The expression of Toll-like receptors 2, 4 and 9 in kidneys of patients with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis

The podocytes' inflammatory responses in experimental GN are independent of canonical MYD88-dependent toll-like receptor signaling

Podocytes form the kidney filtration barrier and continuously adjust to external stimuli to preserve their integrity even in the presence of inflammation. It was suggested that canonical toll-like receptor signaling, mediated by the adaptor protein MYD88, plays a crucial role in initiating inflammatory responses in glomerulonephritis (GN). We explored the influence of podocyte-intrinsic MYD88 by challenging wild-type (WT) and podocyte-specific Myd88 knockout (MyD88pko) mice, with a model of experimental GN (nephrotoxic nephritis, NTN). Next-generation sequencing revealed a robust upregulation of inflammatory pathways and changes in cytoskeletal and cell adhesion proteins in sorted podocytes from WT mice during disease. Unchallenged MyD88pko mice were healthy and showed no proteinuria, normal kidney function and lacked morphological changes. During NTN, MyD88pko exhibited a transient increase in proteinuria in comparison to littermates, while histological damage, podocyte ultrastructure in STED imaging and frequencies of infiltrating immune cells by flow cytometry were unchanged. MYD88-deficiency led to subtle changes in the podocyte transcriptome, without a significant impact on the overall podocyte response to inflammation, presumably through MYD88-independent signaling pathways. In conclusion, our study reveals a comprehensive analysis of podocyte adaptation to an inflammatory environment on the transcriptome level, while MYD88-deficiency had only limited impact on the course of GN suggesting additional signaling through MYD88-independent signaling.

The role of toll-like receptors (TLRs) and their therapeutic applications in glomerulonephritis

One of the most important features of innate immunity is the presence of a special group of pattern recognition receptors (PRRs) called toll-like receptors (TLRs), which recognize pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs), resulting in a quick and effective immune response to them. Glomerulonephritis (GN) is one of the most important categories of renal disorders characterized by destructive responses of the immune system to the glomerulus. To date, the association of TLRs as important innate immune system members with GN has been one of the topics that attracted the attention of researchers in this field. However, the exact role of these receptors in the immunopathogenesis of GN has not yet been fully discussed. Therefore, this study aims to overview the role of TLRs in GN and the possibility of using them as a potential therapeutic target.

Identification and validation of immune-associated NETosis subtypes and biomarkers in anti-neutrophil cytoplasmic antibody associated glomerulonephritis

Background

NETosis is a new form of cell death, marked by DNA chromatin release from dead neutrophils. While it aids in microbe defense, it may worsen inflammation in autoimmune diseases, causing tissue harm. The impact of NETosis on Anti-neutrophil Cytoplasmic Antibody-associated Glomerulonephritis (ANCA-GN) remains unexplored and requires investigation.

Methods

First, a weighted gene co-expression network analysis (WGCNA) was conducted to uncover differential expression of neutrophil extranuclear trap-associated genes (DE-NETs) in ANCA-GN. The NETosisScore model was established through the single sample gene set enrichment analysis (ssGSEA), which categorized all patients into high-risk and low-risk groups. The accuracy of model was assessed by ROC curve. The biological function of various subgroups was explored through Gene Set Variation Analysis (GSVA), while the abundance of immune cell infiltration was measured with CIBERSORT. Furthermore, the key NETosis-related genes (NRGs) were identified using three machine learning algorithms, and their relationship with renal function was analyzed through the NephroseqV5 database. Through the application of qPCR and immunohistochemical staining techniques, the mRNA and protein expression levels of NRGs were determined in patients with ANCA-GN and control.

Results

A NETosisScore model was developed from 18 DE-NETs using the ssGSEA algorithm. The model's ability to predict ANCA-GN patients with a ROC AUC of 0.921. The high-risk group in ANCA-GN showed enrichment of immune-related pathways and greater infiltration of immune cells, as revealed by KEGG enrichment analysis and CIBERSORT. Using three machine learning algorithms, we identified six NRGs. Significant positive correlations were found between NRGs and CCR, macrophages, T-cell co-inhibition, and TIL. Further KEGG analysis revealed that the functions of NRGs may be closely related to the toll-like receptor signaling pathway. The levels of NRGs increased as kidney function declined and were positively correlated with Scr (serum creatinine) and negatively correlated with GFR (glomerular filtration rate), qPCR analysis showed increased expression of most NRGs in ANCA-GN patients. Furthermore, immunohistochemical staining confirmed higher expression of all NRGs in ANCA-GN patients.

