Complement deposition in renal histopathology of patients with ANCA-associated pauci-immune glomerulonephritis

Complement as a major mediator of ANCA vasculitis and a target for precision therapy

INTRODUCTION

Complement was long thought not to be involved in ANCA vasculitis pathogenesis until studies in murine models demonstrated its central role. The current theory is ANCA-activated neutrophils degranulate and release factors that activate complement, which, in turn, recruits more neutrophils and causes an inflammatory amplification loop that results in the vascular inflammation characteristic of disease. Targeting this amplification loop through complement inhibition has proven to be effective in ANCA vasculitis treatment.

AREAS COVERED

A PubMed search was conducted using key terms 'ANCA vasculitis' AND 'complement system.' We review the findings from experimental mouse models, in vitro studies, and human ANCA vasculitis that support a role for complement activation in disease pathogenesis. We also summarize results from pivotal clinical studies demonstrating the safety and efficacy of complement inhibition in ANCA vasculitis treatment.

EXPERT OPINION

While complement activation is undoubtedly involved in ANCA vasculitis pathogenesis, less clear is whether measuring complement activation markers can reliably assess disease activity, predict those who will benefit from complement-targeting therapy, or identify patients in stable remission and able to stop therapy. Better understanding the clinical implications of complement activation will shed more light on the utility of complement inhibition and facilitate precision medicine in ANCA vasculitis.

Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis in China: Epidemiology, Management, Prognosis, and Outlook

Background

Increasing evidence indicates that clinicopathologic phenotypes and ANCA serotypes may differ ethnically and geographically. This review highlights the progress in the prevalence, pathogenesis, management, and outcomes of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) in China.

Summary

AAV is not rare in China. Cumulative evidence has demonstrated a significant preponderance of microscopic polyangiitis (MPA) and myeloperoxidase (MPO)-ANCA AAV in China. Even in patients with granulomatosis with polyangiitis (GPA), there is a predominance of MPO-ANCA over proteinase 3 (PR3)-ANCA, presenting a unique subset. The pathogenesis of AAV is multifactorial, with the role of complement activation being highlighted during recent years. Treatment strategies for AAV in China have also been refined recently. A rapid tapering of glucocorticoids to minimize exposure has been recommended by the Chinese guidelines. Along with a better understanding of the disease, B cell-targeted therapy and complement-targeted therapy are developing. A considerable number of patients in China received rituximab treatment and achieved remission. However, infection risk and associated mortality still remain concerns. Therefore, less rituximab exposure should be considered and evaluated in Chinese AAV patients. Prognostic factors have been reviewed. Of note, along with improved outcomes, there is an increase of cardiovascular and malignant-related death, warranting specific care. Recently, a modified renal risk score model has been validated for early risk prediction in Chinese AAV patients. Moreover, emerging biomarkers for AAV, including complement components, have been identified in Chinese patients.

Key Messages

There is a preponderance of MPA and MPO-ANCA in China. Treatment strategies for Chinese AAV patients generally align with those in western countries, and to some extent, less aggressive. Prognostic factors and emerging biomarkers for AAV in China have been identified. Further challenges include optimizing interventions, minimizing treatment-related comorbidities, improving disease monitoring, and enhancing life qualities of AAV patients.

Presentation and progression of MPO-ANCA interstitial lung disease

The association between MPO-ANCA-associated vasculitis (AAV) and interstitial lung disease (ILD) has been well established. Pulmonary fibrosis may coexist with, follow, or even precede the diagnosis of AAV, and its presence adversely affects the prognosis. The optimal approach to investigating ANCA in patients with ILD remains a subject of ongoing debate. Here we aim to describe presentation and progression of MPO-ANCA ILD. We conducted a retrospective evaluation of a cohort of individuals diagnosed with MPO-ANCA ILD, with or without accompanying renal impairment, at the Immunology and Cell Therapy Unit, Careggi University Hospital, Florence, Italy, between June 2016 and June 2022. Clinical records, imaging studies, pathologic examinations, and laboratory test results were collected. Among the 14 patients identified with MPO-ANCA ILD, we observed a significant association between MPO-ANCA titers assessed at the time of ILD diagnosis and renal involvement. Renal impairment in these cases often manifested as subclinical or slowly progressive kidney damage. Interestingly, complement C3 deposits were consistently found in all renal biopsy specimens, thereby suggesting the potential for novel therapeutic targets in managing renal complications associated with MPO-ANCA ILD. The presentation of MPO-ANCA vasculitis as ILD can be the first and only clinical manifestation. MPO-ANCA levels at ILD diagnosis could warn on the progression to renal involvement in patients with MPO-ANCA ILD, hence caution is needed because renal disease can be subclinical or smoldering.

End stage renal disease in patient with microscopic polyangiitis and atypical hemolytic-uremic syndrome arose 3 weeks after the third dose of anti-SARS-CoV2 vaccine mRNA-1273: A case report with literature revision

RATIONALE

Immune system deregulation, including AAV, is a key event that may potentially evolve into ESRD. Abnormal activation of the cAP is also a cardinal feature of TMA, particularly aHUS. The kidney is the most frequently involved organ, and renal-limited forms of TMA are often encountered in clinical practice. Isolated case reports described the occurrence of renal TMA in AAV patients. Some cases of both de novo and relapses of AAV and/or TMAs after anti-SARS-CoV2 vaccination have been reported. We reported, for the 1st time, a case of patients with new-onset MPA and aHUS occurring 3 weeks after the third dose of mRNA-1273 vaccine anti-SARS-CoV2.

PATIENT CONCERNS

We present a 67-year-old man, affected by arterial hypertension, reported, after mRNA-1273 vaccine anti-SARS-CoV2, anuria, fatigue, anorexia and nausea. Laboratory data revealed acute renal failure.

DIAGNOSIS

Positivity of MPO-ANCA was observed. 7 days after admission, we observed a worsening of anemia and thrombocytopenia with haptoglobin reduction, LDH increase and presence of schistocytes. Plasma levels of ADAMTS-13 were normal. A renal biopsy was performed, and findings were consistent with microscopic polyangiitis, with features of micro-thrombotic glomerulopathy. Genetic tests revealed absence of hybrid genes associated with the increased risk of aHUS.

INTERVENTIONS AND OUTCOMES

We started renal replacement treatment, including hemodialysis, and pulsed methylprednisolone, with no improvement of laboratory parameters. Then, plasma exchange was performed leading to partial haematological response. Only with Eculizumab, a human C5 inhibitor, we observed a normalization of haptoglobin levels and platelets' count. However, three months after discharge, the patient still required hemodialysis.

