Antineutrophil cytoplasm antibodies directed against myeloperoxidase augment leukocyte-microvascular interactions in vivo

Expression and significance of Fractalkine/CX3CL1 in MPO-AAV-associated glomerulonephritis rats

OBJECTIVE

To investigate the expression and significance of Fractalkine (CX3CL1, FKN) in serum and renal tissue of myeloperoxidase and anti-neutrophil cytoplasmic antibody associated vasculitis (MPO-AAV) rats.

METHODS

Thirty Wistar-Kyoto (WKY) rats were randomly divided into: Control group, MPO-AAV group (400 µg/kg MPO mixed with Freund's complete adjuvant i.p), MPO-AAV + Anti-FKN group (400 µg/kg MPO mixed with Freund's complete adjuvant i.p), anti-FKN group (1 µg/ rat /day, i.p) after 6 weeks. MPO-AAV associated glomerulonephritis model was established by intraperitoneal injection of MPO + Freund's complete adjuvant with 10 mice in each group. The concentration of MPO-ANCA and FKN in serum was detected by Enzyme-linked immunosorbent assay (ELISA). Hematoxylin-eosin (HE) staining was used to detect pathological changes of kidney tissue. Western blot and immunofluorescence staining were used to detect the expression and localization of FKN protein in kidney tissue. Renal function test indicators: 24-hour urinary protein (UAER), blood urea nitrogen (BUN), serum creatinine (Scr). The expression levels of p65NF-κB and IL-6 was detected by Immunohistochemical assays.

RESULTS

Compared with the control group, the serum MPO-ANCA antibody expression level in the MPO-AAV group was significantly increased (P < 0.01), and the contents of UAER, BUN and Scr were significantly up-regulated at 24 h (P < 0.01). Compared with the control group, the glomeruli in the MPO-AAV group had different degrees of damage, infiltration of inflammatory cell, and membrane cell hyperplasia and renal tubule edema. Compared with the control group, rats in the MPO-AAV group had significantly higher levels of FKN in serum and renal tissues (P < 0.01), and high expression of p65NF-κB and IL-6 in renal tissues (P < 0.01) (P < 0.05), whereas anti-FKN reversed the expression of the above factors. In MPO-AAV renal tissue, FKN was mainly expressed in the cytoplasm of renal tubular epithelial cells and glomerular podocytes. In addition, the contents of 24 h UAER, BUN and Scr of renal function in MPO-AAV rats were significantly decreased (P < 0.01) and the damage of renal tissue was significantly ameliorated after the administration of antagonistic FKN.

CONCLUSION

FKN may play a key role in the pathogenesis of MPO-AAV associated glomerulonephritis.

Myeloperoxidase-specific antineutrophil cytoplasmic antibody-associated vasculitis

Myeloperoxidase (MPO)-specific antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (MPO-ANCA-associated vasculitis) is one of two major ANCA-associated vasculitis variants characterised by systemic necrotising vasculitis with few or no immune deposits. MPO-ANCA-associated vasculitis predominantly affects small blood vessels and, in contrast to its counterpart proteinase 3-ANCA-associated vasculitis, is generally not associated with granulomatous inflammation. The kidneys and lungs are the most commonly affected organs. The pathogenesis of MPO-ANCA-associated vasculitis is characterised by loss of tolerance to the neutrophil enzyme MPO. This loss of tolerance leads to a chronic immunopathological response where neutrophils become both the target and effector of autoimmunity. MPO-ANCA drives neutrophil activation, leading in turn to tissue and organ damage. Clinical trials have improved the therapeutic approach to MPO-ANCA-associated vasculitis. However, there remains substantial unmet need regarding relapse frequency, toxicity of current treatment, and long-term morbidity. In this Series paper, we present the current state of research regarding pathogenesis, diagnosis, and treatment of MPO-ANCA-associated vasculitis.

Unravelling the Link between the Gut Microbiome and Autoimmune Kidney Diseases: A Potential New Therapeutic Approach

The gut microbiota and short chain fatty acids (SCFA) have been associated with immune regulation and autoimmune diseases. Autoimmune kidney diseases arise from a loss of tolerance to antigens, often with unclear triggers. In this review, we explore the role of the gut microbiome and how disease, diet, and therapy can alter the gut microbiota consortium. Perturbations in the gut microbiota may systemically induce the translocation of microbiota-derived inflammatory molecules such as liposaccharide (LPS) and other toxins by penetrating the gut epithelial barrier. Once in the blood stream, these pro-inflammatory mediators activate immune cells, which release pro-inflammatory molecules, many of which are antigens in autoimmune diseases. The ratio of gut bacteria Bacteroidetes/Firmicutes is associated with worse outcomes in multiple autoimmune kidney diseases including lupus nephritis, MPO-ANCA vasculitis, and Goodpasture's syndrome. Therapies that enhance SCFA-producing bacteria in the gut have powerful therapeutic potential. Dietary fiber is fermented by gut bacteria which in turn release SCFAs that protect the gut barrier, as well as modulating immune responses towards a tolerogenic anti-inflammatory state. Herein, we describe where the current field of research is and the strategies to harness the gut microbiome as potential therapy.

ANCA-Associated Vasculitis: Practical Issues in Management

ANCA associated vasculitides are multi-system autoimmune diseases which are increasing in prevalence. In this review we will discuss the clinical manifestations and review the management options. We highlight the various trials of induction and maintenance therapy and discuss the areas of unmet need. These include understanding which patients are at highest risk of relapse, clinical adaptation of improved biomarkers of disease activity and tools to discuss long term prognosis.

Animal models for anti-neutrophil cytoplasmic antibody-associated vasculitis: Are current models good enough?

Antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) is a rare and severe systemic autoimmune disease characterized by pauci-immune necrotizing inflammation of small blood vessels. AAV involves multiple organ systems throughout the body. Our knowledge of the pathogenesis of AAV has increased considerably in recent years, involving cellular, molecular and genetic factors. Because of the controlled environment with no other confounding factors, animal models are beneficial for studying the mechanistic details of disease development and for providing novel therapeutic targets with fewer toxic side effects. However, the complexity and heterogeneity of AAV make it very difficult to establish a single animal model that can fully represent the entire clinical spectrum found in patients. The aim of this review is to overview the current status of animal models for AAV, outline the pros and cons of methods, and propose potential directions for future research.

In Vitro Evaluation of the Antiamoebic Activity of Kaempferol against Trophozoites of Entamoeba histolytica and in the Interactions of Amoebae with Hamster Neutrophils

Entamoeba histolytica (E. histolytica) is a parasite in humans that provokes amoebiasis. The most employed drug is metronidazole (MTZ); however, some studies have reported that this drug induces genotoxic effects. Therefore, it is necessary to explore new compounds without toxicity that can eliminate E. histolytica. Flavonoids are polyphenolic compounds that have demonstrated inhibition of growth and dysregulation of amoebic proteins. Despite the knowledge acquired to date, action mechanisms are not completely understood. The present work evaluates the effect of kaempferol against E. histolytica trophozoites and in the interactions with neutrophils from hamster, which is a susceptibility model. Our study demonstrated a significant reduction in the amoebic viability of trophozoites incubated with kaempferol at 150 μM for 90 min. The gene expression analysis showed a significant downregulation of Pr (peroxiredoxin), Rr (rubrerythrin), and TrxR (thioredoxin reductase). In interactions with amoebae and neutrophils for short times, we observed a reduction in ROS (reactive oxygen species), NO (nitric oxide), and MPO (myeloperoxidase) neutrophil activities. In conclusion, we confirmed that kaempferol is an effective drug against E. histolytica through the decrease in E. histolytica antioxidant enzyme expression and a regulator of several neutrophil mechanisms, such as MPO activity and the regulation of ROS and NO.

