Pathogenesis Of ANCA-associated Vasculitis Research Articles

A historical study of American patients with anti-neutrophil cytoplasmic antibody negative pauci-immune glomerulonephritis.

Anti-neutrophil cytoplasmic antibodies (ANCA) play an important role in the pathogenesis of ANCA-associated vasculitis. The lack of ANCA antibodies may indicate a variation in clinical presentation and outcomes of this disease. We identified 74 adult patients between 1995 and 2009 with the diagnosis of pauci-immune glomerulonephritis. Demographics, histological features, and treatment outcomes were compared between ANCA-positive and ANCA-negative patients. These factors were correlated with renal function at presentation and follow-up. Of the 74 patients, 57 were ANCA-positive, and 17 were ANCA-negative. Demographics and mean Birmingham Vasculitis Activity Score were similar between ANCA-negative and ANCA-positive patients at presentation. Renal function was significantly worse at presentation in the ANCA-negative patients (eGFR 16.59 vs. 31.89ml/min/1.73m(2), p = 0.03). Patients in the ANCA-negative group had a significantly higher interstitial fibrosis score compared to the ANCA-positive group (2.1 vs.1.6, p = 0.04). The median time to remission was shorter in the ANCA-negative patients (51 vs. 78days, p = 0.01). Long-term renal function and 1-year patient and renal survival were similar between ANCA-negative and ANCA-positive patients. Baseline eGFR, percentage of normal glomeruli, glomerular sclerosis, and tubulointerstitial scarring predicted eGFR at 1year in both groups similarly. This is the first historical review of American patients with pauci-immune glomerulonephritis, comparing patients with ANCA-negative and ANCA-positive serology. Although ANCA-negative patients present with lower eGFR and more interstitial fibrosis, 1-year and long-term outcomes in both groups are similar.

Update on the treatment of ANCA associated vasculitis

The introduction of glucocorticoids and cyclophosphamide has transformed ANCA associated vasculitis (AAV) from a fatal to a largely treatable condition. Over the past 40 years, considerable progress has been made in refining immunosuppressive regimens with a focus on minimising toxicity. As knowledge of the pathogenesis of AAV grows, it is mirrored by the availability of biological agents. Lymphocyte and cytokine targeted agents have been evaluated for the treatment of AAV and are entering the routine therapeutic arena with the potential to improve patient outcomes. Rituximab has transformed management of AAV in the past decade. However, there remains unmet need in the treatment of AAV; the majority of patients will relapse within five years of diagnosis despite maintenance immunosuppression; a small number of patients remain refractory to current therapies and treatment toxicity continues to contribute to mortality and chronic disability. As in rare diseases, treatment advances in vasculitis depend on international collaborative research networks to both establish an evidence base for newer agents and develop recommendations for optimal patient management.

Emerging concepts in the pathogenesis of antineutrophil cytoplasmic antibody-associated vasculitis.

Antineutrophil cytoplasmic antibodies (ANCAs) remain central to our current understanding of the pathogenesis of ANCA-associated vasculitis (AAV), and this review considers recent developments in the context of four key questions: are there targets for ANCA beyond myeloperoxidase (MPO) and proteinase 3 (PR3); are all ANCA pathogenic; how are ANCAs generated; and how do ANCA cause disease? B-cell epitope mapping raises the possibility that only a subset of ANCA may be pathogenic. Anti-lysosomal-associated membrane protein 2 autoantibodies have recently emerged as a novel form of ANCA and can be found in anti-MPO and anti-PR3 negative disease. These also provide recent evidence for molecular mimicry in the pathogenesis of AAV, but a definitive proof in human AAV remains elusive. Neutrophil extracellular traps may represent an important mechanism by which MPO and PR3 are taken up by dendritic cells for presentation to the adaptive immune system, and the role of the alternative pathway of complement in AAV has recently been emphasized, with therapeutic implications. Our current understanding of the pathogenesis of AAV not only reinforces the central role of neutrophils but also provides a sound rationale for B-cell and complement-directed therapies.