LESSONS

To our knowledge we observed the first case aHUS, without genetic predisposition, associated with MPA occurring after the third dose of anti-SARS-CoV2 vaccine. This case report highlights the potential link between anti-SARS-CoV2 vaccine as a trigger of MPA and aHUS. This systematic review offers additional perspectives. It is plausible to hypothesize that the vaccine was the trigger for the development of these 2 diseases.Solid evidence on the mechanisms of interaction between vaccine and immune system, the role of genetic predisposition, and other variables, will shed additional light on the controversial link between anti-SARS-CoV2 vaccine and autoimmunity.

Identification of potential biomarkers and therapeutic targets for antineutrophil cytoplasmic antibody-associated glomerulonephritis

Exploring key genes for antineutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (ANCA-GN) is of great significance. Through bioinformatics analysis, 79 immune protein-differentially expressed genes (IP-DEGs) were obtained. Six hub genes (PTPRC, CD86, TLR2, IL1B, CSF-1R, and CCL2) were identified and verified to be increased in ANCA-GN patients. Random forest algorithm and ROC analysis showed that CSF-1R was a potential biomarker. Plasma CSF-1R levels increased significantly in ANCA-GN-active patients compared with remission stage and control. Correlation analysis revealed that CSF-1R levels had positive relationship with serum creatinine and Birmingham scoring, while inversely correlated with eGFR. Multivariate analysis revealed that plasma CSF-1R were an independent poor prognostic variable for end-stage renal disease or death, after adjusting for age and gender (HR = 3.05, 95% CI = 1.45-6.43, p = 0.003). Overall, we revealed that the CSF-1R is related to disease activity and might be a vital gene associated with the pathogenesis of ANCA-GN.

Sex disparities in clinicopathological features and outcomes of patients with myeloperoxidase-ANCA-associated vasculitis: a retrospective study of 366 cases in a single Chinese center

There are a few studies that reported sex disparities in clinical features, pathological features and outcomes among ANCA-associated vasculitis (AAV) patients, but studies focusing on sex-specific differences of myeloperoxidase (MPO)-AAV patients are scarce. Therefore, the purpose of this study was to analyze sex differences in clinicopathological features and outcomes of MPO-AAV. Patients diagnosed with MPO-AAV in Xiangya Hospital from January 2010 to June 2021 were included in the study and separated into female and male groups. The differences in clinical manifestations, laboratory parameters, pathological features and prognosis between the two groups were retrospectively analyzed. Three hundred and sixty-six patients were included and divided into female group (n = 176) and male group (n = 190). The age of the male group was 62.41 ± 10.49 years, significantly higher than that of the female group (58.69 ± 16.39, p = 0.011). Compared with the female group, the male group had a shorter duration of disease, higher levels of hemoglobin, eosinophil count, proteinuria, serum C4, and lower levels of serum globulin, serum IgG and serum IgM (p < 0.05). No significant differences in kidney pathological features were observed between the two groups. During a median follow-up of 37.6 months, there was no significant difference in renal survival and patient survival between the two groups, but male patients had a worse composite outcome of renal and patient survival compared with the female patients (p = 0.044). This study found that male patients with MPO-AAV had a higher age of onset, shorter duration of disease, higher levels of hemoglobin, eosinophil count, proteinuria, serum C4, and lower levels of serum globulin, serum IgG and serum IgM. Male patients fared worse than female patients in terms of the composite outcome of renal and patient survival.

Low levels of complement factor C3 at diagnosis can predict outcome in antineutrophil antibody associated vasculitis

INTRODUCTION

Experimental data support the involvement of complement in the pathogenesis of antineutrophil antibody associated vasculitis, and clinical studies describe a more severe disease phenotype in patients with antineutrophil antibody associated vasculitis and complement activation. In the present study, we looked for an association between circulating serum complement factor 3 levels at diagnosis and outcomes.

METHODS

One hundred sixty-four patients with antineutrophil antibody associated vasculitis who underwent kidney biopsy at our center during the last 15 years were retrospectively reviewed. Patients were categorized according to their serum complement factor 3 level at diagnosis. Patient and renal survival were compared between those above and below the median serum complement factor 3 at diagnosis.

RESULTS

During the first year, 6 patients died and 53 reached end-stage renal disease. Death or end-stage renal disease at one-year were significantly more common in the low serum complement factor 3 group (44 vs. 29%, p = 0.037). In the multivariable analysis, serum complement factor 3 was the strongest negative outcome predictor (HR, 95%CI 0.118, (0.021-0.670)). The lower the serum complement factor 3 level at baseline, the higher the risk of dialysis and death. The risk was particularly high for both endpoints if the serum complement factor 3 concentration was below 0.9 g/l at baseline.

CONCLUSION

Complement activation at diagnosis may identify a distinct subgroup of patients with antineutrophil antibody associated vasculitis and higher risk for poor outcomes. However, it remains to be proven whether inhibition of serum complement factor 3 is beneficial and safe in the clinical setting.

Serum Complement C4 Levels Are a Useful Biomarker for Predicting End-Stage Renal Disease in Microscopic Polyangiitis

This study aimed to evaluate the risk factors for end-stage renal disease (ESRD) in microscopic polyangiitis (MPA). In total, 74 patients with MPA were enrolled, and we compared the baseline clinical characteristics and disease activity between MPA patients who have progressed to ESRD and those without ESRD to select predictive factors for ESRD. Out of 74 patients, 12 patients (16.2%) had ESRD during follow-up. Serum C4 levels were significantly higher in MPA patients who have progressed to ESRD than in those without ESRD (p = 0.009). Multivariate analyses revealed that high serum creatinine levels (odds ratio (OR) 4.4, 95% confidence interval (CI) 1.25-15.5) and high serum C4 levels (OR 1.24, 95% CI 1.03-1.49) were risk factors for ESRD. Using receiver operating characteristic analysis, the cut-off value for initial serum C4 levels and serum creatinine levels were 29.6 mg/dL and 3.54 mg/dL, respectively. Patients with MPA with a greater number of risk factors (serum C4 levels > 29.6 mg/dL and serum creatinine levels > 3.54 mg/dL) had a higher ESRD progression rate. Serum C4 levels were significantly positively correlated with serum creatinine levels and kidney Birmingham vasculitis activity score (p = 0.02 and 0.04, respectively). These results suggest that serum C4 levels are useful tools for assessing renal disease activity and prognosis in MPA.

The role of complement in glomerulonephritis-are novel therapies ready for prime time?

The complement system plays a key pathogenic role in glomerular diseases with a diverse range of aetiologies, including C3 glomerulopathy, immunoglobulin A nephropathy, membranous nephropathy, ANCA-associated vasculitis and lupus nephritis. Several novel therapies targeting complement activity have recently been developed, which have now been approved or are in the late stages of clinical development. In this review, potential benefits and challenges of targeting the complement system in glomerular disease are discussed. We summarize current understanding of the role of complement, and the novel targeted therapies that are being developed for the treatment of glomerular disease.

