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

Anti-factor H autoantibodies in patients with lupus nephritis

INTRODUCTION

Lupus nephritis (LN) is a disease marked by autoantibodies against complement components. Autoantibodies against negative complement regulator factor H (anti-FH) are prevalent in aHUS, are associated with deletion of factor H-related protein 1 (FHR1) gene, and have overt functional consequences. They are also observed in C3 glomerulopathies. The frequency and relevance of anti-FH in LN are poorly studied.

AIM

The aim of our investigation was to screen for the presence of anti-FH and FHR1 gene deletion in a cohort of LN patients and to evaluate their association with LN activity.

METHOD

ELISA test and Western blot for detection of anti-FH and FHR1 deletion were used, respectively. Patients' clinical and laboratory parameters regarding anti-FH role were processed by statistical analysis.

RESULTS

Anti-FH were found at low level in a small number of LN patients - 11.7% (7/60) and were not associated with deletion of FHR1. Anti-FH did not correlate with ANA titers, anti-dsDNA, C3/C4 hypocomplementemia, eGFR, proteinuria, or active urinary sediment in LN patients. A weak correlation was found between anti-FH and anti-C3 levels. Anti-FH were linked with endocapillary proliferation and histological activity index. Four anti-FH positive patients had severe to moderate LN as per the BILAG renal score.

CONCLUSIONS

Anti-FH autoantibodies are an accessory finding in LN and are more likely to manifest during the active phase of the disease. Due to their low frequency and plasma levels, they do not seem suitable for routine laboratory investigation in patients with LN.

Promotion of an Antitumor Immune Program by a Tumor-specific, Complement-activating Antibody

Tumor-targeting Abs can be used to initiate an antitumor immune program, which appears essential to achieve a long-term durable clinical response to cancer. We previously identified an anti-complement factor H (CFH) autoantibody associated with patients with early-stage non-small cell lung cancer. We cloned from their peripheral B cells an mAb, GT103, that specifically recognizes CFH on tumor cells. Although the underlying mechanisms are not well defined, GT103 targets a conformationally distinct CFH epitope that is created when CFH is associated with tumor cells, kills tumor cells in vitro, and has potent antitumor activity in vivo. In the effort to better understand how an Ab targeting a tumor epitope can promote an effective antitumor immune response, we used the syngeneic CMT167 lung tumor C57BL/6 mouse model, and we found that murinized GT103 (mGT103) activates complement and enhances antitumor immunity through multiple pathways. It creates a favorable tumor microenvironment by decreasing immunosuppressive regulatory T cells and myeloid-derived suppressor cells, enhances Ag-specific effector T cells, and has an additive antitumor effect with anti-PD-L1 mAb. Furthermore, the immune landscape of tumors from early-stage patients expressing the anti-CFH autoantibody is associated with an immunologically active tumor microenvironment. More broadly, our results using an mAb cloned from autoantibody-expressing B cells provides novel, to our knowledge, mechanistic insights into how a tumor-specific, complement-activating Ab can generate an immune program to kill tumor cells and inhibit tumor growth.

The human factor H protein family - an update

Complement is an ancient and complex network of the immune system and, as such, it plays vital physiological roles, but it is also involved in numerous pathological processes. The proper regulation of the complement system is important to allow its sufficient and targeted activity without deleterious side-effects. Factor H is a major complement regulator, and together with its splice variant factor H-like protein 1 and the five human factor H-related (FHR) proteins, they have been linked to various diseases. The role of factor H in inhibiting complement activation is well studied, but the function of the FHRs is less characterized. Current evidence supports the main role of the FHRs as enhancers of complement activation and opsonization, i.e., counter-balancing the inhibitory effect of factor H. FHRs emerge as soluble pattern recognition molecules and positive regulators of the complement system. In addition, factor H and some of the FHR proteins were shown to modulate the activity of immune cells, a non-canonical function outside the complement cascade. Recent efforts have intensified to study factor H and the FHRs and develop new tools for the distinction, quantification and functional characterization of members of this protein family. Here, we provide an update and overview on the versatile roles of factor H family proteins, what we know about their biological functions in healthy conditions and in diseases.