Interleukin-6 in ANCA-associated vasculitis: Rationale for successful treatment with tocilizumab

ObjectiveMicroscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA) are systemic, necrotizing, small-vessel vasculitis associated with circulating anti-neutrophil cytoplasmic autoantibodies (ANCA), and thus called ANCA-associated vasculitides (AAV). The aim of the present study is to evaluate a potential role of interleukin (IL)-6 and its pathway in the pathogenesis of AAV and to review previous evidence of IL-6 in MPA and GPA. MethodsBlood and histological samples from 10 untreated myeloperoxidase (MPO)-ANCA/proteinase 3 (PR3)-ANCA-positive patients with active AAV were studied. Serum levels of cytokines/chemokines were evaluated by means of a Bio-Plex Multiple Cytokine Assay. IL-6 production at sites of active vasculitis was assessed by means of both immunohistochemistry and in situ hybridization techniques. We also treated a patient with MPA who was resistant or allergic to conventional treatments with a 12-month course of the IL-6 inhibitor tocilizumab and followed him up for 24 additional months. We also reviewed all the published cases in the English literature of histologically confirmed MPA or GPA, in which elevated IL-6 serum levels or intralesional IL-6 expression were reported. ResultsIL-6 serum levels were significantly increased in patients with AAV as compared to controls (median = 51.96pg/mL; range: 34.11–84.30; versus 0.68pg/mL; range: 0.01–1.81; P < 0.005). Also, IL-6 was expressed and produced at sites of active vasculitis. Treatment with tocilizumab was able to induce a complete and sustained disease remission in a patient with severe multisystemic MPA, as well as normalization of circulating levels of IL-6-associated pro-inflammatory cytokines and chemokines. Previous evidence of IL-6 pathway activation in AAV is scarce. Increased serum levels of IL-6 were reported in seven clinical studies for a total of approximately 120 patients, mainly affected by GPA. ConclusionThe finding of an activated IL-6 pathway in patients with AAV, together with the observed effects of tocilizumab monotherapy, provides evidence for a possible central role of IL-6 in the pathogenesis of AAV and suggests its targeting as a potential treatment.

Biologic Treatment in Glomerular Disease

to the standard immunosuppressive treatment demon-strating its limitations and the current unmet need of, at least, similarly effective and less toxic treatment. To illus-trate the close connection between a better understanding of the pathogenesis of the disease and targeted treatment, the papers on the pathogenesis of ANCA-associated vas-culitis [2], lupus nephritis [3], the role of anti-PLA2R an- tibodies [4] in membranous nephropathy and comple-ment in membranoproliferative glomerulonephritis [5] precede the articles dedicated to the treatment of second-ary [6–8] and primary glomerulonephritides [9–11]The . final contribution opens new horizons by reviewing the emerging biologic treatments [12] . We hope you enjoy this introduction to the complex area of the pathogenesis and targeted treatment of glo-merular disease and that this information will contribute to greater awareness, earlier diagnosis and referral, better treatment and improved outcome for patients with im-mune-mediated glomerular diseases. The classification of glomerular disease has been based almost entirely on renal histology, but an increasing un-derstanding of the pathogenesis is now introducing change relevant to the development of newer therapies. The introduction of corticosteroid and immunosuppres-sive drugs undoubtedly improved the outcome of patients with many forms of nephrotic syndrome, lupus nephritis and ANCA-associated vasculitis, but this non-specific treatment has been associated with serious short- and long-term toxicity, especially in patients with frequently relapsing disease. During the last 10 years, new biologic (targeted) treatment has expanded our therapeutic arma-mentarium, especially in refractory, relapsing or intoler-ant patients with ANCA-associated vasculitis, lupus ne-phritis and less commonly for other glomerular diseases.This special topic section of

AB0040 Role of Innate Immunity in the Pathogenesis of Anca-Associated Vasculitis

BackgroundNatural killer (NK) cells represent one of the main effectors of the innate immune response. Toll-like receptors (TLRs) are a family of evolutionally-conserved host defense mechanism against pathogens. Recent evidence...

