Anti-neutrophil cytoplasmic autoantibodies with specificity for myeloperoxidase in patients with systemic vasculitis and idiopathic necrotizing and crescentic glomerulonephritis

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.

Classification Criteria for ANCA Associated Vasculitis - Ready for Prime Time?

PURPOSE OF REVIEW

This review aims to summarize the evolution and recent developments in the classification of ANCA associated vasculitis (AAV) and to summarize evaluations of the 2022 ACR/EULAR classification criteria of AAV in several cohorts.

RECENT FINDINGS

The classification of AAV has been a field of controversy for some time. The parallel existence of classification criteria and disease definitions produced some overlap in classification, leading to challenges when comparing different cohorts. The 2022 ACR/EULAR classification criteria derived from the largest study ever conducted in vasculitis account for significant changes in vasculitis classification with the integration of ANCA and modern imaging. These criteria show good performance compared to previous ones but also raise questions as ANCA serotypes have substantial impact on classification. In addition, there are some discrepancies with earlier agreed histopathological features of AAV disease phenotypes. During the last 35 years, several sets of classification criteria have evolved to facilitate epidemiologic studies and clinical trials in AAV. While some of these criteria have been in use for many years, they were criticized due to either not using ANCA or not integrating surrogate markers for vasculitis but also due to overlapping when used in parallel. The long-awaited new ACR/EULAR criteria for AAV were published in 2022 and are the result of a large international study, introducing for the first time ANCA and modern imaging in the classification of AAV. Though the criteria show good performance, they bring several other challenges with practical application.

Comparative analysis of renal decline rates in microscopic polyangiitis: unveiling the slowly progressive phenotype

Although rapidly progressive glomerulonephritis (RPGN) is the main renal phenotype of microscopic polyangiitis (MPA), we aim to clarify the clinical features of slowly progressive MPA. This retrospective observational study included 12 patients diagnosed with MPA in our hospital between January 2012 and February 2022. We investigated the differences in surrogate markers, rate of decline of estimated glomerular filtration rate (eGFR) between the slowly progressive and rapidly progressive MPA groups. Of the 12 patients with MPA, 3 (25.0%) had slowly progressive MPA: MPA within 30% decrease in eGFR 3 months pretreatment, all of whom developed RPGN during the course. Patients with slowly progressive MPA had lower levels of C-reactive protein, myeloperoxidase anti-neutrophil cytoplasmic antibodies, and interleukin-6; higher levels of sialylated carbohydrate antigen KL-6. Slowly progressive MPA is not uncommon in our hospital. A linear relationship was found between slower rate of eGFR decline and lower surrogate markers of disease activity. Some MPA cases have slowly progressive glomerulonephritis leading to RPGN, which may be clinically characterized by low disease activity. It may be useful to measure myeloperoxidase anti-neutrophil cytoplasmic antibody in chronic kidney disease with concomitant urinary abnormalities to diagnose MPA with slowly progressive glomerulonephritis.

Regulatory T cells effectively downregulate the autoimmune anti-MPO response and ameliorate anti-MPO induced glomerulonephritis in mice

Regulation of autoreactive cells is key for both prevention and amelioration of autoimmune disease. A better understanding of the key cell population(s) responsible for downregulation of autoreactive cells would provide necessary foundational insight for cellular-based therapies in autoimmune disease. Utilizing a mouse model of anti-myeloperoxidase (MPO) glomerulonephritis, we sought to understand which immune cells contribute to downregulation of the anti-MPO autoimmune response. MPO-/- mice were immunized with whole MPO to induce an anti-MPO response. Anti-MPO splenocytes were then transferred into recipient mice (Rag2-/- mice or WT mice). Anti-MPO titers were followed over time. After anti-MPO splenocyte transfer, WT mice are able to downregulate the anti-MPO response while anti-MPO titers persist in Rag2-/- recipients. Reconstitution with WT splenocytes into Rag2-/- recipients prior to anti-MPO splenocyte transfer enabled mice to downregulate the anti-MPO immune response. Therefore, wildtype splenocytes contain a cellular population that is capable of downregulating the autoimmune response. Through splenocyte transfer, antibody depletion experiments, and purified cell population transfers, we confirmed that the regulatory T cell (Treg) population is responsible for the downregulation of the anti-MPO autoimmune response. Further investigation revealed that functional Tregs from WT mice are capable of downregulating anti-MPO antibody production and ameliorate anti-MPO induced glomerulonephritis. These data underscore the importance of functional Tregs for control of autoimmune responses and prevention of end-organ damage due to autoimmunity.

The role of ANCA in the management of cocaine-induced midline destructive lesions or ENT pseudo-granulomatosis with polyangiitis: a London multicentre case series

OBJECTIVE

In this multicentric study involving three London hospitals, we compared ANCA-positive and ANCA-negative cocaine-induced midline destructive lesions (CIMDL) patients to assess how presence of antineutrophil cytoplasmic antibodies (ANCA) may correlate with disease severity. Our secondary aims are to better classify etiology centered around ANCA positivity and, consequently, better disease management.

METHODS

A retrospective review was performed to identify patients with CIMDL seen between January 2019 and December 2022. Population data including age, sex, presentation, endoscopic findings, duration of cocaine use and active use of cocaine, type of treatment, laboratory (including ANCA serology), radiological, and histological findings were collected.

RESULTS

Forty CIMDL patients (25 male, median age of 42 years) were identified. The majority of them (72.5%) presented with either a septal perforation, a saddle nose deformity (22.5%), and/or a palatal fistula (20.0%). ANCA was positive in 71.1% of cases (66.7% p-ANCA). No statistically significant differences in the general characteristics, type of treatment, laboratory results, radiological or histological findings were observed when comparing ANCA-positive and ANCA-negative CIMDL patients or when comparing p-ANCA and c-ANCA patients. Similarly, no statistically significant difference was obtained when comparing the pattern of distribution of lesions between the two groups.

CONCLUSIONS

A large percentage of CIMDL patients showed positive ANCA test (71.1%) and in the majority of the cases a p-ANCA pattern specifically targeting PR3 (p-ANCA, PR3 + MPO-). However, ANCA positivity or presence of a specific ANCA pattern was not associated with more severe presentation or more aggressive disease. Given its similarities to granulomatosis with polyangiitis (GPA), we recommend the use of the term "cocaine-induced ENT pseudo-GPA" instead of CIMDL.

LEVEL OF EVIDENCE

IV Laryngoscope, 134:2609-2616, 2024.

Very Slowly Progressive Microscopic Polyangiitis: Comparative Analysis with Rapidly Progressive Forms

Microscopic polyangiitis (MPA) is predominantly characterized by rapidly progressive glomerulonephritis (RPGN) associated with myeloperoxidase anti-neutrophil cytoplasmic antibodies (MPO-ANCA). Nonetheless, up to 30% of cases of ANCA-associated vasculitis (AAV) may exhibit a more indolent progression toward renal failure, an aspect less frequently discussed and understood in medical literature. This study seeks to clarify the clinical and pathological distinctions between the slowly and rapidly progressive forms of MPA, thereby enhancing understanding of their distinct pathogeneses and treatment responses. We conducted a comparative analysis of two patients diagnosed with MPA under the 2022 American College of Rheumatology/the European Alliance of Associations for Rheumatology (ACR/EULAR) classification. Evaluations included laboratory tests such as serum creatinine levels, serology for MPO-ANCA, and renal biopsies. Patient 1 exhibited a mere 1.07% decrease in estimated glomerular filtration rate (eGFR) over 6 months, significantly below the RPGN threshold, and demonstrated sclerotic glomerular pathology without active inflammation. This patient also showed lower levels of MPO-ANCA, Birmingham Vasculitis Activity Score (BVAS), and C-reactive protein. Conversely, Patient 2 experienced an 89.9% reduction in eGFR over the same timeframe, accompanied by acute systemic inflammation. The comparative clinical analysis of these cases illuminates clear differences in disease activity. Slowly progressive MPA is marked by lesser disease activity that fosters chronic inflammation, leading to a more gradual decline in renal function. Early diagnosis, facilitated by initial measurements of MPO-ANCA, can enhance disease management and improve patient outcomes.