Complement factor H: a novel innate immune checkpoint in cancer immunotherapy

The elimination of cancer cells critically depends on the immune system. However, cancers have evolved a variety of defense mechanisms to evade immune monitoring, leading to tumor progression. Complement factor H (CFH), predominately known for its function in inhibiting the alternative pathway of the complement system, has recently been identified as an important innate immunological checkpoint in cancer. CFH-mediated immunosuppression enhances tumor cells' ability to avoid immune recognition and produce an immunosuppressive tumor microenvironment. This review explores the molecular underpinnings, interactions with immune cells, clinical consequences, and therapeutic possibilities of CFH as an innate immune checkpoint in cancer control. The difficulties and opportunities of using CFH as a target in cancer immunotherapy are also explored.

Avacopan for the treatment of ANCA-associated vasculitis: an update

INTRODUCTION

Glucocorticoids (GC) have been part of the standard treatment of anti-neutrophil cytoplasm autoantibodies (ANCA)-associated vasculitides (AAV) for more than 60 years. Various therapeutic advances have occurred over the past 2 decades and led to a significant reduction of GC exposure, but most patients still have to suffer from complications of GC, including infections, metabolic abnormalities, and cardiovascular morbidity. In 2007, activation of the complement pathway was demonstrated to play a role in the pathogenesis of AAV. Avacopan, an oral competitive inhibitor of the C5a receptor (C5aR1, CD88), was then developed, with an additional aim to decrease the use of GC.

AREAS COVERED

In this article, we briefly summarize the rationale for targeting the complement pathway in AAV, and review relevant findings from pre-clinical, phase I, II, and III studies, subsequent and more recent case reports and series on the efficacy and safety of avacopan.

EXPERT OPINION

Based on the results of these studies, avacopan was approved in most countries since late 2021, as an adjunctive induction treatment for patients with AAV. Several newer questions now are pending answers, including as to how avacopan should be used in real-world practice, beyond how it was given in the original clinical trials.

New Insights into Pathogenesis and Treatment of ANCA-Associated Vasculitis: Autoantibodies and Beyond

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is a group of rare systemic diseases affecting small-caliber vessels. The damage caused by AAV mainly involves the lung and kidneys. AAV includes three different types: granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Although the different phenotypic forms of AAV share common features, recent studies have shown that there are significant differences in terms of pathogenetic mechanisms involving both the adaptive and innate immune systems. Advances in our understanding of pathogenesis have enabled the development of immuno-targeted therapies. This review illustrates the characteristics of the various forms of AAV and the new therapies available for this disease that can have lethal consequences if left untreated.

Pathogenesis of anti-neutrophil cytoplasmic antibody-associated vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) encompasses a group of potentially life-threatening disorders characterized by necrotizing small vessel vasculitis with positive serum ANCA. To date, the pathogenesis of AAV has not been fully elucidated, but remarkable progress has been achieved in the past few decades. In this review, we summarize the mechanism of AAV. The pathogenesis of AAV involves various factors. ANCA, neutrophils, and the complement system play key roles in disease initiation and progression, forming a feedback amplification loop leading to vasculitic injury. Neutrophils activated by ANCA undergo respiratory burst and degranulation, as well as releasing neutrophils extracellular traps (NETs), thus causing damage to vascular endothelial cells. Activated neutrophils could further activate the alternative complement pathway, leading to the generation of complement 5a (C5a), which amplifies the inflammatory response by priming neutrophils for ANCA-mediated overactivation. Neutrophils stimulated with C5a and ANCA could also activate the coagulation system, generate thrombin, and subsequently cause platelet activation. These events in turn augment complement alternative pathway activation. Moreover, disturbed B-cell and T-cell immune homeostasis is also involved in disease development. In-depth investigation in pathogenesis of AAV might help to offer more effective targeted therapies.

