Involvement of protein kinase C in C5a-primed neutrophils for ANCA-mediated activation

Role of complement activation in anti-neutrophil cytoplasmic antibody-associated glomerulonephritis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is an autoimmune disease characterized by necrotizing inflammation of small or medium vessels, causing ANCA associated glomerulonephritis (AAGN). AAGN is defined as pauci-immune glomerulonephritis with no or little immune deposition; hence, activation of the complement system in AAV was overlooked until recently. However, many studies in mice and humans have revealed a crucial role for complement system activation in the development of AAGN. Circulating and urinary detection of various complement components associated with AP activation, which have been broadly correlated with the clinical activity of AAGN, has been reported and may be useful for predicting renal outcome at the time of diagnosis and setting up personalized treatments. Moreover, recent investigations have suggested the possible contribution of the complement classical or lectin pathway activation in the development of AAGN. Thus, as therapeutic options targeting complement components are making rapid strides, the primary complement pathway involved in AAGN disease progression remains to be elucidated: this will directly impact the development of novel therapeutic strategies with high specificity and reduced side effects. This review summarizes and discusses the most recent evidence on the crucial roles of the complement system in the development of AAGN and possible therapeutic strategies that target complement components for disease management.

Beyond Systemic Lupus Erythematosus and Anti-Phospholipid Syndrome: The Relevance of Complement From Pathogenesis to Pregnancy Outcome in Other Systemic Rheumatologic Diseases

Evidence about the relevance of the complement system, a highly conserved constituent of the innate immunity response that orchestrates the elimination of pathogens and the inflammatory processes, has been recently accumulated in many different rheumatologic conditions. In rheumatoid arthritis, complement, mainly the classical pathway, contributes to tissue damage especially in seropositive subjects, with complement activation occurring in the joint. Data about complement pathways in psoriatic arthritis are dated and poorly consistent; among patients with Sjögren syndrome, hypocomplementemia exerts a prognostic role, identifying patients at risk of extra-glandular manifestations. Hints about complement involvement in systemic sclerosis have been recently raised, following the evidence of complement deposition in affected skin and in renal samples from patients with scleroderma renal crisis. In vasculitides, complement plays a dual role: on one hand, stimulation of neutrophils with anti-neutrophil cytoplasmic antibodies (ANCA) results in the activation of the alternative pathway, on the other, C5a induces translocation of ANCA antigens, favouring the detrimental role of antibodies. Complement deposition in the kidneys identifies patients with more aggressive renal disease; patients with active disease display low serum levels of C3 and C4. Even though in dermatomyositis sC5b-9 deposits are invariably present in affected muscles, data on C3 and C4 fluctuation during disease course are scarce. C3 and C1q serum levels have been explored as potential markers of disease activity in Takayasu arteritis, whereas data in Behçet disease are limited to in vitro observations. Pregnancies in women with rheumatologic conditions are still burdened by a higher rate of pregnancy complications, thus the early identification of women at risk would be invaluable. A fine-tuning of complement activation is required from a physiological progression of pregnancy, from pre-implantation stages, through placentation to labour. Complement deregulation has been implicated in several pregnancy complications, such as recurrent abortion, eclampsia and premature birth; low complement levels have been shown to reliably identify women at risk of complications. Given its physiologic role in orchestrating pregnancy progression and its involvement as pathogenic effector in several rheumatologic conditions, complement system is an attractive candidate biomarker to stratify the obstetric risk among women with rheumatologic conditions.

Sphingosine-1-phosphate in anti-neutrophil cytoplasmic antibody-associated vasculitis: coagulation-related clinical indicators and complications

BACKGROUND

Sphingosine-1-phosphate (S1P) plays a significant role in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV).

METHODS

We collected the plasma samples from 40 patients with AAV and 10 healthy volunteers. The plasma levels of S1P were tested by enzyme-linked immunosorbent assay (ELISA). The levels of serum creatinine (Scr) were tested by rate method, and then the estimated glomerular filtration rate (eGFR) of the patients was calculated from the Scr, age, and gender. Prothrombin time (PT), partial thromboplastin time (APTT), thrombin time (TT), fibrinogen (FIB), fibrinogen reduction product (FDP), D-dimer and C-reactive protein (CRP) were tested by turbidimetric inhibition immunoassays. Platelets (PLTs) were tested by fluorescently labeled electrical impedance method.

