the development and function of innate and adaptive immune cells have also been revealed in previous studies. Recent studies also indicate that aberrant AhR signaling may be related to autoimmune diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), multiple sclerosis (MS), autoimmune uveitis (AU), autoimmune diabetes, Behcet's disease (BD) and myasthenia gravis (MG). Moreover, administration of AhR ligands or drugs has been proven effective for improving pathological outcomes in some autoimmune diseases or models. In this review, we summarize the effects of AhR on several innate and adaptive immune cells associated with autoimmunity, and the mechanism on how AhR participates in autoimmune diseases. In addition, we also discuss therapeutic potential and application prospect of AhR in autoimmune diseases, so as to provide valuable information for exploring novel and effective approaches to autoimmune disease treatments.

Stimulation of Mononuclear Cells Through Toll-Like Receptor 9 Induces Release of Microvesicles Expressing Double-Stranded DNA and Galectin 3-Binding Protein in an Interferon-α-Dependent Manner

Background: Microvesicles (MVs) expressing the type 1 interferon (IFN)-inducible protein galectin-3 binding protein (G3BP) may play a pathogenic role in systemic lupus erythematosus (SLE). Co-expression of double-stranded DNA (dsDNA) on such MVs may render them immunogenic and targets for anti-dsDNA antibodies. Little is known about the mechanisms underlying generation of this MV population. In this study, we investigated how Toll-like receptors (TLRs), IFN-α, and T cells are involved in this process in healthy subjects.

Methods: Peripheral blood mononuclear cells (PBMCs) isolated from 12 healthy donors were stimulated in-vitro for 24 h with a series of TLR-agonists or the T cell activating antibody OKT3 or were subjected to apoptosis by incubation with staurosporine. MVs in the supernatants were subsequently isolated by differential centrifugation and were quantified and characterized with respect to expression of G3BP and dsDNA by flow cytometry.

Results: Stimulation of PBMCs with the TLR9-agonist and strong IFN-α inducer ODN2395 significantly increased the release of MVs expressing G3BP. The production of MVs with this phenotype was markedly enhanced by co-stimulation of T cells. Furthermore, dependency on IFN-α in the generation of G3BP-expressing MVs was indicated by a marked reduction following addition of the IFN-α inhibitor IFN alpha-IFNAR-IN-1 hydrochloride.

Conclusion: Release of G3BP-expressing MVs from healthy donor PBMCs is induced by stimulation of TLR9 in an IFN-α-dependent manner and is enhanced by co-stimulation of T cells.

Heightened TLR7/9-Induced IL-10 and CXCL13 Production with Dysregulated NF-ҝB Activation in CD11chiCD11b+ Dendritic Cells in NZB/W F1 Mice

Systemic lupus erythematosus (SLE) is a chronic, multifactorial autoimmune disease that predominantly affects young females. Dysregulation of different immune cell populations leads to self-tolerance breakdown and subsequent multiple organ damage as the disease develops. Plasmacytoid dendritic cells (pDCs) are potent producers of type I interferon (IFN), while myeloid dendritic cells (mDCs) are more specialized in antigen presentations. We have previously reported that bone-marrow (BM)-derived pDCs from the murine lupus model New Zealand black/white F1 (BWF1) possess abnormalities. Therefore, this study continues to investigate what aberrant properties peripheral pDCs and mDCs possess in BWF1 and how they mediate SLE progression, by comparing their properties in pre-symptomatic and symptomatic mice. Results showed that CD11c^hiCD11b⁺ myeloid DCs expanded during the disease state with down-regulation of co-stimulatory molecules and major histocompatibility complex class II molecules (MHC II), but their capacity to stimulate T cells was not hampered. During the disease state, this subset of mDCs displayed heightened toll-like receptors 7 and 9 (TLR 7/9) responses with increased interleukin 10 (IL-10) and C-X-C motif chemokine ligand 13 (CXCL13) expressions. Moreover, the expressions of myeloid differentiation primary response 88 (Myd88) and nuclear factor kappa B subunit 1 (Nfkb1) were higher in CD11c^hiCD11b⁺ DCs at the disease stage, leading to higher nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 phosphorylation activity. In summary, we reported aberrant phenotypic properties with enhanced TLR7/9 responses of CD11c^hiCD11b⁺ DCs in SLE mediated by aberrant NF-κB signaling pathway. Our findings add additional and novel information to our current understanding of the role of DCs in lupus immunopathogenesis. Lastly, molecular candidates in the NF-κB pathway should be exploited for developing therapeutic targets for SLE.