Old known and possible new biomarkers of ANCA-associated vasculitis

Antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) comprises a group of multisystem disorders involving severe, systemic, small-vessel vasculitis with short- and long term serious and life-threating complications. Despite the simplification of treatment, fundamental aspects concerning assessment of its efficacy and its adaptation to encountered complications or to the relapsing/remitting/subclinical disease course remain still unknown. The pathogenesis of AAV is complex and unique, and despite the progress achieved in the last years, much has not to be learnt. Foremost, there is still no accurate marker enabling us to monitoring disease and guide therapy. Therefore, the disease management relays often on clinical judgment and follows a" trial and error approach". In the recent years, an increasing number of new molecules s have been explored and used for this purpose including genomics, B- and T-cell subpopulations, complement system factors, cytokines, metabolomics, biospectroscopy and components of our microbiome. The aim of this review is to discuss both the role of known historical and clinically established biomarkers of AAV, as well as to highlight potential new ones, which could be used for timely diagnosis and monitoring of this devastating disease, with the goal to improve the effectiveness and ameliorate the complications of its demanding therapy.

IAPs antagonist SM164 ameliorates experimental MPO-ANCA-associated vasculitis via enhancing fatty acid oxidation in neutrophils

OBJECTIVES

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of life-threatening autoimmune diseases. Inhibitors of apoptosis proteins (IAPs) are a class of molecules engaged in cell death and inflammation, interventions of which are proven effective in a number of inflammatory diseases. Here we tested whether targeting IAPs could ameliorate AAV and explored the potential mechanism.

METHODS

We collected 19 kidney specimens from patients with myeloperoxidase (MPO)-AAV to investigate the expression of IAPs. The IAPs pan-inhibitor SM164 was used to treat the experimental autoimmune vasculitis (EAV) rat model of AAV. RNA sequencing of renal cortex and enrichment analysis were developed to interpret gene expression. Functional experiments were performed to investigate the role of SM164 on neutrophils and endothelial cells.

RESULTS

The expressions of three IAPs (cIAP1, cIAP2 and XIAP) were upregulated in kidneys of AAV patients compared with normal controls. SM164 dramatically reduced renal injury in EAV rats. Transcriptomic analysis revealed prominent alterations in fatty acid oxidation and respiratory burst following SM164 treatment. Functional studies demonstrated that SM164 inhibited neutrophil activation induced by MPO-ANCA positive IgG or serum from MPO-AAV patients, and such inhibitory effect was abolished by gene silencing or pharmacological inhibition of fatty acid oxidation. SM164 also inhibited the adhesion of neutrophils to endothelial cells with little effect on the endothelial injury induced by serum from MPO-AAV patients.

CONCLUSION

Inhibition of IAPs with SM164 played a protective role in AAV through enhancing intracellular fatty acid oxidation in neutrophils.

Mechanisms of vascular damage in ANCA vasculitis

The discovery of anti-neutrophil cytoplasmic antibodies (ANCA) and their antigenic targets, myeloperoxidase (MPO) and proteinase 3 (PR3), has led to further understanding as to the pathophysiologic processes that underlie vascular and tissue damage in ANCA vasculitis. ANCA trigger neutrophil activation leading to vascular damage in ANCA vasculitis. However, decades of study have determined that neutrophil activation alone is not sufficient to cause disease. Inflammatory stimuli are drivers of ANCA autoantigen expression and ANCA production. Certain infections or bacterial peptides may be crucial players in the initial steps of ANCA immunopathogenesis. Genetic and epigenetic alterations of gene encoding for MPO and PR3 provide additional disturbances to the immune homeostasis which provide a substrate for pathogenic ANCA formation from an adaptive immune system predisposed to autoreactivity. Promoted by inflammatory cytokines, ANCA binding leads to neutrophil activation, a process characterized by conformational changes, production and release of cytotoxic substances, and alternative complement pathway activation, thus creating an intense inflammatory milieu. This cascade of events perpetuates a vicious cycle of further inflammatory cell recruitment and activation, culminating in tissue necrosis. Our understanding of the pathogenic process in ANCA vasculitis paves the way for the development of therapies targeting crucial steps in this process. The greater appreciation of the role for complement, monocytes, and the adaptive immune system has already led to novel complement blockers and is poised to lead to further innovations which will allow for tailored antigen- or cell-specific immunotherapy targeting the autoimmune process without exposure to undue risks or toxicities.

