Complement alternative pathway in ANCA-associated vasculitis: Two decades from bench to bedside

Short-term effectiveness and safety of rituximab versus cyclophosphamide for life-threatening ANCA-associated vasculitis: a propensity score analysis of the real-world nationwide database

OBJECTIVES

Life-threatening antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) with rapidly progressive glomerulonephritis (RPGN) and/or alveolar haemorrhage (AH) has a poor prognosis. Rituximab (RTX) is as effective as cyclophosphamide (CY) in remission induction therapy; however, the effectiveness and safety of RTX have not been established in life-threatening AAV. This study aimed to investigate the short-term effectiveness and safety of RTX in life-threatening AAV with RPGN and/or AH.

METHODS

Between April 2018 and March 2020, cases treated with systemic glucocorticoids and RTX or intravenous CY (IVCY) was extracted from a Japanese nationwide inpatient database. Effectiveness was evaluated by in-hospital mortality and severe renal dysfunction requiring haemodialysis (HD) at discharge. Safety was evaluated by the in-hospital incidence of infections. The propensity score (PS) for RTX was estimated. Multivariable Cox and logistic regression with adjustment for PS were conducted to estimate the association of RTX with outcomes.

RESULTS

From 16 001 612 hospitalised records, 687 life-threatening AAV cases were extracted. No significant difference in in-hospital mortality (adjusted HR 1.06; 95% CI 0.62 to 1.80) was found between the groups. Although the RTX group had a lower risk of fungal infections (adjusted OR (aOR) 0.45; 95% CI 0.23 to 0.84) and pneumocystis pneumonia (aOR 0.58; 95% CI 0.32 to 1.00), they might have an increased risk of severe renal dysfunction requiring HD at discharge (aOR 2.58; 95% CI 1.02 to 6.91).

CONCLUSIONS

In life-threatening AAV, RTX has similar short-term effectiveness on mortality to IVCY. Although RTX might have a lower risk of fungal infections and pneumocystis pneumonia, the short-term renal prognosis might be inferior to IVCY.

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.

Renal involvement in eosinophilic granulomatosis with polyangiitis

Eosinophilic granulomatosis with polyangiitis (EGPA) is a necrotizing vasculitis, which typically affects small-to medium-sized blood vessels. It is characterized by the presence of tissue infiltrates rich in eosinophils, along with the formation of granulomatous lesions. About 40% of cases have positive anti-neutrophil cytoplasm antibodies (ANCA), with predominant perinuclear staining, and anti-myeloperoxidase (anti-MPO) specificity in about 65% of cases. Typical manifestations of EGPA include the late onset of asthma, nasal and sinus-related symptoms, peripheral neuropathy, and significant eosinophilia observed in the peripheral blood. In contrast to granulomatosis with polyangiitis and microscopic polyangiitis, renal involvement in EGPA is less frequent (about 25%) and poorly studied. Necrotizing pauci-immune crescentic glomerulonephritis is the most common renal presentation in patients with ANCA-positive EGPA. Although rarely, other forms of renal involvement may also be observed, such as eosinophilic interstitial nephritis, mesangial glomerulonephritis, membranous nephropathy, or focal sclerosis. A standardized treatment for EGPA with renal involvement has not been defined, however the survival and the renal outcomes are usually better than in the other ANCA-associated vasculitides. Nonetheless, kidney disease is an adverse prognostic factor for EGPA patients. Larger studies are required to better describe the renal involvement, in particular for patterns different from crescentic glomerulonephritis, and to favor the development of a consensual therapeutic approach. In this article, in addition to personal data, we will review recent findings on patient clinical phenotypes based on ANCA, genetics and the impact of biological drugs on disease management.

[Complement in vasculitis associated with anti-neutrophil cytoplasm antibodies with renal involvement: pathogenic, prognostic and therapeutic implications]

Antineutrophil cytoplasmic antibody-associated vasculitides are primary vasculitides that affect small vessels in various organs, including the kidney. Renal involvement is characterized by the presence of glomerulonephritis with crescents and necrosis in light microscopy and a pauci-immune pattern in immunofluorescence. The participation of complement in the pathogenesis of these entities has been valued in recent years, initially in animal models and later in studies in humans, by demonstrating the presence of fragments of the alternative complement pathway, in plasma and urine, together with complement deposits in glomeruli and small vessels of patients affected by antineutrophil cytoplasmic antibody vasculitis. The presence of complement in these entities confers a worse general and renal prognosis.

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.

Targeting immune checkpoints in anti-neutrophil cytoplasmic antibodies associated vasculitis: the potential therapeutic targets in the future

Anti-neutrophil cytoplasmic autoantibodies (ANCA) associated vasculitis (AAV) is a necrotizing vasculitis mainly involving small blood vessels. It is demonstrated that T cells are important in the pathogenesis of AAV, including regulatory T cells (Treg) and helper T cells (Th), especially Th2, Th17, and follicular Th cells (Tfh). In addition, the exhaustion of T cells predicted the favorable prognosis of AAV. The immune checkpoints (ICs) consist of a group of co-stimulatory and co-inhibitory molecules expressed on the surface of T cells, which maintains a balance between the activation and exhaustion of T cells. CD28, inducible T-cell co-stimulator (ICOS), OX40, CD40L, glucocorticoid induced tumor necrosis factor receptor (GITR), and CD137 are the common co-stimulatory molecules, while the programmed cell death 1 (PD-1), cytotoxic T lymphocyte-associated molecule 4 (CTLA-4), T cell immunoglobulin (Ig) and mucin domain-containing protein 3 (TIM-3), B and T lymphocyte attenuator (BTLA), V-domain Ig suppressor of T cell activation (VISTA), T-cell Ig and ITIM domain (TIGIT), CD200, and lymphocyte activation gene 3 (LAG-3) belong to co-inhibitory molecules. If this balance was disrupted and the activation of T cells was increased, autoimmune diseases (AIDs) might be induced. Even in the treatment of malignant tumors, activation of T cells by immune checkpoint inhibitors (ICIs) may result in AIDs known as rheumatic immune-related adverse events (Rh-irAEs), suggesting the importance of ICs in AIDs. In this review, we summarized the features of AAV induced by immunotherapy using ICIs in patients with malignant tumors, and then reviewed the biological characteristics of different ICs. Our aim was to explore potential targets in ICs for future treatment of AAV.