Interstitial lung diseases associated with ANCA positivity: A different disease spectrum from interstitial pneumonia with autoimmune features

BACKGROUND

Anti-neutrophil cytoplasmic antibody (ANCA) is a type of autoantibodies associated with vasculitis. ANCA positivity is commonly observed in interstitial lung disease (ILD) patients. 7%-10% of ANCA-positive ILD patients don't present any symptoms of systemic vasculitis and are termed ANCA-positive idiopathic interstitial pneumonia (ANCA-IIP). Some researchers propose that ANCA-IIP should be categorized as interstitial pneumonia with autoimmune features (IPAF), although the official ATS/ERS statements exclude ANCA-IIP from this classification. Whether ANCA-IIP should be categorized into the entity of IPAF is still debatable.

METHODS

Patients diagnosed with ANCA-IIP and those with IPAF were analyzed in a retrospective study of ILD. The clinical outcomes were determined through pulmonary function tests (PFTs) after a one-year follow-up, as well as assessing all-cause mortality.

RESULTS

27 patients with ANCA-IIP and 143 patients with IPAF were analyzed from a cohort of 995 patients with ILD. Patients in the ANCA-IIP group had an older age and a high proportion of males compared to those in the IPAF group. PFT results at baseline were similar between the two groups, except for a better FEV1% in the ANCA-IIP group. Glucocorticoid and immunosuppressive therapy improved pulmonary function in patients with IPAF, but it continued to deteriorate after one year of treatment in the ANCA-IIP group. Furthermore, the all-cause mortality rate was significantly higher in the ANCA-IIP group than in the IPAF group (22.2% vs. 6.3%, P = 0.017).

CONCLUSION

The responses to glucocorticoid and immunosuppressive therapy differ between the ANCA-IIP and IPAF groups, leading to divergent prognoses. Therefore, it is inappropriate to classify ANCA-IIP as part of IPAF.

Systemic vasculitis involving the kidney: the nephropathologist's point of view

Kidneys are often targets of systemic vasculitis (SVs), being affected in many different forms and representing a possible sentinel of an underlying multi-organ condition. Renal biopsy still remains the gold standard for the identification, characterization and classification of these diseases, solving complex differential diagnosis thanks to the combined application of light microscopy (LM), immunofluorescence (IF) and electron microscopy (EM). Due to the progressively increasing complexity of renal vasculitis classification systems (e.g. pauci-immune vs immune complex related forms), a clinico-pathological approach is mandatory and adequate technical and interpretative expertise in nephropathology is required to ensure the best standard of care for our patients. In this complex background, the present review aims at summarising the current knowledge and challenges in the world of renal vasculitis, unveiling the potential role of the introduction of digital pathology in this setting, from the creation of hub-spoke networks to the future application of artificial intelligence (AI) tools to aid in the diagnostic and scoring/classification process.

Verification, implementation and harmonization of automated chemiluminescent immunoassays for MPO- and PR3-ANCA detection

OBJECTIVES

Antineutrophil cytoplasmic antibody (ANCA) testing assists clinicians diagnose ANCA-associated vasculitis (AAV). We aimed to verify and harmonize chemiluminescent immunoassays for the detection of myeloperoxidase (MPO)- and proteinase 3 (PR3)-ANCA.

METHODS

An in-house ELISA, a capture ELISA, and a chemiluminescent assay QUANTA Flash on a BIO-FLASH analyzer were used to detect MPO- and PR3-ANCA in sera from 39 patients with AAV, 55 patients with various non-AAV, and 66 patients with connective tissue diseases. The results of the assays were evaluated, and their clinical performance was assessed. The precision and linearity of the QUANTA Flash assays were determined, and likelihood ratios (LRs) for AAV at diagnosis were calculated.

RESULTS

The precision and linearity of the QUANTA Flash assays were confirmed. Overall agreement between 97.5 and 98.8 % and Cohen's kappa coefficients between 0.861 and 0.947 were observed for the results of the QUANTA Flash assays and ELISAs. The diagnostic sensitivity, specificity, and ROC analysis of the assays for AAV were statistically similar (in-house ELISA 89.7 %, 95.0 %, and 0.937; capture ELISA 92.3 %, 98.3 %, and 0.939; and QUANTA Flash 89.7 %, 95.9 %, and 0.972). For the QUANTA Flash assay results, the interval-specific LRs for AAV at diagnosis were: 0-8 CU had LR 0.08, 8-29 CU had LR 1.03, 29-121 CU had LR 7.76, 121-191 CU had LR 12.4, and >191 CU had LR ∞.

CONCLUSIONS

The QUANTA Flash MPO and PR3 assays provide precise and consistent results and have comparable clinical utility for AAV. The calculated LRs were consistent with published LRs, confirming the utility of LRs for harmonization of ANCA results.

Diagnosis of Autoimmune Hepatitis

Autoimmune hepatitis (AIH) presents a diagnostic challenge because it is relatively rare and heterogenous in presentation. This article presents the currently adopted approach to AIH diagnosis and explores the challenges with accurately identifying this disease entity. AIH offers no pathognomonic findings, instead relies on clinical presentation, serology, and histology to make the diagnosis. Diagnostic scoring systems support clinical judgment and serve as valuable tools in diagnosis and research. Histological analysis remains the cornerstone of diagnosis and to this day biopsy is essential to make the diagnosis.

Incidence of Systemic Vasculitis and Clinical Outcomes in Systemic Sclerosis: 2-Years Follow-Up of Asymptomatic Positive for Anti-Neutrophilic Cytoplasmic Antibody

Purpose

Anti-neutrophilic cytoplasmic antibody (ANCA)-associated vasculitis (AAV) overlap with systemic sclerosis (SSc) is uncommon. We aimed to determine the incidence of AAV and define clinical outcomes relevant to asymptomatic screening positive for ANCA in SSc after 2 years of follow-up.

Patients and Methods

The study was a cohort study of 185 Thai adult SSc patients testing for ANCA and having a 2-year follow-up at the Scleroderma Clinic, Khon Kaen University, Thailand. The incidence of AAV and outcomes of those who tested positive for ANCA were evaluated.

Results

A total of 185 SSc patients were tested for ANCA, of whom 21.6% were positive for either cytoplasmic ANCA, perinuclear ANCA (p-ANCA), anti-myeloperoxidase (anti-MPO), or anti-proteinase3 antibody. Only one 52-year-old female patient with dcSSc, negative for initial ANCA test, developed AAV (microscopic polyangiitis) 7 months after the first ANCA test for an incidence of AAV of 0.27 per 100-person-years (95% CI 0.01-1.5). She was positive for p-ANCA and anti-MPO. Eight of those who had an initial test were positive for ANCA and underwent a repeated test. Only two cases persisted as positive for ANCA (1 anti-MPO and 1 anti-PR3) and had no clinicals suspicious of vasculitis. Four cases that had ANCA turned to a negative result.