ANCA Associated Vasculitis Subtypes: Recent Insights and Future Perspectives

The ANCA associated vasculitides (AAVs) affect a range of internal organs including ear nose and throat, respiratory tract, kidneys, skin and nervous system. They include granulomatosis with polyangiitis (GPA), eosinophilic granulomatosis with polyangiitis (EGPA) and microscopic polyangiitis (MPA). The AAVs are treated with high dose glucocorticoids, immunosuppressants, and targeted biological medications. Since the 1990s classification criteria for the AAVs have been based on clinical features, laboratory tests and basic imaging; an initiative to update the classification criteria incorporating newer tests, for example, anti-neutrophil cytoplasmic antibodies (ANCA) and novel imaging techniques will be published this year. There is also evidence for classification of patients based on ANCA subtype; those with anti-proteinase 3 antibodies (PR3) or anti-myeloperoxidase antibodies (MPO) have differences in response to treatment and clinical outcomes. An update is described within this review. The pathogenesis of AAV involves necrotizing inflammation of small to medium blood vessels involving multiple immunological pathways. We present an update on emerging evidence related to auto-antibodies, complement and lymphocyte pathways. This review describes emerging treatment regimens, including evidence for plasma exchange in severe disease and the inhibitor of the complement C5a receptor (C5aR) inhibitor, Avacopan. Lastly, patient reported outcomes are key secondary outcomes in randomised controlled trials and increasingly clinical practice, we report development in disease specific and glucocorticoid-specific PROs.

Clinical significance and role of CXCL16 in anti-neutrophil cytoplasmic autoantibody-associated vasculitis

Anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) is a group of potentially life-threatening autoimmune diseases. The kidney and lung are the most common and most severely affected organs. Previous studies have shown that the chemokine ligand CXCL16 and its receptor CXCR6 play an important role in kidney disease. However, whether CXCL16/CXCR6 is involved in the pathogenesis of AAV remains elusive. In this study, the levels of CXCL16 and its specific receptor CXCR6 were investigated. According to kidney outcome, patients were divided into two groups, specifically one with high CXCL16 levels and one with low CXCL16 levels, by cut-off values using receiver operating characteristic (ROC) curves. The clinical parameters and histological features were further compared between the two groups. The ability of CXCL16 to induce neutrophil chemotaxis was analysed using a Transwell migration assay in a coculture system of conditional immortalized human glomerular endothelial cells (ciGEnCs) and neutrophils. We observed that the levels of CXCL16 were significantly increased in the circulation, along with the expression in renal tissue of AAV patients compared to healthy controls (HCs). CXCR6 expression on neutrophils was significantly higher in patients with AAV than in HCs. There were positive correlations between the levels of CXCL16 and serum creatinine, IL-6, CRP, and TNF-α and negative correlations with eGFR. The serum levels of CXCL16 could act as a predictive biomarker of renal outcome in AAV. CXCL16 secretion was upregulated in ciGEnCs treated with AAV serum. CXCL16 released from ciGEnCs contributed to neutrophil migration. Furthermore, neutrophil migration was attenuated by silencing CXCL16 expression via transfection with short hairpin RNA (shRNA) sequences and lentivirus. Taken together, these data suggest that the inhibition of the CXCL16/CXCR6 axis may provide new therapeutic strategies targeting AAV.