Low Concentrations of C5a Complement Receptor Antibodies Are Linked to Disease Activity and Relapse in Antineutrophil Cytoplasmic Autoantibody-Associated Vasculitis

OBJECTIVE

To examine concentrations of circulating antibodies targeting C3a and C5a complement receptors in antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) and analyze their association with disease activity.

METHODS

Concentrations of antibodies against C3a and C5a complement receptors (anti-C3aR and anti-C5aR) and plasma complement fragments C3a and C5a were determined in patients with AAV (n = 110; granulomatosis with polyangiitis [GPA; n = 82] or microscopic polyangiitis [MPA; n = 28]), systemic lupus erythematosus (SLE) patients as disease controls (n = 36), and healthy donors (n = 220). C3aR and C5aR expression by circulating neutrophils, monocytes, and T cells was analyzed using flow cytometry. Clinical data were assessed at time of serum sampling and during follow-up for 60 months.

RESULTS

In AAV, anti-C3aR and anti-C5aR antibodies were decreased (P = 0.0026 and P ≤ 0.0001, respectively). In remission, anti-C3aR antibody concentrations rose to values comparable to healthy donors, whereas anti-C5aR antibody concentrations did not. In GPA, anti-C5a and anti-C5aR antibody concentrations inversely correlated with each other (r = -0.6831, P = 0.0127). In newly diagnosed GPA, decreased concentrations of anti-C5aR antibodies but not anti-C3aR antibodies were associated with disease activity (P = 0.0009). Moreover, low anti-C5aR antibodies were associated with relapse in GPA (hazard ratio 3.54, P = 0.0009) and MPA (hazard ratio 4.41, P = 0.0041). The frequency of C5aR-expressing cells within T cell populations was increased in GPA (P = 0.0021 for CD4+ T cells; P = 0.0118 for CD8+ T cells), but not in MPA.

CONCLUSION

Low concentrations of anti-C5aR antibodies reflect disease activity and are associated with an increased risk for relapse in AAV.

Neutrophils in ANCA-associated vasculitis: Mechanisms and implications for management

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of systemic autoimmune diseases, which is typified by inflammatory necrosis predominantly affecting the small vessels and often accompanied by positive ANCA. Clinically, AAV primarily includes microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), and eosinophilic granulomatosis with polyangiitis (EGPA). It has been found that in AAV pathogenesis, both innate and adaptive immunity are related to neutrophil function mutually. Many proteins, such as myeloperoxidase (MPO) and proteinase 3 (PR3), in neutrophil cytoplasm lead to the production of proteins such as MPO-ANCA and PR3-ANCA by activating adaptive immunity. In addition, through the process of neutrophil extracellular trap (NET) formation, activation of an alternative complement pathway and the respiratory burst can stimulate the neutrophils close to vascular endothelial cells and will participate the vessel inflammation. This review aims to reveal the potential mechanisms regulating the association between the neutrophils and various types of AAVs and to emphasize the results of recent findings on these interactions. Moreover, multiple underlying signaling pathways involved in the regulation of neutrophils during AAV processes have also been discussed. The ultimate goal of this review is to identify novel biomarkers and therapeutic targets for AAV management in the future.

ANCA Associated Vasculitis (AAV): A Review for Internists

Anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV) compromise a rare group of necrotizing small to medium vessel vasculitides that constitute three distinct disorders: granulomatosis with polyangiitis (GPA) (formerly known as Wegener's granulomatosis), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA) (formerly known as Churg-Strauss syndrome).AAV is characterized by the usual presence of circulating autoantibodies to the neutrophil proteins leukocyte proteinase 3 (PR3-ANCA) or myeloperoxidase (MPO-ANCA). These antibodies can activate neutrophils and the complement system resulting in vessel wall inflammation and damage.The clinical presentation of AAV varies from non-severe (non-life threatening) to severe often with potentially life-threatening multi-organ involvement. Early recognition and diagnosis are crucial. In the past two decades, advances in understanding the pathophysiology of AAV have led to development of new treatments and resulted in significant improvement in general outcomes and survival rates.This narrative review will focus on GPA and MPA. We will highlight clinical manifestations, diagnosis, disease monitoring, and treatment strategies in patients with AAV.

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.

Pathogenic T-Cell Responses in Immune-Mediated Glomerulonephritis

Glomerulonephritis (GN) comprises a group of immune-mediated kidney diseases affecting glomeruli and the tubulointerstitium. Glomerular crescent formation is a histopathological characteristic of severe forms of GN, also referred to as crescentic GN (cGN). Based on histological findings, cGN includes anti-neutrophil cytoplasmic antibody (ANCA)-associated GN, a severe form of ANCA-associated vasculitis, lupus nephritis associated with systemic lupus erythematosus, Goodpasture’s disease, and IgA nephropathy. The immunopathogenesis of cGN is associated with activation of CD4+ and CD8+ T cells, which particularly accumulate in the periglomerular and tubulointerstitial space but also infiltrate glomeruli. Clinical observations and functional studies in pre-clinical animal models provide evidence for a pathogenic role of Th1 and Th17 cell-mediated immune responses in cGN. Emerging evidence further argues that CD8+ T cells have a role in disease pathology and the mechanisms of activation and function of recently identified tissue-resident CD4+ and CD8+ T cells in cGN are currently under investigation. This review summarizes the mechanisms of pathogenic T-cell responses leading to glomerular damage and renal inflammation in cGN. Advanced knowledge of the underlying immune mechanisms involved with cGN will enable the identification of novel therapeutic targets for the replacement or reduction in standard immunosuppressive therapy or the treatment of refractory disease.