RESULTS

The plasma levels of S1P were significantly higher in AAV patients than in healthy volunteers. Correlation analysis showed that plasma levels of S1P were negatively correlated with glomerular filtration (P=0.022, r = -0.306), and positively correlated with circulating levels of Birmingham vasculitis activity score (BVAS), PLT and D-dimer, (P=0.004, r = 0.443; P<0.001, r = 0.654; P=0.006, r = 0.427). The 40 patients with AAV were classified into three groups: the thromboembolism group (with complications of cerebral infarction and myocardial infarction, n=6), cerebral ischemia group (n=4), and cerebral hemorrhage group (n=2). The plasma levels of S1P were highest in the thromboembolism group and lowest in the cerebral hemorrhage group (P=0.003).

CONCLUSIONS

Plasma levels of S1P were associated with circulating levels of D-dimer, PLT and BVAS in the patients with AAV. Hence, plasma S1P level can be used as a biomarker to predict coagulation-related complications in AAV.

Myeloperoxidase influences the complement regulatory activity of complement factor H

Objective

The interaction between neutrophils and activation of alternative complement pathway plays a critical role in the pathogenesis of ANCA-associated vasculitis (AAV). MPO, which can be released from ANCA-stimulated neutrophils, was recently demonstrated to be capable of activating the alternative complement pathway. Here we aimed to investigate the interaction between MPO and factor H (FH), a key regulator of the alternative pathway, and its effect on the functional activities of FH.

Methods

Detection of FH and MPO on neutrophil extracellular traps (NETs) induced by serum from AAV patients and in kidney biopsies of AAV patients was performed by immunostaining. In vitro binding between MPO and FH was examined by ELISA and surface plasmon resonance. The influence of MPO on the complement regulatory activity of FH was further assessed.

Results

FH deposited and co-localized with MPO in NETs. In kidney biopsies from AAV patients, MPO was closely adjacent to FH in glomerular capillaries. We demonstrated that MPO binds to FH with an apparent nanomolar affinity and identified short consensus repeats 1-4 of FH as the major binding sites. In terms of functional analysis, MPO inhibited the interaction between FH and C3b and the decay-accelerating activity of FH. The fluid phase and surface cofactor activities of FH upon C3b inactivation were inhibited by MPO.

Conclusion

Our findings indicate that MPO binds to FH and influences the complement regulatory activity of FH. MPO-FH interaction may participate in the pathogenesis of AAV by contributing to activation of the alternative complement pathway.

Macrophage migration inhibitory factor is involved in antineutrophil cytoplasmic antibody-mediated activation of C5a-primed neutrophils

Background

C5a is important for antineutrophil cytoplasmic antibody (ANCA)-mediated activation of neutrophils. The present study aimed to assess the role of macrophage migration inhibitory factor (MIF) in ANCA-mediated activation of C5a-primed neutrophils. The effects of MIF on ANCA-mediated neutrophil respiratory burst and degranulation were determined. In addition, the effect of a MIF antagonist on the activation of C5a-primed neutrophils was assessed.

Results

MIF treatment resulted in increased membrane proteinase-3 (mPR3) expression on neutrophils and enhanced myeloperoxidase (MPO) amounts in neutrophil culture supernatants. The concentration of MIF was significantly higher in the neutrophils supernatant primed with C5a (negative control: 14.2 ± 1.16 ng/ml; C5a: 45.8 ± 2.8 ng/ml, P < 0.001 vs. negative control; C5a + IgG: 44.8 ± 1.93 ng/ml, P < 0.001 vs. negative control; C5a + MPO-ANCA: 73.0 ± 5.5 ng/ml, P < 0.001 vs. C5a; and C5a + PR3-ANCA: 69.4 ± 5.35 ng/ml, P < 0.001 vs. C5a). MIF primed neutrophils to undergo respiratory burst and degranulation in response to ANCA. Indeed, mean fluorescence intensity (a measure of respiratory burst) was significantly higher in MIF-primed neutrophils activated with MPO-ANCA-positive IgG or PR3-ANCA-positive IgG compared with non-primed neutrophils. Meanwhile, a MIF antagonist reduced oxygen radical production in C5a-primed neutrophils treated with patient-derived ANCA-positive IgG.