Proteinase 3 promotes formation of multinucleated giant cells and granuloma-like structures in patients with granulomatosis with polyangiitis

OBJECTIVES

Granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) are autoimmune vasculitides associated with antineutrophil cytoplasm antibodies that target proteinase 3 (PR3) or myeloperoxidase (MPO) found within neutrophils and monocytes. Granulomas are exclusively found in GPA and form around multinucleated giant cells (MGCs), at sites of microabscesses, containing apoptotic and necrotic neutrophils. Since patients with GPA have augmented neutrophil PR3 expression, and PR3-expressing apoptotic cells frustrate macrophage phagocytosis and cellular clearance, we investigated the role of PR3 in stimulating giant cell and granuloma formation.

METHODS

We stimulated purified monocytes and whole peripheral blood mononuclear cells (PBMCs) from patients with GPA, patients with MPA or healthy controls with PR3 or MPO and visualised MGC and granuloma-like structure formation using light, confocal and electron microscopy, as well as measuring the cell cytokine production. We investigated the expression of PR3 binding partners on monocytes and tested the impact of their inhibition. Finally, we injected zebrafish with PR3 and characterised granuloma formation in a novel animal model.

RESULTS

In vitro, PR3 promoted monocyte-derived MGC formation using cells from patients with GPA but not from patients with MPA, and this was dependent on soluble interleukin 6 (IL-6), as well as monocyte MAC-1 and protease-activated receptor-2, found to be overexpressed in the cells of patients with GPA. PBMCs stimulated by PR3 formed granuloma-like structures with central MGC surrounded by T cells. This effect of PR3 was confirmed in vivo using zebrafish and was inhibited by niclosamide, a IL-6-STAT3 pathway inhibitor.

CONCLUSIONS

These data provide a mechanistic basis for granuloma formation in GPA and a rationale for novel therapeutic approaches.

Pathogenesis of anti-neutrophil cytoplasmic antibody-associated vasculitis

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

Advances in remission induction therapy for ANCA-associated vasculitis

Since its first description 40 years ago, huge strides have been made in the management of ANCA-associated vasculitis with improved patient outcomes. The use of cyclophosphamide and/or B-cell depleting therapy alongside glucocorticoids remains the cornerstone of therapy in organ or life-threatening disease, but recent trials have re-evaluated existing treatment strategies, alongside the development of new treatment targets. This has led to refinement of the role of plasma exchange, the use of reduced dosing of oral glucocorticoids with improved patient outcomes, as well as other treatment adjuvants/options of steroid minimization including C5a receptor antagonism and IL-5 inhibition. In this review we examine developments in remission induction therapy for ANCA-associated vasculitis.

A Review of Anti-IL-5 Therapies for Eosinophilic Granulomatosis with Polyangiitis

Eosinophilic granulomatosis with polyangiitis (EGPA), previously known as Churg-Strauss syndrome, is a systemic disorder characterized by asthma, eosinophilia, and vasculitis primarily affecting small vessels. Although this disease is classified as an anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis along with microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA), observations suggest that eosinophils play a vital role in the pathophysiology of EGPA. Therefore, biopsy specimens derived from patients with EGPA demonstrated an increase in eosinophils within the vascular lumen and extravascular interstitium, especially in patients negative for ANCA. In addition, active secretion of eosinophil intracellular components by cytolysis and piecemeal degranulation occurs in the extravascular interstitium and bloodstream. Although the treatment for EGPA is described in the context of ANCA-associated vasculitis along with MPA and GPA, a therapeutic approach to suppress eosinophils is also considered. Monoclonal antibodies directed against interleukin-5 (IL-5) or its receptors are good therapeutic agents because IL-5 plays an important role in eosinophil growth, activation, and survival. Currently, mepolizumab (Nucala), reslizumab (Cinqair), and benralizumab (Fasenra) have been studied for use in patients with EGPA. These monoclonal antibodies were initially approved for use in patients with severe eosinophilic asthma. Mepolizumab is now approved for treating EGPA following the success of phase 3 randomized controlled trial. Therefore, further studies are needed to clarify long-term safety and efficacy of anti-IL-5 agents and establish indications of individual therapeutic agents tailored to individual conditions of patients with EGPA.

The Presence of Antineutrophil Cytoplasmic Antibodies and Antiphospholipid Antibodies in Patients with Severe Acute Respiratory Syndrome Coronavirus 2: A Case-Control Study among Sudanese Patients

Patients infected with COVID-19 are at an increased risk for thrombosis, suggesting a possible role of COVID-19 in the induction of coagulopathy. This study aimed to investigate the presence of prothrombotic antineutrophil cytoplasmic antibodies (ANCA) and antiphospholipid antibodies (aPLs) in the course of COVID-19 infection and to correlate these markers with severity and fatality, suggesting that COVID-19-induced autoimmune thrombosis is a possible axis in the inflammatory circuit of this infection. To investigate this, we conducted a case-control study which included patients with a positive reverse transcription-polymerase chain reaction (RT-PCR) test of COVID-19 and a control group with negative COVID-19 PCR and antibody (IgG-IgM and IgA nucleoprotein) ELISA results. An indirect immunofluorescence assay using granulocyte biochips (Aesku slides from AESKU DIAGNOSTICS, Germany) was used to detect ANCA (IgG), as well as multiplex ELISA for the detection of antiphospholipid antibodies for all patients with COVID-19 and for the control group. The results revealed the detection of antiphospholipid antibodies (IgG) in one patient out of the 45 patients in the case group. 1/45(2.2%) and 7/45(15.6%) tested positive for ANCA. Five were men and two were females, with one case revealed to be positive for both aPL and ANCA. A cytoplasmic reaction on the eosinophil granulocytes was observed in 2 cases; both were positive for ANCA. Other markers (CRP, APTT, PT, INR, ESR, and neutrophil and lymphocyte counts) were included in the study, along with demographic data. No aPL or ANCA reactions were detected for any of the control groups. These findings suggest that aPL and ANCA may be induced during the course of inflammation in COVID-19 and possibly contribute to the disease's severity and mortality.

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.

Down-regulated FcγRII expression on plasma cells is associated with the disease activity of ANCA-associated vasculitis

Objectives

Inhibitory FcγRIIB/CD32B on B cells are critical for immunity regulation to help maintain peripheral tolerance. Altered FcγRIIB expression on B cells has been observed in several autoimmune diseases, and animal studies suggested that FcγRIIB on B cells participates in the pathogenesis of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Here, we investigated the expression of FcγRII (FcγRIIB) on various B cell subsets and the correlation of FcγRII/CD32 expression with disease activity in AAV patients.