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

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

The rational use of complement inhibitors in kidney diseases

The development of complement inhibitors represented one of the major breakthroughs in clinical nephrology in the last decade. Complement inhibition has dramatically transformed the outcome of one of the most severe kidney diseases, the atypical hemolytic uremic syndrome (aHUS), a prototypic complement-mediated disorder. The availability of complement inhibitors has also opened new promising perspectives for the management of several other kidney diseases in which complement activation is involved to a variable extent. With the rapidly growing number of complement inhibitors tested in a rapidly increasing number of indications, a rational use of this innovative and expensive new therapeutic class has become crucial. The present review aims to summarize what we know, and what we still ignore, regarding complement activation and therapeutic inhibition in kidney diseases. It also provides some clues and elements of thoughts for a rational approach of complement modulation in kidney diseases.

The management of anti-neutrophil cytoplasmic antibody-associated vasculitis: what has changed in the last 10 years?

The management of anti-neutrophil cytoplasmic antibody-associated vasculitis has substantially improved in the last decade. For the induction of remission, rituximab is increasingly used in place of cyclophosphamide, particularly for patients with proteinase 3 (PR3)-associated vasculitis or relapsing disease, and those wishing to preserve their fertility. A lower dose regimen of glucocorticoids, with a more rapidly tapering schedule, is preferable and is as effective and safer than the standard-dose regimen. Avacopan, the complement C5a receptor inhibitor, is effective in the treatment of associated vasculitis and may replace glucocorticoids in the future. Plasma exchange provides no additional benefit for patients with severe anti-neutrophil cytoplasmic antibody-associated vasculitis, although it is still used in selected patients on a case-by-case basis. Rituximab is preferred for the maintenance of remission, repeated at fixed time intervals. The duration for which immunosuppressive therapy should be given is uncertain, but is generally longer for patients with PR3 disease or persistent anti-neutrophil cytoplasmic antibody positivity. The anti-interleukin 5 monoclonal antibody, mepolizumab, is effective for the treatment of non-severe eosinophilic granulomatosis with polyangiitis. Several other targeted therapies are in the pipeline and further progress is expected in the coming years.

Identification of differentially expressed genes and pathways in kidney of ANCA-associated vasculitis by integrated bioinformatics analysis

The antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systematic of relatively rare autoimmune diseases with unknown cause. Kidney involvement is one of the most common clinical manifestations, and the degree of renal damage is closely associated with the development and prognosis of AAV. In this study, we utilized the Robust Rank Aggreg (RRA) method in R to integrate GSE104948, GSE104954, GSE108109, GSE108112, and GSE108113 profile datasets loaded from Gene Expression Omnibus (GEO) database and identified a set of differentially expressed genes (DEGs) in kidney between AAV patients and living donors. Then, the results of gene ontology (GO) functional annotation showed that immunity and metabolism involved process of AAV both in glomerulus and tubulointerstitial. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that following pathways, such as complement and coagulation cascades pathway; Staphylococcus aureus infection; disease-COVID-19; and systemic lupus erythematosus (SLE) pathway play a crucial role in AAV. Next, the results analyzed by protein–protein interaction (PPI) network and Cytoscape software exhibited the hub genes ALB, TYROBP, and CYBB existed in both glomerular and tubulointerstitial compartments datasets. Finally, KEGG analysis using genes of two most important modules also further validated complement and coagulation cascades pathway and S. aureus infection existed both in glomerulus and tubulointerstitial compartments datasets. In conclusion, this study identified key genes and pathways involved in kidney of AAV, which was benefit to further uncover the mechanisms underlying the development and progress of AAV, biomarkers, and potential therapeutic targets as well.

Complement activation prior to symptom onset in myeloperoxidase ANCA-associated vasculitis but not proteinase 3 ANCA associated vasculitis - A Swedish biobank study

OBJECTIVE

Increased soluble levels of complement effectors have been demonstrated in active anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), but the timing of complement activation in the autoimmune inflammation remains elusive. This study investigated whether the complement system is activated before onset of symptoms in AAV.

METHOD

The Swedish National Patient Register and Cause of Death register were linked to registers of five biobanks to identify individuals sampled before AAV symptom onset. Diagnosis of AAV and time-point for symptom onset were confirmed by reviewing medical records. We identified 64 presymptomatic individuals with serum samples > 1 month < 10 years from AAV symptom onset and 122 matched controls. Complement factors (C2, C5) and activation markers (C5a, C4b) were measured using Luminex technology.

RESULTS

Presymptomatic individuals had higher levels of C5 up to 6.5 years before symptom onset, compared with controls [median (IQR) 80.7 (131.9) vs 46.6 (63.4) µg/mL, p = 0.05]. Levels of C5a increased significantly during the pre-dating time (p = 0.033) until symptom onset. The complement levels were significantly higher in presymptomatic myeloperoxidase (MPO)-ANCA⁺ individuals versus MPO-ANCA^- and proteinase-3-ANCA⁺ individuals. C5 was significantly increased in cases with renal involvement at diagnosis versus controls (p = 0.022), whereas levels of both C5 and C5a were significantly increased in presymptomatic individuals diagnosed with microscopic polyangiitis after onset compared with controls (C5: p = 0.027; C5a: p = 0.027).