CD4+CD25+LAG3+ T Cells With a Feature of Th17 Cells Associated With Systemic Lupus Erythematosus Disease Activity

Systemic lupus erythematosus (SLE) is an autoimmune disease that involves multiple immune cell subsets. We analyzed immune cell subsets in human peripheral blood mononuclear cells (PBMC) in order to identify the cells that are significantly associated with SLE disease activity and treatment. The frequencies of various subsets of CD4⁺ T cells, B cells, monocytes and NK cells in PBMC were assessed in 30 healthy controls (HC), 30 rheumatoid arthritis (RA) patients and 26 SLE patients using flow cytometry. The correlations between subset frequencies in SLE and clinical traits including Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) were examined. Changes in subset frequencies after the treatment in SLE patients were investigated. We focused on CD25⁺LAG3⁺ T cells and investigated their characteristics, including cytokine secretion, mRNA expression and suppression capacity. We assessed correlations between CD25⁺LAG3⁺ T cells and SLEDAI by Spearman's rank correlation coefficient. CD25⁺LAG3⁺ T cells were significantly increased in SLE whereas there were few in RA and HC groups. CD25⁺LAG3⁺ T cell frequencies were significantly correlated with SLEDAI and were increased in patients with a high SLEDAI score (> 10). CD25⁺LAG3⁺ T cells produced both IL-17 and FOXP3, expressed mRNA of both FOXP3 and RORC and lacked suppressive capacity. CD25⁺LAG3⁺ T cells were associated with disease activity of SLE. CD25⁺LAG3⁺ T cells had features of both CD25⁺FOXP3⁺ regulatory T cells (CD25⁺ Treg) and Th17. CD25⁺LAG3⁺ T cells could be associated with the inflammatory pathophysiology of SLE.

Self-DNA at the Epicenter of SLE: Immunogenic Forms, Regulation, and Effects

Self-reactive B cells generated through V(D)J recombination in the bone marrow or through accrual of random mutations in secondary lymphoid tissues are mostly purged or edited to prevent autoimmunity. Yet, 10–20% of all mature naïve B cells in healthy individuals have self-reactive B cell receptors (BCRs). In patients with serologically active systemic lupus erythematosus (SLE) the percentage increases up to 50%, with significant self-DNA reactivity that correlates with disease severity. Endogenous or self-DNA has emerged as a potent antigen in several autoimmune disorders, particularly in SLE. However, the mechanism(s) regulating or preventing anti-DNA antibody production remain elusive. It is likely that in healthy subjects, DNA-reactive B cells avoid activation due to the unavailability of endogenous DNA, which is efficiently degraded through efferocytosis and various DNA-processing proteins. Genetic defects, physiological, and/or pathological conditions can override these protective checkpoints, leading to autoimmunity. Plausibly, increased availability of immunogenic self-DNA may be the key initiating event in the loss of tolerance of otherwise quiescent DNA-reactive B cells. Indeed, mutations impairing apoptotic cell clearance pathways and nucleic acid metabolism-associated genes like DNases, RNases, and their sensors are known to cause autoimmune disorders including SLE. Here we review the literature supporting the idea that increased availability of DNA as an immunogen or adjuvant, or both, may cause the production of pathogenic anti-DNA antibodies and subsequent manifestations of clinical disease such as SLE. We discuss the main cellular players involved in anti-DNA responses; the physical forms and sources of immunogenic DNA in autoimmunity; the DNA-protein complexes that render DNA immunogenic; the regulation of DNA availability by intracellular and extracellular DNases and the autoimmune pathologies associated with their dysfunction; the cytosolic and endosomal sensors of immunogenic DNA; and the cytokines such as interferons that drive auto-inflammatory and autoimmune pathways leading to clinical disease. We propose that prevention of DNA availability by aiding extracellular DNase activity could be a viable therapeutic modality in controlling SLE.

Extracellular DNA traps in inflammation, injury and healing

Following strong activation signals, several types of immune cells reportedly release chromatin and granular proteins into the extracellular space, forming DNA traps. This process is especially prominent in neutrophils but also occurs in other innate immune cells such as macrophages, eosinophils, basophils and mast cells. Initial reports demonstrated that extracellular traps belong to the bactericidal and anti-fungal armamentarium of leukocytes, but subsequent studies also linked trap formation to a variety of human diseases. These pathological roles of extracellular DNA traps are now the focus of intensive biomedical research. The type of pathology associated with the release of extracellular DNA traps is mainly determined by the site of trap formation and the way in which these traps are further processed. Targeting the formation of aberrant extracellular DNA traps or promoting their efficient clearance are attractive goals for future therapeutic interventions, but the manifold actions of extracellular DNA traps complicate these approaches.

Classical dendritic cells regulate acute lung inflammation and injury in mice with lipopolysaccharide‑induced acute respiratory distress syndrome

