Autoantibodies to hLAMP-2 in ANCA-negative pauci-immune focal necrotizing GN

Antineutrophil cytoplasmic antibody-negative pauci-immune glomerulonephritis in a patient with Waldenstrom macroglobulinaemia

Waldenstrom macroglobulinaemia (WM), the predominant subtype of lymphoplasmacytic lymphoma with bone marrow involvement and serum IgM paraprotein, is a haematological condition commonly associated with renal parenchymal involvement. However, antineutrophil cytoplasmic antibody (ANCA)-negative pauci-immune crescentic glomerulonephritis (PICGN) in kidney infiltrated by lymphoma is very rare, with only two cases described in chronic lymphocytic leukaemia in English literature so far. We herein report the first patient with WM developing ANCA-negative PICGN. He was a 76-year-old male who presented with elevated serum globulin level and bilateral groin lymph node enlargement, subsequently diagnosed to have WM after pathologic examination of the bone marrow and groin lymph node. One month later, he was found to have acute kidney injury and proteinuria. Renal biopsy confirmed the presence of parenchymal involvement by WM accompanied by PICGN; while ANCA testing was negative. He was treated with pulse methylprednisolone followed by oral prednisolone. In addition, six courses of intravenous rituximab and oral cyclophosphamide were given. There was significant improvement in both his renal and haematological conditions. The clinical course of this case suggested that ANCA-negative PICGN may represent a paraneoplastic syndrome and a rare manifestation of WM-associated renal lesion. Early kidney biopsy and prompt treatment may improve the outcome of patients.

Anti-LAMP-2 Antibody Seropositivity in Children with Primary Systemic Vasculitis Affecting Medium- and Large-Sized Vessels

Chronic primary systemic vasculitis (PSV) comprises a group of heterogeneous diseases that are broadly classified by affected blood vessel size, clinical traits and the presence (or absence) of anti-neutrophil cytoplasmic antibodies (ANCA) against proteinase 3 (PR3) and myeloperoxidase (MPO). In small vessel vasculitis (SVV), ANCA are not present in all patients, and they are rarely detected in patients with vasculitis involving medium (MVV) and large (LVV) blood vessels. Some studies have demonstrated that lysosome-associated membrane protein-2 (LAMP-2/CD107b) is a target of ANCA in SVV, but its presence and prognostic value in childhood MVV and LVV is not known. This study utilized retrospective sera and clinical data obtained from 90 children and adolescents with chronic PSV affecting small (SVV, n = 53), medium (MVV, n = 16), and large (LVV, n = 21) blood vessels. LAMP-2-ANCA were measured in time-of-diagnosis sera using a custom electrochemiluminescence assay. The threshold for seropositivity was established in a comparator cohort of patients with systemic autoinflammatory disease. The proportion of LAMP-2-ANCA-seropositive individuals and sera concentrations of LAMP-2-ANCA were assessed for associations with overall and organ-specific disease activity at diagnosis and one-year follow up. This study demonstrated a greater time-of-diagnosis prevalence and sera concentration of LAMP-2-ANCA in MVV (52.9% seropositive) and LVV (76.2%) compared to SVV (45.3%). Further, LAMP-2-ANCA-seropositive individuals had significantly lower overall, but not organ-specific, disease activity at diagnosis. This did not, however, result in a greater reduction in disease activity or the likelihood of achieving inactive disease one-year after diagnosis. The results of this study demonstrate particularly high prevalence and concentration of LAMP-2-ANCA in chronic PSV that affects large blood vessels and is seronegative for traditional ANCA. Our findings invite reconsideration of roles for autoantigens other than MPO and PR3 in pediatric vasculitis, particularly in medium- and large-sized blood vessels.

A pan-cancer analysis of prognostic significance and immunological role of lysosomal-associated membrane protein 3