CONCLUSION

Activation of the complement system is an early event in the pathogenesis of AAV and is mainly associated with MPO-ANCA⁺ AAV and with microscopic polyangiitis.

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.

New Insights into the Pathogenesis and Treatment Strategies in IgA Nephropathy

Background

Immunoglobulin A nephropathy (IgAN) is the most common form of primary glomerulonephritis worldwide. It is defined by mesangial IgA deposition, with consequent mesangial cell proliferation, inflammation, and tubulointerstitial fibrosis.

Summary

Approximately 30% of affected patients will progress to end-stage kidney disease within 20 years of diagnosis. Currently, there is no disease-specific treatment available and management recommendations are, in general, limited to optimization of lifestyle measures and use of renin-angiotensin-aldosterone system blockers. More recently, advances in the understanding of the pathogenesis of IgAN have informed the development of novel therapeutic strategies that are now being tested in clinical trials. These have focused on different areas that include modulating the production of poorly galactosylated IgA1, which is central to the development of IgAN, and inhibiting the downstream signaling pathways and complement activation that are triggered following mesangial IgA1 deposition. In this review, we will summarize important pathogenic mechanisms in IgAN and highlight important areas of interest where treatment strategies are being developed.

Key messages

IgAN is a common form of primary glomerulonephritis for which there is no current approved specific therapy. Recent advances in the understanding of its pathogenesis have led to the development of novel therapies, with the hope that new treatment options will be available soon to treat this condition.

Complement Factor D as a Strategic Target for Regulating the Alternative Complement Pathway

The complement system is central to first-line defense against invading pathogens. However, excessive complement activation and/or the loss of complement regulation contributes to the development of autoimmune diseases, systemic inflammation, and thrombosis. One of the three pathways of the complement system, the alternative complement pathway, plays a vital role in amplifying complement activation and pathway signaling. Complement factor D, a serine protease of this pathway that is required for the formation of C3 convertase, is the rate-limiting enzyme. In this review, we discuss the function of factor D within the alternative pathway and its implication in both healthy physiology and disease. Because the alternative pathway has a role in many diseases that are characterized by excessive or poorly mediated complement activation, this pathway is an enticing target for effective therapeutic intervention. Nonetheless, although the underlying disease mechanisms of many of these complement-driven diseases are quite well understood, some of the diseases have limited treatment options or no approved treatments at all. Therefore, in this review we explore factor D as a strategic target for advancing therapeutic control of pathological complement activation.

Hepatosplenomegaly in liver cirrhosis is caused by reactive oxygen species formation, an increase in apoptosis and autophagy, and pronounced autoimmune reactions

Various factors of infectious and toxic genesis can lead to the liver cirrhosis, often accompanied by complications such as recurrent bleeding due to portal hypertension against the background of hepatosplenomegaly. Metabolic changes and disturbances in immunoreactivity occur in the liver and spleen. To substantiate the choice of personalized treatment tactics for patients with hepatosplenomegaly, we investigated individual metabolic predictors and immunopathological processes in patients with: liver cirrhosis and hepatitis B (HBV) and/or hepatitis C (HCV) viruses (I group, n = 52); with herpes viruses CMV (cytomegalovirus) and EBV (Epstein-Barr virus) (II group, n = 48), and with splenomegaly and frequent recurrent bleeding associated with hereditary enzymopathies (III group, n = 15). We used the methods of immunoturbidimetry; enzyme immunoassay; light, fluorescence and confocal microscopy. In group I (HBV/HCV), we revealed a decrease in the C4 component; a significant increase in the phagocytic index and phagocytic number, a reduced number of active phagocytes and the digestion index; a decrease in the IL-1β content and an increase in IL-18 and IL-6. In group II (CMV/EBV), we revealed a high activity of the C3 and a low activity of the C4 component against the background of a high level of ROS in neutrophils; the antineutrophil antibodies (ANCA) formation in 85.7% of patients (71.4% –perinuclear antibodies (pANCA) to myeloperoxidase; 14.3% – cytoplasmic antibodies (CANCA) to proteinase 3). Also, in group II, an increased level of pro-inflammatory cytokines IFN-γ, IL-1β, TNF-α, IL-18 and anti-inflammatory IL-6 was detected. Changes in links of immunity in II group led to the formation of autoimmune reactions in 64.7% of patients, which was expressed in the development of a broad range of antinuclear antibodies ANA (11 specificities, including ANA to chromatin and chromatin-associated proteins, to proteins cytoskeleton, enzymes and enzyme complexes). In group III, we revealed a low absorption capacity of neutrophils, a high frequency of antineutrophil antibodies pANCA occurrence and cANCA (in 67.2% of the examined), and low concentration of TNF-α. The developed model of the stepwise change of immunological markers makes it possible to substantiate the choice of a complex targeted treatment, including antiviral and immunotropic therapy.

Neutrophils as Drivers of Immune Dysregulation in Autoimmune Diseases with Skin Manifestations

Dysregulation in the phenotype and function of neutrophils may play important roles in the initiation and perpetuation of autoimmune responses, including conditions affecting the skin. Neutrophils can have local and systemic effects on innate and adaptive immune cells as well as on resident cells in the skin, including keratinocytes (KCs). Aberrant formation/clearance of neutrophil extracellular traps (NETs) in systemic autoimmunity and chronic inflammatory diseases have been associated with the externalization of modified autoantigens in peripheral blood and tissues. NETs can impact the function of many cells, including macrophages, lymphocytes, dendritic cells, fibroblasts, and KCs. Emerging evidence has unveiled the pathogenic key roles of neutrophils in systemic lupus erythematosus, idiopathic inflammatory myopathies, psoriasis, hidradenitis suppurativa, and other chronic inflammatory conditions. As such, neutrophil-targeting strategies represent promising therapeutic options for these diseases.