Conclusion

AAV is a rare complication in SSc, so ANCA may not have any role as a screening test for AAV as it cannot predict the development of AAV in SSc. We suggest testing for ANCA only in SSc patients with clinicals suspicious of AAV.

Neoself Antigens Presented on MHC Class II Molecules in Autoimmune Diseases

Major histocompatibility complex (MHC) class II molecules play a crucial role in immunity by presenting peptide antigens to helper T cells. Immune cells are generally tolerant to self-antigens. However, when self-tolerance is broken, immune cells attack normal tissues or cells, leading to the development of autoimmune diseases. Genome-wide association studies have shown that MHC class II is the gene most strongly associated with the risk of most autoimmune diseases. When misfolded self-antigens, called neoself antigens, are associated with MHC class II molecules in the endoplasmic reticulum, they are transported by the MHC class II molecules to the cell surface without being processed into peptides. Moreover, neoself antigens that are complexed with MHC class II molecules of autoimmune disease risk alleles exhibit distinct antigenicities compared to normal self-antigens, making them the primary targets of autoantibodies in various autoimmune diseases. Elucidation of the immunological functions of neoself antigens presented on MHC class II molecules is crucial for understanding the mechanism of autoimmune diseases.

Dipeptidyl peptidase 1 inhibition as a potential therapeutic approach in neutrophil-mediated inflammatory disease

Neutrophils have a critical role in the innate immune response to infection and the control of inflammation. A key component of this process is the release of neutrophil serine proteases (NSPs), primarily neutrophil elastase, proteinase 3, cathepsin G, and NSP4, which have essential functions in immune modulation and tissue repair following injury. Normally, NSP activity is controlled and modulated by endogenous antiproteases. However, disruption of this homeostatic relationship can cause diseases in which neutrophilic inflammation is central to the pathology, such as chronic obstructive pulmonary disease (COPD), alpha-1 antitrypsin deficiency, bronchiectasis, and cystic fibrosis, as well as many non-pulmonary pathologies. Although the pathobiology of these diseases varies, evidence indicates that excessive NSP activity is common and a principal mediator of tissue damage and clinical decline. NSPs are synthesized as inactive zymogens and activated primarily by the ubiquitous enzyme dipeptidyl peptidase 1, also known as cathepsin C. Preclinical data confirm that inactivation of this protease reduces activation of NSPs. Thus, pharmacological inhibition of dipeptidyl peptidase 1 potentially reduces the contribution of aberrant NSP activity to the severity and/or progression of multiple inflammatory diseases. Initial clinical data support this view. Ongoing research continues to explore the role of NSP activation by dipeptidyl peptidase 1 in different disease states and the potential clinical benefits of dipeptidyl peptidase 1 inhibition.

Evolution of Therapy for ANCA-Associated Vasculitis with Kidney Involvement

ANCA-associated vasculitis (AAV) belongs to a group of small vessel systemic vasculitides characterized by granulomatous and neutrophilic inflammation of various tissues. Patients often have circulating autoantibodies targeting neutrophilic antigens. Although AAV was once associated with severe end-organ damage and extremely high mortality rates, the use of glucocorticoids and cyclophosphamide led to a paradigm change in its treatment. Over the past 20 years, significant progress in understanding the immunopathogenesis of AAV has enabled development of targeted immunotherapies, providing a much better prognosis for patients. This review describes the evolution of treatment of AAV, particularly for patients with kidney involvement.

Clair EW, Ytterberg SR, Stone JH, Robinson WH, Specks U. Activation of a Latent Epitope Causing Differential Binding of Antineutrophil Cytoplasmic Antibodies to Proteinase 3

OBJECTIVE

Proteinase 3 (PR3) is the major antigen for antineutrophil cytoplasmic antibodies (ANCAs) in the systemic autoimmune vasculitis, granulomatosis with polyangiitis (GPA). PR3-targeting ANCAs (PR3-ANCAs) recognize different epitopes on PR3. This study was undertaken to study the effect of mutations on PR3 antigenicity.

METHODS

The recombinant PR3 variants, iPR3 (clinically used to detect PR3-ANCAs) and iHm5 (containing 3 point mutations in epitopes 1 and 5 generated for epitope mapping studies) immunoassays and serum samples from patients enrolled in ANCA-associated vasculitis (AAV) trials were used to screen for differential PR3-ANCA binding. A patient-derived monoclonal ANCA 518 (moANCA518) that selectively binds to iHm5 within the mutation-free epitope 3 and is distant from the point mutations of iHm5 was used as a gauge for remote epitope activation. Selective binding was determined using inhibition experiments.

RESULTS

Rather than reduced binding of PR3-ANCAs to iHm5, we found substantially increased binding of the majority of PR3-ANCAs to iHm5 compared to iPR3. This differential binding of PR3-ANCA to iHm5 is similar to the selective moANCA518 binding to iHm5. Binding of iPR3 to monoclonal antibody MCPR3-2 also induced recognition by moANCA518.

CONCLUSION

The preferential binding of PR3-ANCAs from patients, such as the selective binding of moANCA518 to iHm5, is conferred by increased antigenicity of epitope 3 on iHm5. This can also be induced on iPR3 when captured by monoclonal antibody MCPR2. This previously unrecognized characteristic of PR3-ANCA interactions with its target antigen has implications for studying antibody-mediated autoimmune diseases, understanding variable performance characteristics of immunoassays, and design of potential novel treatment approaches.

An unusual form of kidney injury without glomerulonephritis in microscopic polyangiitis: a case report

BACKGROUND

Microscopic polyangiitis (MPA), a kind of antineutrophil cytoplasmic autoantibody associated vasculitis (AAV), predominantly affects small-sized vessels. MPA is a significant cause of the pulmonary-renal syndrome. Pauci-immune necrotizing and crescentic glomerulonephritis is the typical renal histological feature of AAV. Tubulointerstitial lesions may occur and mostly form with inflammatory cell infiltration in the interstitium. However, a few cases reported only tubulointerstitial involvement without glomerular lesions in patients with MPA.

CASE PRESENTATION

We present an MPA case, a 70-year-old male patient diagnosed with acute kidney injury accompanying the dialysis requirement. Only acute tubulointerstitial nephritis was revealed in kidney biopsy without evidence of glomerular injury. Also, interstitial pulmonary fibrosis was determined on computerized tomography, and myeloperoxidase antineutrophil cytoplasmic autoantibody was positive. Consequently, we have considered the main diagnosis as MPA. We did not prefer a standard tubulointerstitial nephritis treatment regimen due to the presence of life-threatening systemic vasculitis. Treatment was established like crescentic glomerulonephritis. Induction therapy consisted of pulse steroid, cyclophosphamide, and plasmapheresis. Unfortunately, severe SARS-CoV-2 infection caused death during induction therapy in this case.

CONCLUSIONS

The lack of glomerular injury and solely interstitial inflammation is atypical regarding AAV involvement in the kidney. This diversity might be initially considered as only a simple histological elaboration. However, it is a significant entity for guiding the treatment of AAV.

Adult and childhood vasculitis

Vasculitis refers to heterogeneous clinicopathologic disorders that share the histopathology of inflammation of blood vessels. Unrecognized and therefore untreated, vasculitis of the nervous system leads to pervasive injury and disability, making this a disorder of paramount importance to all clinicians. There has been remarkable progress in the pathogenesis, diagnosis, and treatment of primary CNS and PNS vasculitides, predicated on achievement in primary systemic forms. Primary neurological vasculitides can be diagnosed with assurance after intensive evaluation that incudes tissue confirmation whenever possible. Clinicians must choose from among the available immune modulating, suppressive, and targeted immunotherapies to induce and maintain remission status and prevent relapse, unfortunately without the benefit of RCTs, and tempered by the recognition of anticipated medication side effects. It may be said that efforts to define a disease are attempts to understand the very concept of the disease. This has been especially evident in systemic and neurological disorders associated with vasculitis. For the past 100 years, since the first description of granulomatous angiitis of the brain, the CNS vasculitides have captured the attention of generations of clinical investigators around the globe to reach a better understanding of vasculitides involving the central and peripheral nervous system. Since that time it has become increasingly evident that this will necessitate an international collaborative effort.