Conclusions

MIF can prime neutrophils to undergo ANCA-mediated respiratory burst and degranulation. Blocking MIF resulted in reduced ANCA-mediated activation of C5a-primed neutrophils. These findings indicated that the interaction between MIF and C5a may contribute to ANCA-mediated neutrophil activation.

Gene mutations associated with thrombosis detected by whole-exome sequencing in paroxysmal nocturnal hemoglobinuria

BACKGROUND

Thrombosis is a most common and lethal complication of paroxysmal nocturnal hemoglobinuria (PNH), which is a complex progression and its mechanism remains unclear. We tried to explore the possible genetic background of thrombosis in PNH patients and provide potential gene mutations associated with thrombosis in PNH patients.

METHODS

The CD59^- cells of 7 PNH and 6 PNH- aplastic anemia (AA) patients were sorted by flow cytometry and sequenced by whole-exome sequencing (WES). The sequencing results and target mutation genes were analyzed and screened, respectively, and Kyoto Encyclopedia of Genes and Genomes (KEGG) signal pathway enrichment analysis was carried out. Finally, the expression of target genes was detected in 22 PNH (including seven cases with thrombus) and 20 normal controls, and the correlation between the expression of mRNA and the clinical thrombus-related indexes was analyzed.

RESULTS

The mutation genes screened from 4 PNH with thrombus were BMPR2, F8, ITGA2B, THBD, and THBS1. The pathways enriched by these genes included Notch, Wnt, and arachidonic acid metabolism signaling pathways, which may be related to the pathogenesis of thrombosis in PNH. The BMPR2, THBD, and THBS1 gene expression was significantly different between PNH with and without thrombus group, and the THBS1 gene expression was positively correlated with D-Dimer and su-PAR levels.

CONCLUSIONS

Genetic defects have a non-negligible effect on the incidence of thrombosis, and therefore, gene mutations maybe a genetic risk factor in PNH, which increase the incidence of thrombosis.

Complement Factor H Inhibits Anti-Neutrophil Cytoplasmic Autoantibody-Induced Neutrophil Activation by Interacting With Neutrophils

Our previous study demonstrated that plasma levels of complement factor H (FH) were inversely associated with the disease activity of patients with anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV). In addition to serving as an inhibitor of the alternative complement pathway, there is increasing evidence demonstrating direct regulatory roles of FH on several cell types. Here, we investigated the role of FH in the process of ANCA-mediated activation of neutrophils and neutrophil–endothelium interaction. We demonstrated that FH bound to neutrophils by immunostaining and flow cytometry. Interestingly, ANCA-induced activation of neutrophils, including respiratory burst and degranulation, was inhibited by FH. Although FH enhanced neutrophils adhesion and migration toward human glomerular endothelial cells (hGEnCs), it inhibited ANCA-induced activation of neutrophils in the coculture system of hGEnCs and neutrophils. Moreover, the activation and injury of hGEnCs, reflected by the level of endothelin-1 in the supernatant of cocultures, was markedly reduced by FH. However, we found that FH from patients with active AAV exhibited a deficient ability in binding neutrophils and inhibiting ANCA-induced neutrophil activation in fluid phase and on endothelial cells, as compared with that from healthy controls. Therefore, our findings indicate a novel role of FH in inhibiting ANCA-induced neutrophil activation and protecting against glomerular endothelial injury. However, FH from patients with active AAV are deficient in their ability to bind neutrophils and inhibit neutrophil activation by ANCA. It further extends the current understanding of the pathogenesis of AAV, thus providing potential clues for intervention strategies.

Pathogenesis and treatment of ANCA-associated vasculitis-a role for complement

The antineutrophil cytoplasm autoantibody (ANCA)-associated vasculitides (AAV), although rare in childhood, can have devastating effects on affected organs, especially the kidney. In this review we present an update on the pathogenesis and treatment of ANCA vasculitis, with a particular emphasis on the role of the alternative pathway of complement. The rationale and evidence for the current treatment strategies are summarized. Targeting the activation of neutrophils by the anaphylatoxin C5a may serve as an additional therapeutic strategy, however the results of clinical studies are awaited.