ANCA and anti-glomerular basement membrane double-positive patients: A systematic review of the literature

INTRODUCTION

Double-positive patients (DPP) exhibiting anti-glomerular basement membrane (GBM) and anti-neutrophil cytoplasmic antibodies (ANCAs) belong to an entity that is newly and poorly described, mainly in short series. We aimed to better characterize the epidemiological features, clinical presentation and therapeutic outcomes of these patients through a systematic review.

METHODS

We performed a systematic review of English-, German-, Spanish- and French-written publications from February 1987 to March 2020 reporting cases of DPP using the following databases: PubMed, Scielo, ScienceDirect, Google Scholar, The Cochrane Library, Open Grey, The Grey Literature Report, Clinicaltrials.gov and International Clinical Trial Registry Platform of the World Health Organization.

RESULTS

In total, 538 DPP were identified from 90 articles. Their clinical presentations were often severe, and the majority exhibited acute kidney failure (91.8%) with a median initial serum creatinine level of 873 μmol/L; 50.7% had alveolar haemorrhage. Other manifestations were present in 30.3% of DPP, mainly ear, nose, throat and articular manifestations. ANCAs were predominantly directed against MPO (n = 377/523; 72.1%) compared to PR3 (n = 107/523; 20.5%), with rare cases of triple positivity (n = 15/538; 2.9%). Although most patients received initial immunosuppressive therapy (n = 285/317; 89.9%), the one-year overall, renal and relapse-free survival rates were 64.8%, 38.7% and 71.1%, respectively.

CONCLUSION

DPP are associated with the characteristics of two eponymous vasculitis types, responsible for a poor overall and renal prognosis. Thus, simultaneous testing of both antibodies and systematic renal biopsy should be recommended in every patient with rapidly progressive glomerulonephritis to recognize this difficult-to-treat and rare disease.

Relationship between Renal Damage and Serum Complement C3 in Children with Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis

BACKGROUND

Anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) disease is a well-known antibody-induced autoimmune disease. The pathogenesis of AAV has not yet been completely clarified, but may be related to heredity, infection, environmental factors, cellular immunity, etc. In recent years, complement in AAV pathogenesis has become the latest research hotspot, and the decrease of serum complement C3 is associated with poor prognosis of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis. In the current study, we investigated the associations between serum complement C3 and kidney injury in AAV children.

METHODS

Twenty-four children with AAV admitted to our hospital from June 2014 to June 2019 were divided into the low C3 group and the normal C3 group. All the children have undergone renal biopsy. The clinical manifestations, laboratory tests, renal pathology, treatment, and prognosis of the 2 groups were observed. The primary end point was end-stage renal disease (ESRD).

RESULTS

It was shown that kidney injury was more obvious in patients with low C3 than in patients with normal C3 serum. The values of ESR, Scr, and UA before treatment in the low C3 group were higher than those in the normal C3 group (p < 0.01); the values of RBC, Hb, PLT, ALB, LDH, and eGFR in the normal C3 group were higher than those in the low C3 group (p < 0.01). The values of urinary protein and NAG enzyme in the low C3 group were higher than those in the normal C3 group (p < 0.01). The area of glomerular abandonment, sclerosis, segmental sclerosis, crescent, cellular crescent, cellular fibrous crescent, fibrous crescent, segmental loop necrosis, and the number of cases with acute renal tubulointerstitial lesions in the low C3 group were bigger than those in the normal C3 group (p < 0.05 and < 0.01). The number of cases with C3 deposition in the low C3 group was higher than that in the normal C3 group (p < 0.05). The number of patients receiving CRRT and PE in the low C3 group was higher than that in the normal C3 group (p < 0.05 and < 0.01). In this study, 3 children entered the stage of ESRD and 1 died in the low C3 group.

CONCLUSION

The kidney injury of AAV children with low complement C3 is serious, and the prognosis is poor. We should pay attention to the influence of decreased complement C3 on the condition and prognosis of AAV children.

Avacopan for the treatment of ANCA-associated vasculitis

Introduction: Anti-neutrophil cytoplasm autoantibodies (ANCA)-associated vasculitides (AAVs) are a group of rare heterogeneous diseases characterized by blood vessel inflammation resulting in organ destruction and death. Although various treatment strategies have resulted in marked improvement in vasculitis-specific outcomes, many patients with AAV continue to suffer from complications related to the prolonged use of glucocorticoids (GC) such as infections, metabolic abnormalities, and increased cardiovascular morbidity. Recently, activation of the alternative complement pathway has been implicated in the augmentation of the damage caused by AAV via the complement C5a receptor (C5aR1, CD88). Specifically targeting this pathway may lead to improved outcomes in patients with AAV.Areas covered: In this article, we have summarized the rationale for targeting the complement pathway in AAV. The relevant pre-clinical, phase I, II and III findings with emphasis on the efficacy, and safety of avacopan, a new oral competitive inhibitor that interferes with the binding of C5a to C5aR1 (CD88), are reviewed.Expert opinion: These results are encouraging, may led to major changes in the treatment approach for AAV, and give rise to future studies utilizing complement inhibitors in AAV patients, and potentially in other immune mediated diseases.

Lymphopenia at diagnosis of ANCA-vasculitis with renal involvement is correlated with severity and renal prognosis

BACKGROUND

Lymphopenia is commonly observed in autoimmune diseases, where it has been associated with disease activity or prognosis. However, in ANCA-associated vasculitis (AAV) only few, small-scale studies have been targeted to this issue. Research has not yet focused on AAV with renal involvement (AAV-RI) patients. Thus, the aim of this study was to analyze the association between lymphocyte counts and outcomes in a large cohort of AAV-RI patients.