Cathelicidin antimicrobial peptide as a serologic marker and potential pathogenic factor in antineutrophil cytoplasmic antibody-associated vasculitis

Antineutrophil cytoplasmic antibodies are associated with pauci-immune small-vessel vasculitis and crescentic glomerulonephritis. Cathelicidin LL37 is the human member of a family of antimicrobial peptides that are released from activated neutrophils and monocytes at sites of acute inflammation. Zhang and colleagues evaluated serum levels of cathelicidin LL37 and interferon-alpha in patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV) and glomerulonephritis. Increased levels of cathelicidin LL37 and interferon-alpha were associated with AAV patients, particularly those with glomerular crescent formation. Cathelicidin LL37 may also be involved in the pathogenesis of AAV and thus could be a target for novel therapy. Cathelicidin LL37 is a promising new biomarker for active AAV, including aggressive crescentic glomerulonephritis, and may prove to be both a prognostic marker and a guide for treatment.

Impact of rituximab trials on the treatment of ANCA-associated vasculitis

ANCA-associated vasculitis (AAV) is a subgrouping of autoimmune disorders characterized by a chronic relapsing course. Induction therapy is usually effective, but 70% of patients will relapse and 20% develop refractory disease. In the relapsing and refractory subgroups, treatment is complicated by the cumulative exposure to toxic drugs that contribute to poor long-term outcomes. The anti-CD20 monoclonal antibody rituximab (RTX) depletes B cells, and the success of this targeted therapy has contributed to the evidence supporting a central role for B cells in AAV pathogenesis. Initial proof of RTX effectiveness originated from small, prospective trials and retrospective surveys conducted in AAV patients with relapsing and refractory disease; high remission rates permitted the reduction of glucocorticoids (GCS) doses and withdrawal of immunosuppressives. There has been controversy over the effectiveness of RTX in patients with predominantly granulomatous manifestations, where response rates have varied between studies, in part due to different RTX dosing regimens. These studies were followed by comparison of RTX against cyclophosphamide (CYC) for remission induction of new or relapsing AAV in two randomized trials, which led to the licensing of RTX for this indication. Subsequent attention has been turned to the use of RTX as a relapse prevention agent, to the potential for GCS sparing and to RTX-associated toxicity. We will discuss the impact that the results of RTX clinical trials have had on the management of AAV patients.

Pathogenesis of ANCA-Associated Vasculitis: New Possibilities for Intervention

The antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) comprise granulomatosis with polyangiitis (GPA), primarily associated with antibodies to proteinase 3 (PR3-ANCA); microscopic polyangiitis (MPA); and eosinophilic granulomatosis with polyangiitis (EGPA), both principally associated with antibodies to myeloperoxidase (MPO-ANCA). Genetic and environmental factors are involved in their etiopathogenesis, with a possible role for silica exposure in AAVs and Staphylococcus aureus infection in GPA. The distinct associations of PR3-ANCA and MPO-ANCA with different HLA class II antigens, which are stronger than those with the associated diseases, suggest a pathogenic role for those ANCAs and indicate that GPA and MPA are different diseases. Both in vitro and in vivo experimental data have shown that MPO-ANCA can induce necrotizing small-vessel vasculitis and glomerulonephritis. The additional role of the alternative pathway of complement activation has been demonstrated in human and experimental pathology. Also, T cells seem to be involved in lesion development, particularly in the kidney. Granuloma formation, as seen in PR3-ANCA-associated GPA, is not well explained by the presence of autoantibodies in experimental models. Here, T cells seem crucial. Recently obtained insights into the pathogenesis of AAVs have led to more targeted treatment of these life-threatening diseases.