Methods

Blood samples of patients with AAV in active stage and in remission were collected. FcγRII/CD32 expressions on various B cell subsets of the whole blood were detected by flow cytometry, and their correlation with clinical and pathological data was analyzed.

Results

The expression of FcγRII/CD32 on plasma cells was significantly lower in AAV patients in active stage than those in both AAV patients in remission and healthy donors. Furthermore, the expression of FcγRII/CD32 on plasma cells negatively correlated with Birmingham Vasculitis Activity Scores and percentages of cellular crescents in renal biopsies.

Conclusion

Hence there is a down-regulation of FcγRIIB/CD32B expression on B cells in patients with AAV, which is associated with the disease activity of AAV.

The presentation, etiologies, pathophysiology, and treatment of pulmonary renal syndrome: A review of the literature

Pulmonary renal syndrome (PRS) is a constellation of different disorders that cause both rapidly progressive glomerulonephritis and diffuse alveolar hemorrhage. While antineutrophil cytoplasmic antibody associated vasculitis and anti-glomerular basement membrane disease are the predominant causes of PRS, numerous other mechanisms have been shown to cause this syndrome, including thrombotic microangiopathies, drug exposures, and infections, among others. This syndrome has high morbidity and mortality, and early diagnosis and treatment is imperative to improve outcomes. Treatment generally involves glucocorticoids and immunosuppressive agents, but treatment targeted to the underlying disorder can improve outcomes and mitigate side effects. Familiarity with the wide range of possible causes of PRS can aid the clinician in workup, diagnosis and early initiation of treatment. This review provides a summary of the clinical presentation, etiologies, pathophysiology, and treatment of PRS.

Glomerulonephritis and autoimmune vasculitis are independent of P2RX7 but may depend on alternative inflammasome pathways

P2RX7, an ionotropic receptor for extracellular adenosine triphosphate (ATP), is expressed on immune cells, including macrophages, monocytes, and dendritic cells and is upregulated on nonimmune cells following injury. P2RX7 plays a role in many biological processes, including production of proinflammatory cytokines such as interleukin (IL)-1β via the canonical inflammasome pathway. P2RX7 has been shown to be important in inflammation and fibrosis and may also play a role in autoimmunity. We have developed and phenotyped a novel P2RX7 knockout (KO) inbred rat strain and, taking advantage of the human-resembling unique histopathological features of rat models of glomerulonephritis, we induced three models of disease: nephrotoxic nephritis, experimental autoimmune glomerulonephritis, and experimental autoimmune vasculitis. We found that deletion of P2RX7 does not protect rats from models of experimental glomerulonephritis or the development of autoimmunity. Notably, treatment with A-438079, a P2RX7 antagonist, was equally protective in WKY WT and P2RX7 KO rats, revealing its 'off-target' properties. We identified a novel ATP/P2RX7/K⁺ efflux-independent and caspase-1/8-dependent pathway for the production of IL-1β in rat dendritic cells, which was absent in macrophages. Taken together, these results comprehensively establish that inflammation and autoimmunity in glomerulonephritis is independent of P2RX7 and reveals the off-target properties of drugs previously known as selective P2RX7 antagonists. Rat mononuclear phagocytes may be able to utilise an 'alternative inflammasome' pathway to produce IL-1β independently of P2RX7, which may account for the susceptibility of P2RX7 KO rats to inflammation and autoimmunity in glomerulonephritis. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Early ultrastructural lesions of anti-neutrophil cytoplasmic antibody- versus complement-associated vasculitis

This study aims to describe electron microscopic findings of vasculitis associated with anti-neutrophil cytoplasmic antibody (ANCA) and complement. Sural nerve biopsy specimens were obtained from 10 patients with microscopic polyangiitis (MPA), a representative ANCA-associated vasculitis, and six patients with nonsystemic vasculitic neuropathy (NSVN), who were negative for ANCA but positive for complement deposition. In patients with MPA, attachment of neutrophils to epineurial vascular endothelial cells, migration of neutrophils to the extravascular space via the penetration of the endothelial layer, and release of neutrophil components to the extracellular space were observed. Such neutrophil-associated lesions were not observed in patients with NSVN. Nonetheless, morphological changes in epineurial vascular endothelial cells, such as increases in cytoplasmic organelles and cytoplasmic protrusions into the vascular lumen, were observed in patients with NSVN. Since these findings were observed where light microscopy-based findings suggestive of vasculitis (e.g., the disruption of vascular structures and fibrinoid necrosis) were absent, they were considered early lesions that preceded the formation of the so-called necrotizing vasculitis. In conclusion, this study enabled the visualization of distinctive early ultrastructural lesions associated with ANCA and complement. Further studies are needed to elucidate the molecular basis of the induction of these fine structural changes, which will contribute to the development of targeted therapies based on specific mechanisms of vasculitis.

Elevated Level of Serum Interleukin-21 and Its Influence on Disease Activity in Anti-Neutrophil Cytoplasmic Antibodies Against Myeloperoxidase-Associated Vasculitis

Interleukin-21 (IL-21) has been shown to play an important role in the immune system. This study aimed to investigate the changes in the level of IL-21 in patients with anti-neutrophil cytoplasmic antibodies against myeloperoxidase (MPO-ANCA)-associated vasculitis (MPO-AAV), as well as explore its influence on disease activity and the potential mechanism. Flow cytometry was performed to detect the percentage of follicular helper T cells (Tfh) among CD4⁺T cells (Tfh%); the percentage of Tfh-expressing inducible costimulator (ICOS) among Tfh cells (ICOS⁺Tfh%); the percentage of Tfh-expressing programmed cell death protein 1 (PD-1) among Tfh cells (PD-1⁺Tfh%); and mean fluorescence intensity of Tfh-expressing ICOS or PD-1 in the peripheral blood. An enzyme-linked immunosorbent assay was used to measure the levels of serum IL-21 and MPO-ANCA. The Birmingham Vasculitis Activity Score was used to evaluate disease activity. Our results revealed that the level of IL-21 in the patient group was significantly higher than that in the healthy control group (1324.2 ± 125.3 pg/mL vs. 704.2 ± 41.1 pg/mL, P < 0.001), and it was an independent factor affecting the disease activity (P = 0.022). Thus, blocking the activity of IL-21 may represent a potential novel target for the future treatment of MPO-AAV.

Increased frequency of IgD-CD27hiCD38hi B cells and its association with the renal involvement in ANCA-associated vasculitis

Background

B cells have been highlighted in the pathogenesis of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) by the identification of activated B cells in granulomatous lesions and the efficacy of B cell depletion in treatment of AAV patients in the current study; we aimed to investigate the frequency of a specific B cell subset, IgD-CD27^hiCD38^hi B cells in AAV patients, and its association with the disease severity of AAV.

Methods

Blood samples of patients with AAV in active stage and in remission were collected. The frequency of IgD-CD27^hiCD38^hi B cells was detected by flow cytometry, and its correlation with clinicopathological parameters was analyzed.

Results

Our results showed a significant increase of circulating IgD-CD27^hiCD38^hi B cells in AAV patients in active stage compared with patients in remission and healthy donors, and the frequency of IgD-CD27^hiCD38^hi B cells correlated with the severity of renal involvement, including serum creatinine, estimated glomerular filtration rate, and percentages of total crescents in renal biopsies.