Unmet needs in ANCA-associated vasculitis: Physicians' and patients' perspectives

In recent years, clinical research has increased significantly and therapies for antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis have improved. However, there are still unanswered questions and unmet needs about AAV patients. The purpose of this review is to examine the frontiers of research related to emerging biomarkers eventually predicting relapse, and new therapeutic approaches, not to mention new quality of life assessment tools. Identifying predictors of relapse may help optimize therapeutic strategies, minimize disease recurrence, and reduce treatment-related side effects. In addition, it is important to recognize that patients may suffer long-term consequences of the disease and its treatment, which, although life-saving, is often associated with significant side effects. Our goal, therefore, is to highlight what has been achieved, the pitfalls, and what still needs to be done, comparing the views of physicians and patients.

Genetics of ANCA-associated vasculitis: role in pathogenesis, classification and management

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) comprises granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA), that share features of pauci-immune small-vessel vasculitis and the positivity of ANCA targeting proteinase-3 (PR3-ANCA) or myeloperoxidase (MPO-ANCA). AAV syndromes are rare, complex diseases and their aetio-pathogenesis is mainly driven by the interaction between environmental and genetic factors. In patients with GPA and MPA, the genetic associations are stronger with ANCA specificity (PR3- versus MPO-ANCA) than with the clinical diagnosis, which, in keeping with the known clinical and prognostic differences between PR3-ANCA-positive and MPO-ANCA-positive patients, supports an ANCA-based re-classification of these disorders. EGPA is also made up of genetically distinct subsets, which can be stratified on ANCA-status (MPO ANCA-positive versus ANCA-negative); these subsets differ in clinical phenotype and possibly in their response to treatment. Interestingly, MPO-ANCA-positive patients with either MPA or EGPA have overlapping genetic determinants, thus strengthening the concept that this EGPA subset is closely related to the other AAV syndromes. The genetics of AAV provides us with essential information to understand its varied phenotype. This Review discusses the main findings of genetic association studies in AAV, their pathogenic implications and their potential effect on classification, management and prognosis.

Vasculitis: What Have We Learned in the Last 50 Years?

Realizing in the fall of 2021 that I had started medical school exactly 50 years ago, on September 7, 1971, I thought that it would be interesting for the 2022 Dunlop-Dottridge Lecture to briefly review what we knew about vasculitis prior to 1971 and then reflect on what we have learned since.

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.

The Spectrum of Autoantibodies in Adult Patients With Idiopathic Pulmonary Hemosiderosis: A Brief Review of the Literature

While autoimmune antibodies or autoantibodies have been reported sporadically in adult patients with idiopathic pulmonary hemosiderosis (IPH), their true prevalence is unknown. The question as to whether any difference exists between antibody-positive and negative patients has not been explored. The primary objective of this paper was to assess the spectrum of autoantibody testing and its positivity rate. The other objectives included a comparative analysis of demographics, symptom onset, clinical manifestations, and differences in clinical outcomes between antibody-positive (cohort A) and negative (cohort B) patients. To that end, we conducted a retrospective review of the relevant published literature. Multiple databases were searched to retrieve studies published between 1990 and 2022.

A total of 35 studies, involving 38 patients, were identified. Five of these patients had a positive autoantibody. Patients in cohort A were older and more likely to be male. The frequencies of testing for these antibodies were as follows: antineutrophil cytoplasmic antibody (ANCA): 37/38 (97.4%), antinuclear antibody (ANA): 31/38 (81.6%), and anti-glomerular basement membrane antibody (anti-GBM): 30/38 (78.9%); 5/38 (13.2%) patients tested positive for an autoantibody, and two of these patients were positive for ANA, two for antithyroid antibody, and one patient tested positive for ANCA, rheumatoid factor (RF), and granulocyte monocyte-colony stimulating factor (GM-CSF) antibody. There was no difference between the cohorts regarding their clinical presentations, recurrence risks, and survival.

The occurrence of autoantibodies is uncommon in adult IPH patients. This is in contrast with the pediatric IPH patient population, where the prevalence is much higher (26.4% vs. 13.2%), and the antibodies are more diverse. Unlike pediatric patients, adult patients with autoantibodies do not necessarily have worse outcomes.

CSF2-dependent monocyte education in the pathogenesis of ANCA-induced glomerulonephritis

Objectives

Myeloid cell activation by antineutrophil cytoplasmic antibody (ANCA) is pivotal for necrotising vasculitis, including necrotising crescentic glomerulonephritis (NCGN). In contrast to neutrophils, the contribution of classical monocyte (CM) and non-classical monocyte (NCM) remains poorly defined. We tested the hypothesis that CMs contribute to antineutrophil cytoplasmic antibody-associated vasculitis (AAV) and that colony-stimulating factor-2 (CSF2, granulocyte-macrophage colony-stimulating factor (GM-CSF)) is an important monocyte-directed disease modifier.

Methods

Myeloperoxidase (MPO)-immunised MPO^−/− mice were transplanted with haematopoietic cells from wild-type (WT) mice, C–C chemokine receptor 2 (CCR2)^−/− mice to abrogate CM, or transcription factor CCAAT–enhancer-binding protein beta (C/EBPβ)^−/− mice to reduce NCM, respectively. Monocytes were stimulated with CSF2, and CSF2 receptor subunit beta (CSF2rb)-deficient mice were used. Urinary monocytes and CSF2 were quantified and kidney Csf2 expression was analysed. CSF2-blocking antibody was used in the nephrotoxic nephritis (NTN) model.

Results

Compared with WT mice, CCR2^−/− chimeric mice showed reduced circulating CM and were protected from NCGN. C/EBPβ^−/− chimeric mice lacked NCM but developed NCGN similar to WT chimeric mice. Kidney and urinary CSF2 were upregulated in AAV mice. CSF2 increased the ability of ANCA-stimulated monocytes to generate interleukin-1β and to promote T_H17 effector cell polarisation. CSF2rb^−/− chimeric mice harboured reduced numbers of kidney T_H17 cells and were protected from NCGN. CSF2 neutralisation reduced renal damage in the NTN model. Finally, patients with active AAV displayed increased urinary CM numbers, CSF2 levels and expression of GM-CSF in infiltrating renal cells.

Conclusions

CMs but not NCMs are important for inducing kidney damage in AAV. CSF2 is a crucial pathological factor by modulating monocyte proinflammatory functions and thereby T_H17 cell polarisation.