Classical dendritic cells (cDCs) are involved in the pathogenesis of inflammatory lung diseases; however, their contributions in acute respiratory distress syndrome (ARDS), which is pathophysiologically inflammatory, remain unknown. The present study aimed to explore the regulatory effects of pulmonary cDCs on acute lung inflammation and injury in lipopolysaccharide (LPS)-induced ARDS. Fms-like tyrosine kinase 3-ligand (FLT3L) and lestaurtinib, a specific activator and an inhibitor of FLT3 signaling respectively, were used separately for the pretreatment of C57BL/6 mice for 5 consecutive days. ARDS was induced by intratracheal injection of LPS, and mice were sacrificed 6 and 24 h later. Flow cytometry was used to measure the aggregation and maturation of pulmonary cDCs. The ratio of lung wet weight to body weight (LWW/BW) and histopathological analyses were assessed to evaluate lung edema and lung injury. Tumor necrosis factor-α and interleukin (IL)-6 levels were measured by ELISA to evaluate acute lung inflammation. The levels of interferon-γ, IL-1β, IL-4 and IL-10, and the expression of the transcription factors T-box-expressed-in-T-cells (T-bet) and GATA binding protein 3, were quantified by ELISA, RT-qPCR and western blotting to evaluate the balance of the Th1/Th2 response. Myeloperoxidase (MPO) activity was measured to evaluate neutrophil infiltration. The results demonstrated that the aggregation and maturation of pulmonary cDCs reached a peak at 6 h after LPS challenge, followed by a significant decrease at 24 h. FLT3L pretreatment further stimulated the aggregation and maturation of pulmonary cDCs, resulting in elevated lung MPO activity and increased T-bet expression, which in turn led to aggravated LWW/BW, acute lung inflammation and injury. However, lestaurtinib pretreatment inhibited the aggregation and maturation of pulmonary cDCs, decreased lung MPO activity and T-bet expression, and eventually improved LWW/BW, acute lung inflammation and injury. The present results suggested that pulmonary cDCs regulated acute lung inflammation and injury in LPS-induced ARDS through the modulation of neutrophil infiltration and balance of the Th1/Th2 response.

Innate Immune Cells' Contribution to Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the presence of autoantibodies against nuclear antigens, immune complex deposition, and tissue damage in the kidneys, skin, heart and lung. Because of the pathogenic role of antinuclear antibodies and autoreactive T cells in SLE, extensive efforts have been made to demonstrate how B cells act as antibody-producing or as antigen-presenting cells that can prime autoreactive T cell activation. With the discovery of new innate immune cells and inflammatory mediators, innate immunity is emerging as a key player in disease pathologies. Recent work over the last decade has highlighted the importance of innate immune cells and molecules in promoting and potentiating SLE. In this review, we discuss recent evidence of the involvement of different innate immune cells and pathways in the pathogenesis of SLE. We also discuss new therapeutics targets directed against innate immune components as potential novel therapies in SLE.

Increased salivary microvesicles are associated with the prognosis of patients with oral squamous cell carcinoma

Microvesicles (MVs), which are cell-derived membrane vesicles present in body fluids, are closely associated with the development of malignant tumours. Saliva, one of the most versatile body fluids, is an important source of MVs. However, the association between salivary MVs (SMVs) and oral squamous cell carcinoma (OSCC), which is directly immersed in the salivary milieu, remains unclear. SMVs from 65 patients with OSCC, 21 patients with oral ulcer (OU), and 42 healthy donors were purified, quantified and analysed for their correlations with the clinicopathologic features and prognosis of OSCC patients. The results showed that the level of SMVs was significantly elevated in patients with OSCC compared to healthy donors and OU patients. Meanwhile, the level of SMVs showed close correlations with the lymph node status, and the clinical stage of OSCC patients. Additionally, the ratio of apoptotic to non-apoptotic SMVs was significantly decreased in OSCC patients with higher pathological grade. Consistently, poorer overall survival was observed in patients with lower ratio of apoptotic to non-apoptotic SMVs. In conclusion, the elevated level of SMVs is associated with clinicopathologic features and decreased survival in patients with OSCC, suggesting that SMVs are a potential biomarker and/or regulator of the malignant progression of OSCC.

Microparticles from Endothelial Cells and Immune Cells in Patients with Takayasu Arteritis

AIM

This study was designed to analyze microparticles (MPs) from endothelial cells (EMPs) and immune cells from healthy individuals and paitents with Takayasu arteritis (TA), and any possible relationships between MPs and TA acitivity.

METHODS

MPs derived from the plasma of 51 subjects were analyzed, including 32 patients with TA and 19 healthy individuals. Flow cytometry was performed with Annexin (Anx)-V and antibodies against surface markers of endothelial cells (CD144), T cells (CD3), B cells (CD19), and monocytes (CD14).

RESULTS

The concentrations of total EMPs, AnxV＋ EMPs and AnxV- EMPs were significantly increased when comparing patients with TA and healthy controls (54×10³ vs. 32×10³ MPs /ml, P=0.0004; 22×10³ vs. 12×10³ MPs /ml, P=0.0006; and 31×10³ vs. 19×10³ MPs /ml, P=0.0005), and comparing active TA patients with remission ones (85×10³ vs. 45×10³ MPs /ml, P=0.016; 39×10³ vs. 14×10³ MPs /ml, P=0.0092; and 47×10³ vs.29×10³ MPs /ml, P=0.0371). In addition, the concentrations of total EMPs (odds ratio [OR]=1.024, 95% confidence interval [CI]: 1.001 to 1.048, P=0.037), AnxV＋(OR=1.089, 95%CI: 1.011 to 1.172, P=0.024), and AnxV- EMPs (OR=1.029, 95% CI: 1.002 to 1.056, P=0.034) were positively related to TA activity. With multiple linear regression analysis, platelet was associated with both total and AnxV- EMP concentrations independently, while erythrocyte sedimentation rate was independently correlated with AnxV＋EMPs.

CONCLUSION

Concentrations of endothelial microparticles are correlated with inflammation in Takayasu arteritis and may be useful markers to assess disease activity.