Conclusions

The results indicated that IgD-CD27^hiCD38^hi B cells could reflect disease severity of renal involvement in AAV.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02796-9.

Mechanisms of vascular damage in ANCA vasculitis

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

Antineutrophil cytoplasmic antibody positivity and clinical implications in COVID-19

Aim: To investigate clinical implications of antineutrophil cytoplasmic antibody (ANCA) positivity detected in COVID-19 patients during follow up. Materials and methods: A retrospective survey in a hospital database was carried out to detect COVID-19 patients in which ANCAs had been tested. Clinical, laboratory and imaging data were collected from this hospital database and compared between ANCA-negative and -positive patients. Results: ANCAs were tested in 87 COVID-19 patients. Eight had positivity in at least one ANCA test. COVID-19 symptoms on admission and rate of pulmonary involvement were similar. Acute phase reactant levels were higher in ANCA-positive patients. Rate of mortality was higher in the ANCA-positive group without statistical significance. Conclusion: ANCA positivity detected during COVID-19 in patients without a prior diagnosis of any rheumatic condition may be related with worse outcomes.

ANCA-Associated Vasculitic Neuropathies: A Review

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is a systemic disorder that frequently affects the peripheral nervous system and consists of three distinct conditions: microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA, previously Wegener’s granulomatosis), and eosinophilic granulomatosis with polyangiitis (EGPA, previously Churg-Strauss syndrome). The neuropathic features associated with this condition usually include mononeuritis multiplex, which reflects the locality of lesions. Findings suggestive of vasculitis are usually found in the epineurium and occur diffusely throughout the nerve trunk. Nerve fiber degeneration resulting from ischemia is sometimes focal or asymmetric and tends to become conspicuous at the middle portion of the nerve trunk. The attachment of neutrophils to endothelial cells in the epineurial vessels is frequently observed in patients with ANCA-associated vasculitis; neutrophils play an important role in vascular inflammation by binding of ANCA. The positivity rate of ANCA in EGPA is lower than that in MPA and GPA, and intravascular and tissue eosinophils appear to participate in neuropathy. Immunotherapy for ANCA-associated vasculitis involves the induction and maintenance of remission to prevent the relapse of the disease. A combination of glucocorticoids along with cyclophosphamide, rituximab, methotrexate, or mycophenolate mofetil is considered depending on the severity of the condition of the organ to induce remission. A combination of low-dose glucocorticoids and azathioprine, rituximab, methotrexate, or mycophenolate mofetil is recommended to maintain remission. The efficacy of anti-interleukin-5 therapy (i.e., mepolizumab) was demonstrated in the case of refractory or relapsing EGPA. Several other new agents, including avacopan, vilobelimab, and abatacept, are under development for the treatment of ANCA-associated vasculitis. Multidisciplinary approaches are required for the diagnosis and management of the disorder because of its systemic nature. Furthermore, active participation of neurologists is required because the associated neuropathic symptoms can significantly disrupt the day-to-day functioning and quality of life of patients with ANCA-associated vasculitis.

Avacopan: An Oral Complement 5a Inhibitor for ANCA-associated Vasculitis

The oral complement 5a receptor antagonist, avacopan, was recently studied in phase II and III clinical trials in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). This article summarizes the study findings and considers the implications for future care of patients with AAV. Avacopan was proven to be safe and noninferior to glucocorticoids for AAV in a study where patients with severe newly diagnosed or relapsing AAV were initially treated with either rituximab or cyclophosphamide. Greater improvement in the glomerular filtration rate, reduced numbers of relapses and better health-related quality of life were observed in the avacopan group compared with the prednisone group. Patients in the avacopan group also had fewer glucocorticoid-associated adverse events and, despite complement inhibition, there were no cases of Neisseria meningitidis infection reported in either group. Future studies should address the long-term safety of avacopan and whether it can completely replace glucocorticoids in AAV-induction protocols and for the management of minor disease relapses.

Characterisation of an enhanced preclinical model of experimental MPO-ANCA autoimmune vasculitis

Experimental autoimmune vasculitis (EAV) is a model of antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) induced by immunisation of susceptible rat strains with myeloperoxidase (MPO). Animals develop circulating MPO-ANCA, pulmonary haemorrhage, and glomerulonephritis, although renal injury is mild and recovers spontaneously without treatment. In this study we aimed to augment the severity of glomerulonephritis. Following induction of EAV on day 0, a sub-nephritogenic dose of nephrotoxic serum (NTS) containing heterologous antibodies to glomerular basement membrane was administered on day 14. This resulted in a significant increase in disease severity at day 28 compared to MPO immunisation alone - with more urinary abnormalities, infiltrating glomerular leucocytes, and crescent formation that progressed to glomerular and tubulointerstitial scarring by day 56, recapitulating important features of human disease. Importantly, the glomerulonephritis remained pauci-immune, and was strictly dependent on the presence of autoimmunity to MPO, as there was no evidence of renal disease following administration of sub-nephritogenic NTS alone or after immunisation with a control protein in place of MPO. Detailed phenotyping of glomerular leucocytes identified an early infiltrate of non-classical monocytes following NTS administration that, in the presence of autoimmunity to MPO, may initiate the subsequent influx of classical monocytes which augment glomerular injury. We also showed that this model can be used to test novel therapeutics by using a small molecule kinase inhibitor (fostamatinib) that rapidly attenuated both glomerular and pulmonary injury over a 4-day treatment period. We believe that this enhanced model of MPO-AAV will prove useful for the study of glomerular leucocyte behaviour and novel therapeutics in AAV in the future. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Characterization of a Rat Model of Myeloperoxidase-Anti-Neutrophil Cytoplasmic Antibody-Associated Crescentic Glomerulonephritis

BACKGROUND/AIM

Necrotizing crescentic glomerulonephritis (GN) associated with anti-neutrophil cytoplasmic antibodies (ANCA) against myeloperoxidase (MPO) is a devastating disease that quickly progresses to kidney failure. Current therapies are broadly immunosuppressive and associated with adverse effects. We wanted to set up a model that could be suitable for testing narrowly targeted therapies.

METHODS

The model was constructed in male Wistar Kyoto rats through injections of human MPO (hMPO) and pertussis toxin, followed by a sub-nephritogenic dose of sheep anti-rat glomerular basement membrane (GBM) serum to boost the disease. Rats were monitored for 35 days. Rats given hMPO alone, saline, or human serum albumin with or without anti-GBM serum were also studied.

RESULTS

Rats receiving hMPO developed circulating anti-hMPO and anti-rat MPO antibodies. Challenging hMPO-immunized rats with the anti-GBM serum led to more glomerular neutrophil infiltration and MPO release, and severe haematuria, heavy proteinuria, and higher blood urea nitrogen than hMPO alone. Pauci-immune GN developed with crescents, affecting 25% of glomeruli. The majority of crescents were fibrocellular. Necrotizing lesions and Bowman capsule ruptures were detected. Cells double positive for claudin-1 (a marker of parietal epithelial cells [PECs]) and neural cell adhesion molecule (NCAM; progenitor PECs) were present in crescents. Double staining for NCAM and Ki-67 established proliferative status of progenitor PECs. Podocyte damage was associated with endothelial and GBM changes by electron microscopy. Monocyte/macrophages and CD4+ and CD8+ T cells accumulated in glomeruli and the surrounding area and in the tubulointerstitium. Lung haemorrhage also manifested.