METHODS

We used the Maine-Anjou AAV registry that retrospectively gathers data on consecutive patients affected by AAV in four French Nephrology Centers, recorded since January 2000. We analyzed clinical, biological, and histological data at diagnosis of AAV-RI. Risk factors for end-stage kidney disease (ESKD) were analyzed. Event-free survival was also assessed.

RESULTS

Among the 145 patients included in the study, those with lymphopenia at diagnosis had a lower renal function at baseline (eGFR 13 mL/min vs 26 mL/min, p = 0.002) and were more likely to require kidney replacement therapy (51% vs 25%, p = 0.003). Lymphopenia was correlated with histological lesions and especially with the percentage of sclerotic glomeruli (p = 0.0027). ESKD-free survival was lower in lymphopenic patients (p < 0.0001). In multivariate Cox analysis, lymphopenia was an independent risk factor for ESKD (HR 4.47 (95% confidence interval: [2.06-9.72], p < 0.001).

CONCLUSION

Lymphopenia correlates with the severity of AAV glomerulonephritis at diagnosis and predicts poor renal outcome. In this view, lymphopenia could be used as a simple and cost-effective biomarker to assess renal prognosis at AAV-RI diagnosis.

Serological Biomarkers and Indices for the Current Activity and Prognosis of ANCA-Associated Vasculitis: Experience in a Single Centre in Korea

Small vessel vasculitis is composed of two types of vasculitis based on immune-complex deposits, immune-complex vasculitis and antineutrophil cytoplasmic antibody-associated vasculitis (AAV) according to the 2012 Chapel Hill Consensus Conferences Nomenclature of Vasculitis. In general, the current disease-states are assessed in three ways in real clinical practice such as activity, damage and functional status. Birmingham vasculitis activity score (BVAS, version 3) and five-factor score were calculated for assessing the cross-sectional activity and for predicting the prognosis of AAV, respectively. Since BVAS includes a wide spectrum of nine systemic items with differently weighted scores based on new-onset/worsening or persistent each symptom, it has been considered as the most reliable tool to assess AAV activity to date. However, since BVAS represents both cross-sectional and chronic clinical features, it has a limitation in flexibly reflecting the cross-sectional activity or severity of AAV. In addition, the heterogeneous items of BVAS are difficult to reflect the close correlation between BVAS and AAV pathogenesis. It is practically difficult to discover new biomarkers or indices that exceed the reliability of AAV-specific indices or acute-phase reactants established by long clinical experience. However, efforts to discover and develop new biomarkers or indices are expected to complement the clinical unmet need of existing AAV-specific indices and acute-phase reactants. In this review, we reviewed the serological biomarkers and indices that have been reported to date and introduced studies that investigated serological biomarkers and indices in Korean patients with AAV.

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.

Advances in cutaneous vasculitis research and clinical care

Vasculitis is characterized by inflammation and destruction of blood vessels, resulting in downstream ischemic tissue damage. Diagnosis of vasculitis is a careful exercise in clinical-pathologic correlation, depending upon the clinical manifestations, organs involved, the size of affected blood vessels, imaging, and laboratory findings. While some vasculitis subtypes may be confined to the skin, serious internal organ involvement or underlying disease states may also occur. Accordingly, the skin plays an important role in the diagnostic process and may be prognostically important in some cases, signifying more severe systemic disease. The skin also provides opportunities for tissue-based translational research, improving understanding of disease pathophysiology. Dermatologists, therefore, play a critical role in evaluating vasculitis and helping to advance vasculitis clinical care and research. Recent updates in vasculitis nomenclature and terminology, evidence-based diagnosis, pathogenesis, and investigations of targeted therapies are changing vasculitis research and leading to fundamental shifts in disease management. Treatment advances favoring evidence-based and targeted, rather than broadly immunosuppressive, therapies are in development, while a multicenter trial for skin-limited vasculitis is ongoing. Collaborative multidisciplinary research networks are key to current and future advances in vasculitis research. In this review, we describe recent developments in vasculitis clinical care and research, starting with a discussion of efforts to develop diagnostic and classification criteria, followed by updates on the evaluation and treatment of vasculitis.

Anti-Pentraxin Antibodies in Autoimmune Diseases: Bystanders or Pathophysiological Actors?

Pentraxins are soluble innate immunity receptors involved in sensing danger molecules. They are classified as short (CRP, SAP) and long pentraxin subfamilies, including the prototypic long pentraxin PTX3. Pentraxins act mainly as bridging molecules favoring the clearance of microbes and dead cells. They are also involved in many other biological processes, such as regulation of complement activation, inflammation and tissue homeostasis. Autoantibodies directed against pentraxins have been reported in various autoimmune diseases, especially in systemic lupus erythematosus and ANCA-associated vasculitis. In this review, we review the main biological characteristics and functions of pentraxins and summarize data concerning autoantibodies directed against pentraxins in the context of autoimmune diseases and discuss their potential pathological role.