Pathogenesis-based new perspectives of management of ANCA-associated vasculitis

While the pathogenesis of anti-neutrophil cytoplasmic autoantibody associated vasculitis (AAV) is still not fully elucidated, there is a mounting evidence that it is initiated by inflammation and activation of innate immunity in the presence of predisposing factors, innate immunity, aberrant responses of the adaptive immune system, and complement system activation. Biologics targeting inflammation-related molecules in the immune system have been explored to treat AVV, and these treatments have provided revolutionary advances. When focusing on the pathogenic mechanisms of AVV, this review presents the new findings regarding novel therapeutic approaches for the management of these conditions.

Renal diseases and the role of complement: Linking complement to immune effector pathways and therapeutics

The complement system is an ancient and phylogenetically conserved key danger sensing system that is critical for host defense against pathogens. Activation of the complement system is a vital component of innate immunity required for the detection and removal of pathogens. It is also a central orchestrator of adaptive immune responses and a constituent of normal tissue homeostasis. Once complement activation occurs, this system deposits indiscriminately on any cell surface in the vicinity and has the potential to cause unwanted and excessive tissue injury. Deposition of complement components is recognized as a hallmark of a variety of kidney diseases, where it is indeed associated with damage to the self. The provenance and the pathophysiological role(s) played by complement in each kidney disease is not fully understood. However, in recent years there has been a renaissance in the study of complement, with greater appreciation of its intracellular roles as a cell-intrinsic system and its interplay with immune effector pathways. This has been paired with a profusion of novel therapeutic agents antagonizing complement components, including approved inhibitors against complement components (C)1, C3, C5 and C5aR1. A number of clinical trials have investigated the use of these more targeted approaches for the management of kidney diseases. In this review we present and summarize the evidence for the roles of complement in kidney diseases and discuss the available clinical evidence for complement inhibition.

Plasma Exchange in ANCA-Associated Vasculitis: A Narrative Review

Therapeutic plasma exchange (TPE) is an adjunctive intervention to immunosuppression for the treatment of severe renal involvement or lung hemorrhage in patients with ANCA-associated vasculitis (AAV). Patients with AAV have an increased risk for progression to end-stage kidney disease (ESKD) or death despite advances in immunosuppressive therapy. The potential pathogenicity of ANCA makes TPE a reasonable treatment approach for the life-threatening complications of AAV. The efficacy of intensive TPE in rapidly progressive glomerulonephritis was originally described in small studies almost four decades ago. Further randomized trials examined the addition of TPE to standard of care, exhibiting mixed results in both patient and renal survival. The largest clinical trial to date, PEXIVAS, failed to demonstrate a clear benefit for TPE in severe AAV. In light of new evidence, the role of TPE remains controversial across the vasculitis medical community. The purpose of this review is to summarize the clinical indications and the current available data for the use of TPE in patients with severe AAV.

Complement Factor H Family Proteins Modulate Monocyte and Neutrophil Granulocyte Functions

Besides being a key effector arm of innate immunity, a plethora of non-canonical functions of complement has recently been emerging. Factor H (FH), the main regulator of the alternative pathway of complement activation, has been reported to bind to various immune cells and regulate their functions, beyond its role in modulating complement activation. In this study we investigated the effect of FH, its alternative splice product FH-like protein 1 (FHL-1), the FH-related (FHR) proteins FHR-1 and FHR-5, and the recently developed artificial complement inhibitor mini-FH, on two key innate immune cells, monocytes and neutrophilic granulocytes. We found that, similar to FH, the other factor H family proteins FHL-1, FHR-1 and FHR-5, as well as the recombinant mini-FH, are able to bind to both monocytes and neutrophils. As a functional outcome, immobilized FH and FHR-1 inhibited PMA-induced NET formation, but increased the adherence and IL-8 production of neutrophils. FHL-1 increased only the adherence of the cells, while FHR-5 was ineffective in altering these functions. The adherence of monocytes was increased on FH, recombinant mini-FH and FHL-1 covered surfaces and, except for FHL-1, the same molecules also enhanced secretion of the inflammatory cytokines IL-1β and TNFα. When monocytes were stimulated with LPS in the presence of immobilized FH family proteins, FH, FHL-1 and mini-FH enhanced whereas FHR-1 and FHR-5 decreased the secretion of TNFα; FHL-1 and mini-FH also enhanced IL-10 release compared to the effect of LPS alone. Our results reveal heterogeneous effects of FH and FH family members on monocytes and neutrophils, altering key features involved in pathogen killing, and also demonstrate that FH-based complement inhibitors, such as mini-FH, may have effects beyond their function of inhibiting complement activation. Thus, our data provide new insight into the non-canonical functions of FH, FHL-1, FHR-1 and FHR-5 that might be exploited during protection against infections and in vaccine development.