CONCLUSION

This model reflects histological lesions of human ANCA-associated rapidly progressive GN and may be useful for investigating new therapies.

The risk factors for early mortality and end-stage renal disease in anti-neutrophil cytoplasmic antibody-associated glomerulonephritis: experiences from a single center

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a common disease with high mortality. Kidney involvement in AAV commonly performances as ANCA-associated glomerulonephritis (AAGN). We aimed to identify the risk factors for mortality and end-stage renal disease(ESRD) within 6 months since diagnosis in AAGN patients. A total of 350 AAGN patients were enrolled in our center between 2004 and 2017 retrospectively. We analyzed the demographic, clinical and follow-up data. Factors for mortality and ESRD were investigated with univariate and multivariate Cox regression models. The median follow-up time was 60.8 (IQR 31.2, 84.5) months and 40 (11.4%) patients died within the first 6 months. In the multivariate analysis, age ≥ 65 years (HR = 2.245, 95%CI 1.085-4.645, P = 0.029), high leukocyte counts (HR = 1.089, 95%CI 1.015-1.168, P = 0.018), high Birmingham Vasculitis Activity Score (BVAS) (HR = 1.089, 95%CI 1.017-1.165, P = 0.014), infection (HR = 2.023, 95%CI 1.013-4.042, P = 0.046) and low serum albumin (HR = 0.916, 95%CI 0.845-0.992, P = 0.030) were independent risk factors for all-cause mortality in the first 6 months. A total of 95 patients reached ESRD within the first 6 months. The renal survival rate was 72.9% at 6 months. Multivariate analysis showed that high BVAS (HR = 1.198, 95%CI 1.043-1.376, P = 0.011), high daily urine protein (HR = 1.316, 95%CI 1.046-1.656, P = 0.019) and low eGFR (HR = 0.877, 95%CI 0.804-0.957, P = 0.003) were independent risk factors for ESRD. The mortality and ESRD rates were high in the first 6 months for AAGN patients. High disease activity evaluated by BVAS impacted both on patients' survival and renal survival, while over 65 years of age and infection were risk factors for mortality.

Antineutrophil cytoplasmic antibodies (ANCA) - their role in pathogenesis, diagnosis, and treatment monitoring of ANCA-associated vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) constitutes a group of rare diseases characterized by necrotizing inflammation of small blood vessels and the presence of ANCA. Increasing clinical and experimental evidences support their pathogenic role in AAV, but the exact mechanism is not fully understood. Recently, the important role of neutrophil extracellular traps (NETs) in pathogenesis of AAV is underlined. There is an indication that NETs can be a source for the formation of ANCA. The most common ANCA target antigens are myeloperoxidase (MPO) and proteinase 3 (PR3). Though the mechanism of action of ANCA is still under exploration, ANCA serology is being increasingly used for classification of AAV and revealed as kenner in defining various disease subsets associated with different genetic background, clinical features, treatment response, and prognosis. Controversy exists regarding the utility of serial measurements of ANCA in patients with AAV to monitor treatment and predict disease relapse.

The biology, pathogenetic role, clinical implications, and open issues of serum anti-neutrophil cytoplasmic antibodies

Anti-neutrophil cytoplasmic antibodies (ANCA) are a group of autoantibodies, predominantly IgG, involved in the pathogenesis of several autoimmune disorders, detected either through indirect immunofluorescence or enzyme-linked immunosorbent assay. By means of indirect immunofluorescence, the main patterns are C-ANCA (cytoplasmic) and P-ANCA (perinuclear), while proteinase 3 (PR3) and myeloperoxidase (MPO) represent the main autoantigens in granulomatosis with polyangiitis and microscopic polyangiitis, both belonging to the family of ANCA-associated vasculitis (AAV). While several experiments established the pathogenicity of MPO-ANCA, evidence remains elusive for PR3-ANCA and an additional target antigen, i.e. LAMP2, has been postulated with specific clinical relevance. The presence of a subset of AAV without ANCA may be explained by the presence of further target antigens or the presence of molecules in blood which make ANCA undetectable. A rise in ANCA titers is not necessarily predictive of a flare of disease in AAV if not accompanied by clinical manifestations. ANCA may develop through variable mechanisms, such as autoantigen complementarity, apoptosis impairment, neutrophil extracellular traps dysfunction and molecular mimicry. We will provide herein a comprehensive review of the available evidence on the biological mechanisms, pathogenetic role, and clinical implications of ANCA testing and disease management. Further, we will address the remaining open challenges in the field, including the role of ANCA in inflammatory bowel disease and in cocaine-induced vasculitis.

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.

Infection-induced myeloperoxidase specific antineutrophil cytoplasmic antibody (MPO-ANCA) associated vasculitis: A systematic review

BACKGROUND

We conducted a systematic review to identify cases of infection-induced anti-myeloperoxidase (MPO) antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV).

METHODS

PubMed/Medline databases were searched from inception to July of 2020, according to PRISMA guidelines.

RESULTS

Among the 618 abstracts identified, 18 articles describing 23 patients (60.9% female, mean age 50.5 years) were included. Median time between infection and vasculitis development was 3 months. Five (21.7%) patients expired during follow-up. Vasculitis regressed after the resolution of infection in 12/23 (52.2%). ANCA titers decreased significantly on follow-up in 14/16 patients and in all survivors in which they were measured. Pathogens reported included Mycobacterium spp., Coccidioides spp., Rickettsia rickettsii, Staphylococcus spp., EBV, CMV and Dengue virus.

CONCLUSIONS

MPO-AAV can occur after infection and may regress after its resolution. Infection should be considered in cases of MPO-AAV, as immunosuppressive treatment can have catastrophic results if the infection is not adequately treated.

Is There a Role for Plasma Exchange in ANCA-Associated Vasculitis?

Purpose of review

This review summarises the evidence for the use of therapeutic plasma exchange (TPE) in anti-neutrophil cytoplasm antibody (ANCA)–associated vasculitis. TPE is an extra-corporeal treatment which efficiently removes IgG and other pathogenic small molecules from the blood. There are several mechanistic reasons why this should be of benefit in AAV including the well-described pathogenicity of ANCA.

Recent findings

The recently published PEXIVAS trial is the largest study of TPE in AAV to date. It did not show a benefit for adjunctive TPE on a primary end point of ESRD or death. There was no difference in serious adverse events between those treated with TPE and those treated with immunosuppressive drugs alone.

Conclusions

Based on the results of PEXIVAS, most patients with AAV should not be treated with adjunctive TPE. However, there are subgroups of patients with AAV for whom TPE may still be of benefit, including those with double positivity for anti-GBM antibodies and ANCA.