Differential Interaction of Platelet-Derived Extracellular Vesicles With Circulating Immune Cells: Roles of TAM Receptors, CD11b, and Phosphatidylserine

Secretion and exchange of biomolecules by extracellular vesicles (EVs) are crucial in intercellular communication and enable cells to adapt to alterations in their microenvironment. EVs are involved in a variety of cellular processes under physiological conditions as well as in pathological settings. In particular, they exert profound effects on the innate immune system, and thereby are also capable of modulating adaptive immunity. The mechanisms underlying their interaction with their recipient cells, particularly their preferential association with monocytes and granulocytes in the circulation, however, remain to be further clarified. Surface molecules exposed on EVs are likely to mediate immune recognition and EV uptake by their recipient cells. Here, we investigated the involvement of Tyro3, Axl, and Mer (TAM) tyrosine kinase receptors and of integrin CD11b in the binding of platelet-derived EVs, constituting the large majority of circulating EVs, to immune cells in the circulation. Flow cytometry and Western Blotting demonstrated a differential expression of TAM receptors and CD11b on monocytes, granulocytes, and lymphocytes, as well as on monocyte subsets. Of the TAM receptors, only Axl and Mer were detected at low levels on monocytes and granulocytes, but not on lymphocytes. Likewise, CD11b was present on circulating monocytes and granulocytes, but remained undetectable on lymphocytes. Differentiation of monocytes into classical, intermediate, and non-classical monocyte subsets revealed distinct expression patterns of Mer and activated CD11b. Co-incubation of isolated monocytes and granulocytes with platelet-derived EVs showed that the binding of EVs to immune cells was dependent on Ca⁺⁺. Our data do not support a particular role for TAM receptors or for activated CD11b in the association of platelet-derived EVs with monocytes and granulocytes in the circulation, as anti-TAM antibodies did not interfere with EV binding to isolated immune cells, as binding was not dependent on the presence of TIM4 acting synergistically with TAM receptors, and as neither low levels of Gas6, required as a linker between phosphatidylserine (PS) on the EV surface and TAM receptors on immune cells, nor masking of PS on the EV surface did interfere with EV binding.

Microparticles as autoantigens in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by the production of antibodies to components of the cell nucleus (antinuclear antibodies or ANAs) and the formation of immune complexes with nuclear antigens. These complexes can drive pathogenesis by depositing in the tissue to incite inflammation or induce cytokine production by cells of the innate immune system. While ANAs can bind to purified nuclear molecules, nuclear autoantigens in vivo most likely exist attached to other molecules or embedded in larger structures. Among these structures, microparticles (MPs) are membrane bound vesicles that are released from dead and dying cells by a blebbing process; MPs can also be released during activation of platelets. The presence of MPs in the blood or tissue culture media can be assayed by flow cytometry on the basis of light scattering as well as binding of marker antibodies to identify the cell of origin. As shown by biochemical analyses, MPs contain an ensemble of intracellular components including nuclear, cytoplasmic and membrane molecules. Because of the display of these molecules on the particle surface or in an otherwise accessible form, ANAs, including anti-DNA, can bind to particles. Levels of MPs are increased in the blood of patients with SLE, with flow cytometry demonstrating the presence of IgG-containing particles. In addition to forming immune complexes, MPs can directly stimulate immune responses. Together, these findings suggest an important role of particles in the pathogenesis of SLE and their utility as biomarkers.

The characteristics and pivotal roles of triggering receptor expressed on myeloid cells-1 in autoimmune diseases

Triggering receptor expressed on myeloid cells-1 (TREM-1) engagement can directly trigger inflammation or amplify an inflammatory response by synergizing with TLRs or NLRs. Autoimmune diseases are a family of chronic systemic inflammatory disorders. The pivotal role of TREM-1 in inflammation makes it important to explore its immunological effects in autoimmune diseases. In this review, we summarize the structural and functional characteristics of TREM-1. Particularly, we discuss recent findings on TREM-1 pathway regulation in various autoimmune diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), inflammatory bowel disease (IBD), type 1 diabetes (T1D), and psoriasis. This receptor may potentially be manipulated to alter the inflammatory response to chronic inflammation and possible therapies are explored in this review.

DNA as a self-antigen: nature and regulation

High-affinity antibodies to double-stranded DNA are a hallmark of systemic lupus erythematosus (SLE) and are thought to contribute to disease flares and tissue inflammation such as nephritis. Notwithstanding their clinical importance, major questions remain about the development and regulation of these pathogenic anti-DNA responses. These include the mechanisms that prevent anti-DNA responses in healthy subjects, despite the constant generation of self-DNA and the abundance of DNA-reactive B cells; the nature and physical form of antigenic DNA in SLE; the regulation of DNA availability as an antigen; and potential therapeutic strategies targeting the pathogenic DNA in SLE. This review summarizes current progress in these directions, focusing on the role of secreted DNases in the regulation of antigenic extracellular DNA.