SAT0183 Autoantibodies for Several Antigens in Neutrophil Cytoplasm other than PR3 and MPO Promote Release of Nets from Neutrophils

BackgroundNeutrophil extracellular traps (NETs) were first described as web-like structures that trap and neutralize microbes at sites of infection. NETs are comprised of chromatin components and neutrophil cytoplasmic proteins. Because...

SAT0163 B-Cell Homeostasis is Disturbed by Immunosuppressive Therapies and After Treatment with Rituximab in Patients with Anca-Associated Vasculitides

BackgroundB-lymphocytes are involved in the pathogenesis of ANCA-associated vasculitides (AAVs), but the knowledge about alterations in peripheral blood B-lymphocytes of AAV patients and the changes in B-lymphocyte subsets after immunosuppressive...

Relationship among antineutrophil cytoplasmic antibody, blood urea nitrogen and complement in patients with eosinophilic granulomatosis polyangiitis (Churg-Strauss syndrome)

Eosinophilic granulomatosis with polyangiitis (EGPA), also known as Churg-Strauss syndrome, is an antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis characterized by a history of asthma, hypereosinophilia. The prevalence of ANCA in EGPA is less common than in other ANCA-associated vasculitis. Increasing evidence of complement activation in the pathogenesis of ANCA-associated vasculitis has been provided by studies in animal models. We examined EGPA patients with cutaneous manifestations as an initial sign and investigated the correlations among clinical, serological and histopathological findings. We focused on differences among ANCA, blood urea nitrogen and complement levels such as complement 3 (C3), C4 and total complement hemolytic activity (CH50). We retrospectively investigated the records of 22 patients (11 male and 11 female) with EGPA admitted to our hospital from 1997-2012. Ten of the 22 patients (46%) were positive for serum myeloperoxidase (MPO)-ANCA. In contrast, all the patients were negative for serum proteinase 3 ANCA. There was a significantly positive correlation between serum CH50 and C4 levels in patients with EGPA. Serum blood urea nitrogen (BUN) levels differed significantly between MPO-ANCA-positive and -negative patients. Serum CH50 levels were higher in MPO-ANCA-positive patients compared to negative patients. Serum BUN levels were higher in elevated CH50 patients compared to normal and low CH50-negative patients. We propose that positive findings for MPO-ANCA with CH50 high activity may be a risk factor for developing renal insufficiency. Assuming there are correlations between the presence of ANCA and complements, earlier diagnosis based on initial efficacious treatment for EGPA.

Complement is crucial in the pathogenesis of ANCA-associated vasculitis

Renal lesions in ANCA-associated vasculitis (AAV) show an absence or paucity of immune deposits. Therefore, complement was not considered a major pathogenic factor. Data from an animal model of AAV, however, suggest involvement of the alternative pathway of complement. The paper by Gou et al. demonstrates activation also of the alternative and final common pathways in patients with AAV. Thus, the complement system might be a target for treatment in human AAV.

Complement in antineutrophil cytoplasmic antibody-associated vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis is a group of autoimmune disorders. It was previously assumed that the complement system is not involved in the development of ANCA-associated vasculitis due to its "pauci-immune" feature in renal histology. However, increasing evidence indicates that activation of the complement system, especially via the alternative complement pathway, plays a crucial role in the pathogenesis of ANCA-associated vasculitis. In this brief review, we discuss the evidence, including invivo, invitro, and clinical studies, for complement system activation in ANCA-associated vasculitis.