Lysosomal dysfunction can drive carcinogenesis. Lysosomal-associated membrane protein 3 (LAMP3), is a member of the Lysosome Associated Membrane Proteins and is involved in the malignant phenotype such as tumour metastasis and drug resistance, while the mechanisms that regulate the malignant progression of tumour remain vague. Our study aims to provide a more systematic and comprehensive understanding of the role of LAMP3 in the progression of various cancers by various databases.We explored the role of LAMP3 in pan-cancer using The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) database. Multiple online web platforms and software were used for data analysis, including HPA, TIMER, TISIDB, GEPIA, UALCAN, Kaplan-Meier plotter, DAVID and TIGER. The immunohistochemistry was used to quantify the LAMP3 and PD-L1 expression levels in cancer.High LAMP3 expression was found in most cancers and differentially expressed across molecular and immune subtypes. The expression of LAMP3 was involved in the immune-associated processes of Antigen processing and presentation, Th17 cell differentiation, Th1 and Th2 cell differentiation, and the immune-associated pathways of T cell receptor and B cell receptor signalling pathways in most cancers. It also correlated with genetic markers of immunomodulators in various cancers. LAMP3 and PD-L1 expression in BRCA and HNSC tissues was higher than that in corresponding adjacent normal tissues by immunohistochemistry. There is a significant correlation between the expression of LAMP3 and PD-L1.Our study elucidates that LAMP3 has different expression patterns and genetic alteration patterns in different tumours. It is a potential biomarker for immune-related cancer diagnosis, prognosis and efficacy prediction.

Comparison of Clinico-pathologic features and outcomes of ANCA negative and ANCA positive pauci immune crescentic glomerulonephritis: A single centre study

Introduction

Pauci-immune crescentic glomerulonephritis (PICN) is an important cause of rapidly progressive renal failure. 10-40% of PICN cases have ANCA (antineutrophil cytoplasmic antibody) negative serology. The present study compared clinico-pathologic features, Brix's renal risk score, Berden's histopathological classes and differences in outcome between ANCAnegative vs ANCA positive PICN patients.

Materials and Methods

Sixty-one patients of biopsy-proven PICN were studied. Biochemical findings and ANCA serology were recorded. Renal biopsy slides were reviewed along with direct immunofluorescence. Clinical and histological features were compared between ANCA negative and positive PICN using the Man Whitney U test and Chi-square test. Patients were compared for distribution in Berden's histological classes and Brix's renal risk categories. Patient and renal survival were compared using Kaplan-Meier survival analysis.

Results

ANCA negative PICN patients were younger (44.9 ± 16.5 years vs 53.6 ± 15.1 years, P = 0.049). Nasal (0 vs 18%, P = 0.035) and pulmonary involvement (9% vs 38%, P = 0.014) were lower in ANCA negative group. Both ANCA groups had similar renal biochemical profiles, percentage normal glomeruli, 16.3 ± 18.2 vs 21.7 ± 20.4 and percentage glomeruli with crescents, 64.5 ± 28.1 vs 64.3 ± 27.1. Twenty-seven per cent of ANCA negative cases fell in the sclerotic class in Berden's classification vs just 2.5% in ANCA positive group (p = 0.037) without significant difference in Brix's renal risk categories (p = 0.329). Thirteen per cent of ANCA negative patients achieved complete remission on treatment compared to 33% in ANCA positive patients. Patient survival and overall probability of progressing to ESRD were similar in the two groups.

Conclusion

ANCA negative PICN cases present at younger ages. Nasal and pulmonary involvement is uncommon in these patients. Patient survival and progression to ESRD are similar in both ANCA groups.

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.

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.

Metabolomics combined with clinical analysis explores metabolic changes and potential serum metabolite biomarkers of antineutrophil cytoplasmic antibody-associated vasculitis with renal impairment

Background

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is an autoimmune systemic disease, and the majority of AAV patients have renal involvement presenting as rapid progressive glomerulonephritis (GN). Currently, the clinically available AAV markers are limited, and some of the newly reported markers are still in the nascent stage. The particular mechanism of the level changes of various markers and their association with the pathogenesis of AAV are not well defined. With the help of metabolomics analysis, this study aims to explore metabolic changes in AAV patients with renal involvement and lay the foundation for the discovery of novel biomarkers for AAV-related kidney damage.

Methods

We performed liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based on serum samples from patients with AAV (N = 33) and healthy controls (N = 33) in order to characterize the serum metabolic profiling. The principal component analysis (PCA) and orthogonal partial least-squares-discriminant analysis (OPLS-DA) were used to identify the differential metabolites. Least Absolute Shrinkage and Selection Operator (LASSO) and eXtreme Gradient Boosting (XGBoost) analysis were further conducted to identify the potential diagnostic biomarker. A receiver operating characteristic (ROC) curve analysis was conducted to evaluate the diagnostic performance of the identified potential biomarker.