Conclusion

NETosisScore model accurately predicts high-risk patients in ANCA-GN with enriched immune pathways, 6 NRGs identified as potential biomarkers.

Protective effect of IAXO-102 on renal ischemia-reperfusion injury in rats

Ischemia/reperfusion injury (IRI) is a common cause of kidney damage, characterized by oxidative stress and inflammation. In this study, we investigated the potential protective effects of IAXO-102, a chemical compound, on experimentally induced IRI in male rats. The bilateral renal IRI model was used, with 24 adult male rats randomly divided into four groups (N=6): sham group (laparotomy without IRI induction), control group (laparotomy plus bilateral IRI for 30 minutes followed by 2 hours of reperfusion), vehicle group (same as control but pre-injected with the vehicle), and treatment group (similar to control but pre-injected with IAXO-102). We measured several biomarkers involved in IRI pathophysiology using enzyme-linked immunosorbent assay (ELISA), including High mobility group box1 (HMGB1), nuclear factor kappa b-p65 (NF-κB p65), interleukin beta-1 (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), 8-isoprostane, Bcl-2 associated X protein (BAX), heat shock protein 27 (HSP27), and Bcl-2. Statistical analysis was performed using one-way ANOVA and Tukey post hoc tests. Our results showed that IAXO-102 significantly improved kidney function, reduced histological alterations, and decreased the inflammatory response (IL-1, IL-6, and TNF) caused by IRI. IAXO-102 also decreased apoptosis by reducing pro-apoptotic Bax and increasing anti-apoptotic Bcl-2 without impacting HSP27. In conclusion, our findings suggest that IAXO-102 had a significant protective effect against IRI damage in the kidneys.

Natural products from plants and microorganisms: Novel therapeutics for chronic kidney disease via gut microbiota regulation

Dysbiosis of gut microbiota plays a fundamental role in the pathogenesis and development of chronic kidney disease (CKD) and its complications. Natural products from plants and microorganisms can achieve recognizable improvement in renal function and serve as an alternative treatment for chronic kidney disease patients with a long history, yet less is known on its beneficial effects on kidney injury by targeting the intestinal microbiota. In this review, we summarize studies on the effects of natural products from plants and microorganisms, including herbal medicines and their bioactive extracts, polysaccharides from plants and microorganisms, and phytochemicals, on the prevention and treatment of chronic kidney disease through targeting gut microflora. We describe the strategies of these anti-CKD effects in animal experiments including remodulation of gut microbiota structure, reduction of uremic toxins, enhancement of short-chain fatty acid (SCFA) production, regulation of intestinal inflammatory signaling, and improvement in intestinal integrity. Meanwhile, the clinical trials of different natural products in chronic kidney disease clinical practice were also analyzed and discussed. These provide information to enable a better understanding of the renoprotective effects of these effective natural products from plants and microorganisms in the treatment of chronic kidney disease. Finally, we propose the steps to prove the causal role of the intestinal microflora in the treatment of chronic kidney disease by natural products from plants and microorganisms. We also assess the future perspective that natural active products from plants and microorganisms can beneficially delay the onset and progression of kidney disease by targeting the gut flora and highlight the remaining challenges in this area. With the continuous deepening of studies in recent years, it has been proved that gut microbiota is a potential target of natural active products derived from plants and microorganisms for chronic kidney disease treatment. Fully understanding the functions and mechanisms of gut microbiota in these natural active products from plants and microorganisms is conducive to their application as an alternative therapeutic in the treatment of chronic kidney disease.