Ribosomal Protein SA-Positive Neutrophil Elicits Stronger Phagocytosis and Neutrophil Extracellular Trap Formation and Subdues Pro-Inflammatory Cytokine Secretion Against Streptococcus suis Serotype 2 Infection

Streptococcus suis serotype 2 (SS2), an important zoonotic pathogen that causes septicemia, arthritis, and irreversible meningitis in pigs and humans, can be transmitted to humans from pigs. S. suis causes huge economic losses to the swine industry and poses a serious threat to public health. Previously, we found that the brain tissues of mice with SS2-induced meningitis showed disrupted structural integrity and significantly enhanced polymorphonuclear neutrophil (PMN) infiltration. We showed that the brain tissues of SS2-infected mice had increased ribosomal protein SA (RPSA)-positive PMN counts. However, the inflammatory responses of RPSA⁺ PMNs to SS2 and their effects on the blood-brain barrier (BBB) remain unclear. Therefore, in studying the pathogenesis of SS2-induced meningitis, it is essential that we explore the functions of RPSA⁺ PMNs and their effects on the BBB. Herein, using flow cytometry and immunofluorescence microscopy analyses, we found that RPSA expression enhances PMN-induced phagocytosis and PMN-induced formation of neutrophil extracellular traps (NETs), which facilitate further elimination of bacteria. PMN surface expression of RPSA also alleviates local inflammation and tissue injuries by inhibiting secretion of the pro-inflammatory cytokines, TNF-α and IL-6. Moreover, the single-cell BBB model showed that RPSA disrupts BBB integrity by downregulating expression of tight junction-associated membrane proteins on PMNs. Taken together, our data suggest that PMN-surface expression of RPSA is a double-edged sword. RPSA+ PMN owns a stronger ability of bacterial cleaning and weakens inflammatory cytokines release which are useful to anti-infection, but does hurt BBB. Partly, RPSA+ PMN may be extremely useful to control the infection as a therapeutic cellular population, following novel insights into the special PMN population.

Biomarkers in ANCA-Associated Vasculitis: Potential Pitfalls and Future Prospects

Over the past 3 decades, significant advancements in the understanding of the pathophysiology of ANCA-associated vasculitis has led to the development of a multitude of potential candidate biomarkers. Accompanied by the advent of increasingly effective therapeutic strategies, the need for a dependable biomarker to help determine the extent of disease activity and risk of relapse is ever present. Implementation of such a biomarker would enable tailored therapy, optimizing disease control while helping to mitigate unnecessary exposure to therapy and potential treatment-related damage. Although far from perfect, ANCA serology and B-cell population are the two main staple biomarker tools widely used in practice to help supplement clinical assessment. Over recent years, the application and progress of more novel biomarker tools have arisen in both organ-limited and multisystem disease, including genomics, urinary proteins, degradation products of the alternative complement system, cytokines, metabolomics, and biospectroscopy. Validation studies and clinical translation of these tools are required, with serial assessment of disease activity and determination of therapy according to biomarker status correlated with patient outcomes.