Prevalence of autoantibodies in pediatric patients with idiopathic pulmonary hemosiderosis: a scoping review of the literature in the period 1980-2021

Idiopathic pulmonary hemosiderosis (IPH) is a rare disease of unknown etiology. Due to the frequent findings of autoimmune antibodies - autoantibodies, immunologic causation of the diffuse alveolar hemorrhage in IPH has been proposed, to assess the prevalence/frequency and type of autoantibodies in pediatric patients with IPH. In addition, the patient demographics, diagnostic modalities used to diagnose IPH, treatment, and outcomes were also evaluated. Scoping review: The PubMed, Medline, and Embase databases were searched with appropriate MeSH terms to identify relevant papers consistent with the defined inclusion criteria. Thirteen observational studies comprising a total of 352 pediatric patients were included in this review. The majority of subjects were girls 217 out of 352 (61.6%). The mean and median ages of patients ranged from 3.1-6.5 years to 2.3-7 years, respectively. In the 10 studies that specified the number of patients in their cohorts with either at least one positive autoantibody or no antibody, the overall prevalence of autoantibodies was 76 out of 288 patients (26.4%). The prevalence of specific antibodies was as follows: ANA, 20.3%; ANCA, 17%; anti-dsDNA, 9.1%; RF, 12%; anti-SMA, 23.2%; and celiac antibodies, 25.9%. Cow's milk protein allergy was present in 16.2% of the children. The significance of an association between IPH and the presence of autoantibodies has not been clarified. The autoantibodies could be suggestive of an overall immune dysregulation rather than causation. However, limited evidence based on a single study suggests that the presence of ANA may be associated with a higher risk of recurrence and worse outcomes. Further research, including prospective studies, will be crucial to explore a possible genetic linkage between vasculitides, systemic rheumatologic diseases, and IPH.

Targeting Cathepsin C in PR3-ANCA Vasculitis

BACKGROUND

The ANCA autoantigens proteinase 3 (PR3) and myeloperoxidase (MPO) are exclusively expressed by neutrophils and monocytes. ANCA-mediated activation of these cells is the key driver of the vascular injury process in ANCA-associated vasculitis (AAV), and neutrophil serine proteases (NSPs) are disease mediators. Cathepsin C (CatC) from zymogens activates the proteolytic function of NSPs, including PR3. Lack of NSP zymogen activation results in neutrophils with strongly reduced NSP proteins.

METHODS

To explore AAV-relevant consequences of blocking NSP zymogen activation by CatC, we used myeloid cells from patients with Papillon-Lefèvre syndrome, a genetic deficiency of CatC, to assess NSPs and NSP-mediated endothelial cell injury. We also examined pharmacologic CatC inhibition in neutrophil-differentiated human hematopoietic stem cells, primary human umbilical vein cells, and primary glomerular microvascular endothelial cells.

RESULTS

Patients with Papillon-Lefèvre syndrome showed strongly reduced NSPs in neutrophils and monocytes. Neutrophils from these patients produced a negative PR3-ANCA test, presented less PR3 on the surface of viable and apoptotic cells, and caused significantly less damage in human umbilical vein cells. These findings were recapitulated in human stem cells, in which a highly specific CatC inhibitor, but not prednisolone, reduced NSPs without affecting neutrophil differentiation, reduced membrane PR3, and diminished neutrophil activation upon PR3-ANCA but not MPO-ANCA stimulation. Compared with healthy controls, neutrophils from patients with Papillon-Lefèvre syndrome transferred less proteolytically active NSPs to glomerular microvascular endothelial cells, the cell type targeted in ANCA-induced necrotizing crescentic glomerulonephritis. Finally, both genetic CatC deficiency and pharmacologic inhibition, but not prednisolone, reduced neutrophil-induced glomerular microvascular endothelial cell damage.

CONCLUSIONS

These findings may offer encouragement for clinical studies of adjunctive CatC inhibitor in patients with PR3-AAV.

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

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

Autoimmune Hepatitis: Serum Autoantibodies in Clinical Practice

Circulating autoantibodies are a key diagnostic tool in autoimmune hepatitis (AIH), being positive in 95% of the cases if tested according to dedicated guidelines issued by the International Autoimmune Hepatitis Group. They also allow the distinction between type 1 AIH, characterized by positive anti-nuclear and/or anti-smooth muscle antibody, and type 2 AIH, characterized by positive anti-liver kidney microsomal type 1 and/or anti-liver cytosol type 1 antibody. Anti-soluble liver antigen is the only AIH-specific autoantibody, and is found in 20-30% of both type 1 and type 2 AIH. Anti-neutrophil cytoplasmic antibody is frequently positive in type 1 AIH, being associated also with inflammatory bowel disease and with primary/autoimmune sclerosing cholangitis. The reference method for autoantibody testing remains indirect immunofluorescence on triple tissue (rodent liver, kidney and stomach), allowing both the detection of the majority of liver-relevant reactivities, including those autoantibodies whose molecular target antigens are unknown. Of note, the current knowledge of the clinical significance of autoantibodies relies on studies based on this technique. However, immunofluorescence requires trained laboratory personnel, is observer-dependent, and lacks standardization, leading to ongoing attempts at replacing this method with automated assays, the sensitivity, and specificity of which, however, require further studies before they can be used as a reliable alternative to immunofluorescence; currently, they may be used as complementary to immunofluorescence.

Antineutrophil cytoplasmic antibody-associated interstitial lung disease: a review

Over the past three decades, an increasing number of publications have reported the association between interstitial lung disease (ILD) and anti-neutrophil cytoplasmic antibody (ANCA) or ANCA-associated vasculitis (AAV). With this increased awareness, we have reviewed the literature to date and provide an update in this narrative review. The vast majority of cases of ILD have been shown to be in the setting of positive anti-myeloperoxidase antibody and can be present in up to 45% of patients of microscopic polyangiitis, though cases of ILD associated with proteinase 3 ANCA have rarely been reported. Pulmonary fibrosis and ANCA positivity can occur with or without systemic involvement. The pathogenetic mechanisms establishing the relationship between ANCA and the development of pulmonary fibrosis remain unclear. Histologic and radiographic features of ANCA-ILD most commonly reveal usual interstitial pneumonia or non-specific interstitial pneumonia patterns, though other atypical features such as bronchiolitis have been described. ILD in the setting of AAV has been associated with worse outcomes, and thus early identification and treatment in these patients is appropriate. We advocate that ANCA antibody testing be performed as a baseline evaluation in patients presenting with idiopathic interstitial pneumonia. Suggested treatment of ANCA-ILD includes immunosuppression and/or antifibrotic agents, though supporting data and clinical trials to substantiate use of these therapies are needed.

Experimentally Induced Anti-Myeloperoxidase Vasculitis Is Not Attenuated in Factor B or VISTA Deficient Mice

Background

Anti-neutrophil cytoplasmic antibody vasculitis is characterized by antibodies to myeloperoxidase or proteinase 3. Previous work in murine anti-myeloperoxidase vasculitis has shown a role for the alternative pathway complement component factor B and the anaphylatoxin C5a. However, mice deficient in properdin, which stabilizes the alternative pathway convertase, were not protected. V-Type immunoglobulin domain-containing suppressor of T-cell activation (VISTA)-deficient mice were protected in the nephrotoxic nephritis model but the role of VISTA in anti-myeloperoxidase vasculitis is unknown.

Objectives

This study had 2 aims. First, we attempted to reproduce previous findings on the role of factor B in anti-myeloperoxidase vasculitis. Second, we examined the role of VISTA in this model, in order to see if the protection in the nephrotoxic nephritis model extended to anti-myeloperoxidase vasculitis.

Methods

Anti-myeloperoxidase vasculitis was induced in wild type, factor B, or VISTA deficient mice. Disease was assessed by quantifying glomerular crescents and macrophages, in addition to albuminuria and serum creatinine.

Results

When wild type and factor B deficient mice were compared, there were no differences in any of the histological or biochemical parameters of disease assessed. Similarly, when wild type or VISTA deficient mice were compared, there were no differences.

Conclusions

Factor B deficient mice were not protected which is in contrast to previous studies. Therefore alternative pathway activation is not essential in this model, under the conditions used in this study. VISTA deficient mice were not protected, suggesting that therapies targeting VISTA may not be effective in vasculitis.