ANCA-associated vasculitis

The anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) are a group of disorders involving severe, systemic, small-vessel vasculitis and are characterized by the development of autoantibodies to the neutrophil proteins leukocyte proteinase 3 (PR3-ANCA) or myeloperoxidase (MPO-ANCA). The three AAV subgroups, namely granulomatosis with polyangiitis (GPA), microscopic polyangiitis and eosinophilic GPA (EGPA), are defined according to clinical features. However, genetic and other clinical findings suggest that these clinical syndromes may be better classified as PR3-positive AAV (PR3-AAV), MPO-positive AAV (MPO-AAV) and, for EGPA, by the presence or absence of ANCA (ANCA⁺ or ANCA^-, respectively). Although any tissue can be involved in AAV, the upper and lower respiratory tract and kidneys are most commonly and severely affected. AAVs have a complex and unique pathogenesis, with evidence for a loss of tolerance to neutrophil proteins, which leads to ANCA-mediated neutrophil activation, recruitment and injury, with effector T cells also involved. Without therapy, prognosis is poor but treatments, typically immunosuppressants, have improved survival, albeit with considerable morbidity from glucocorticoids and other immunosuppressive medications. Current challenges include improving the measures of disease activity and risk of relapse, uncertainty about optimal therapy duration and a need for targeted therapies with fewer adverse effects. Meeting these challenges requires a more detailed knowledge of the fundamental biology of AAV as well as cooperative international research and clinical trials with meaningful input from patients.

Urinary soluble CD163 as a biomarker of disease activity and relapse in antineutrophil cytoplasm antibody-associated glomerulonephritis

Background

Antineutrophil cytoplasm antibody (ANCA)-associated vasculitis is a chronic relapsing and remitting autoimmune disease. Urinary soluble CD163 (usCD163) has been proposed as a biomarker of active renal vasculitis. We aimed to assess the potential usefulness of usCD163 for diagnosing renal relapse in patients with ANCA-associated glomerulonephritis.

Methods

One hundred and fifty-six samples from 47 patients with ANCA-associated glomerulonephritis belonging to two different cohorts (incident and prevalent) and 20 healthy controls were studied. Patients from the incident cohort were prospectively followed up, and usCD163 concentrations were measured every 3 months. Renal relapses were identified and changes in usCD163 concentrations were analysed.

Results

Normalized usCD163 concentrations were elevated at disease onset in all patients with active renal vasculitis, with a median concentration of 601 ng/mmol (interquartile range 221–1404 ng/mmol). On the other hand, usCD163 concentrations were undetectable among control patients with renal vasculitis in remission. Except for non-responders, usCD163 concentrations progressively decreased in all patients after treatment. In the presence of vasculitis relapse, there was a consistent increase in usCD163 concentrations, compared with previous values. The area under the receiver-operating characteristic curve of absolute and relative changes in usCD163 concentrations to identify relapse of ANCA-associated glomerulonephritis was 0.96 [95% confidence interval (CI) 0.91–1.00; P = 0.001] and 0.95 (95% CI 0.90–1.00; P = 0.001), respectively. Sensitivity and specificity for a relative increase of 20%, or an absolute increase of 20 ng/mmol, in usCD163 concentrations were 100% for both, and 89.3% and 87.5%, respectively. Urinary sCD163 concentrations significantly correlated with Birmingham Vasculitis Activity Score scores at Month 6 (r = 0.737; P = 0.006) and Month 12 (r = 0.804; P = 0.005).

Conclusions

usCD163 represents an accurate biomarker for the detection of active renal vasculitis and relapse. Its close association with disease activity provides additional information for monitoring treatment response.

Animal Models of ANCA Associated Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV) is a rare and severe autoimmune multisystemic disease. Its pathogenesis involves multiple arms of the immune system, as well as complex interactions between immune cells and target organs. Experimental animal models of disease can provide the crucial link from human disease to translational research into new therapies. This is particularly true in AAV, due to low disease incidence and substantial disease heterogeneity. Animal models allow for controlled environments in which disease mechanisms can be defined, without the clinical confounders of environmental and lifestyle factors. To date, multiple animal models have been developed, each of which shed light on different disease pathways. Results from animal studies of AAV have played a crucial role in enhancing our understanding of disease mechanisms, and have provided direction toward newer targeted therapies. This review will summarize our understanding of AAV pathogenesis as has been gleaned from currently available animal models, as well as address their strengths and limitations. We will also discuss the potential for current and new animal models to further our understanding of this important condition.

Spleen tyrosine kinase inhibition is an effective treatment for established vasculitis in a pre-clinical model

The anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitides (AAV) are a group of life-threatening multi-system diseases characterized by necrotising inflammation of small blood vessels and crescentic glomerulonephritis. ANCA are thought to play a direct pathogenic role. Previous studies have shown that spleen tyrosine kinase (SYK) is phosphorylated during ANCA-induced neutrophil activation in vitro. However, the role of SYK in vivo is unknown. Here, we studied its role in the pathogenesis of experimental autoimmune vasculitis, a pre-clinical model of myeloperoxidase-ANCA-induced pauci-immune systemic vasculitis in the Wistar Kyoto rat. Up-regulation of SYK expression in inflamed renal and pulmonary tissue during early autoimmune vasculitis was confirmed by immunohistochemical and transcript analysis. R406, the active metabolite of fostamatinib, a small molecule kinase inhibitor with high selectivity for SYK, inhibited ANCA-induced pro-inflammatory responses in rat leucocytes in vitro. In an in vivo study, treatment with fostamatinib for 14 days after disease onset resulted in rapid resolution of urinary abnormalities, significantly improved renal and pulmonary pathology, and preserved renal function. Short-term exposure to fostamatinib did not significantly affect circulating myeloperoxidase-ANCA levels, suggesting inhibition of ANCA-induced inflammatory mechanisms in vivo. Finally, SYK expression was demonstrated within inflammatory glomerular lesions in ANCA-associated glomerulonephritis in patients, particularly within CD68⁺ve monocytes/macrophages. Thus, our data indicate that SYK inhibition warrants clinical investigation in the treatment of AAV.

A novel 4-dimensional live-cell imaging system to study leukocyte-endothelial dynamics in ANCA-associated vasculitis

Neutrophils, monocytes and the endothelium are critical to ANCA-associated vasculitis (AAV) pathogenesis. This study aimed to develop a 4-dimensional (4D) live-cell imaging system that would enable investigation of spatial and temporal dynamics of these cells in health and disease. We further aimed to validate this system using autologous donor serum from AAV patients and polyclonal ANCA IgG, as well as exploring its potential in the pre-clinical testing of putative therapeutic compounds. Neutrophils and monocytes were isolated from peripheral venous blood of AAV patients or healthy controls and co-incubated on an endothelial monolayer in the presence of autologous serum. Alternatively, polyclonal ANCA IgG was used, following TNF-α priming, and imaged in 4-dimensions for 3 h using a spinning disc confocal microscope. Volocity 6.3^® analysis software was used for quantification of leukocyte dynamics. The use of autologous serum resulted in increased neutrophil degranulation (p = .002), transmigration (p = .0096) and monocyte transcellular transmigration (p = .0013) in AAV patients. Polyclonal MPO-ANCA IgG induced neutrophil degranulation (p < .001) in this system. C5aR1 antagonism reduced neutrophil degranulation (p < .0002). We have developed a novel 4D in vitro system that allows accurate quantification of multiple neutrophil- and monocyte-endothelial interactions in AAV in a single assay. This system has the potential to highlight dynamics key to pathophysiology of disease, as well investigating the impact of potential therapeutics on these functions.