Renoprotective Potential of the Ultra-Pure Lipopolysaccharide from Rhodobacter Sphaeroides on Acutely Injured Kidneys in an Animal Model

One of the main causes of acute kidney injury is ischemic reperfusion injury (IRI). Inflammatory response, apoptotic damages, and oxidative stress-related injuries are all involved in the pathogenesis of IRI. Toll-like receptors (TLR) are strongly associated with IRIs, especially TLR4, which is markedly induced in response to IRI. Accordingly, the current study aimed to investigate the potential renoprotective effect of ultrapure lipopolysaccharide from Rhodobacter sphaeroides (ULPS-RS) at two doses in an animal model of bilateral IRI. A total of 30 adult male rats were divided randomly into five equal groups of control (laparotomy plus bilateral renal IRI), vehicle (same as the control group, but pretreated with the vehicle), sham (laparotomy only), ULPS-RS (same as the control group, but pretreated with 0.1 mg/kg of ULPS-RS), and ULPS-RSH (same as the control group, but pretreated with 0.2 mg/kg of ULPS-RS). Subsequent to 30 min of ischemia and 2 h of reperfusion, serum samples were collected for measuring urea, creatinine, and neutrophil gelatinase-associated lipocalin. Afterward, tissue samples were obtained from all animals to measure inflammatory mediators (interleukin 6, interleukin 1β, and tumor necrosis factor α), oxidative stress marker (8-isoprostane), apoptosis mediators (B cell lymphoma 2 [Bcl2]), and Bcl2-associated X protein (Bax). In the control group, all of the measured parameters were significantly elevated in response to IRI, except for Bcl2, which decreased significantly. On the other hand, exactly opposite effects were observed in the ULPS-RS treated groups indicating the nephroprotective effect of this compound against IRI at both tested doses. The findings reveal for the first time that ULPS-RS has the therapeutic potential of attenuating the renal dysfunction induced by IRI.

The innate immune system in human kidney inflammaging

Elderly individuals with chronic disorders tend to develop inflammaging, a condition associated with elevated levels of blood inflammatory markers, and increased susceptibility to chronic disease progression. Native and adaptive immunity are both involved in immune system senescence, kidney fibrosis and aging. The innate immune system is characterized by a limited number of receptors, constantly challenged by self and non-self stimuli. Circulating and kidney resident myeloid and lymphoid cells are all equipped with pattern recognition receptors (PRRs). Recent reports on PRRs show kidney overexpression of toll-like receptors (TLRs) in inflammaging autoimmune renal diseases, vasculitis, acute kidney injury and kidney transplant rejection. TLR upregulation leads to proinflammatory cytokine induction, fibrosis, and chronic kidney disease progression. TLR2 blockade in a murine model of renal ischemia reperfusion injury prevented the escape of natural killer cells and neutrophils by inflammaging kidney injury. Tumor necrosis factor-α blockade in endothelial cells with senescence-associated secretory phenotype significantly reduced interleukin-6 release. These findings should encourage experimental and translational clinical trials aimed at modulating renal inflammaging by native immunity blockade.

Monocytes and macrophages in ANCA-associated vasculitis

Anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitides (AAV) are characterized by inflammation of small-to-medium-sized blood vessels and the presence of autoantibodies against cytoplasmic proteases sited in neutrophils and monocytes. Increasing evidence indicates a substantial role of monocytes and macrophages in the pathogenesis of AAV. Activated monocytes and macrophages contribute to necroinflammation in peripheral vasculitic lesions as well as to central and peripheral mechanisms of autoimmunity. The intermediate monocyte subset (CD14⁺⁺CD16⁺) is increased and monocytes show elevated expression of CD14, Toll-like receptor 2/4, MHCII and integrins, likely reflecting activation and increased monocyte extravasation. Monocytes differentiate locally predominantly into alternatively activated (M2) macrophages, which are known for cell-clearance and phagocytosis, but may ultimately lead to fibrosis. Phagocytotic function of macrophages can be impaired by surface expression of cytoplasmic proteases on apoptotic neutrophils and causes release of inflammatory cytokines and immunogenic contents, presumably resulting in a vicious circle of increased neutrophil, T and B cell activation and consequent ANCA production. Considering their crucial role in initiating necroinflammation as well as fibrogenesis, monocytes and macrophages may represent a logic first-line target for new treatment options in AAV.