Haemostasis and innate immunity - a complementary relationship: A review of the intricate relationship between coagulation and complement pathways

Coagulation and innate immunity are linked evolutionary processes that orchestrate the host defence against invading pathogens and injury. The complement system is integral to innate immunity and shares numerous interactions with components of the haemostatic pathway, helping to maintain physiological equilibrium. The term 'immunothrombosis' was introduced in 2013 to embrace this process, and has become an area of much recent interest. What is less apparent in the literature however is an appreciation of the clinical manifestations of the coagulation-complement interaction and the consequences of dysregulation of either system, as seen in many inflammatory and thrombotic disease states, such as sepsis, trauma, atherosclerosis, antiphospholipid syndrome (APS), paroxysmal nocturnal haemoglobinuria (PNH) and some thrombotic microangiopathies to name a few. The growing appreciation of this immunothrombotic phenomenon will foster the drive for novel therapies in these disease states, including anticoagulants as immunomodulators and targeted molecular therapies.

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.

The functional activities of complement factor H are impaired in patients with ANCA-positive vasculitis

Increasing evidences have demonstrated that the activation of the alternative complement pathway is crucial for the pathogenesis of anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV). Our recent study found that circulating levels of complement factor H (FH), a key regulator of the alternative pathway, were associated with disease activity. In the current study, functional activities of FH were assessed to further explore the potential role of FH in the pathogenesis of AAV. We found that the two patients with ANCA-negative pauci-immune necrotizing crescentic glomerulonephritis exhibited relatively normal functional activities of FH. However, patients with ANCA-positive vasculitis exhibited deficient functional activities of FH, in terms of interaction with and the regulation of C3b, binding to mCRP and endothelial cells, and the protection of host cells against complement attack. Our findings indicate that functional activities of FH are deficient in patients with ANCA-positive vasculitis, potentially contributing to the disease development.

The interaction between C5a and sphingosine-1-phosphate in neutrophils for antineutrophil cytoplasmic antibody mediated activation

Introduction

C5a plays an crucial role in antineutrophil cytoplasmic antibody (ANCA)-mediated neutrophil recruitment and activation. The current study further investigated the interaction between C5a and sphingosine-1-phosphate (S1P) in neutrophils for ANCA-mediated activation.

Methods

The plasma levels of S1P from 29 patients with ANCA-associated vasculitis (AAV) in active stage and in remission were tested by enzyme-linked immunosorbent assay (ELISA). The generation of S1P was tested in C5a-triggered neutrophils. The effect S1P receptor antagonist was tested on respiratory burst and degranulation of C5a-primed neutrophils activated with ANCA.

Results

The plasma level of circulating S1P was significantly higher in patients with AAV with active disease compared with patients in remission (2034.2 ± 438.5 versus 1489.3 ± 547.4 nmol/L, P < 0.001). S1P can prime neutrophils for ANCA-induced respiratory burst and degranulation. Compared with non-triggered neutrophils, the mean fluorescence intensity (MFI) value for CD88 expression was up-regulated significantly in S1P-triggered neutrophils. S1P receptor antagonist decreased oxygen radical production in C5a primed neutrophils induced by ANCA-positive IgG from patients. Blocking S1P inhibited C5a-primed neutrophil migration.

Conclusions

S1P triggered by C5a-primed neutrophils could further activate neutrophils. Blocking S1P could attenuate C5a-induced activation of neutrophils by ANCA. The interaction between S1P and C5a plays an important role in neutrophils for ANCA-mediated activation.