Patient stratification and genomics: flares, fizzlers and foxes

Diseases have traditionally been defined predominantly by clinical criteria, sometimes with the assistance of “conventional” laboratory data. Recent advances in genomic technology have begun to find previously undiscovered sub-divisions within what were thought to be single diagnoses, sometimes with significant clinical implications. This talk will discuss the potential for such technologies to redefine the classification and treatment of autoimmune diseases, using two recent examples from Cambridge. The first is the use of a Genome Wide Association Study to determine the genetic underpinning of ANCA-associated Vasculitis (AAV). This study has confirmed a genetic component to AAV pathogenesis, and demonstrated that the AAV clinical syndromes granulomatosis with polyangiitis (GPA: formerly Wegener’s) and microscopic polyangiitis (MPA) are genetically distinct diseases better defined by ANCA specificity for proteinase-3 (PR3) or myeloperoxidase (MPO) rather than clinical syndrome. In addition the response against the autoantigen PR3 (encoded by PRTN3) was found to be a central etiological feature of PR3-ANCA associated vasculitis. Thus PR3- and MPO-ANCA-associated vasculitis must be considered as distinct autoimmune syndromes [1]. The second example will describe the use of whole genome transcriptome analysis of purified CD8 T cells to define two sub-groups within patients with a number of inflammatory diseases (including SLE, AAV, Crohn’s disease and ulcerative colitis). These otherwise “invisible” groups have markedly different long term outcomes [2,3]. This has implications for therapy, and has led to the development of a biomarker now entering clinical trials. Follow-up studies have led to the discovery of a new inflammatory pathway controlling TNFα and IL-10 production that might drive this difference in outcome.

Pathogenesis of ANCA-Associated Vasculitis

Antineutrophil cytoplasmic autoantibodies (ANCA)-associated vasculitides (AAV) are a group of systemic vasculitis syndromes characterized by inflammation and necrosis of blood vessel walls. Genetic, epigenetic, and environmental factors contribute to the etiology and pathogenesis of AAV. On the basis of currently available clinical and experimental evidence, it is reasonable to believe that, in predisposed patients, different triggers can lead to the production of autoantibodies (ANCA) that, in the context of an inflammatory environment, can cause tissue inflammation and vascular injury. Several different pathways and mechanisms in the pathogenesis of AAV are described in this contemporary review.

Physiopathologie des vascularites ANCA-positives

ANCA-associated vasculitides comprise granulomatosis with polyangiitis (GPA) (formerly names Wegener's granulomatosis), Churg-Strauss syndrome (SCS) (which will be renamed GPA and eosinophilia) and microscopic polyangiitis (MPA). Immune cells (dendritic and non dendritic cells) and inflammatory cells (neutrophils, monocytes, macrophages) and resident cells (endothelial cells, fibroblasts) are implicated in the pathophysiology of ANCA-associated vasculitides. One of the targets of ANCA, myeloperoxydase, is only present in the azurophil granules of neutrophils, whereas the other target of these antibodies, proteinase 3, is also present at the internal face of cytoplasmic membrane of neutrophils, as well as at their surface. Anti-myeloperoxydase ANCA are pathogenicin vitroandin vivo, whereas the pathogenicity of anti-proteinase 3 ANCA has only been demonstrated in vitro and recent studies suggest a pathogenic role of ANCA anti-PR3 in mouse model. Two phenotypes of GPA can be distinguished: a granulomatous form, localized to the respiratory tract with Th1 immune response features, and a vasculitic form with Th2 immune response features. Recently, an increase in TH17 lymphocytes at the acute phase and a defect in T regulatory cells at the chronic phase have been identified in GPA. The role of B-lymphocytes in the pathogenesis of ANCA-associated vasculitides is now well documented by the effectiveness of rituximab in the treatment of this condition.