Granulomatous Inflammation in ANCA-Associated Vasculitis

ANCA-associated vasculitis (AAV) comprises granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). While systemic vasculitis is a hallmark of all AAV, GPA is characterized by extravascular granulomatous inflammation, preferentially affecting the respiratory tract. The mechanisms underlying the emergence of neutrophilic microabscesses; the appearance of multinucleated giant cells; and subsequent granuloma formation, finally leading to scarred or destroyed tissue in GPA, are still incompletely understood. This review summarizes findings describing the presence and function of molecules and cells contributing to granulomatous inflammation in the respiratory tract and to renal inflammation observed in GPA. In addition, factors affecting or promoting the development of granulomatous inflammation such as microbial infections, the nasal microbiome, and the release of damage-associated molecular patterns (DAMP) are discussed. Further, on the basis of numerous results, we argue that, in situ, various ways of exposure linked with a high number of infiltrating proteinase 3 (PR3)- and myeloperoxidase (MPO)-expressing leukocytes lower the threshold for the presentation of an altered PR3 and possibly also of MPO, provoking the local development of ANCA autoimmune responses, aided by the formation of ectopic lymphoid structures. Although extravascular granulomatous inflammation is unique to GPA, similar molecular and cellular patterns can be found in both the respiratory tract and kidney tissue of GPA and MPA patients; for example, the antimicrobial peptide LL37, CD163⁺ macrophages, or regulatory T cells. Therefore, we postulate that granulomatous inflammation in GPA or PR3-AAV is intertwined with autoimmune and destructive mechanisms also seen at other sites.

Danger-associated molecular pattern molecules and the receptor for advanced glycation end products enhance ANCA-induced responses

Objectives

The pro-inflammatory activities of the calgranulins and HMGB1 can be counteracted by sRAGE, the soluble form of their shared receptor. To understand the role of these molecules in AAV and their potential as therapeutic targets we have studied (i) the relationship between these DAMPS and disease activity; (ii) the expression of RAGE and sRAGE in biopsy tissue and peripheral blood; and (iii) the effect of these molecules on ANCA-mediated cytokine production.

Methods

We examined circulating levels of calgranulins (S100A8/A9 and S100A12), HMGB1 and sRAGE by ELISA. RAGE was examined in AAV kidney and lung biopsies by immunohistochemistry and RAGE expression was monitored in peripheral blood by qPCR. In vitro, the effect of co-stimulating PBMC with ANCA and S100A8/A9 on cytokine production was studied by ELISA.

Results

We found significantly raised levels of calgranulins and HMGB1 in active AAV regardless of clinical phenotype (PR3+/MPO+ AAV). Levels of calgranulins showed significant correlations with each other. RAGE protein and message was raised in peripheral blood and in cells infiltrating kidney and lung biopsy tissue, while sRAGE was lowered. Furthermore, ANCA-mediated production of IL-8 from PBMC was significantly enhanced by the presence of S100A8/A9 in a RAGE/TLR4-dependent manner.

Conclusions

Raised circulating calgranulins provide a good marker of disease activity in AAV and are unlikely to be counteracted by sRAGE. Increased RAGE expression in AAV indicates receptor stimulation in active disease that may exacerbate ANCA-induced cytokine production. Targeting the RAGE pathway may provide a useful therapeutic approach in AAV.

Toll-like Receptors as Potential Therapeutic Targets in Kidney Diseases

Toll-like Receptors (TLRs) are members of pattern recognition receptors and serve a pivotal role in host immunity. TLRs response to pathogen-associated molecular patterns encoded by pathogens or damage-associated molecular patterns released by dying cells, initiating an inflammatory cascade, where both beneficial and detrimental effects can be exerted. Accumulated evidence has revealed that TLRs are closely associated with various kidney diseases but their roles are still not well understood. This review updated evidence on the roles of TLRs in the pathogenesis of kidney diseases including urinary tract infection, glomerulonephritis, acute kidney injury, transplant allograft dysfunction and chronic kidney diseases.