Cleaved N-terminal histone tails distinguish between NADPH oxidase (NOX)-dependent and NOX-independent pathways of neutrophil extracellular trap formation

OBJECTIVES

Neutrophil extracellular traps (NETs) act in various rheumatic diseases. Although NET formation was originally described as a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX)-dependent pathway, it appears that there are also NOX-independent pathways of NET release. Currently, no tools are available that can discriminate between both NET-forming pathways. We aimed to develop a serological method allowing the discrimination between NETs generated through NOX-dependent or NOX-independent pathways.

METHODS

Histones from in vitro generated NOX-dependent and NOX-independent NETs were characterised with a panel of lupus-derived antibodies against N-terminal histone tails using immunofluorescence microscopy, western blot and ELISA. NETs in patients with NET-associated diseases, that is, rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), psoriatic arthritis (PsA) and sepsis, were characterised in sandwich ELISAs employing antibodies against myeloperoxidase (MPO) and N-terminal histone tails as detecting and capturing antibodies, respectively. Functional responses of endothelial cells to NOX-dependent and NOX-independent NETs were assessed as well.

RESULTS

Neutrophil elastase cleaves the N-terminal tails of core histones during NOX-dependent, but not during NOX-independent NET formation. Consequently, the detection of MPO-histone complexes with antibodies against N-terminal histone tails allows discrimination between NETs formed through a NOX-dependent or NOX-independent manner. Characterisation of in vivo circulating NETs revealed the presence of NOX-independent NETs in RA, SLE and sepsis, but NOX-dependent NETs in PsA. NOX-independent NETs displayed an increased capacity to activate endothelial cells when compared with NOX-dependent NETs.

CONCLUSIONS

These results indicate heterogeneity in NET-forming pathways in vivo and highlight the need for disease-specific strategies to prevent NET-mediated pathology.

Ion Channels and Transporters in Inflammation: Special Focus on TRP Channels and TRPC6

Allergy and autoimmune diseases are characterised by a multifactorial pathogenic background. Several genes involved in the control of innate and adaptive immunity have been associated with diseases and variably combine with each other as well as with environmental factors and epigenetic processes to shape the characteristics of individual manifestations. Systemic or local perturbations in salt/water balance and in ion exchanges between the intra- and extracellular spaces or among tissues play a role. In this field, usually referred to as elementary immunology, novel evidence has been recently acquired on the role of members of the transient potential receptor (TRP) channel family in several cellular mechanisms of potential significance for the pathophysiology of the immune response. TRP canonical channel 6 (TRPC6) is emerging as a functional element for the control of calcium currents in immune-committed cells and target tissues. In fact, TRPC6 influences leukocytes’ tasks such as transendothelial migration, chemotaxis, phagocytosis and cytokine release. TRPC6 also modulates the sensitivity of immune cells to apoptosis and influences tissue susceptibility to ischemia-reperfusion injury and excitotoxicity. Here, we provide a view of the interactions between ion exchanges and inflammation with a focus on the pathogenesis of immune-mediated diseases and potential future therapeutic implications.

Apoptosis-derived membrane vesicles drive the cGAS-STING pathway and enhance type I IFN production in systemic lupus erythematosus

OBJECTIVE

Despite the importance of type I interferon (IFN-I) in systemic lupus erythematosus (SLE) pathogenesis, the mechanisms of IFN-I production have not been fully elucidated. Recognition of nucleic acids by DNA sensors induces IFN-I and interferon-stimulated genes (ISGs), but the involvement of cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS) and stimulator of interferon genes (STING) in SLE remains unclear. We studied the role of the cGAS-STING pathway in the IFN-I-producing cascade driven by SLE serum.

METHODS

We collected sera from patients with SLE (n=64), patients with other autoimmune diseases (n=31) and healthy controls (n=35), and assayed them using a cell-based reporter system that enables highly sensitive detection of IFN-I and ISG-inducing activity. We used Toll-like receptor-specific reporter cells and reporter cells harbouring knockouts of cGAS, STING and IFNAR2 to evaluate signalling pathway-dependent ISG induction.

RESULTS

IFN-I bioactivity and ISG-inducing activities of serum were higher in patients with SLE than in patients with other autoimmune diseases or healthy controls. ISG-inducing activity of SLE sera was significantly reduced in STING-knockout reporter cells, and STING-dependent ISG-inducing activity correlated with disease activity. Double-stranded DNA levels were elevated in SLE. Apoptosis-derived membrane vesicles (AdMVs) from SLE sera had high ISG-inducing activity, which was diminished in cGAS-knockout or STING-knockout reporter cells.

CONCLUSIONS

AdMVs in SLE serum induce IFN-I production through activation of the cGAS-STING pathway. Thus, blockade of the cGAS-STING axis represents a promising therapeutic target for SLE. Moreover, our cell-based reporter system may be useful for stratifying patients with SLE with high ISG-inducing activity.

Insights Gained From the Study of Pediatric Systemic Lupus Erythematosus

The pathophysiology of systemic lupus erythematosus (SLE) has been intensely studied but remains incompletely defined. Currently, multiple mechanisms are known to contribute to the development of SLE. These include inadequate clearance of apoptotic debris, aberrant presentation of self nucleic antigens, loss of tolerance, and inappropriate activation of T and B cells. Genetic, hormonal, and environmental influences are also known to play a role. The study of lupus in children, in whom there is presumed to be greater genetic influence, has led to new understandings that are applicable to SLE pathophysiology as a whole. In particular, characterization of inherited disorders associated with excessive type I interferon production has elucidated specific mechanisms by which interferon is induced in SLE. In this review, we discuss several monogenic forms of lupus presenting in childhood and also review recent insights gained from cytokine and autoantibody profiling of pediatric SLE.