Neutrophil Heterogeneity as Therapeutic Opportunity in Immune-Mediated Disease

Neutrophils are versatile innate effector cells essential for immune defense but also responsible for pathologic inflammation. This dual role complicates therapeutic targeting. However, neither neutrophils themselves nor the mechanisms they employ in different forms of immune responses are homogeneous, offering possibilities for selective intervention. Here we review heterogeneity within the neutrophil population as well as in the pathways mediating neutrophil recruitment to inflamed tissues with a view to outlining opportunities for therapeutic manipulation in inflammatory disease.

Calprotectin as a smoldering activity detection tool and renal prognosis biomarker in ANCA associated vasculitis

BACKGROUND

Calprotectin is produced by neutrophils and macrophages, and released during the acute phase of the ANCA vasculitis. The aim of our study was to determine if serum and urine calprotectin are disease activity and prognosis biomarkers in ANCA vasculitis patients during remission.

METHODS

Forty-two ANCA vasculitis patients were included. Twenty-seven patients were in remission phase under immunosuppressive therapy, and 15 patients were in the acute phase. Four healthy controls were included. We determined calprotectin in serum and urine samples at the time of the inclusion. We recorded the incidence of relapse and the evolution of GFR, proteinuria, hematuria, and C reactive protein and ANCA titer during 24 months of follow-up.

RESULTS

In remission phase, serum calprotectin was higher than in healthy controls but lower compared to acute patients (p = 0.05). Serum calprotectin at inclusion was higher in patients who increased proteinuria during follow-up (p = 0.04), with hematuria (p = 0.08), and with non-decreasing ANCA titer (p = 0.0019). Serum calprotectin at inclusion in stable patients who subsequently decreased GFR during follow-up was higher compared with those with a stable or improving GFR (p = 0.03). Urine calprotectin was lower in patients with sclerotic histology in remission (p = 0.03) and acute phase (p = 0.12) compared to the rest of histologies.

CONCLUSIONS

Worsening of renal function, hematuria, rising proteinuria and non-decreasing ANCA correlated with higher levels of serum calprotectin at recruitment. Low urine calprotectin was found in patients with sclerotic histology. Calprotectin during remission in ANCA vasculitis may be useful to identify subclinical inflammation and worse renal prognosis patients.

Recent advances in understanding of the pathogenesis of ANCA-associated vasculitis

Anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitides (AAV) are rare systemic autoimmune diseases characterised by inflammation of small blood vessels. Recent developments have been made in our understanding of the pathogenesis of these diseases, including the pathogenic role of ANCA, neutrophils and monocytes as mediators of injury, dysregulation of the complement system, and the role of T and B cells. Current treatment strategies for AAV are based on broad immunosuppression, which may have significant side effects. Advances in understanding of the pathogenesis of disease have led to the identification of new therapeutic targets which may lead to treatment protocols with less-toxic side effects. The aim of this review is to summarise current information and recent advances in understanding of the pathogenesis of AAV.

ANCA-Associated Vasculitis: Pathogenesis, Models, and Preclinical Testing

Our understanding of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis has developed greatly since the discovery of ANCA, directed against neutrophil components, in 1982. Observations in human disease, and increasingly sophisticated studies in vitro and in rodent models in vivo, have allowed a nuanced understanding of many aspects of the immunopathogenesis of disease, including the significance of ANCA as a diagnostic and monitoring tool as well as a mediator of microvascular injury. The mechanisms of leukocyte recruitment and tissue injury, and the role of T cells increasingly are understood. Unexpected findings, such as the role of complement, also have been uncovered through experimental studies and human observations. This review focusses on the pathogenesis of ANCA-associated vasculitis, highlighting the challenges in finding new, less-toxic treatments and potential therapeutic targets in this disease. The current suite of rodent models is reviewed, and future directions in the study of this complex and fascinating disease are suggested.

Age-determined severity of anti-myeloperoxidase autoantibody-mediated glomerulonephritis in mice

Background

Anti-neutrophil cytoplasmic antibody associated vasculitis (AAV) is a typical disease of the elderly. In AAV, there is an age-specific increase in disease incidence with age being a predictor of disease outcome. In this study, we aimed to determine the contribution of age to the development of AAV employing a mouse model of anti-myeloperoxidase (MPO) antibody-mediated glomerulonephritis.

Methods

Anti-MPO IgG and lipopolysaccharide (LPS)-mediated glomerulonephritis was induced in 3- and 18-month-old C57Bl6 mice. Clinical and pathological parameters of disease severity, alterations in the immune system and kidney specific changes in these mice were evaluated.

Results

Eighteen-month-old mice developed increased disease severity upon injection of anti-MPO IgG/LPS compared with 3-month-old mice. This was evidenced by increased albuminuria, more extensive glomerular capillary necrosis and increased glomerular neutrophil accumulation. Glomerular crescent formation was mild in both young and old mice. Old mice displayed higher plasma interleukin-6 levels as well as higher proportions of circulating neutrophils and activated monocytes compared with young mice. In addition, renal mRNA levels of inflammatory genes and endothelial adhesion molecules were higher in 18-month-old mice compared with 3-month-old mice.

Conclusion

In conclusion, our results indicate that aged mice develop more severe clinical and pathological disease upon induction of anti-MPO IgG/LPS-mediated glomerulonephritis. These findings may be attributed to age-related changes in the immune system as well as in the kidney itself.

ANCA Glomerulonephritis and Vasculitis

ANCA vasculitis has an associated autoimmune response that produces ANCAs that induce distinct pathologic lesions. Pauci-immune necrotizing and crescentic GN is a frequent component of ANCA vasculitis. ANCA vasculitis is associated with ANCA specific for myeloperoxidase (MPO-ANCA) or proteinase 3 (PR3-ANCA). A diagnosis of ANCA vasculitis should always specify the serotype as MPO-ANCA positive, PR3-ANCA positive, or ANCA-negative. To fully characterize a patient, the serotype also should be accompanied by the clinicopathologic variant if this can be determined: microscopic polyangiitis, granulomatosis with polyangiitis (Wegener), eosinophilic granulomatosis with polyangiitis (Churg-Strauss), or renal-limited vasculitis. ANCA vasculitis is most prevalent in individuals >50 years old. There are racial/ethnic and geographic influences on the prevalence, serotype frequencies, and clinicopathologic phenotypes. There is clinical, in vitro, and animal model evidence that ANCAs cause disease by activating neutrophils to attack small vessels. Immunomodulatory and immunosuppressive therapies are used to induce remission, maintain remission, and treat relapses. Over recent years, there have been major advances in optimizing treatment by minimizing toxic therapy and utilizing more targeted therapy.