Animal Models of ANCA Associated Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV) is a rare and severe autoimmune multisystemic disease. Its pathogenesis involves multiple arms of the immune system, as well as complex interactions between immune cells and target organs. Experimental animal models of disease can provide the crucial link from human disease to translational research into new therapies. This is particularly true in AAV, due to low disease incidence and substantial disease heterogeneity. Animal models allow for controlled environments in which disease mechanisms can be defined, without the clinical confounders of environmental and lifestyle factors. To date, multiple animal models have been developed, each of which shed light on different disease pathways. Results from animal studies of AAV have played a crucial role in enhancing our understanding of disease mechanisms, and have provided direction toward newer targeted therapies. This review will summarize our understanding of AAV pathogenesis as has been gleaned from currently available animal models, as well as address their strengths and limitations. We will also discuss the potential for current and new animal models to further our understanding of this important condition.

Antagonism of major histocompatibility complex class II invariant chain peptide during chronic lipopolysaccharide treatment rescues autoregulatory behavior

Toll-like receptor 4 (TLR4) activation contributes to vascular dysfunction in pathological conditions such as hypertension and diabetes, but the role of chronic TLR4 activation on renal autoregulatory behavior is unknown. We hypothesized that subclinical TLR4 stimulation with low-dose lipopolysaccharide (LPS) infusion increases TLR4 activation and blunts renal autoregulatory behavior. We assessed afferent arteriolar autoregulatory behavior in male Sprague-Dawley rats after prolonged LPS (0.1 mg·kg^-1·day^-1 sq) infusion via osmotic minipump for 8 or 14 days. Some rats also received daily cotreatment with either anti-TLR4 antibody (1 μg ip), competitive antagonist peptide (CAP; 3 mg/kg ip) or tempol (2 mmol/l, drinking water) throughout the 8-day LPS treatment period. Autoregulatory behavior was assessed using the in vitro blood-perfused juxtamedullary nephron preparation. Selected physiological measures, systolic blood pressure and baseline diameters were normal and similar across groups. Pressure-dependent vasoconstriction averaged 72 ± 2% of baseline in sham rats, indicating intact autoregulatory behavior. Eight-day LPS-treated rats exhibited significantly impaired pressure-mediated vasoconstriction (96 ± 1% of baseline), whereas it was preserved in rats that received anti-TLR4 antibody (75 ± 3%), CAP (84 ± 2%), or tempol (82 ± 2%). Using a 14-day LPS (0.1 mg·kg^-1·day^-1 sq) intervention protocol, CAP treatment started on day 7, where autoregulatory behavior is already impaired. Systolic blood pressures were normal across all treatment groups. Fourteen-day LPS treatment retained the autoregulatory impairment (95 ± 2% of baseline). CAP intervention starting on day 7 rescued pressure-mediated vasoconstriction with diameters decreasing to 85 ± 1% of baseline. These data demonstrate that chronic subclinical TLR4 activation impairs afferent arteriolar autoregulatory behavior through mechanisms involving reactive oxygen species and major histocompatibility complex class II activation.

Intrarenal Toll-like receptor 4 and Toll-like receptor 2 expression correlates with injury in antineutrophil cytoplasmic antibody-associated vasculitis

In antineutrophil cytoplasmic antibody-associated vasculitis (AAV), Toll-like receptors (TLRs) may be engaged by infection-associated patterns and by endogenous danger signals, linking infection and innate inflammation with this autoimmune disease. This study examined intrarenal TLR2, TLR4, and TLR9 expression and renal injury in AAV, testing the hypothesis that increased TLR expression correlates with renal injury. Patients with AAV exhibited both glomerular and tubulointerstitial expression of TLR2, TLR4, and TLR9, with TLR4 being the most prominent in both compartments. Glomerular TLR4 expression correlated with glomerular segmental necrosis and cellular crescents, with TLR2 expression correlating with glomerular segmental necrosis. The extent and intensity of glomerular and tubulointerstitial TLR4 expression and the intensity of glomerular TLR2 expression inversely correlated with the presenting estimated glomerular filtration rate. Although myeloid cells within the kidney expressed TLR2, TLR4, and TLR9, TLR2 and TLR4 colocalized with endothelial cells and podocytes, whereas TLR9 was expressed predominantly by podocytes. The functional relevance of intrarenal TLR expression was further supported by the colocalization of TLRs with their endogenous ligands high-mobility group box 1 and fibrinogen. Therefore, in AAV, the extent of intrarenal TLR4 and TLR2 expression and their correlation with renal injury indicates that TLR4, and to a lesser degree TLR2, may be potential therapeutic targets in this disease.