Crescentic Glomerulonephritis: Pathogenesis and Therapeutic Potential of Human Amniotic Stem Cells

Chronic kidney disease (CKD) leads to significant morbidity and mortality worldwide. Glomerulonephritis (GN) is the second leading cause of CKD resulting in end stage renal failure. The most severe and rapidly progressive type of GN is characterized by glomerular crescent formation. The current therapies for crescentic GN, which consist of broad immunosuppressive drugs, are partially effective, non-specific, toxic and cause many serious side effects including infections, cancer, and cardiovascular problems. Therefore, new and safer therapies are needed. Human amniotic epithelial cells (hAECs) are a type of stem cell which are isolated from the placenta after birth. They represent an attractive and novel therapeutic option for the treatment of various inflammatory conditions owing to their unique and selective immunosuppressive ability, as well as their excellent safety profile and clinical applicability. In this review, we will discuss the immunopathogenesis of crescentic GN, issues with currently available treatments and how hAECs offer potential to become a new and harmless treatment option for this condition.

Case Report: ANCA-Associated Vasculitis Presenting With Rhabdomyolysis and Pauci-Immune Crescentic Glomerulonephritis After Pfizer-BioNTech COVID-19 mRNA Vaccination

As the coronavirus disease 2019 (COVID-19) pandemic is ongoing and new variants of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) are emerging, there is an urgent need for COVID-19 vaccines to control disease outbreaks by herd immunity. Surveillance of rare safety issues related to these vaccines is progressing, since more granular data emerge with regard to adverse events of COVID-19 vaccines during post-marketing surveillance. Interestingly, four cases of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) presenting with pauci-immune crescentic glomerulonephritis (GN) after COVID-19 mRNA vaccination have already been reported. We here expand our current knowledge of this rare but important association and report a case of AAV presenting with massive rhabdomyolysis and pauci-immune crescentic GN after Pfizer-BioNTech COVID-19 mRNA vaccination. As huge vaccination programs are ongoing worldwide, post-marketing surveillance systems must continue to assess vaccine safety important for the detection of any events associated with COVID-19 vaccination. This is especially relevant in complex diseases where diagnosis is often challenging, as in our patient with AAV presenting with massive rhabdomyolysis and pauci-immune crescentic GN.

Methimazole-Induced ANCA Vasculitis: A Case Report

Rapidly progressive glomerulonephritis (RPGN) is a syndrome which presents rapid loss of renal function. Vasculitis represents one of the major causes, often related to anti-neutrophil cytoplasmic antibodies (ANCA). Herein, we report a case of methimazole-induced ANCA-associated vasculitis. A 35-year-old woman complained of weight loss and fatigue for 2 weeks and attended the emergency room with alveolar hemorrhage. She had been diagnosed with Graves’ disease and had been taking methimazole in the past 6 months. Her physical examination showed pulmonary wheezing, hypertension and signs of respiratory failure. Laboratory tests revealed urea 72 mg/dL, creatinine 2.65 mg/dL (eGFR CKD-EPI: 20 mL/min/1.73 m²), urine analysis with >100 red blood cells per high-power field, 24 h-proteinuria: 1.3 g, hemoglobin 6.6 g/dL, white-cell count 7700/mm³, platelets 238,000/mm³, complement within the normal range, negative viral serological tests and ANCA positive 1:80 myeloperoxidase pattern. Chest tomography showed bilateral and diffuse ground-glass opacities, and bronchial washing confirming alveolar hemorrhage. A renal biopsy using light microscopy identified 27 glomeruli (11 with cellular crescentic lesions), focal disruption in glomerular basement membrane and fibrinoid necrosis areas, tubulitis and mild interstitial fibrosis. Immunofluorescence microscopy showed IgG +2/+3, C3 +3/+3 and Fibrinogen +3/+3 in fibrinoid necrosis sites. She was subsequently diagnosed with crescentic pauci-immune glomerulonephritis, mixed class, in the setting of a methimazole-induced ANCA vasculitis. The patient was treated with methimazole withdrawal and immunosuppressed with steroids and cyclophosphamide. Four years after the initial diagnosis, she is currently being treated with azathioprine, and her exams show creatinine 1.30 mg/dL (eGFR CKD-EPI: 52 mL/min/1.73 m²) and negative p-ANCA.

The many roles of myeloperoxidase: From inflammation and immunity to biomarkers, drug metabolism and drug discovery

This review provides a practical guide to myeloperoxidase (MPO) and presents to the reader the diversity of its presence in biology. The review provides a historical background, from peroxidase activity to the discovery of MPO, to its role in disease and drug development. MPO is discussed in terms of its necessity, as specific individuals lack MPO expression. An underlying theme presented throughout brings up the question of the benefit and burden of MPO activity. Enzyme structure is discussed, including accurate masses and glycosylation sites. The catalytic cycle of MPO and its corresponding pathways are presented, with a discussion of the importance of the redox couples of the different states of MPO. Cell lines expressing MPO are discussed and practically summarized for the reader, and locations of MPO (primary and secondary) are provided. Useful methods of MPO detection are discussed, and how these can be used for studying disease processes are implied through the presentation of MPO as a biomarker. The presence of MPO in neutrophil extracellular traps is presented, and the activators of the former are provided. Lastly, the transition from drug metabolism to a target for drug development is where the review concludes.

Occurrence and Antigenic Specificity of Perinuclear Anti-Neutrophil Cytoplasmic Antibodies (P-ANCA) in Systemic Autoimmune Diseases

Perinuclear anti-neutrophilic cytoplasmic antibodies (P-ANCA) recognize heterogeneous antigens, including myeloperoxidase (MPO), lactoferrin, elastase, cathepsin-G and bactericidal/permeability-increasing protein. Although P-ANCA have diagnostic utility in vasculitides, they may also be found in patients with various other systemic autoimmune rheumatic diseases (SARDs). Nevertheless, the clinical significance and the targets recognized by P-ANCA in such patients remain unclear. For this purpose, herein we investigated the occurrence of ANCA-related antigenic specificities in 82 P-ANCA-positive sera by multiplex ELISA, as well as their association with other autoantibodies. The P-ANCA-positive sera corresponded to patients with vasculitides (n = 24), systemic lupus erythematosus (n = 28), antiphospholipid syndrome (n = 5), Sjögren’s syndrome (n = 7), rheumatoid arthritis (n = 3), systemic scleroderma (n = 1), sarcoidosis (n = 1) and Hashimoto′s thyroiditis (n = 13). In most P-ANCA-positive patients studied (51/82, 62.3%), these autoantibodies occurred in high titers (>1:160). The analysis of P-ANCA-positive sera revealed reactivity to MPO in only 50% of patients with vasculitides, whereas it was infrequent in the other disease groups studied. Reactivity to other P-ANCA-related autoantigens was also rarely detected. Our findings support that high P-ANCA titers occur in SARD. The P-ANCA-positive staining pattern is associated with MPO specificity in vasculitides, while in other autoimmune diseases, it mostly involves unknown autoantigens.