CD83 Antibody Inhibits Human B Cell Responses to Antigen as well as Dendritic Cell-Mediated CD4 T Cell Responses

Anti-CD83 Ab capable of Ab-dependent cellular cytotoxicity can deplete activated CD83+ human dendritic cells, thereby inhibiting CD4 T cell-mediated acute graft-versus-host disease. As CD83 is also expressed on the surface of activated B lymphocytes, we hypothesized that anti-CD83 would also inhibit B cell responses to stimulation. We found that anti-CD83 inhibited total IgM and IgG production in vitro by allostimulated human PBMC. Also, Ag-specific Ab responses to immunization of SCID mice xenografted with human PBMC were inhibited by anti-CD83 treatment. This inhibition occurred without depletion of all human B cells because anti-CD83 lysed activated CD83+ B cells by Ab-dependent cellular cytotoxicity and spared resting (CD83-) B cells. In cultured human PBMC, anti-CD83 inhibited tetanus toxoid-stimulated B cell proliferation and concomitant dendritic cell-mediated CD4 T cell proliferation and expression of IFN-γ and IL-17A, with minimal losses of B cells (<20%). In contrast, the anti-CD20 mAb rituximab depleted >80% of B cells but had no effect on CD4 T cell proliferation and cytokine expression. By virtue of the ability of anti-CD83 to selectively deplete activated, but not resting, B cells and dendritic cells, with the latter reducing CD4 T cell responses, anti-CD83 may be clinically useful in autoimmunity and transplantation. Advantages might include inhibited expansion of autoantigen- or alloantigen-specific B cells and CD4 T cells, thus preventing further production of pathogenic Abs and inflammatory cytokines while preserving protective memory and regulatory cells.

Apoptotic cell-induced AhR activity is required for immunological tolerance and suppression of systemic lupus erythematosus in mice and humans

The transcription factor AhR modulates immunity at multiple levels. Here we report phagocytes exposed to apoptotic cells exhibited rapid activation of AhR, which drove production of interleukin 10. Activation of AhR was dependent on interactions between apoptotic-cell DNA and the pattern-recognition receptor TLR9 that was required for prevention of immune responses to DNA and histones in vivo. Moreover, disease progression in murine systemic lupus erythematosus (SLE) correlated with strength of the AhR signal, and disease course could be altered by modulation of AhR activity. Deletion of AhR in the myeloid lineage caused systemic autoimmunity in mice and an increased AhR transcriptional signature correlated with disease in patients with SLE. Thus, AhR activity induced by apoptotic cell phagocytes maintains peripheral tolerance.

Elevated extracellular nucleosomes and their relevance to inflammation in stage 5 chronic kidney disease

BACKGROUND

Chronic kidney disease is a disorder characterized by a pro-inflammatory state that is associated with increased morbidity and mortality. Endogenous damage-associated molecular patterns, including nucleosomes, may contribute to this persistent inflammation. The aim of this study was to profile and evaluate the clinical significance of circulating nucleosomes in patients with Stage 5 chronic kidney disease (CKD5) on hemodialysis (HD).

METHODS

Under institutional review board approval, plasma samples were collected from 90 CKD5-HD patients (45 male and 45 female) prior to hemodialysis. Normal human plasma samples (25 male and 25 female) were used as a control group. Commercial enzyme-linked immunosorbent and colorimetric assays were used to profile nucleosome levels and biochemical markers of kidney injury, inflammation, thrombosis, and renal function in CKD5-HD and control groups. Clinical laboratory parameters were documented from the electronical medical record and correlated to nucleosome levels in the CKD5-HD cohort.

RESULTS

In comparison to healthy volunteers, the plasma from CKD5-HD patients exhibited markedly elevated nucleosomes (P<0.0001). Furthermore, nucleosome levels correlated with WBC count (P=0.025, R=0.243) and CRP (P=0.019, R=0.266) levels. No correlation was found between nucleosomes and the other parameters studied.

CONCLUSIONS

Our findings indicate extracellular nucleosomes are significantly elevated in CKD5-HD, suggesting increased cell death and/or inflammation. The observed correlations between nucleosomes and parameters of inflammation is suggestive of a complex, systemic inflammatory process underlying renal deterioration, consistent with the literature. Thus, nucleosomes may play a role in the pathogenesis and outcome of CKD5-HD.