Acute toll-like receptor 4 activation impairs rat renal microvascular autoregulatory behaviour

AIM

Little is known about how toll-like receptor 4 (TLR4) influences the renal microvasculature. We hypothesized that acute TLR4 stimulation with lipopolysaccharide (LPS) impairs afferent arteriole autoregulatory behaviour, partially through reactive oxygen species (ROS).

METHODS

We assessed afferent arteriole autoregulatory behaviour after LPS treatment (1 mg kg^-1 ; i.p.) using the in vitro blood-perfused juxtamedullary nephron preparation. Autoregulatory behaviour was assessed by measuring diameter responses to stepwise changes in renal perfusion pressure. TLR4 expression was assessed by immunofluorescence, immunohistochemistry and Western blot analysis in the renal cortex and vasculature.

RESULTS

Baseline arteriole diameter at 100 mmHg averaged 15.2 ± 1.2 μm and 12.2 ± 1.0 μm for control and LPS groups (P < 0.05) respectively. When perfusion pressure was increased in 15 mmHg increments from 65 to 170 mmHg, arteriole diameter in control kidneys decreased significantly to 69 ± 6% of baseline diameter. In the LPS-treated group, arteriole diameter remained essentially unchanged (103 ± 9% of baseline), indicating impaired autoregulatory behaviour. Pre-treatment with anti-TLR4 antibody or the TLR4 antagonist, LPS-RS, preserved autoregulatory behaviour during LPS treatment. P2 receptor reactivity was normal in control and LPS-treated rats. Pre-treatment with Losartan (angiotensin type 1 receptor blocker; (AT₁ ) 2 mg kg^-1 ; i.p.) increased baseline afferent arteriole diameter but did not preserve autoregulatory behaviour in LPS-treated rats. Acute exposure to Tempol (10^-3 mol L^-1 ), a superoxide dismutase mimetic, restored pressure-mediated vasoconstriction in kidneys from LPS-treated rats.

CONCLUSION

These data demonstrate that TLR4 activation impairs afferent arteriole autoregulatory behaviour, partially through ROS, but independently of P2 and AT₁ receptor activation.

The Increased Expression of Toll-Like Receptor 4 in Renal and Skin Lesions in Lupus Erythematosus

Toll-like receptor 4 (TLR-4), a bacterial lipopolysaccharide sensor, is an innate immunity essential modulator. It is expressed on both immune and non-immune cells and may contribute to the cutaneous and renal manifestations during lupus erythematosus (LE). Our purpose is to evaluate TLR-4 expression and analyzing its role in lupus nephritis (LN) and chronic cutaneous lupus erythematosus (CLE) pathogenesis. TLR-4 immunohistochemical staining was performed on 30 LN renal biopsies compared with 11 healthy renal tissues and 30 skin biopsies from CLE patients compared with 15 normal individuals. CLE patients' biopsies showed a strong and diffuse TLR-4 expression throughout the epidermis and labeled inflammatory infiltrate and glands in the dermis whereas controls' skin expressed weakly TLR-4 only in the epidermis basal layer. LN glomeruli and tubules showed an increased and more intense TLR-4 expression compared with normal controls where TLR-4 expression was weak and rarely detected in glomeruli, diffuse and weak in tubules. A significant difference in TLR-4 expression between LN classes, both in glomeruli and tubules, was observed. These data confirm an up-regulation of TLR-4 expression in the affected tissues of CLE and LN patients and highlight the critical role of TLR-4 in the pathogenesis of cutaneous and renal disorders in LE.

Chronic Kidney Disease: The Gut-Kidney Connection?