Sphingosine-1-phosphate receptor modulator FTY720 attenuates experimental myeloperoxidase-ANCA vasculitis in a T cell-dependent manner

Sphingosine-1-phosphate (S1P) is a pleiotropic lysosphingolipid derived from the metabolism of plasma membrane lipids. The interaction between S1P and its ubiquitously expressed G-protein-coupled receptors (S1PR1-5) is crucial in many pathophysiological processes. Emerging evidence suggested a potential role for S1P receptors in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). In the present study, we investigated the effects of three different S1P receptors modulators (FTY720, SEW2871 and TY52156) in a recognized rat model of experimental autoimmune vasculitis (EAV). The effects of treatments were evaluated with clinico-pathological parameters including hematuria, proteinuria, crescent formation, pulmonary hemorrhage, etc. In vitro functional studies were performed in a Jurkat T-cell line following stimulations of serum from myeloperoxidase-AAV patients. We found that only the FTY720 treatment significantly alleviated hematuria and proteinuria, and diminished glomerular crescent formation, renal tubulointerstitial lesions and pulmonary hemorrhage in EAV. The attenuation was accompanied by less renal T-cell infiltration, up-regulated mRNA of S1PR1 and down-regulated IL-1β in kidneys, but not altered circulating ANCA levels, suggesting that the therapeutic effects of FTY720 were B-cell independent. Further in vitro studies demonstrated that FTY720 incubation could significantly inhibit the proliferation, adhesion, and migration, and increase apoptosis of T cells. In conclusion, the S1P modulator FTY720 could attenuate EAV through the reduction and inhibition of T cells, which might become a novel treatment of ANCA-associated vasculitis.

The role of complement in antineutrophil cytoplasmic antibody-associated vasculitis

PURPOSE OF REVIEW

To provide a comprehensive overview of the current insight into the role of complement activation in antineutrophil cytoplasmic antibody-associated vasculitis (AAV). In addition, the therapeutic options targeting the complement system in AAV are discussed.

RECENT FINDINGS

It has become increasingly clear that complement, and more specifically signalling through the C5a receptor, contributes to the immunopathology of AAV. This has led to the design of clinical trials with a C5a receptor blocker. The first results show a reduction in tissue damage and a favourable safety profile, as other parts of the complement defence system are left intact.

SUMMARY

Although AAV was initially regarded as a pauci-immune disease, it is now well established that, in addition to autoantibodies, complement plays an essential role in the disease process. Animal models delivered the first insight, but the effective therapeutic interventions using complement inhibitors provided the proof that indeed complement activation contributes to disease activity and tissue damage in human AAV.

Complement inhibition in ANCA vasculitis

A role for the alternative complement pathway has emerged in the understanding of ANCA vasculitis pathogenesis. Current therapies of ANCA vasculitis are limited by partial efficacy and toxicity and many patients pursue a relapsing course. Improved therapies are needed. Inhibition of the alternative complement pathway component C5a is attractive due to its role in neutrophil activation and migration, and engagement of other inflammatory and thrombotic mechanisms. Two inhibitors of C5a are in clinical development for ANCA vasculitis: avacopan, an oral C5a receptor inhibitor has demonstrated efficacy, safety and steroid sparing in two Phase II trials; and IFX-1, a monoclonal antibody to C5a which is entering Phase II development. Complement inhibition has the potential to contribute to remission induction protocols achieving a higher quality of remission as well as replacing steroids. Confirmation of safety, especially infective risk, and the potential to replace steroids depends on further studies and a role in relapse prevention needs to be explored.

Pathological severity determines the renal recovery for anti-myeloperoxidase antibody-associated vasculitis requiring dialysis at disease onset: a retrospective study

Background

Many patients with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) need dialysis at disease onset due to severe kidney injury. Determining whether they can become dialysis independent is an important clinical assessment.