Anti-Neutrophil Cytoplasmic Antibodies: To Care or Not to Care

Anti-neutrophil cytoplasmic antibodies (ANCA) associated vasculitis is a disease process with a wide range of presentations, from asymptomatic or minimally symptomatic disease with positive laboratory testing, to florid acute end-organ damage. Consensus has not been established as to the frequency and/or protocol by which ANCA testing should be repeated. We present the case of a 53-year-old woman who initially came to medical attention with persistent dyspnea and pulmonary infiltrates presumed to be due to acute exacerbation of chronic diastolic congestive heart failure. Extensive infectious disease testing was negative, but ANCA testing was positive. However, because antinuclear antibody (ANA) interference in the original sample rendered the test result difficult to interpret, the test was not repeated. The patient presented eight months after the initial hospitalization with acute hypoxemic respiratory failure requiring intubation, with an ANCA titer of 1:1280 with a negative ANA titer, and renal biopsy-proven severe crescentic glomerulonephritis. In the discussion of our case, we review the importance of interpreting ANCA testing in the correct clinical context. The ANCA laboratory testing requires cautious interpretation, and diagnosed ANCA-associated vasculitis (AAV) requires vigilance for prompt and proactive treatment.

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.

Chemokine/Cytokine Levels Correlate with Organ Involvement in PR3-ANCA-Associated Vasculitis

Background: ANCA-associated vasculitis (AAV) is a rare small vessel disease characterized by multi-organ involvement. Biomarkers that can measure specific organ involvement are missing. Here, we ask whether certain circulating cytokines and chemokines correlate with renal involvement and if distinct cytokine/chemokine patterns can differentiate between renal, ear/nose/throat, joints, and lung involvement of AAV. Methods: Thirty-two sets of Birmingham vasculitis activity score (BVAS), PR3-ANCA titers, laboratory marker, and different cytokines were obtained from 17 different patients with AAV. BVAS, PR3-ANCA titers, laboratory marker, and cytokine concentrations were correlated to different organ involvements in active AAV. Results: Among patients with active PR3-AAV (BVAS > 0) and kidney involvement we found significant higher concentrations of chemokine ligand (CCL)-1, interleukin (IL)-6, IL21, IL23, IL-28A, IL33, monocyte chemoattractant protein 2 (MCP2), stem cell factor (SCF), thymic stromal lymphopoietin (TSLP), and thrombopoietin (TPO) compared to patients without PR3-ANCA-associated glomerulonephritis. Patients with ear, nose, and throat involvement expressed higher concentrations of MCP2 and of the (C-X-C motif) ligand-12 (CXCL-12) compared to patients with active AAV and no involvement of these organs. Conclusion: We identified distinct cytokine patterns for renal manifestation and for ear, nose and throat involvement of PR3-AAV. Distinct plasma cytokines might be used as non-invasive biomarkers of organ involvement in AAV.

Serum PR3-ANCA Is a Predictor of Primary Nonresponse to Anti-TNF-α Agents in Patients with Ulcerative Colitis

Background

Anti-tumor necrosis factor-α (TNF-α) agents are effective for moderately to severely active ulcerative colitis (UC). Nonetheless, a proportion of patients fail to respond to these agents as therapy for induction of remission. Recent studies indicated that perinuclear anti-neutrophil cytoplasmic antibody (p-ANCA) may predict response to anti-TNF-α agents in UC patients. However, whether PR3-ANCA can predict primary nonresponse (PNR) to anti-TNF-α agents has not yet been evaluated. The aim of this study was to examine whether PR3-ANCA can predict PNR to anti-TNF-α in UC patients.

Methods

This was a single-center retrospective study. Data were extracted from 50 patients with UC who had measurements of PR3-ANCA and received anti-TNF-α agents for the first time as induction therapy. The primary endpoint of this study was a proportion of patients with PNR stratified by PR3-ANCA positivity. PNR to anti-TNF-α agents was defined as failure to achieve reduction in partial Mayo score by 2 or more points and change to other therapeutics within 6 weeks.

Results

Fourteen (28%) of the 50 patients were PR3-ANCA positive. Seventeen (34%) of the 50 patients demonstrated PNR. Eleven (78.6%) of the 14 PR3-ANCA-positive patients demonstrated PNR, while 6 (16.7%) of the 36 PR3-ANCA-negative patients demonstrated PNR. Multivariate analysis demonstrated that PR3-ANCA positivity was associated with PNR to anti-TNF-α agents (odds ratio 19.29, 95% CI: 3.30-172.67; p = 0.002).

Conclusion

PR3-ANCA positivity can predict PNR to anti-TNF-α agents in UC patients.

Interstitial Lung Disease and Anti-Myeloperoxidase Antibodies: Not a Simple Association

Anti-neutrophil cytoplasmic antibodies (ANCA), mainly anti-myeloperoxidase (MPO) antibodies, have been frequently identified in patients with idiopathic pulmonary fibrosis (IPF). However, their role remains unclear, and only 7–23% of these patients develops clinically overt vasculitis. We aimed to investigate the clinical, serological, and radiological features and prognosis of anti-MPO-positive interstitial lung disease (ILD) patients. Fifty-eight consecutive patients firstly referred for idiopathic interstitial pneumonia and showing serological positivity of anti-MPO antibodies were retrospectively enrolled. For each patient, clinical data, lung function testing, chest high-resolution computed tomography (HRCT) pattern, and survival were recorded. Thirteen patients developed a rheumatic disease during a median follow-up of 39 months. Usual interstitial pneumonia (UIP) was the most frequent ILD pattern, significantly influencing the patients’ survival. In fact, while the 52-week survival of the overall population was 71.4 ± 7.5%, significantly higher than IPF, survivals of anti-MPO patients with UIP pattern and IPF were similar. Forced vital capacity and diffusion lung capacity for CO significantly declined in 37.7 and 41.5% of cases, respectively, while disease progression at chest HRCT was observed in 45.2%. A careful clinical history and evaluation should always be performed in ILD patients with anti-MPO antibodies to quickly identify patients who are developing a systemic rheumatic disease.

Killing three birds with one BPI: Bactericidal, opsonic, and anti-inflammatory functions

Bactericidal/permeability-increasing protein (BPI) is an anti-microbial protein predominantly expressed in azurophilic granules of neutrophils. BPI has been shown to mediate cytocidal and opsonic activity against Gram-negative bacteria, while also blunting inflammatory activity of lipopolysaccharide (LPS). Despite awareness of these functions in vitro, the magnitude of the contribution of BPI to innate immunity remains unclear, and the nature of the functional role of BPI in vivo has been submitted to limited investigation. Understanding this role takes on particular interest with the recognition that autoimmunity to BPI is tightly linked to a specific infectious trigger like Pseudomonas aeruginosa in chronic lung infection. This has led to the notion that anti-BPI autoantibodies compromise the activity of BPI in innate immunity against P. aeruginosa, which is primarily mediated by neutrophils. In this review, we explore the three main mechanisms in bactericidal, opsonic, and anti-inflammatory of BPI. We address the etiology and the effects of BPI autoreactivity on BPI function. We explore BPI polymorphism and its link to multiple diseases. We summarize BPI therapeutic potential in both animal models and human studies, as well as offer therapeutic approaches to designing a sustainable and promising BPI molecule.

IL-10 in Mast Cell-Mediated Immune Responses: Anti-Inflammatory and Proinflammatory Roles

Mast cells (MCs) play critical roles in Th2 immune responses, including the defense against parasitic infections and the initiation of type I allergic reactions. In addition, MCs are involved in several immune-related responses, including those in bacterial infections, autoimmune diseases, inflammatory bowel diseases, cancers, allograft rejections, and lifestyle diseases. Whereas antigen-specific IgE is a well-known activator of MCs, which express FcεRI on the cell surface, other receptors for cytokines, growth factors, pathogen-associated molecular patterns, and damage-associated molecular patterns also function as triggers of MC stimulation, resulting in the release of chemical mediators, eicosanoids, and various cytokines. In this review, we focus on the role of interleukin (IL)-10, an anti-inflammatory cytokine, in MC-mediated immune responses, in which MCs play roles not only as initiators of the immune response but also as suppressors of excessive inflammation. IL-10 exhibits diverse effects on the proliferation, differentiation, survival, and activation of MCs in vivo and in vitro. Furthermore, IL-10 derived from MCs exerts beneficial and detrimental effects on the maintenance of tissue homeostasis and in several immune-related diseases including contact hypersensitivity, auto-immune diseases, and infections. This review introduces the effects of IL-10 on various events in MCs, and the roles of MCs in IL-10-related immune responses and as a source of IL-10.