Genetically Distinct Subsets within ANCA-Associated Vasculitis

BackgroundAntineutrophil cytoplasmic antibody (ANCA)–associated vasculitis is a severe condition encompassing two major syndromes: granulomatosis with polyangiitis (formerly known as Wegener's granulomatosis) and microscopic polyangiitis. Its cause is unknown, and there is debate about whether it is a single disease entity and what role ANCA plays in its pathogenesis. We investigated its genetic basis.MethodsA genomewide association study was performed in a discovery cohort of 1233 U.K. patients with ANCA-associated vasculitis and 5884 controls and was replicated in 1454 Northern European case patients and 1666 controls. Quality control, population stratification, and statistical analyses were performed according to standard criteria.ResultsWe found both major-histocompatibility-complex (MHC) and non-MHC associations with ANCA-associated vasculitis and also that granulomatosis with polyangiitis and microscopic polyangiitis were genetically distinct. The strongest genetic associations were with the antigenic specificity of ANCA, not with the clinical syndrome. Anti–proteinase 3 ANCA was associated with HLA-DP and the genes encoding α1-antitrypsin (SERPINA1) and proteinase 3 (PRTN3) (P=6.2×10−89, P=5.6×10−12, and P=2.6×10−7, respectively). Anti–myeloperoxidase ANCA was associated with HLA-DQ (P=2.1×10−8).ConclusionsThis study confirms that the pathogenesis of ANCA-associated vasculitis has a genetic component, shows genetic distinctions between granulomatosis with polyangiitis and microscopic polyangiitis that are associated with ANCA specificity, and suggests that the response against the autoantigen proteinase 3 is a central pathogenic feature of proteinase 3 ANCA–associated vasculitis. These data provide preliminary support for the concept that proteinase 3 ANCA–associated vasculitis and myeloperoxidase ANCA–associated vasculitis are distinct autoimmune syndromes. (Funded by the British Heart Foundation and others.)

Pathogenesis of ANCA-associated vasculitis

To provide an update on animal models of antineutrophil cytoplasmic autoantibody (ANCA)-mediated vasculitis and highlight recent insights gained from studies in these models pertaining to immunopathogenesis. Animal models support the pathogenic potential of myeloperoxidase (MPO)-ANCA. Alternative pathway complement activation has been identified as a novel inflammatory pathway in disease induction and a potential target for intervention. Interventions targeting B cells, antibodies, and signal transduction pathways may hold promise as well. The role of T cells is beginning to be explored, and studies indicate a prominent role for Th17 responses. The link between infection and ANCA vasculitis is well established. In animal models, Toll-like receptor (TLR)4 ligation is involved in disease induction. Ligation of TLRs contributes to the initiation of anti-MPO autoimmune responses in which TLR2 activation induces a Th17 response and TLR9 activation directs a Th1 response. An animal model for PR3-ANCA vasculitis is not available yet but models with a humanized immune system are being developed and show promising first results. Animal models of MPO-ANCA vasculitis have contributed substantially to our understanding of disease immunopathogenesis and have illuminated novel targets for intervention. The development of PR3-ANCA animal models remains a challenge but recent observations in humanized model systems offer hope.

Decreased Numbers of Blood Dendritic Cells and Defective Function of Regulatory T Cells in Antineutrophil Cytoplasmic Antibody-Associated Vasculitis

BackgroundDendritic cells (DC) and regulatory cells (Treg) play pivotal roles in controlling both normal and autoimmune adaptive immune responses. DC are the main antigen-presenting cells to T cells, and they also control Treg functions. In this study, we examined the frequency and phenotype of DC subsets, and the frequency and function of Treg from patients with ANCA-associated vasculitis (AAV).Methodology/Principal FindingsBlood samples from 19 untreated patients with AAV during flares and before any immunosuppressive treatment were analyzed, along with 15 AAV patients in remission and 18 age-matched healthy controls. DC and Treg numbers, and phenotypes were assessed by flow cytometry, and in vitro suppressive function of Treg was determined by co-culture assay. When compared to healthy volunteers, absolute numbers of conventional and plasmacytoid DC were decreased in AAV patients. During the acute phase this decrease was significantly more pronounced and was associated with an increased DC expression of CD62L. Absolute numbers of Treg (CD4+CD25highCD127low/− Tcells) were moderately decreased in patients. FOXP3 and CD39 were expressed at similar levels on Treg from patients as compared to controls. The suppressive function of Treg from AAV patients was dramatically decreased as compared to controls, and this defect was more pronounced during flares than remission. This Treg functional deficiency occurred in the absence of obvious Th17 deviation.ConclusionIn conclusion, these data show that AAV flares are associated with both a decrease number and altered phenotype of circulating DC and point to a role for Treg functional deficiency in the pathogenesis of AAV.