Prognostic value of complement serum C3 level and glomerular C3 deposits in anti-glomerular basement membrane disease

Background and objectives

Activation of the complement system is involved in the pathogenesis of anti-glomerular basement membrane (anti-GBM) disease. Glomerular deposits of complement 3 (C3) are often detected on kidney biopsies. The primary objective of this study was to analyze the prognostic value of the serum C3 level and the presence of C3 glomerular deposits in patients with anti-GBM disease.

Methods

We conducted a retrospective cohort study of 150 single-positive patients with anti-GBM disease diagnosed between 1997 and 2017. Patients were categorized according to the serum C3 level (forming a low C3 (C3<1.23 g/L) and a high C3 (C3≥1.23 g/L) groups) and positivity for C3 glomerular staining (forming the C3+ and C3- groups). The main outcomes were kidney survival and patient survival.

Results

Of the 150 patients included, 89 (65%) were men. The median [interquartile range (IQR)] age was 45 [26-64]. At diagnosis, kidney involvement was characterized by a median [IQR] peak serum creatinine (SCr) level of 578 [298-977] µmol/L, and 106 (71%) patients required dialysis. Patients in the low C3 group (72 patients) had more severe kidney disease at presentation, as characterized by higher prevalences of oligoanuria, peak SCr ≥500 µmol/L (69%, vs. 53% in the high C3 group; p=0.03), nephrotic syndrome (42%, vs. 24%, respectively; p=0.02) and fibrous forms on the kidney biopsy (21%, vs. 8%, respectively; p=0.04). Similarly, we observed a negative association between the presence of C3 glomerular deposits (in 52 (41%) patients) and the prevalence of cellular forms (83%, vs. 58% in the C3- group; p=0.003) and acute tubulo-interstitial lesions (60%, vs. 36% in the C3- group; p=0.007). When considering patients not on dialysis at diagnosis, the kidney survival rate at 12 months was poorer in the C3+ group (50% [25-76], vs. 91% [78-100] in the C3- group; p=0.01), with a hazard ratio [95% confidence interval] of 5.71 [1.13-28.85] (p=0.04, after adjusting for SCr).

Conclusion

In patients with anti-GBM disease, a low serum C3 level and the presence of C3 glomerular deposits were associated with more severe disease and histological kidney involvement at diagnosis. In patients not on dialysis at diagnosis, the presence of C3 deposits was associated with worse kidney survival.

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.

The complement system in antineutrophil cytoplasmic antibody-associated vasculitis: pathogenic player and therapeutic target

PURPOSE OF REVIEW

The purpose of this review is to discuss the role of the complement system in the pathogenesis of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) as well as the employment of complement inhibitors in AAV treatment.

RECENT FINDINGS

AAV has traditionally been considered a pauci-immune disease until recent findings demonstrated the pathogenic role of the complement system. The complement alternative pathway is crucial in AAV, and C5a seems to be a key molecule for AAV to develop. Avacopan, a C5a-receptor (C5aR) antagonist, proved effective in achieving AAV remission and ameliorating kidney function.

SUMMARY

The increased circulating levels of some complement components - as well as the consumption of others - in patients with AAV suggested a systemic activation of the complement system. Low C3 levels correlate with a more aggressive disease and a worse renal prognosis. In ANCA-associated glomerulonephritis, renal deposits of C3d and properdin, suggestive of local alternative pathway activation, correlate with glomerular crescents and proteinuria. The interaction between C5a and neutrophil triggers alternative pathway activation, suggesting the central role of C5a in AAV pathogenesis. Avacopan, a C5aR inhibitor, showed beneficial effects in AAV and represents a promising therapy to achieve sustained remission and to spare glucocorticoids.

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.

What is the prognosis of ANCA-associated glomerulonephritis with immune deposition?

Objectives

This study aimed to analyze histological and clinical characteristics of patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) showing renal involvement to investigate the associations between immune complexes (IC) and clinicopathological indicators, and explore the renal outcomes of AAV.

Methods

We retrospectively evaluated the histopathological features and clinical characteristics of 80 renal biopsies of patients with AAV with renal involvement. Renal morphology was classified into two (with and without the presence of IC and complement deposition). Endpoints included end-stage kidney disease (ESKD) and death.

Results

Compared with patients without IC, patients with immune deposition had lower complement C3 (0.80 ± 0.27 vs. 0.93 ± 0.20, p = 0.024), more severe hematuria [133 (46–299) vs. 33 (15–115), p = 0.001] but had milder chronic pathology, including chronic tubular atrophy (p = 0.03), chronic interstitial fibrosis (p = 0.049). Patients in the immune deposition group showed a tendency to have more severe crescent formation and less glomerulosclerosis, but the difference was not statistically significant. Endpoints such as death and ESKD were not significantly different between the two groups.

Conclusions

Immune deposition may indicate lower complement C3, more severe hematuria and glomerular lesions, milder tubular atrophy, and interstitial fibrosis, but it cannot predict the renal outcome.

Histopathological prognostic factors in ANCA-associated glomerulonephritis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) are a group of multisystemic autoimmune diseases characterized by necrotizing inflammation of small vessels. Kidney involvement is frequent in granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA), and accounts for a significant proportion of the morbidity and mortality related to these diseases. Despite improvement in therapeutic management of ANCA-glomerulonephritis (ANCA-GN), end-stage kidney disease (ESKD) still occurs in up to 30% of affected patients within 5 years following diagnosis. Thus, identifying patients for whom aggressive immunosuppressive therapy will be more beneficial than deleterious is of great importance. Several clinical, biological and histological factors have been proposed as predictors of ESKD. The kidney biopsy is essential not only for the diagnosis, but also for evaluating renal prognosis. In this review, we discuss the prognostic value of renal lesions at the diagnosis of ANCA-GN by analyzing each compartment of the nephron. We also review existing ESKD risk classification in ANCA-GN and finally propose an example of a standardized pathology report that could be used in routine practice.

The Complement System and ANCA Associated Vasculitis in the Era of Anti-Complement Drugs

ANCA (anti-neutrophil cytoplasmic antibody)-associated vasculitis (AAV) is the condition in which ANCA, as an autoantibody, is associated with the pathogenesis of vasculitis in small blood vessels, mainly in the ear, nose, throat, kidney, lung, and nerves. These diseases are important because they can be fatal due to renal failure and pulmonary hemorrhage if not promptly and appropriately treated. Recently accumulated evidence has shown that C5a produced by the complement alternative pathway primes neutrophils, which in turn activate the complement alternative pathway, leading to the pathogenesis of AAV. Avacopan (CCX168), a C5aR antagonist was shown to be effective against AAV, and it has been a novel therapeutic option, becoming a novel anti-complement drug to modulate inflammatory diseases.