Results

A total of 455 metabolites were detected by LC-MS analysis. PCA and OPLS-DA demonstrated a significant difference between AAV patients with renal involvement and healthy controls, and 135 differentially expressed metabolites were selected, with 121 upregulated and 14 downregulated. Ninety-two metabolic pathways were annotated and enriched based on the KEGG database. N-acetyl-L-leucine, Acetyl-DL-Valine, 5-hydroxyindole-3-acetic acid, and the combination of 1-methylhistidine and Asp-phe could accurately distinguish AAV patients with renal involvement from healthy controls. And 1-methylhistidine was found to be significantly associated with the progression and prognosis of AAV with renal impairment. Amino acid metabolism exhibits significant alternations in AAV with renal involvement.

Conclusion

This study identified metabolomic differences between AAV patients with renal involvement and non-AAV individuals. Metabolites that could accurately distinguish patients with AAV renal impairment from healthy controls in this study, and metabolites that were significantly associated with disease progression and prognosis were screened out. Overall, this study provides information on changes in metabolites and metabolic pathways for future studies of AAV-related kidney damage and lays a foundation for the exploration of new biomarkers of AAV-related kidney damage.

Type of ANCA May Be Indispensable in Distinguishing Subphenotypes of Different Clinical Entities in ANCA-Associated Vasculitis

The traditional nomenclature system for classifying antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) based on clinical phenotype describes granulomatosis with polyangiitis (GPA), eosinophilic granulomatosis with polyangiitis (EGPA) and microscopic polyangiitis (MPA) as distinct clinical entities. This classification has proved its expedience in clinical trials and everyday clinical practice; yet, a substantial overlap in clinical presentation still exists and often causes difficulties in prompt definition and clinical distinction. Additionally, new insights into the AAV pathogenesis point out that PR3 and MPO-AAV may not represent expressions of the same disease spectrum but rather two distinct disorders, as they display significant differences. Thus, it is supported that a classification based on ANCA serotype (PR3-ANCA, MPO-ANCA or ANCA-negative) could be more accurate and also closer to the nature of the disease compared to the phenotype-based one. This review aims to elucidate the major differences between PR3 and MPO-AAV in terms of epidemiology, pathogenesis, histological and clinical manifestations and response to therapeutic approaches.

The Association of Serum Anti-Lysosomal-Associated Membrane Protein-2 Antibody with Vasculitis Combined with Hypertension

The aim of this study was to explore the association of serum anti-lysosomal-associated membrane protein-2 (anti-LAMP-2) antibody with vasculitis combined with hypertension (VAS-HTN). A total of 51 VAS-HTN patients, 46 essential hypertension (EH) patients, and 46 healthy controls (HC) were included in the study. Serum anti-LAMP-2 antibody levels are increased in VAS-HTN patients as compared with EH and HC (all $P<0.05$ ). Serum anti-LAMP-2 antibody levels were significantly higher in active stage patients than those in non-active stage patients and HC (all $P<0.05$ ). The correlation analysis showed a significant positive correlation between serum anti-LAMP-2 antibody levels and the Birmingham Vasculitis Activity Score (BVAS) and hypersensitive C-reactive protein (Hs-CRP) (all $P<0.05$ ). Among the subsets of VAS-HTN, the levels of serum anti-LAMP-2 antibody were remarkably higher in all VAS-HTN subsets compared with HC (all $P<0.05$ ). More interestingly, the levels of serum anti-LAMP-2 antibody were remarkably increased in polyarteritis nodosa (PAN) patients compared with ANCA-associated vasculitis and Takayasu arteritis patients (all $P<0.05$ ). In addition, there was a significant positive correlation between serum anti-LAMP-2 antibody levels and BAVS and Hs-CRP in PAN patients (all $P<0.05$ ). Multivariate logistic regression analysis showed that the anti-LAMP-2 antibody was independently associated with VAS-HTN. The levels of serum anti-LAMP-2 antibody were remarkably increased in VAS-HTN patients compared to EH and HC and might reflect the disease activity. The anti-LAMP-2 antibody may be a potential biomarker for diagnosis and estimating the disease activity in VAS-HTN.

Serum ANCA and Overall Mortality: A 10-Year Retrospective Cohort Study on 1,024 Italian Subjects

Background

Antineutrophil cytoplasmic antibodies (ANCA) are primarily involved in the pathogenesis of ANCA-associated vasculitides (AAV). However, ANCA may also be present in healthy subjects and in patients with autoimmune disorders different from AAV. We hypothesized that serum ANCA are associated with a worse prognosis in disorders other than AAV.