Clinicopathological Analysis of 34 Cases of Primary Antineutrophil Cytoplasmic Antibody-Associated Vasculitis in Chinese Children

Background: This study aimed to summarize the clinicopathological features and prognostic risk factors of primary antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) in children. Methods: Clinical and prognostic data for children admitted to our center with AAV between September 2003 and September 2020 were studied retrospectively. The incidence and risk factors of end-stage renal disease (ESRD) were calculated and analyzed. Results: Thirty-four children were enrolled; 28 were female, with a median onset age of 10 years. Except for one case negative for ANCA, the other 33 patients were diagnosed with microscopic polyangiitis (MPA). The most frequently involved organ was the kidney (100.0%), followed by the lungs (58.8%) and heart (50.0%). Twenty children (58.8%) progressed to ESRD with a median course of 3 months, and they were more likely to present respiratory and cardiovascular system involvement than were the non-ESRD group (P < 0.05). Patients in the ESRD group also had a higher serum creatinine level, 24-h protein excretion, Pediatric Vasculitis Activity Score (PVAS), and a lower level of estimated glomerular filtration rate (eGFR), hemoglobin, and complement C3 than had those in the non-ESRD group (P < 0.05). The main pathological manifestations were crescentic and sclerotic classes in the ESRD group and focal class in the non-ESRD group. After 6 months of induction therapy, 90.0% of cases achieved complete or partial remission. The multivariate logistic regression model showed that baseline eGFR < 60 ml/min/1.73 m² was an independent risk factor for progressing to ESRD (OR = 0.016, 95% CI = 0.001~0.412, P = 0.012). Conclusions: AAV in children usually occurs in teenage girls, and the most commonly involved organ is the kidney, of which hematuria is the most common symptom, followed by proteinuria, abnormal renal function (eGFR < 90 ml/min/1.73 m²), etc. The primary type of AAV is MPA. Nearly 60% of patients progressed to ESRD with a median course of 3 months. Baseline eGFR < 60 ml/min/1.73 m² is an independent risk factor for ESRD progression in AAV children.

Treatment of Rare Inflammatory Kidney Diseases: Drugs Targeting the Terminal Complement Pathway

The complement system comprises the frontline of the innate immune system. Triggered by pathogenic surface patterns in different pathways, the cascade concludes with the formation of a membrane attack complex (MAC; complement components C5b to C9) and C5a, a potent anaphylatoxin that elicits various inflammatory signals through binding to C5a receptor 1 (C5aR1). Despite its important role in pathogen elimination, priming and recruitment of myeloid cells from the immune system, as well as crosstalk with other physiological systems, inadvertent activation of the complement system can result in self-attack and overreaction in autoinflammatory diseases. Consequently, it constitutes an interesting target for specialized therapies. The paradigm of safe and efficacious terminal complement pathway inhibition has been demonstrated by the approval of eculizumab in paroxysmal nocturnal hematuria. In addition, complement contribution in rare kidney diseases, such as lupus nephritis, IgA nephropathy, atypical hemolytic uremic syndrome, C3 glomerulopathy, or antineutrophil cytoplasmic antibody-associated vasculitis has been demonstrated. This review summarizes the involvement of the terminal effector agents of the complement system in these diseases and provides an overview of inhibitors for complement components C5, C5a, C5aR1, and MAC that are currently in clinical development. Furthermore, a link between increased complement activity and lung damage in severe COVID-19 patients is discussed and the potential for use of complement inhibitors in COVID-19 is presented.

Complement system network in cell physiology and in human diseases

The complement system is a multi-functional system representing the first line host defense against pathogens in innate immune response, through three different pathways. Impairment of its function, consisting in deficiency or excessive deregulated activation, may lead to severe systemic infections or autoimmune disorders. These diseases may be inherited or acquired. Despite many diagnostic tools are currently available, ranging from traditional, such as hemolytic or ELISA based assays, to innovative ones, like next generation sequencing techniques, these diseases are often not recognized. As for therapeutic aspects, strategies based on the use of targeted drugs are now widespread. The aim of this review is to present an updated overview of complement system pathophysiology, clinical implications of its dysfunction and to summarize diagnostic and therapeutic approaches.

Immunopathogenesis of ANCA-Associated Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is an autoimmune disorder which affects small- and, to a lesser degree, medium-sized vessels. ANCA-associated vasculitis encompasses three disease phenotypes: granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). This classification is largely based on clinical presentations and has several limitations. Recent research provided evidence that genetic background, risk of relapse, prognosis, and co-morbidities are more closely related to the ANCA serotype, proteinase 3 (PR3)-ANCA and myeloperoxidase (MPO)-ANCA, compared to the disease phenotypes GPA or MPA. This finding has been extended to the investigation of biomarkers predicting disease activity, which again more closely relate to the ANCA serotype. Discoveries related to the immunopathogenesis translated into clinical practice as targeted therapies are on the rise. This review will summarize the current understanding of the immunopathogenesis of ANCA-associated vasculitis and the interplay between ANCA serotype and proposed disease biomarkers and illustrate how the extending knowledge of the immunopathogenesis will likely translate into development of a personalized medicine approach in the management of ANCA-associated vasculitis.

The alternative complement pathway in ANCA-associated vasculitis: further evidence and a meta-analysis

We compared the common pathway components C3a, C5a and membrane attack complex (MAC), also known as C5b-9, and the alternative pathway components factor B and properdin in patients with ANCA-associated vasculitis (AAV) and healthy controls, and conducted a meta-analysis of the available clinical evidence for the role of complement activation in the pathogenesis of AAV. Complement components were evaluated in 59 patients with newly diagnosed or relapsing granulomatosis with polyangiitis or microscopic polyangiitis and 36 healthy volunteers. In 28 patients, testing was repeated in remission. Next, we performed a meta-analysis by searching databases to identify studies comparing complement levels in AAV patients and controls. A random-effects model was used for statistical analyses. The median concentrations of MAC, C5a, C3a and factor B were higher in active AAV patients (P < 0·001). Achievement of remission was associated with reductions in C3a (P = 0·005), C5a (P = 0·035) and factor B levels (P = 0·045), whereas MAC and properdin levels did not change. In active AAV, there were no effects of ANCA specificity, disease phenotype, previous immunosuppression or disease severity on complement levels. A total of 1122 articles were screened, and five studies, including this report, were entered into the meta-analysis. Plasma MAC, C5a and factor B in patients with active AAV were increased compared to patients in remission (excluding factor B) and controls. Changes in C3a were of borderline significance. Our findings and the results of the meta-analysis support activation of the complement system predominantly via the alternative pathway in AAV patients.