Systemic lupus erythematosus and systemic sclerosis: All roads lead to platelets

Systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) are two phenotypically distincts inflammatory systemic diseases. However, SLE and SSc share pathogenic features such as interferon signature, loss of tolerance against self-nuclear antigens and increased tissue damage such as fibrosis. Recently, platelets have emerged as a major actor in immunity including auto-immune diseases. Both SLE and SSc are characterized by strong platelet system activation, which is likely to be both the witness and culprit in their pathogenesis. Platelet activation pathways are multiple and sometimes redundant. They include immune complexes, Toll-like receptors activation, antiphospholipid antibodies and ischemia-reperfusion associated with Raynaud phenomenon. Once activated, platelet promote immune dysregulation by priming interferon production by immune cells, providing CD40L supporting B lymphocyte functions and providing a source of autoantigens. Platelets are actively implicated in SLE and SSc end-organ damage such as cardiovascular and renal disease and in the promotion of tissue fibrosis. Finally, after understanding the main pathogenic implications of platelet activation in both diseases, we discuss potential therapeutics targeting platelets.

Neutrophil extracellular trap release is associated with antinuclear antibodies in systemic lupus erythematosus and anti-phospholipid syndrome

OBJECTIVES

Increased release of neutrophil extracellular traps (NETs) is implicated in the activation of plasmacytoid dendritic cells, vascular disease and thrombosis in SLE and APS. However, studies comparing NET release between patients with SLE and APS are lacking. Here we evaluated plasma-induced NET release in a large cohort of patients with SLE, SLE + APS and primary APS in relation to clinical and serological parameters.

METHODS

Neutrophils from healthy controls were exposed to plasma of heterologous healthy controls (n = 27) or SLE (n = 55), SLE + APS (n = 38) or primary APS (PAPS) (n = 28) patients and NET release was quantified by immunofluorescence. In a subset of SLE patients, NET release was assessed in longitudinal samples before and after a change in treatment.

RESULTS

Plasma-induced NET release was increased in SLE and APS patients, with the highest NET release found in patients with SLE (±APS). Plasma of 60% of SLE, 61% of SLE + APS and 45% of PAPS patients induced NET release. NET release did not correlate with disease activity in SLE or APS. However, increased levels of anti-nuclear and anti-dsDNA autoantibodies were associated with increased NET release in SLE and APS. Only in SLE patients, elevated NET release and an increased number of low-density granulocytes were associated with a high IFN signature.

CONCLUSION

Increased NET release is associated with autoimmunity and inflammation in SLE and APS. Inhibition of NET release thus could be of potential benefit in a subset of patients with SLE and APS.

Potential Involvement of Platelet-Derived Microparticles and Microparticles Forming Immune Complexes during Monocyte Activation in Patients with Systemic Lupus Erythematosus

Microparticles (MPs) are vesicles derived from the plasma membrane of different cells, are considered a source of circulating autoantigens, and can form immune complexes (MPs-ICs). The number of MPs and MPs-ICs increases in patients with systemic lupus erythematosus (SLE). MPs activate myeloid cells by inducing IL-6 and TNF-α in both SLE and other diseases. Therefore, we propose that the recognition of MPs-ICs by monocytes rather that MPs may define their phenotype and contribute to the inflammatory process in patients with SLE. Thus, the aims of this study were to evaluate the association among circulating MPs-ICs from different cell sources, alterations observed in monocyte subsets, and disease activity in patients with SLE and to establish whether monocytes bind and respond to MPs-ICs in vitro. Circulating MPs and monocyte subsets were characterized in 60 patients with SLE and 60 healthy controls (HCs) using multiparametric flow cytometry. Patients had higher MP counts and frequencies of MPs-CD41a + (platelet-derived) compared with HCs, regardless of disease activity. MPs from patients with SLE were C1q + and formed ICs with IgM and IgG. MPs-IgG + were positively correlated with active SLE (aSLE), whereas MPs-IgM + were negatively correlated. Most of the circulating total ICs-IgG + were located on MPs. The proportion and number of non-classical monocytes were significantly decreased in patients with SLE compared with HCs and in patients with aSLE compared with patients with the inactive disease. Non-classical monocytes obtained from patients with SLE exhibited increased levels of CD64 associated with MPs-IgG +, MPs-C1q +, total circulating ICs-IgG +, and disease activity. The direct effects of MPs and MPs-IgG + on monocytes were evaluated in cell culture. Monocytes from both HCs and patients bound to and internalized MPs and MPs-IgG + independent of CD64. These vesicles derived from platelets (PMPs), mainly PMPs-IgG +, activated monocytes in vitro and increased the expression of CD69, CD64, and pro-inflammatory cytokines such as IL-1β, TNF-α, and IFN-α. Therefore, MPs are one of the most representative sources of the total amount of circulating ICs-IgG + in patients with SLE. MPs-IgG + are associated with SLE activity, and PMPs-IgG + stimulate monocytes, changing their phenotype and promoting pro-inflammatory responses related to disease activity.

From blood coagulation to innate and adaptive immunity: the role of platelets in the physiology and pathology of autoimmune disorders

Thrombosis and cardiovascular complications are common manifestations of a variety of pathological conditions, including infections and chronic inflammatory diseases. Hence, there is great interest in determining the hitherto unforeseen immune role of the main blood coagulation executor-the platelet. Platelets store and release a plethora of immunoactive molecules, generate microparticles, and interact with cells classically belonging to the immune system. The observed effects of platelet involvement in immune processes, especially in autoimmune diseases, are conflicting-from inciting inflammation to mediating its resolution. An in-depth understanding of the role of platelets in inflammation and immunity could open new therapeutic pathways for patients with autoimmune disorders. This review aims to summarize the current knowledge on the role of platelets in the patomechanisms of autoimmune disorders and suggests directions for future research.