Objective

We investigated the association between the overall survival and the presence of serum ANCA in 1,024 Italian subjects with various testing indications in a 10-year interval.

Methods

In this retrospective cohort study, a population of 6,285 patients (many of whom were subsequently excluded due to our criteria) who tested for ANCA at a single center in 10 years was considered, and life status and comorbidities of subjects were collected. We compared the overall survival of ANCA-positive and ANCA-negative patients by means of Kaplan-Meier curves, while a multivariable adjusted Cox regression was used to evaluate the association between the ANCA status and the outcome (death) in terms of hazard ratios (HR) with 95% confidence intervals (CI).

Results

The positivity of perinuclear ANCA (pANCA) increased significantly mortality (HR, 1.60; 95% CI, 1.10–2.32), while cytoplasmic ANCA (cANCA) positivity failed to show a significant association (HR, 1.43; 95% CI, 0.77–2.68). The increased mortality rate was observed for both pANCA and cANCA in patients suffering from rheumatic disorders. No association was found between mortality and anti-MPO (HR, 0.63; 95% CI, 0.20–2.00) or anti-PR3 (HR, 0.98; 95% CI, 0.24–3.96) after adjusting for confounders.

Conclusions

Serum pANCA and cANCA are independent negative prognostic factors in patients with concurrent autoimmune diseases.

ANCA-associated vasculitis after COVID-19

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) are systemic autoimmune diseases that may lead to renal failure due to the infiltration of mononuclear cells and the destruction of small- and medium-sized blood vessels. It has been shown that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may trigger the presentation or exacerbation of autoimmune diseases. Crescentic glomerulonephritis (GN) has rarely been reported in patients with Coronavirus disease-2019 (COVID-19). We present rare two cases with AAV after a recent diagnosis of COVID-19. The first case was 26-year-old male patient, who was presented with acute kidney injury after COVID-19. Serum creatinine increased and active urine sediment was seen. Serological evaluation showed anti-myeloperoxidase antibody was at a level of 80.6 U/mL. Kidney biopsy showed necrotizing GN with cellular crescents. Methylprednisolone, cyclophosphamide and plasma exchange were administered. He was discharged with hemodialysis. Second case was a 36-year-old female who was hospitalized because of fever, cough and dyspnea. After she was diagnosed with COVID-19, she had total hearing loss, with cavitary lesions on bilateral lung parenchyma and an acute kidney injury. Serological evaluation showed an elevated anti-proteinase-3 with a level of 1:32. Kidney biopsy showed necrotizing GN with cellular crescents. Renal function improved after methylprednisolone and cyclophosphamide treatment. With a systematic review of the literature, we found four cases of new-onset AAV due to COVID-19. Herein, we discuss two cases and provide a literature review on cases of new-onset pauci-immune GN after COVID-19 infection.

ANCA-Negative Pauci-Immune Necrotizing Glomerulonephritis: A Case Series and a New Clinical Classification

RATIONALE & OBJECTIVE

Pauci-immune necrotizing glomerulonephritis (PING) is usually associated with the presence of antineutrophil cytoplasmic antibodies (ANCA). However, a minority (2%-3%) of patients with PING do not have detectable ANCA. We assessed the clinical spectrum and outcome of patients with ANCA-negative PING.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

74 patients with ANCA-negative PING diagnosed in 19 French nephrology centers between August 2006 and December 2018 were included in the series. Patients' medical files were reviewed, and kidney biopsies were centrally reexamined by pathologists who were masked to the diagnosis.

FINDINGS

Median age at diagnosis was 69 (IQR, 61-76) years. The clinical and pathological features were remarkable for a high frequency of extrarenal manifestations (54%), nephrotic syndrome (32%), and endocapillary hypercellularity (31%). Three main subtypes of ANCA-negative PING were observed: infection-associated (n=9[12%]), malignancy-associated (n=6[8%]), and primary (n=57[77%]). For patients with primary PING, induction treatment included mainly corticosteroids (n=56[98%]), cyclophosphamide (n=37[65%]), and rituximab (n=5[9%]). Maintenance treatment consisted mainly of corticosteroids (n=42[74%]), azathioprine (n=18[32%]), and mycophenolate mofetil (n=11[19%]). After a median follow-up period of 28 months, 28 (38%) patients had died and 20 (27%) developed kidney failure (estimated glomerular filtration rate<15mL/min/1.73m²). Eleven (21%) patients (9 with primary and 2 with malignancy-associated PING) relapsed.