The effect of discontinuation of maintenance therapy in Chinese patients with MPO-ANCA associated vasculitis who were in long-term stable remission

There is a consensus that maintenance therapy should be used to prevent relapse of myeloperoxidase-anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (MPO-AAV), but there is a debate about the optimal duration of maintenance therapy. Therefore, the purpose of this study was to determine whether discontinuation of maintenance therapy in MPO-AAV patients who were in long-term stable remission affects relapse, renal survival and patient survival. Seventy-nine patients with MPO-AAV diagnosed at Xiangya hospital from June 2010 to June 2019 who were in stable remission for at least 18 months following maintenance therapy were included. Patient records were retrospectively reviewed, and based on whether patients discontinued maintenance therapy 18 months after commencing maintenance therapy, patients were assigned into either the withdrawal group (n = 26) or maintenance group (n = 53). The endpoint was the percentage of relapse, relapse-free survival, renal survival and patient survival during follow-up. Ten relapses (38.5%) occurred in the withdrawal group (n = 26) and 8 relapses (15.1%) occurred in the maintenance group (n = 53) (p = 0.020). Compared to the withdrawal group, the maintenance group had similar relapse-free survival (log-rank test p = 0.099). But maintenance group had a better renal survival (p = 0.035), with no difference in patient survival or adverse events. This study suggests that discontinuing maintenance therapy at 18 months following induction of sustained remission leads to a significant increase in the percentage of relapse, and decreases renal survival in patients with MPO-AAV, but does not decrease relapse-free survival or patient survival.

Long-Term Renal Survival in Antineutrophil Cytoplasmic Antibody-Associated Glomerulonephritis With Complement C3 Deposition

Introduction

Recent studies have revealed the pivotal role of complement activation in the pathogenesis of antineutrophil cytoplasmic antibody–associated glomerulonephritis (ANCA-GN). This study investigated the clinicopathologic and prognostic significance of glomerular C3 deposition in the renal histopathology of patients with ANCA-GN.

Methods

We retrospectively identified 142 patients with ANCA-GN from 6 hospitals in Japan (2004–2020). C3 deposition was defined as C3 staining ≥1+ on a scale of 0 to 2+ using direct immunofluorescence (IF). The primary composite end points included a 30% reduction in estimated glomerular filtration rate (eGFR), end-stage kidney disease (ESKD), and death. We compared clinicopathologic features and long-term outcomes between patients with and without C3 deposition.

Results

C3 deposition was observed in 56 of 142 kidney biopsy samples (39.4%). Patients with C3 deposition had a lower serum C3 level (P = 0.002). During a median follow-up of 2.9 (interquartile range: 0.2–5.7) years, 69 events occurred and the cumulative event-free survival rate at 5 years was significantly lower in the C3-positive group than in the C3-negative group (log-rank: P = 0.002). In multivariable analysis, C3 deposition was significantly associated with the composite end points after adjusting for age, sex, baseline eGFR, serum C3 level, treatment, and the percentage of normal glomerulus, cellular crescents, global sclerosis, and interstitial damage (adjusted hazard ratio [HR] = 2.02, 95% confidence interval: 1.20–3.40, P = 0.008).

Conclusion

This study revealed that ANCA-GN patients with glomerular C3 deposition on IF had worse renal and overall survival rates.

A case report of PR-3-ANCA-positive glomerulonephritis with histological features of GPA associated with infectious endocarditis

RATIONALE

Several renal diseases are associated with infectious endocarditis. However, there are few reports on patients with granulomatosis with polyangiitis (GPA) associated with infectious endocarditis, and there is no consensus for appropriate treatment.

PATIENTS CONCERNS

A 35 -years-old man with congenital ventricular septal defect presented severe anemia, hematuria and proteinuria. The blood and urine examinations showed elevated white blood cells (12,900 cells/μL), C-reactive protein level (13.1 mg/dL) and proteinase 3-anti-neutrophil cytoplasmic antibody (PR3-ANCA) level (11.0 IU/mL), severe anemia (hemoglobin: 6.1 g/dL) and renal dysfunction [estimated glomerular filtration rate (eGFR): 12.7 ml/min.1.78 m2 with hematuria and proteinuria].

DIAGNOSES

The patient was diagnosed with crescentic glomerulonephritis with histological features of GPA associated with infectious endocarditis by renal biopsy and transthoracic echocardiography.

INTERVENTIONS

Antibacterial drugs (ampicillin-sulbactam) were administrated. No immunomodulating agents were used because immunosuppressive drugs may worsen infectious endocarditis. Subsequently, renal function and urinary findings improved. However, infectious endocarditis was not improved. Therefore, valve replacements and ventricular septal closure surgery were conducted.

OUTCOMES

Thereafter, his postoperative course was uneventful, renal function improved (eGFR: 64.3 ml/min.1.78 m2), and PR3-ANCA level normalized.

LESSONS

We reported a case report of PR3-ANCA positive glomerulonephritis with histological features of GPA associated with infectious endocarditis. Physicians might note this renal complication when they manage infectious endocarditis.

Vasculitis: From Target Molecules to Novel Therapeutic Approaches

Systemic vasculitis is a group of diverse diseases characterized by immune-mediated inflammation of blood vessels. Current treatments for vasculitis, such as glucocorticoids and alkylating agents, are associated with significant side effects. In addition, the management of both small and large vessel vasculitis is challenging due to a lack of robust markers of disease activity. Recent research has advanced our understanding of the pathogenesis of both small and large vessel vasculitis, and this has led to the development of novel biologic therapies capable of targeting key cytokine and cellular effectors of the inflammatory cascade. It is anticipated that these novel treatments will lead to more effective and less toxic treatment regimens for patients with systemic vasculitis.

Complement Components C3 and C4 Indicate Vasculitis Manifestations to Distinct Renal Compartments in ANCA-Associated Glomerulonephritis

Acute kidney injury (AKI) is a common and severe complication of antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) causing progressive chronic kidney disease (CKD), end-stage renal disease (ESRD) or death. Pathogenic ANCAs, in particular proteinase 3 (PR3) and myeloperoxidase (MPO), trigger a deleterious immune response resulting in pauci-immune necrotizing and crescentic glomerulonephritis (GN), a common manifestation of glomerular injury in AAV. However, there is growing evidence that activation of the complement pathway contributes to the pathogenesis and progression of AAV. We here aimed to compare glomerular and tubulointerstitial lesions in ANCA GN and extrarenal manifestation of AAV in association with levels of circulating complement components C3c and C4.

METHODS

Plasma levels of C3c and C4 in a total number of 53 kidney biopsies with ANCA GN were retrospectively included between 2015 and 2020. Glomerular and tubulointerstitial lesions were evaluated according to established scoring systems for ANCA GN and analogous to the Banff classification.

RESULTS

We here show that circulating levels of C3c and C4 in ANCA GN were comparable to the majority of other renal pathologies. Furthermore, hypocomplementemia was only detectable in a minor subset of ANCA GN and not correlated with renal or extrarenal AAV manifestations. However, low levels of circulating C3c correlated with AKI severity in ANCA GN independent of systemic disease activity or extrarenal AAV manifestation. By systematic scoring of glomerular and tubulointerstitial lesions, we provide evidence that low levels of circulating C3c and C4 correlated with vasculitis manifestations to distinct renal compartments in ANCA GN.