The Neutrophil's Choice: Phagocytose vs Make Neutrophil Extracellular Traps

Neutrophils recognize particulate substrates of microbial or endogenous origin and react by sequestering the cargo via phagocytosis or by releasing neutrophil extracellular traps (NETs) outside the cell, thus modifying and alerting the environment and bystander leukocytes. The signals that determine the choice between phagocytosis and the generation of NETs are still poorly characterized. Neutrophils that had phagocytosed bulky particulate substrates, such as apoptotic cells and activated platelets, appear to be “poised” in an unresponsive state. Environmental conditions, the metabolic, adhesive and activation state of the phagocyte, and the size of and signals associated with the tethered phagocytic cargo influence the choice of the neutrophils, prompting either phagocytic clearance or the generation of NETs. The choice is dichotomic and apparently irreversible. Defects in phagocytosis may foster the intravascular generation of NETs, thus promoting vascular inflammation and morbidities associated with diseases characterized by defective phagocytic clearance, such as systemic lupus erythematosus. There is a strong potential for novel treatments based on new knowledge of the events determining the inflammatory and pro-thrombotic function of inflammatory leukocytes.

PKM2 Is Required to Activate Myeloid Dendritic Cells from Patients with Severe Aplastic Anemia

Severe aplastic anemia (SAA) is an autoimmune disease in which bone marrow failure is mediated by activated myeloid dendritic cells (mDCs) and T lymphocytes. Recent research has identified a strong immunomodulatory effect of pyruvate kinase M2 (PKM2) on dendritic cells in immune-mediated diseases. In this study, we aimed to explore the role of PKM2 in the activation of mDCs in SAA. We observed conspicuously higher levels of PKM2 in mDCs from SAA patients compared to normal controls at both the gene and protein levels. Concurrently, we unexpectedly discovered that after the mDC-specific downregulation of PKM2, mDCs from patients with SAA exhibited weakened phagocytic activity and significantly decreased and shortened dendrites relative to their counterparts from normal controls. The expression levels of the costimulatory molecules CD86 and CD80 were also reduced on mDCs. Our results also suggested that PKM2 knockdown in mDCs reduced the abilities of these cells to promote the activation of CD8+ T cells (CTLs), leading to the decreased secretion of cytotoxic factors by the latter cell type. These findings demonstrate that mDC activation requires an elevated intrinsic PKM2 level and that PKM2 improves the immune status of patients with SAA by enhancing the functions of mDCs and, consequently, CTLs.

DNA induction of MDM2 promotes proliferation of human renal mesangial cells and alters peripheral B cells subsets in pediatric systemic lupus erythematosus

The study is aimed to investigate the role of MDM2 in the pathogenesis of lupus nephritis (LN) in pediatric SLE (pSLE). We confirmed that MDM2 expression was increased in peripheral blood mononuclear cells (PBMCs) as well as renal specimen of SLE compared with that of controls by western blot and immunofluorescence staining. Percentage of apoptotic and necrotic CD4⁺T, CD8⁺T and B cells were detected by flow cytometry respectively and levels of plasma cell free DNA (cfDNA) were quantified in SLE and healthy controls (HC). We also proved that elevated apoptotic and necrotic CD4⁺T cells were the main cause for increased plasma levels of cfDNA in pSLE. Additionally, upon DNA transfection MDM2 increased while P53 and P21 decreased in human renal mesangial cells (HRMC), with concomitant increase in proliferation rate and proportion of cells in S phase, as demonstrated by cell proliferation assay and cell cycle analysis. However, MDM2 inhibition reversed the trend. Furthermore, percentage of switched memory B cells decreased and proportion of double negative B cells increased upon blockage of MDM2 in PBMC. In summary, our study provided the first evidence that DNA induction of MDM2 promotes proliferation of HRMC and alters peripheral B cells subsets in pSLE. Thus our study has not only elucidated the pathogenesis of MDM2 in pediatric LN but also provided a novel target for drug development. In conclusion, our data suggested that apoptosis, cfDNA and MDM2 could form a pathological axis in SLE, especially in pSLE.

Recent advances in pathophysiology of disseminated intravascular coagulation: the role of circulating histones and neutrophil extracellular traps

Disseminated intravascular coagulation (DIC) is an acquired condition that develops as a complication of systemic and sustained cell injury in conditions such as sepsis and trauma. It represents major dysregulation and increased thrombin generation in vivo. A poor understanding and recognition of the complex interactions in the coagulation, fibrinolytic, inflammatory, and innate immune pathways have resulted in continued poor management and high mortality rates in DIC. This review focuses attention on significant recent advances in our understanding of DIC pathophysiology. In particular, circulating histones and neutrophil extracellular traps fulfil established criteria in DIC pathogenesis. Both are damaging to the vasculature and highly relevant to the cross talk between coagulation and inflammation processes, which can culminate in adverse clinical outcomes. These molecules have a strong potential to be novel biomarkers and therapeutic targets in DIC, which is still considered synonymous with 'death is coming'.