Among strategies for both the prevention and treatment of renal disease, reduction of uremic toxins and bacterial lipopolysaccharides that activates toll-like receptors and improvement in the composition of the microbiome represent valuable and clinically proven approaches. Dietary components-specifically soluble and insoluble prebiotic fibers; phytochemicals such as curcumin, berberine, epigallocatechin gallate, and withanolides that modulate gut immune function and improve detoxification of uremic toxins; and supplemental, clinically tested probiotics-constitute a family of therapeutics that can positively affect patients. In addition, the bidirectional relationship of the microbiome to kidney disease is an important concept in designing a personalized approach to the management of kidney disease, especially with regard to its relationship to cardiovascular disease.

Complement in ANCA-associated vasculitis: mechanisms and implications for management

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of potentially life-threatening autoimmune diseases. The main histological feature in the kidneys of patients with AAV is pauci-immune necrotizing crescentic glomerulonephritis with little immunoglobulin and complement deposition in the glomerular capillary walls. The complement system was not, therefore, initially thought to be associated with the development of AAV. Accumulating evidence from animal models and clinical observations indicate, however, that activation of the complement system - and the alternative pathway in particular - is crucial for the development of AAV, and that the complement activation product C5a has a central role. Stimulation of neutrophils with C5a and ANCA not only results in the neutrophil respiratory burst and degranulation, but also activates the coagulation system and generates thrombin, thus bridging the inflammation and coagulation systems. In this Review, we provide an overview of the clinical, in vivo and in vitro evidence for a role of complement activation in the development of AAV and discuss how targeting the complement system could provide opportunities for therapy.

Association between toll-like receptor 6 expression and auxiliary T cells in the peripheral blood of pediatric patients with allergic purpura

The aim of the present study was to investigate the correlations between toll-like receptor 6 (TLR6) expression in the peripheral blood mononuclear cells (PBMCs) and auxiliary T cells of children with purpura. A total of 42 children with acute Henoch-Schönlein purpura (HSP) were selected for the study, and a further 30 healthy children were selected as a control group. Enzyme-linked immunosorbent assays were performed to detect the levels of plasma interferon (IFN)-γ, interleukin (IL)-4 and IL-17, and flow cytometry was performed to detect the TLR6 protein expression levels in PBMCs. The plasma levels of IL-4, IFN-γ and IL-17 in the HSP group were significantly higher compared with those in the normal control group. TLR6 protein expression was significantly increased in the PBMCs of the HSP patients. The TLR6 protein expression levels in the monocytes of the HSP group significantly positively correlated with the serum IL-4 and IL-17 levels, but not with the serum levels of IFN-γ. Therefore, the results of the present study suggest that the activation of TLR6 may be involved in the immunopathogenesis of HSP, and that the activated TLR6 may mediate this process by upregulating the immune responses of type 2 T helper (Th2) and Th17 cells.

Neutrophil Extracellular Trap-Related Extracellular Histones Cause Vascular Necrosis in Severe GN

Severe GN involves local neutrophil extracellular trap (NET) formation. We hypothesized a local cytotoxic effect of NET-related histone release in necrotizing GN. In vitro, histones from calf thymus or histones released by neutrophils undergoing NETosis killed glomerular endothelial cells, podocytes, and parietal epithelial cells in a dose-dependent manner. Histone-neutralizing agents such as antihistone IgG, activated protein C, or heparin prevented this effect. Histone toxicity on glomeruli ex vivo was Toll-like receptor 2/4 dependent, and lack of TLR2/4 attenuated histone-induced renal thrombotic microangiopathy and glomerular necrosis in mice. Anti-glomerular basement membrane GN involved NET formation and vascular necrosis, whereas blocking NET formation by peptidylarginine inhibition or preemptive anti-histone IgG injection significantly reduced all aspects of GN (i.e., vascular necrosis, podocyte loss, albuminuria, cytokine induction, recruitment or activation of glomerular leukocytes, and glomerular crescent formation). To evaluate histones as a therapeutic target, mice with established GN were treated with three different histone-neutralizing agents. Anti-histone IgG, recombinant activated protein C, and heparin were equally effective in abrogating severe GN, whereas combination therapy had no additive effects. Together, these results indicate that NET-related histone release during GN elicits cytotoxic and immunostimulatory effects. Furthermore, neutralizing extracellular histones is still therapeutic when initiated in established GN.