CONCLUSIONS

We here expand our current knowledge about distinct complement components in association with vasculitis manifestations to different renal compartments in ANCA GN. While low levels of C4 correlated with glomerulitis, our observation that low levels of circulating complement component C3c is associated with interstitial vasculitis manifestation reflected by intimal arteritis implicates that C3c contributes to tubulointerstitial injury in ANCA GN.

Hypocomplementemia is associated with more severe renal disease and worse renal outcomes in patients with ANCA-associated vasculitis: a retrospective cohort study

Background

The complement system has been recently proposed to play an important role in the pathogenesis of ANCA-associated vasculitis (AAV). This study evaluated the value of serum and kidney deposited C3 in predicting renal outcomes in AAV.

Methods

This was a retrospective study of 47 patients with AAV, who were categorized according to their serum C3 levels as hypo- or normo-complementemic and to those with positive or negative kidney biopsy immunofluorescence (IF) for C3. Baseline characteristics as well as progression to end-stage renal disease (ESRD) between the 2 groups were compared.

Results

In total, 23% (11/47) were hypo-complementemic; these patients were older (74 vs. 65 years, p = 0.013), had higher creatinine levels (4.9 vs. 2.2 mg/dL, p = 0.006), were more often hemodialysis dependent (64% vs. 19%, p = 0.009) and progressed more often to ESRD (55% vs. 11%, p = 0.01) compared to normo-complementemic patients (n = 36). On multivariate analysis, serum creatinine at diagnosis (HR = 16.8, 95%CI: 1.354–208.62, p = 0.028) and low serum C3 (HR = 2.492; 95% CI: 1.537–11.567; p = 0.044) were independent predictors for ESRD. Among 25 patients with an available kidney biopsy, 56% had C3 deposition by IF and displayed more often a mixed histological pattern (72% vs. 27%, p = 0.033), low serum C3 levels (42% vs. 18%, p < 0.001) and serious infections during follow-up (57% vs. 18%, p = 0.047) compared to those with negative (n = 11) IF staining.

Conclusion

Almost one of four patients with AAV has low C3 levels at diagnosis which is associated with more severe renal disease and worse renal outcomes (ESRD). This should be taken into account in therapeutic and monitoring strategies.

C3 glomerulonephritis associated with ANCA positivity: a case report

BACKGROUND

C3 glomerulopathy (C3G) is a recent disease classification that is characterized by the presence of glomerular deposits (composed of C3) in the absence of significant amounts of immunoglobulin and comprises dense deposit disease and C3 glomerulonephritis (C3GN). Most C3GN manifests as membranoproliferative, mesangial proliferative glomerulonephritis patterns via light microscopy. Pure membranous nephropathy (MN)-like glomerular lesions are rare manifestations of C3GN. Anti-neutrophil cytoplasmic antibodies (ANCAs) are also seldomly reported to be positive in C3GN. Herein, we report the case of a C3GN patient presenting with an MN-like glomerular pattern with ANCA positivity.

CASE PRESENTATION

A 68-year-old woman was admitted to a local hospital with elevated serum creatinine for two weeks. Laboratory tests showed a hemoglobin level of 85 g/L. Urinalysis was positive for 2 + protein and 360 RBCs/HPF. Blood biochemistry analysis revealed the following concentrations: albumin, 30.3 g/L; globulin, 46.2 g/L; blood urea nitrogen, 19.9 mmol/L; and serum creatinine, 234 µmol/L. The serum C3 level was 0.4950 g/L, and the serum C4 level was 0.1050 g/L. The direct Coombs test was positive. Serologic testing for ANCA revealed the presence of p-ANCA (1:10) by indirect immunofluorescence microscopy assay, as well as the presence of PR3 1.2 (normal range < 1) and MPO 3.5 (normal range < 1) by enzyme immunoassay. Renal biopsy sample pathology showed 2/6 cellular crescents and thickened glomerular basement membranes. Immunofluorescence testing revealed only diffuse, finely granular depositions of C3 along the glomerular capillary walls in frozen and paraffin-embedded tissue sections. Electron microscopy demonstrated the presence of subepithelial electron-dense deposits, similar to those that are observed in membranous nephropathy. Corticosteroid and cyclophosphamide were administered, with a subsequent improvement in renal function.

CONCLUSIONS

We present the rare case of a patient with MN-like C3GN with ANCA positivity. C3GN with ANCA positivity may be represented by more crescents, severe renal dysfunction and more extrarenal manifestations. More cases are needed to elucidate the clinicopathologic features and optimal treatments of these patients.

Differences between myeloperoxidase-antineutrophil cytoplasmic autoantibody (ANCA) and proteinase 3-ANCA associated vasculitis: A retrospective study from a single center in China

In antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides (AAV), the two major target antigens of ANCA are proteinase 3 (PR3) and myeloperoxidase (MPO). Evidence is accumulating that there are distinct differences between patients with PR3-AAV and those with MPO-AAV. In the present study, the clinicopathological features and prognosis of patients with PR3-AAV and MPO-AAV from a single center in China were retrospectively analyzed. A total of 212 Chinese patients with AAV were recruited in the present study; 189/212 (89.15%) patients were classified as having MPO-AAV and 23/212 (10.85%) patients as having PR3-AAV. Compared with those in the PR3-AAV group, patients in the MPO-AAV group were older and less frequently had ear, nose and throat or ophthalmic involvement. MPO-AAV patients had higher levels of serum creatinine and proteinuria at baseline. No significant difference was observed with regard to the pathological changes of the glomeruli and tubulointerstitium between the two groups. The probability of developing end-stage renal disease was significantly higher in patients with MPO-AAV compared with that in patients with PR3-AAV. There was no significant difference in the one-year patient survival rate between the two groups. However, differences in certain clinical characteristics and outcomes were observed between MPO-AAV and PR3-AAV patients. A large national investigation of AAV is required to confirm the concept that PR3-AAV and MPO-AAV are distinct disease entities.

Glomerular Immune Deposition in MPO-ANCA Associated Glomerulonephritis Is Associated With Poor Renal Survival

Background

Rapidly progressive glomerulonephritis caused by antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is typically characterized as pauci-immune glomerulonephritis. However, immune complex (IC) deposition in the glomerulus has been reported in a growing number of studies. Here, we assess the presence of glomerular immune deposits alongside renal outcome in myeloperoxidase (MPO)-ANCA associated glomerulonephritis (MPO-ANCA GN).