Different behavior of myeloperoxidase in two rodent amoebic liver abscess models

The protozoan Entamoeba histolytica is the etiological agent of amoebiasis, which can spread to the liver and form amoebic liver abscesses. Histological studies conducted with resistant and susceptible models of amoebic liver abscesses (ALAs) have established that neutrophils are the first cells to contact invasive amoebae at the lesion site. Myeloperoxidase is the most abundant enzyme secreted by neutrophils. It uses hydrogen peroxide secreted by the same cells to oxidize chloride ions and produce hypochlorous acid, which is the most efficient microbicidal system of neutrophils. In a previous report, our group demonstrated that myeloperoxidase presents amoebicidal activity in vitro. The aim of the current contribution was to analyze in vivo the role of myeloperoxidase in a susceptible (hamsters) and resistant (Balb/c mice) animal models of ALAs. In liver samples of hamsters and mice inoculated intraportally with Entamoeba histolytica trophozoites, the number of neutrophils in ALAs was determined by enzymatic activity. The presence of myeloperoxidase was observed by staining, and its expression and activity were quantified in situ. A significant difference existed between the two animal models in the number of neutrophils and the expression and activity of myeloperoxidase, which may explain the distinct evolution of amoebic liver abscesses. Hamsters and mice were treated with an MPO inhibitor (4-aminobenzoic acid hydrazide). Hamsters treated with ABAH showed no significant differences in the percentage of lesions or in the percentage of amoebae damaged compared with the untreated hamsters. ABAH treated mice versus untreated mice showed larger abscesses and a decreased percentage of damaged amoebae in these lesion at all stages of evolution. Further studies are needed to elucidate the host and amoebic mechanisms involved in the adequate or inadequate activation and modulation of myeloperoxidase.

Mechanisms of Autoantibody-Induced Pathology

Autoantibodies are frequently observed in healthy individuals. In a minority of these individuals, they lead to manifestation of autoimmune diseases, such as rheumatoid arthritis or Graves' disease. Overall, more than 2.5% of the population is affected by autoantibody-driven autoimmune disease. Pathways leading to autoantibody-induced pathology greatly differ among different diseases, and autoantibodies directed against the same antigen, depending on the targeted epitope, can have diverse effects. To foster knowledge in autoantibody-induced pathology and to encourage development of urgently needed novel therapeutic strategies, we here categorized autoantibodies according to their effects. According to our algorithm, autoantibodies can be classified into the following categories: (1) mimic receptor stimulation, (2) blocking of neural transmission, (3) induction of altered signaling, triggering uncontrolled (4) microthrombosis, (5) cell lysis, (6) neutrophil activation, and (7) induction of inflammation. These mechanisms in relation to disease, as well as principles of autoantibody generation and detection, are reviewed herein.

Complement in ANCA-associated vasculitis: mechanisms and implications for management

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of potentially life-threatening autoimmune diseases. The main histological feature in the kidneys of patients with AAV is pauci-immune necrotizing crescentic glomerulonephritis with little immunoglobulin and complement deposition in the glomerular capillary walls. The complement system was not, therefore, initially thought to be associated with the development of AAV. Accumulating evidence from animal models and clinical observations indicate, however, that activation of the complement system - and the alternative pathway in particular - is crucial for the development of AAV, and that the complement activation product C5a has a central role. Stimulation of neutrophils with C5a and ANCA not only results in the neutrophil respiratory burst and degranulation, but also activates the coagulation system and generates thrombin, thus bridging the inflammation and coagulation systems. In this Review, we provide an overview of the clinical, in vivo and in vitro evidence for a role of complement activation in the development of AAV and discuss how targeting the complement system could provide opportunities for therapy.

The role of monocytes in ANCA-associated vasculitides

The anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitides (AAV) are a heterogeneous group of diseases causing inflammation in small blood vessels and linked by the presence of circulating ANCA specific for proteinase 3 (PR3) or myeloperoxidase (MPO). These antigens are present both in the cytoplasmic granules and on the surface of neutrophils, and the effect of ANCA on neutrophil biology has been extensively studied. In contrast, less attention has been paid to the role of monocytes in AAV. These cells contain PR3 and MPO in lysosomes and can also express them at the cell surface. Monocytes respond to ANCA by producing pro-inflammatory and chemotactic cytokines, reactive-oxygen-species and by up-regulating CD14. Moreover, soluble and cell surface markers of monocyte activation are raised in AAV patients, suggesting an activated phenotype that may persist even during disease remission. The presence of monocyte-derived macrophages and giant cells within damaged renal and vascular tissue in AAV also attests to their role in pathogenesis. In particular, their presence in the tertiary lymphoid organ-like granulomas of AAV patients may generate an environment predisposed to maintaining autoimmunity. Here we discuss the evidence for a pathogenic role of monocytes in AAV, their role in granuloma formation and tissue damage, and their potential to both direct and maintain autoimmunity. ANCA-activation of monocytes may therefore provide an explanation for the relapsing-remitting course of disease and its links with infections. Monocytes may thus represent a promising target for the treatment of this group of life-threatening diseases.

ANCA-associated vasculitis - clinical utility of using ANCA specificity to classify patients

The anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) are a heterogeneous group of rare syndromes characterized by necrotizing inflammation of small and medium-sized blood vessels and the presence of ANCAs. Several clinicopathological classification systems exist that aim to define homogeneous groups among patients with AAV, the main syndromes being microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA) and eosinophilic GPA (EGPA). Two main types of ANCA can be detected in patients with AAV. These ANCAs are defined according to their autoantigen target, namely leukocyte proteinase 3 (PR3) and myeloperoxidase (MPO). Patients with GPA are predominantly PR3-ANCA-positive, whereas those with MPA are predominantly MPO-ANCA-positive, although ANCA specificity overlaps only partially with these clinical syndromes. Accumulating evidence suggests that ANCA specificity could be better than clinical diagnosis for defining homogeneous groups of patients, as PR3-ANCA and MPO-ANCA are associated with different genetic backgrounds and epidemiology. ANCA specificity affects the phenotype of clinical disease, as well as the patient's initial response to remission-inducing therapy, relapse risk and long-term prognosis. Thus, the classification of AAV by ANCA specificity rather than by clinical diagnosis could convey clinically useful information at the time of diagnosis.

Lessons from a double-transgenic neutrophil approach to induce antiproteinase 3 antibody-mediated vasculitis in mice

ANCA to either PR3 or MPO are found in patients with necrotizing vasculitis and glomerulonephritis. ANCA binding to their target antigens on neutrophils and subsequent neutrophil activation are pivotal disease mechanisms that lead to vascular inflammation and necrosis. ANCA interaction with PR3 is more complex than with MPO as the neutrophil-specific CD177 receptor is involved in PR3 surface expression and PR3-ANCA-induced neutrophil activation. Modeling human disease is important to clinical research. Highly successful mouse models of MPO-ANCA vasculitis exist; however, recapitulating PR3-ANCA vasculitis has not been successful. We generated double-transgenic (DT) mice that expressed human PR3 and CD177 under a myeloid-specific huMRP8 promoter in an attempt to model PR3-ANCA vasculitis. DT mice strongly expressed the human transgenes in and on murine neutrophils and bound murine and human anti-PR3 antibodies. Nevertheless, passive transfer of these antibodies into LPS-primed DT mice or immunization of C57BL/6 mice with human PR3 followed by irradiation and transplantation of DT bone marrow failed to induce glomerulonephritis. Further analyses revealed that anti-PR3 antibodies did not activate DT neutrophils as shown by superoxide generation. Moreover, we found that mice did not properly process human pro-PR3 into mature PR3 and, consequently, the signaling complex between PR3, CD177, and CD11b, which promotes neutrophil activation by anti-PR3 antibodies, failed to form. We conclude that important species differences in PR3 and CD177 exist between men and mice that prevented successful generation of a murine anti-PR3 antibody model.