Systematic Histological Scoring Reveals More Prominent Interstitial Inflammation in Myeloperoxidase-ANCA Compared to Proteinase 3-ANCA Glomerulonephritis

Background: Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic vasculitis, most frequently presenting as microscopic polyangiitis (MPA) or granulomatosis with polyangiitis (GPA). Kidney involvement is a common and severe complication of ANCA AAV which is observed in a considerable subset of patients, mainly affecting glomeruli. However, tubulointerstitial lesions have also been described in ANCA glomerulonephritis (GN). Therefore, we aim to describe active and chronic tubulointerstitial lesions in ANCA GN subtypes by systematic scoring analogous to the Banff scoring system while also utilizing clinical and laboratory findings. Methods: A total of 49 kidney biopsies with ANCA GN were retrospectively included in a single-center cohort study between 2015–2020. Results: We report that MPO-ANCA GN is associated with more severe deterioration of kidney function independent of systemic markers of AAV disease activity, and is also associated with increased proteinuria in MPO-ANCA GN and a decreased fraction of normal glomeruli. Finally, MPO-ANCA GN showed distinct, active, and chronic tubulointerstitial lesions. Conclusion: New insights into the pathophysiology of both entities, as well as differences in the clinical presentation of MPO- versus PR3-ANCA GN, could potentially pave the way for more precise treatment regimens. Therefore, it is important to understand the differences in histopathological presentation, especially in yet underestimated active tubulointerstitial lesions of ANCA GN subtypes. This research could further improve our understanding of distinct pathophysiological mechanisms.

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

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

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

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Dysregulated complement system primes neutrophils.

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

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

Cardiac involvement in eosinophilic granulomatosis with polyangiitis (formerly Churg-Strauss syndrome): Prospective evaluation at a tertiary referral centre

BACKGROUND

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare systemic vasculitis. Cardiac specific involvement (CSI) is caused by coronary artery vasculitis, but also by myocardial eosinophilic infiltration. To date, the prevalence of CSI associated with EGPA is unresolved. Aim of this study was to systematically assess the prevalence and clinical impact of CSI in a consecutive outpatient EGPA population.

METHODS

Between October 2018 and July 2019, we prospectively enrolled 52 consecutive EGPA patients. All underwent comprehensive evaluation including a standardized questionnaire, physical examination, 12-lead-ECG, echocardiography. Cardiac magnetic resonance and 24 h-Holter were performed as deemed clinically appropriate. Cardiac abnormalities were defined as CSI based on the likelihood of their relation to EGPA vasculitis, after exclusion of alternative diagnoses.

RESULTS

52 enrolled patients, mean age 59±1 years. Thirteen of the 52 patients (25%) were classified as CSI+. CSI was characterized by myocarditis in four patients, non-scar-related regional wall motions abnormalities (RWMA) in three, apical thrombosis in two (one also had RWMA), pericarditis in three and non-atherosclerotic coronary disease (Prinzmetal angina and coronaritis) in 2. Five (38%) of the 13 CSI+ patients, presented an apical aneurysm. Peak eosinophil count at diagnosis was higher in CSI+: 8000 /μl vs CSI-: 3000 /μl, p = 0.017. Overall, 2 patients had severe LV dysfunction, 5 required urgent hospitalization and 8 required long-term cardioactive therapy.

CONCLUSIONS

CSI was present in one-quarter of patients, often associated with high peak eosinophils. Myocarditis, RWMA and apical aneurysms were the most common manifestations. Although rarely severe and life-threatening, CSI often required long-term cardioactive treatment.

Avacopan for the Treatment of ANCA-Associated Vasculitis

BACKGROUND

The C5a receptor inhibitor avacopan is being studied for the treatment of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis.

METHODS

In this randomized, controlled trial, we assigned patients with ANCA-associated vasculitis in a 1:1 ratio to receive oral avacopan at a dose of 30 mg twice daily or oral prednisone on a tapering schedule. All the patients received either cyclophosphamide (followed by azathioprine) or rituximab. The first primary end point was remission, defined as a Birmingham Vasculitis Activity Score (BVAS) of 0 (on a scale from 0 to 63, with higher scores indicating greater disease activity) at week 26 and no glucocorticoid use in the previous 4 weeks. The second primary end point was sustained remission, defined as remission at both weeks 26 and 52. Both end points were tested for noninferiority (by a margin of 20 percentage points) and for superiority.

RESULTS

A total of 331 patients underwent randomization; 166 were assigned to receive avacopan, and 165 were assigned to receive prednisone. The mean BVAS at baseline was 16 in both groups. Remission at week 26 (the first primary end point) was observed in 120 of 166 patients (72.3%) receiving avacopan and in 115 of 164 patients (70.1%) receiving prednisone (estimated common difference, 3.4 percentage points; 95% confidence interval [CI], -6.0 to 12.8; P<0.001 for noninferiority; P = 0.24 for superiority). Sustained remission at week 52 (the second primary end point) was observed in 109 of 166 patients (65.7%) receiving avacopan and in 90 of 164 patients (54.9%) receiving prednisone (estimated common difference, 12.5 percentage points; 95% CI, 2.6 to 22.3; P<0.001 for noninferiority; P = 0.007 for superiority). Serious adverse events (excluding worsening vasculitis) occurred in 37.3% of the patients receiving avacopan and in 39.0% of those receiving prednisone.

CONCLUSIONS

In this trial involving patients with ANCA-associated vasculitis, avacopan was noninferior but not superior to prednisone taper with respect to remission at week 26 and was superior to prednisone taper with respect to sustained remission at week 52. All the patients received cyclophosphamide or rituximab. The safety and clinical effects of avacopan beyond 52 weeks were not addressed in the trial. (Funded by ChemoCentryx; ADVOCATE ClinicalTrials.gov number, NCT02994927.).

Neutrophil Extracellular Traps: New Aspects

Neutrophils are the "first line" of defense against pathogens in the locus of inflammation, where they use effector functions such as phagocytosis, degranulation, and formation of reactive oxygen species (ROS). In 2004, Artuto Zychlinsky characterized one more neutrophil effector function-the release of neutrophil extracellular traps (or NETs). NETs are a modified chromatin "decorated" by bactericidal proteins of granules, nucleus, and cytoplasm. The release of NETs can be activated by diverse physiological and pharmacological stimuli and depends on ROS, for which NADPH oxidase is the main source. In the process of NET formation, the release of bactericidal components of granules into the cytoplasm, modification of histones leading to chromatin decondensation, destruction of the nuclear envelope and cytoplasmic membrane with the involvement of gasdermin D protein, and, finally, the release of chromatin outside the cell occurs. At the same time, uncontrolled formation of NETs is a provoking factor in the development of many inflammatory and autoimmune diseases. NETs were found at autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, psoriasis, and vasculitis; NETs are involved in the pathogenesis of cardiovascular, pulmonary, and oncological diseases. In this review, the main ideas about the mechanisms of NET formation, as well as their role in physiological processes and pathogenesis of a number of diseases (including COVID-19), are discussed.