Methods

Clinical and histopathologic characteristics of 97 patients with MPO-ANCA GN classified by renal biopsy from January 2008 to December 2019 were extracted retrospectively from electronic medical records. The extent of immune deposits in the kidney (C3, C4, C1q, IgA, IgG, IgM) at diagnosis were analyzed by immunofluorescence (IF). Patients were followed up for a median period of 15 months. The response to treatment and outcomes of renal and histological lesion changes were also assessed.

Results

In our study, 41% (40/97) of patients showed positive IF (≥2+) for at least one of the six immunoglobulin or complement components tested. Patients with IC deposits showed higher levels of serum creatinine (p=0.025), lower platelet counts (p=0.009), lower serum complement C3 (sC3) (≤790 ml/L) (p=0.013) and serum IgG (p=0.018) than patients with pauci-immune (PI) deposition at diagnosis. End-stage renal disease was negatively associated with eGFR (HR 0.885, 95% CI 0.837 to 0.935, p<0.0001), platelet count (HR 0.996, 95% CI 0.992 to 1.000, p=0.046) and serum globulin (HR 0.905, 95% CI 0.854 to 0.959, p=0.001). Patients with lower sC3 levels showed a worse renal outcome than the patients with normal sC3 at diagnosis (p=0.003). Analysis of the components of the renal deposits found that patients with IgG deposits exhibited a poorer renal outcome compared to patients that were IgG negative (p=0.028). Moreover, Bowman’s capsule rupture occurred less frequently in patients with IgM deposition compared with IgM negative counterparts (p=0.028). Vascular lesions and granuloma-like lesions had been seen more frequently in cases with IgA deposition than those without IgA deposition (p=0.03 and 0.015, respectively).

Conclusion

In conclusion, patients with immune complex deposits in the kidney showed less platelet count, lower sC3 and sIgG levels, and higher serum creatinine levels. Patients with low sC3 at initial and with continued low sC3 during the treatment displayed a trend toward poorer kidney survival. Moreover, the IC group showed a worse renal outcome than the PI group, further enforcing the present strategy of introducing complement targeted therapies in AAV.

Clinical and pathological analysis of 101 cases of ANCA-associated vasculitic kidney injury

OBJECTIVE

To analyze the clinical and pathological features of patients with anti-neutrophilic cytoplasmic antibody (ANCA)-associated vasculitic (AASV)-kidney injury (AASVKI).

METHODS

From January 2015 to December 2018, a total of 101 AASVKI patients treated in the First Hospital of Jilin University were divided into 2 groups (the pANCA-positive group and the cANCA-positive group) for comparison; 63 patients were performed renal biopsy and divided into 3 groups according to pathological results [the non-crescent nephritis group (non-C), the crescent nephritis group (C), and the sclerotic nephritis group (S)] for comparison.

RESULTS

Compared with the Group pANCA, Group cANCA exhibited higher incidence of eye involvement (P = 0.039) and skin mucosa destruction (P = 0.045), higher serum creatinine (Scr) (P < 0.001), higher 24-h urine protein quantification (P = 0.045), but lower hemoglobin (Hb) (P < 0.001). Compared with Group non-C, Group C had higher Scr (P < 0.001) and urinary red blood cells (P = 0.010), lower estimated glomerular filtration rate (eGFR) (P = 0.003), hemoglobin (HD)-dependence (P = 0.042), and higher mortality rate within 1 year (P = 0.005); compared with Group S, Group C had faster onset of erythrocyte sedimentation rate (ESR) (P = 0.031), higher urinary red blood cells (P = 0.029), and lower incidence of HD-dependence (P = 0.038).

CONCLUSIONS

AASVKI patients with positive cANCA have poor renal function, among whom the patients with crescent type have poorer renal function than those with non-crescent type, have higher urinary red blood cells while lower HD-dependence than those with sclerotic type.

Pathogenesis and pathology of anti-neutrophil cytoplasmic antibody（ANCA）-associated vasculitis

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AAV is characterized by necrotizing small vessel vasculitis with positive serum ANCA.

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MPO/PR3-ANCA and neutrophils play central roles in AAV pathogenicity.

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Dysregulated complement system primes neutrophils.

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MPO-ANCA directly activates neutrophils to induce NETosis followed by releasing NETs.

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B cells, T cells, and dendritic cells also contribute to the pathogenicity of AAV.

Shiga Toxin 2a Binds to Complement Components C3b and C5 and Upregulates Their Gene Expression in Human Cell Lines

Enterohemorrhagic Escherichia coli (EHEC) infections can cause EHEC-associated hemolytic uremic syndrome (eHUS) via its main virulent factor, Shiga toxins (Stxs). Complement has been reported to be involved in the progression of eHUS. The aim of this study was to investigate the interactions of the most effective subtype of the toxin, Stx2a, with pivotal complement proteins C3b and C5. The study further examined the effect of Stx2a stimulation on the transcription and synthesis of these complement proteins in human target cell lines. Binding of Stx2a to C3b and C5 was evaluated by ELISA. Kidney and gut cell lines (HK-2 and HCT-8) were stimulated with varied concentrations of Stx2a. Subsequent evaluation of complement gene transcription was studied by real-time PCR (qPCR), and ELISAs and Western blots were performed to examine protein synthesis of C3 and C5 in supernatants and lysates of stimulated HK-2 cells. Stx2a showed a specific binding to C3b and C5. Gene transcription of C3 and C5 was upregulated with increasing concentrations of Stx2a in both cell lines, but protein synthesis was not. This study demonstrates the binding of Stx2a to complement proteins C3b and C5, which could potentially be involved in regulating complement during eHUS infection, supporting further investigations into elucidating the role of complement in eHUS pathogenesis.

The rise of complement in ANCA-associated vasculitis: from marginal player to target of modern therapy

The complement system plays a central role in autoimmune diseases, including anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Although complement deposition is scarce in AAV pathological samples, complement activation is required for the development of necrotizing crescentic glomerulonephritis (NCGN) in mouse models of AAV and occurs via the alternative pathway. The anaphylatoxin C5a, produced by the final complement pathway, is determinant to drive the disease in animal models. C5a primes human neutrophils and enhances their activation induced by ANCA; activated neutrophils, in turn, release factors that lead to C5a generation, establishing a self-amplifying loop. C5a is also significantly increased in the serum of AAV patients with active disease compared to those in remission or healthy controls. Inhibition of the C5a receptor with avacopan is an emerging therapy that will probably allow AAV treatment with glucocorticoid-free regimens.

Clinical characteristics and prognostic risk factors of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV)

OBJECTIVE

The complement alternative pathway is involved in the development of AVV. Several studies showed that AVV patients with low serum complement C3 (sC3) levels tend to have a poor prognosis. The aim of this study was to determine whether low sC3 measured at AAV onset is a risk factor for survival prognosis in patients with AVV, and further identified other potential risk factors for predicting patient survival prognosis.