Complement in ANCA-associated vasculitis

Antineutrophil cytoplasmic autoantibodies (ANCA) are the likely cause for necrotizing small-vessel vasculitis and crescentic glomerulonephritis. Unlike other forms of crescentic glomerulonephritis induced by immune complexes or anti-glomerular basement membrane antibodies that have conspicuous vessel wall immunoglobulin and complement, there is a paucity, although usually not an absence, of vessel wall immunoglobulin and complement in ANCA-associated glomerulonephritis. Despite this comparatively lower level and more localized distribution of vessel wall complement, experimental and clinical observations strongly incriminate alternative complement pathway activation as critically important in the pathogenesis of ANCA disease. Experimental data in animal models and in vitro experiments has shown that primed neutrophils are activated by ANCA, which generates C5a, which engages C5a receptors on neutrophils. This attracts and in turn primes more neutrophils for activation by ANCA. In patients with ANCA disease, plasma levels of C3a, C5a, soluble C5b-9, and Bb have been reported to be higher in active disease than in remission, whereas no difference was reported in plasma C4d in active versus ANCA disease remission. Thus, experimental and clinical data support the hypothesis that ANCA-induced neutrophil activation activates the alternative complement pathway and generates C5a. C5a not only recruits additional neutrophils through chemotaxis but also primes neutrophils for activation by ANCA. This creates a self-fueling inflammatory amplification loop that results in the extremely destructive necrotizing vascular injury.

B cell-mediated pathogenesis of ANCA-mediated vasculitis

B cells and their progeny that produce and release anti-neutrophil cytoplasmic autoantibodies (ANCA) are the primary cause for an aggressive form of necrotizing small vessel vasculitis. Cytoplasmic ANCA antigens are released at the surface and in the microenvironment of cytokine-primed neutrophils. Binding of ANCA to ANCA antigens activates neutrophils by both Fc receptor engagement and direct Fab'2 binding to antigen on the cell surface. ANCA-activated neutrophils release factors that induce alternative complement pathway activation, which establishes a potent inflammatory amplification loop that causes severe necrotizing vascular inflammation. The origin of the ANCA autoimmune response is unknown but appears to involve genetically determined HLA specificities that allow the autoimmune response to develop. One putative immunogenic mechanism begins with an immune response to a peptide that is complementary to the autoantigen and evolves through an anti-idiotypic network to produce autoantibodies to the autoantigen. Another putative immunogenic mechanism begins with an immune response to a microbe-derived molecular mimic of the autoantigen resulting in antibodies that cross-react with the autoantigen. Release of neutrophil extracellular traps, apoptosis, and increased granule protein expression of ANCA antigens may facilitate the initiation of an ANCA autoimmune response, augment established pathogenic ANCA production, or both. The ANCA B cell autoimmune response is facilitated by quantitatively and qualitatively impaired T cell and B cell suppression and by release from activated neutrophils of B cell-activating factors that enhance B cell proliferation and retard B cell apoptosis.

Alternative complement pathway activation products in urine and kidneys of patients with ANCA-associated GN

BACKGROUND AND OBJECTIVES

Previous study revealed that complement activation products of the alternative pathway could be detected in renal specimens of human ANCA-associated vasculitis. The current study aimed to investigate the clinical and pathologic significance of complement activation products in the urine and kidneys of patients with ANCA-associated vasculitis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Renal biopsy specimens from 29 patients with ANCA-associated vasculitis diagnosed at Peking University First Hospital from January of 2008 to December of 2010 were randomly collected. Urine samples from 27 of 29 patients in active stage and 22 ANCA-associated vasculitis patients in complete remission who were independent of the above-mentioned 29 patients were collected. Urine samples from 28 patients with lupus nephritis and 25 healthy individuals were also collected. The renal deposition of Bb, C3d, and C5b-9 were detected by immunohistochemistry. The urinary levels of Bb, C3a, C5a, and soluble C5b-9 were determined by ELISA.

RESULTS

The deposition, measured by the mean optical density of Bb, which is an alternative complement pathway marker, in glomeruli correlated with the proportion of total crescents (r=0.50, P=0.006), the extent of interstitial infiltrate (r=0.59, P=0.001), interstitial fibrosis (r=0.45, P=0.01), and tubular atrophy (r=0.55, P=0.002), whereas it correlated inversely with the proportion of normal glomeruli (r=-0.49, P=0.008). The urinary levels of Bb, C3a, C5a, and soluble C5b-9 were all significantly higher in active compared with remission stage. The urinary levels of Bb in patients with active ANCA-associated vasculitis correlated with the serum creatinine (r=0.56, P=0.002) and correlated inversely with the proportion of normal glomeruli in renal specimens (r=-0.49, P=0.009).

CONCLUSIONS

The present study provides additional evidence that complement activation through the alternative pathway occurred in the development of ANCA-associated vasculitis. The renal deposition of Bb and urinary Bb levels were associated with the severity of renal injury.