Characteristics and prognosis of ANCA-positive retroperitoneal fibrosis: A systematic literature review

OBJECTIVE

Anti-neutrophil cytoplasmic autoantibody (ANCA)-positive retroperitoneal fibrosis (RPF) is extremely rare. This study aimed to clarify the clinical characteristics and prognosis of patients with ANCA-positive RPF.

METHODS

We conducted a systematic literature review of articles reporting on ANCA-positive RPF from the database inception dates until March 8, 2020.

RESULTS

We identified 19 patients with ANCA-positive RPF with a mean age of 62 years; a male dominance (68.4%) was noted. Most patients presented with systemic symptoms and/or lower back or abdominal pain. Proteinase 3 (PR3) -ANCA positivity was predominant compared with myeloperoxidase (MPO)-ANCA (63.2% vs. 36.8%, respectively), and all patients showed elevated serum C-reactive protein levels. Of note, 26.7% of patients had isolated RPF without any other ANCA-associated systemic organ involvement. Regarding typical manifestations of ANCA- associated vasculitis, ear, nose, and throat involvement occurred in 26.3%, lung involvement in 36.8%, and kidney involvement (rapidly progressive glomerulonephritis) in 31.6% of patients. Necrosis and granulomatous inflammation, vasculitis, and multinucleated giant cells were pathologically observed in tissue sections of RPF, whereas tertiary lymphoid organ formation was not identified. Glucocorticoids with or without other immunosuppressive treatments were effective in most patients, but 4 patients experienced disease relapse during the clinical course. All relapsed patients were positive for PR3-ANCA.

CONCLUSION

Clinical features of ANCA-positive RPF are associated with systemic inflammatory components such as fever and elevated serum C-reactive protein levels. ANCA-. positive RPF presents as an "isolated" involved organ in one-third of patients. Immunosuppressive treatments are effective, but the disease can recur, particularly in PR3-ANCA-positive patients.

Immunotherapy for ANCA-associated vasculitis during the COVID-19 pandemic

Since the first description of infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in China in December 2019, it has evolved into a pandemic and emerged as an unprecedented worldwide crisis overwhelming healthcare systems globally. Analysis of the available literature to date suggests that, in addition to older age, patients with underlying co-morbidities including hypertension, diabetes, heart disease are at higher risk for severe disease with increased mortality. Practitioners around the world also have become increasingly concerned that immunosuppressed patients including those with autoimmune diseases may be at increased risk for developing Coronavirus Disease 2019 (COVID-19) with serious complications. Very little is known about how anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis modifies the susceptibility, clinical presentation and disease course of COVID-19. In this review, we discuss the mechanism of action and challenges of the current therapeutic armamentarium of ANCA-associated vasculitis and outline approaches to management of ANCA-associated vasculitis during the COVID-19 pandemic.

2020 international consensus on ANCA testing beyond systemic vasculitis

This document follows up on a 2017 revised international consensus on anti-neutrophil cytoplasm antibodies (ANCA) testing in granulomatosis with polyangiitis and microscopic polyangiitis and focuses on the clinical and diagnostic value of ANCA detection in patients with connective tissue diseases, idiopathic interstitial pneumonia, autoimmune liver diseases, inflammatory bowel diseases, anti-glomerular basement membrane (GBM) disease, infections, malignancy, and during drug treatment. Current evidence suggests that in certain settings beyond systemic vasculitis, ANCA may have clinical, pathogenic and/or diagnostic relevance. Antigen-specific ANCA targeting proteinase-3 and myeloperoxidase should be tested by solid phase immunoassays in any patient with clinical features suggesting ANCA-associated vasculitis and in all patients with anti-GBM disease, idiopathic interstitial pneumonia, and infective endocarditis associated with nephritis, whereas in patients with other aforementioned disorders routine ANCA testing is not recommended. Among patients with autoimmune liver diseases or inflammatory bowel diseases, ANCA testing may be justified in patients with suspected autoimmune hepatitis type 1 who do not have conventional autoantibodies or in case of diagnostic uncertainty to discriminate ulcerative colitis from Crohn's disease. In these cases, ANCA should be tested by indirect immunofluorescence as the target antigens are not yet well characterized. Many questions concerning the optimal use of ANCA testing in patients without ANCA-associated vasculitis remain to be answered.

[The complement system-a "hot topic" not only for kidney diseases]

Increasing interest in the role of the complement system in systemic and renal disease is based on new pathophysiological and therapeutic insights of the recent past and particularly in genetic analyses in children with atypical hemolytic uremic syndrome (aHUS). aHUS is the prototypical systemic disease associated with excessive activation of the alternative complement pathway and manifests in the kidney, but also in other organs as thrombotic microangiopathy (TMA). Pathomechanisms discovered to induce the overactivation of the alternative complement pathway in aHUS led to the first successful therapeutic application of a C5b9 inhibitor. This suppression of the terminal complement cascade succeeded in inhibiting local tissue damage. Thereafter, thanks to advanced modern technologies, further systemic and renal diseases associated with mutations or auto-antibodies targeting the complement pathway were identified. Hereby, disease onset is frequently associated with an additional trigger, e.g. infection or hormonal alterations/imbalances, against the background of a pre-existing predisposition of the patient.Due to the growing understanding of the regulation, and thus the possibility of therapeutic modulation of the different complement pathways, and due to the increasing availability of a variety of drugs inhibiting the complement system, interest in complement-mediated systemic and renal disease has been steadily increasing, making it a "hot-topic" in medicine in recent years.