METHODS

A retrospective analysis of 52 newly onset AAV patients was performed. The clinical parameters of the AAV patients were collected. The laboratory parameters before immunosuppressive treatment were evaluated. According to the level of sC3, the patients were divided into low sC3 group (n = 19) and normal sC3 group (n = 33). Disease outcome measures included end-stage renal disease (ESRD) or death. The clinical parameters and survival rate between the two groups were compared. Spearson correlation analysis was used to analyze the correlation between sC3 and other laboratory parameters.

RESULTS

Significant differences were found regarding Birmingham Vasculitis Activity Score (BVAS), sC3, sC4, lactate dehydrogenase, blood urea nitrogen, procalcitonin (PCT), and estimated glomerular filtration rate (eGFR) between the two groups (p = 0.006, 0.000, 0.001, 0.049, 0.019, 0.000 and 0.045, respectively). The survival rate of the low sC3 group was significantly lower than that of the normal sC3 group (Log Rank Chi-square = 4.416, P = 0.036). Low sC3 was significantly associated with lower sC4 (r = 0.570, P = 0.000), lower serum albumin (r = 0.311, P = 0.025), lower eGFR (r = 0.289, P = 0.037), higher PCT (r = -0.566, P = 0.000), and higher lactate dehydrogenase (r = -0.323, P = 0.019).

CONCLUSION

This retrospective study demonstrates that AAV patients with low sC3 level at diagnosis tend to have lower baseline eGFR and poorer survival prognosis than those of the normal sC3 level. Furthermore, the high procalcitonin (PCT), low serum albumin and high lactate dehydrogenase in AVV patients may be predictors of poor prognosis.

Systemic complement activation in anti-neutrophil cytoplasmic antibody-associated vasculitis and necrotizing glomerulonephritis

AIM

Due to the accumulating evidence of complement activation in anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV), we decided to investigate the possibility of systemic complement activation in patients with Necrotizing Glomerulonephritis secondary to AAV.

METHODS

Clinical, laboratory and histological findings, and serum levels of complement components, C3a, C5a and Bb fragment of Factor B and C4d, were estimated in patients with AAV and glomerulonephritis, at time of diagnosis, before any treatment had been applied. All patients were treated with the same immunosuppressive protocol and followed up for total 24 months. Twenty age and sex matched healthy individuals served as controls.

RESULTS

Serum levels of all complement components were significantly increased in patients, compared to controls; C5a: 19.9(0.02-48) vs 9.06(2.1-16.3)pg/mL, P = .002, Bb: 7.3(0.02-31.4) vs 0.2(0.02-1.6)pg/mL, P < .0001, C3a: 4.7(0.4-7.2) vs 2.4(1.09-5)pg/mL, P = .05 and C4d: 11.6(0.07-70) vs 0.7(0.07-8.2)pg/mL, P = .001, respectively. There was strong correlation between serum Bb levels and eGFR and FFS2009 score at time of diagnosis (r = -.41, P = .002 and r = .41, P = .003 respectively). Also, serum Bb levels were increased in patients with severe interstitial infiltration (P = .04) and focal necrosis (P = .01) on renal biopsy. Serum Bb levels could also predict renal function outcome during the acute phase of disease, but not at the end of follow up.

CONCLUSION

We provided strong evidence of systemic activation of complement alternative pathway in the development and progression of AAV and glomerulonephritis. Serum Bb seem to play a critical role in the induction, also predicting disease activity and outcome, yet activation of classical pathway cannot be excluded.

Complement profile in microscopic polyangiitis and granulomatosis with polyangiitis: analysis using sera from a nationwide prospective cohort study

OBJECTIVE

The complement cascade, especially the alternative pathway of complement, has been shown in basic research to be associated with anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV). We aimed to elucidate relationships between serum complement components and clinical characteristics in AAV.

METHOD

In a nationwide prospective cohort study (RemIT-JAV-RPGN), we measured the serum levels of C1q, C2, C3, C3b/iC3b, C4, C4b, C5, C5a, C9, factor B, factor D, factor H, factor I, mannose-binding lectin, and properdin in 52 patients with microscopic polyangiitis (MPA) and 39 patients with granulomatosis with polyangiitis (GPA).

RESULTS

The properdin level of MPA and GPA was significantly lower than that of healthy donors. The properdin level was negatively correlated with the Birmingham Vasculitis Activity Score (BVAS) (ρ = -0.2148, p = 0.0409). The factor D level at 6 months was significantly positively correlated with the Vasculitis Damage Index (VDI) at 6, 12, and 24 months (ρ = 0.4207, 0.4132, and 0.3115, respectively). Patients with a higher ratio of C5a to C5 had higher neutrophil percentage and serum immunoglobulin G levels, and significantly lower creatinine levels. Cluster analysis divided the MPA and GPA patients into three subgroups. A principal component (PC) analysis aggregated 15 types of complements into alternative pathway-related PC 1 and complement classical pathway and common pathway-related PC 2.

CONCLUSIONS

The serum levels of properdin and factor D were correlated with the BVAS and the VDI in MPA and GPA, respectively. Our analyses suggested the pathological heterogeneity of MPA and GPA from the aspect of complement components.

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 Activation in Progression of Chronic Kidney Disease

Chronic kidney disease (CKD) is a public health problem worldwide, with increasing incidence and prevalence. The mechanisms underlying the progression to end-stage renal disease (ESRD) is not fully understood. The complement system was traditionally regarded as an important part of innate immunity required for host protection against infection and for maintaining host hemostasis. However, compelling evidence from both clinical and experimental studies has strongly incriminated complement activation as a pivotal pathogenic mediator of the development of multiple renal diseases and progressive replacement of functioning nephrons by fibrosis. Both anaphylatoxins, i.e., C3a and C5a, and membrane attack complex (MAC) contribute to the damage that occurs during chronic renal progression through various mechanisms including direct proinflammatory and fibrogenic activity, chemotactic effect, activation of the renal renin-angiotensin system, and enhancement of T-cell immunity. Evolving understanding of the mechanisms of complement-mediated renal injury has led to the emergence of complement-targeting therapeutics. A variety of specific antibodies and inhibitors targeting complement components have shown efficacy in reducing disease in animal models. Moreover, building on these advances, targeting complement has gained encouraging success in treating patients with renal diseases such as atypical hemolytic uremic syndrome (aHUS). Nevertheless, it still requires a great deal of effort to develop inhibitors that can be applied to treat more patients effectively in routine clinical practice.

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.

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.

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.