Methods

Forty kidney biopsy-proved myeloperoxidase (MPO)-ANCA associated AAV patients who required dialysis at disease onset were enrolled. Relationships between laboratory and pathological characteristics and prognoses were analyzed.

Results

Twenty-five patients obtained dialysis independence within 3 months, while the other 15 patients remained dialysis dependent. No sclerotic class was identified among the 40 patients. Only two biopsies exhibited focal class diagnoses and both these patients recovered their renal function. The renal recovery rate of the 20 patients with mixed class was significantly lower than that of the 18 patients with crescentic class (40.0% vs. 83.3%, p = 0.006). Receiver operating characteristics (ROC) curves showed fibrous crescent+global glomerulosclerosis greater than 32.6% was a strong predictor of dialysis dependence with a sensitivity of 93.3% and specificity of 88.0%. When the percentage of fibrous crescent+global glomerulosclerosis exceeded 47.9%, dialysis independence was not possible. Correlation analysis indicated that platelet counts were negatively correlated with the percentage of fibrous crescent+global glomerulosclerosis (R = -0.448, p = 0.004). Most patients with increased platelets (84.62%) obtained renal recovery. Compared with methylprednisolone pulse therapy, plasma exchange accelerated renal recovery (29.4 ± 15.6 vs. 41.4 ± 11.7 days, p = 0.039).

Conclusions

For MPO-ANCA AAV who required dialysis at disease onset, crescentic and mixed classes accounted for the majority of patients in our cohort. The renal outcome of mixed class patients was worse than that of crescentic class. A high proportion of fibrous crescent+global glomerulosclerosis is a predictor of dialysis dependence. Increased platelet count is associated with active and reversible renal lesions.

ANCA associated vasculitis: The journey to complement-targeted therapies

ANCA associated vasculitis is a serious, very often recurrent disease that despite the current standard treatment with high-dose glucocorticoids and either cyclophosphamide or rituximab, patients have a nine-fold increased mortality risk in the first year compared with healthy controls, attributed to infections, vasculitis activity, and renal disease. During the last few years, novel findings have suggested that activation of the complement system, in particular the alternative complement system, has a significant role in ANCA associated vasculitis pathogenesis. Detection of several components of this system in the circulation and urine reflects disease activity, and thus may be useful for clinical prognosis and to set up personalised treatments. In fact, some components of the complement system, such as C5a, might be potential targets for therapy. In this Review an update on clinical evidence for the role of complement activation in AAV is provided and subsequently we discuss potential therapeutic strategies that target complement components and open the way for clinical use of this target therapy in the near future.

Neutrophils from ANCA-associated vasculitis patients show an increased capacity to activate the complement system via the alternative pathway after ANCA stimulation

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV), including granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA), are autoimmune conditions associated with small vessel inflammation. Earlier studies indicate that complement activation via the alternative pathway plays a major role in the pathogenesis. In this study we have investigated if ANCA-activation of neutrophils from AAV patients leads to activation of the alternative complement pathway. C5a-primed neutrophils (PMN) from 10 AAV patients and 10 healthy controls (HC) were stimulated with PMA or IgG purified from PR3-ANCA positive patients (ANCA IgG). The supernatants were analyzed for release of complement proteins and markers of different granules by ELISA, and release of microparticles (MP) by flow cytometry. The ability of the supernatants to activate the alternative complement pathway was determined by incubation with normal serum and C3bBbP and C5a were measured by ELISA. MP were analyzed by flow cytometry and removed by centrifugation. The supernatants from the AAV patients’ neutrophils produced significantly more C3bBbP compared with HCs (p = 0.0001). C3bBbP levels correlated with the number of MP. After removal of MP from the supernatants, alternative pathway activation was significantly lower. This study shows that primed and ANCA-stimulated neutrophils from AAV patients have a greater ability to activate the alternative complement pathway compared to primed neutrophils from healthy controls. This finding emphasizes the role of complement in the pathogenesis of AAV - underlining the therapeutic potential of C5a and other complement blockade.