Advances in Therapies and Imaging for Systemic Vasculitis

Vasculitis is a systemic disease characterized by immune-mediated injury of blood vessels. Current treatments for vasculitis, such as glucocorticoids and alkylating agents, are associated with significant side effects. Furthermore, the management of both small and large vessel vasculitis is challenging because of a lack of robust markers of disease activity. Recent research has advanced our understanding of the pathogenesis of both small and large vessel vasculitis, and this has led to the development of novel biologic therapies capable of targeting key cytokine and cellular effectors of the inflammatory cascade. In parallel, a diverse range of imaging modalities with the potential to monitor vessel inflammation are emerging. Continued expansion of combined structural and molecular imaging using positron emission tomography with computed tomography or magnetic resonance imaging may soon provide reliable longitudinal tracking of vascular inflammation. In addition, the emergence of radiotracers able to assess macrophage activation and immune checkpoint activity represents an exciting new frontier in imaging vascular inflammation. In the near future, these advances will allow more precise imaging of disease activity enabling clinicians to offer more targeted and individualized patient management.

A rare case of Alport syndrome, atypical hemolytic uremic syndrome and Pauci-immune crescentic glomerulonephritis

Background

Renal thrombotic microangiopathy (TMA) is occasionally seen in biopsies with pauci-immune necrotizing crescentic glomerulonephritis (PCGN). Recent study indicated that the complement activation is more prominent in the ANCA-negative glomerulonephritis.

Case presentation

We report a case of concurrent TMA and PCGN without ANCA positivity. Interestingly, our patient also had biopsy features supportive of Alport syndrome (AS). Genetic studies identified variants and polymorphisms in alternative complement pathway genes that confer substantial risk of developing atypical hemolytic uremic syndrome (aHUS).

Conclusions

Abnormal activation in complement pathway may represent a common pathogenic link between these three distinct entities.

Complement your knowledge with a rare cause of pauci-immune glomerulonephritis

RPGN can be subdivided into three categories on an immunopathologic basis: pauci-immune glomerulonephritis (PIGN), anti-glomerular basement membrane glomerulonephritis (anti-GBM disease), or immune complex-mediated glomerulonephritis (GN). PIGN is the most common cause of RPGN (80% of cases). The most common etiology of PIGN is anti-neutrophil cytoplasmic antibody (ANCA)-associated GN, which accounts for up to 90% of PIGN. PIGN is unique in that few to no immunoglobulin deposits are seen on glomerular immunofluorescence (IF) and electron microscopy (EM), but it is important to remember that dysregulation of the alternative pathway may result in the deposition of complements leading to inflammatory injury even in PIGN. Membranoproliferative glomerulonephritis (MPGN) is a rare, primary glomerular disorder. Both ANCA-associated GN and complement-mediated MPGN will lack immunoglobulin staining on immunofluorescence (IF) and thus present as PIGN on pathologic examination. This may lead to occurrences where these entities mimic one another, therefore necessitating heightened suspicion and close pathologic examination of a renal biopsy with electron microscopy to differentiate the diagnoses. This case highlights a rare case of C3 GN mimicking ANCA-associated GN.

Developments in anti-complement therapy; from disease to clinical trial

The complement system is well known for its role in innate immunity and in maintenance of tissue homeostasis, providing a first line of defence against infection and playing a key role in flagging apoptotic cells and debris for disposal. Unfortunately complement also contributes to pathogenesis of a number of diseases; in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The role of complement in pathogenesis of an expanding number of diseases has driven industry and academia alike to develop an impressive arsenal of anti-complement drugs which target different proteins and functions of the complement cascade. Evidence from genetic and biochemical analyses, combined with improved identification of complement biomarkers and supportive data from sophisticated animal models of disease, has driven a drug development landscape in which the indications selected for clinical trial cluster in three 'target' tissues: the kidney, eye and vasculature. While the disease triggers may differ, complement activation and amplification is a common feature in many diseases which affect these three tissues. An abundance of drugs are in clinical development, some show favourable progression whereas others experience significant challenges. However, these hurdles in themselves drive an ever-evolving portfolio of 'next-generation' drugs with improved pharmacokinetic and pharmacodynamics properties. In this review we discuss the indications which are in the drug development 'spotlight' and review the relevant indication validation criteria. We present current progress in clinical trials, highlighting successes and difficulties, and look forward to approval of a wide selection of drugs for use in man which give clinicians choice in mechanistic target, modality and route of delivery.

Antineutrophil cytoplasmic antibodies-associated glomerulonephritis: From bench to bedside

Antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) is a group of autoimmune disorders that predominantly affects small vessels. The onset of the disease is closely associated with ANCA. Renal involvement, also known as ANCA-associated glomerulonephritis (AGN), is one of the most common manifestations of AAV. In this mini-review, we described the clinical and pathological features of AGN. We then focused on recent studies on the mechanism of acute kidney lesions, including fibrinoid necrosis and crescent formation. Following the basic aspects of kidney injury in AGN, we demonstrated the clinical importance of kidney injury in determining the outcome of patients with AGN. The prognostic value of the 2010 Histopathological Classification of AGN and validating studies were summarized. Finally, treatment and novel therapeutic strategies were introduced addressing the importance of optimizing management of this patient population.

Secondary thrombotic microangiopathy and eculizumab: A reasonable therapeutic option

Understanding the role of the complement system in the pathogenesis of atypical haemolytic uraemic syndrome and other thrombotic microangiopathies (TMA) has led to the use of anti-complement therapy with eculizumab in these diseases, in addition to its original use in patients with paroxysmal nocturnal haemoglobinuria andatypical haemolytic uraemic syndrome. Scientific evidence shows that both primary and secondary TMAs with underlying complement activation are closely related. For this reasons, control over the complement system is a therapeutic target. There are 2scenarios in which eculizumab is used in patients with TMA: primary or secondary TMA that is difficult to differentiate (including incomplete clinical presentations) and complement-mediated damage in various processes in which eculizumab proves to be efficacious. This review summarises the evidence on the role of the complement activation in the pathophysiology of secondary TMAs and the efficacy of anti-complement therapy in TMAs secondary to pregnancy, drugs, transplant, humoral rejection, systemic diseases and glomerulonephritis. Although experience is scarce, a good response to eculizumab has been reported in patients with severe secondary TMAs refractory to conventional treatment. Thus, the role of the anti-complement therapy as a new treatment option in these patients should be investigated.

The C3aR promotes macrophage infiltration and regulates ANCA production but does not affect glomerular injury in experimental anti-myeloperoxidase glomerulonephritis

The anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitides are autoimmune diseases associated with significant morbidity and mortality. They often affect the kidney causing rapidly progressive glomerulonephritis. While signalling by complement anaphylatoxin C5a though the C5a receptor is important in this disease, the role of the anaphylatoxin C3a signalling via the C3a receptor (C3aR) is not known. Using two different murine models of anti-myeloperoxidase (MPO) glomerulonephritis, one mediated by passive transfer of anti-MPO antibodies, the other by cell-mediated immunity, we found that the C3aR did not alter histological disease severity. However, it promoted macrophage recruitment to the inflamed glomerulus and inhibited the generation of MPO-ANCA whilst not influencing T cell autoimmunity. Thus, whilst the C3aR modulates some elements of disease pathogenesis, overall it is not critical in effector responses and glomerular injury caused by autoimmunity to MPO.