LIMITATIONS

Retrospective study and limited number of patients; electron microscopy was not performed to confirm the absence of glomerular immune deposits.

CONCLUSIONS

Within the spectrum of ANCA-negative PING, infection and malignancy-associated forms represent a distinct clinical subset. This new clinical classification may inform the management of ANCA-negative PING, which remains a severe form of vasculitis with high morbidity and mortality rates despite immunosuppressive treatments.

Implication of a lysosomal antigen in the pathogenesis of lupus erythematosus

Naturally-occurring autoantibodies to certain components of autophagy processes have been described in a few autoimmune diseases, but their fine specificity, their relationships with clinical phenotypes, and their potential pathogenic functions remain elusive. Here, we explored IgG autoantibodies reacting with a panel of cytoplasmic endosomal/lysosomal antigens and individual heat-shock proteins, all of which share links to autophagy. Sera from autoimmune patients and from MRL/lpr and NZB/W lupus-prone mice reacted with the C-terminal residues of lysosome-associated membrane glycoprotein (LAMP)2A. No cross-reaction was observed with LAMP2B or LAMP2C variants, with dsDNA or mononucleosomes, or with heat-shock protein A8. Moreover, administering chromatography-purified LAMP2A autoantibodies to MRL/lpr mice accelerated mortality. Furthermore, flow cytometry revealed elevated cell-surface expression of LAMP2A on MRL/lpr B cells. These findings reveal the involvement of a new class of autoantibodies targeting the C-terminus of LAMP2A, a receptor for cytosolic proteins targeted for degradation via chaperone-mediated autophagy. These autoantibodies could affect the autophagy process, which is abnormally upregulated in lupus. The data presented support a novel connection between autophagy dysregulation, autoimmune processes and pathophysiology in lupus.

The Immune Tolerance Role of the HMGB1-RAGE Axis

The disruption of the immune tolerance induces autoimmunity such as systemic lupus erythematosus and vasculitis. A chromatin-binding non-histone protein, high mobility group box 1 (HMGB1), is released from the nucleus to the extracellular milieu in particular environments such as autoimmunity, sepsis and hypoxia. Extracellular HMGB1 engages pattern recognition receptors, including Toll-like receptors (TLRs) and the receptor for advanced glycation endproducts (RAGE). While the HMGB1-RAGE axis drives inflammation in various diseases, recent studies also focus on the anti-inflammatory effects of HMGB1 and RAGE. This review discusses current perspectives on HMGB1 and RAGE's roles in controlling inflammation and immune tolerance. We also suggest how RAGE heterodimers responding microenvironments functions in immune responses.

Biomarkers in ANCA-Associated Vasculitis: Potential Pitfalls and Future Prospects

Over the past 3 decades, significant advancements in the understanding of the pathophysiology of ANCA-associated vasculitis has led to the development of a multitude of potential candidate biomarkers. Accompanied by the advent of increasingly effective therapeutic strategies, the need for a dependable biomarker to help determine the extent of disease activity and risk of relapse is ever present. Implementation of such a biomarker would enable tailored therapy, optimizing disease control while helping to mitigate unnecessary exposure to therapy and potential treatment-related damage. Although far from perfect, ANCA serology and B-cell population are the two main staple biomarker tools widely used in practice to help supplement clinical assessment. Over recent years, the application and progress of more novel biomarker tools have arisen in both organ-limited and multisystem disease, including genomics, urinary proteins, degradation products of the alternative complement system, cytokines, metabolomics, and biospectroscopy. Validation studies and clinical translation of these tools are required, with serial assessment of disease activity and determination of therapy according to biomarker status correlated with patient outcomes.

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.

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.

Narrative Review of Hypercoagulability in Small-Vessel Vasculitis

Pauci-immune necrotizing and crescentic glomerulonephritis (GN) is the most common etiology of rapidly progressive GN. Clinical presentation in those afflicted is usually related to rapid loss of kidney function. We report the case of a 70-year-old woman who came to medical attention for signs and symptoms related to lower-extremity deep vein thrombosis (DVT). At presentation, the patient had biochemical abnormalities consistent with active GN, which quickly progressed to rapid loss in kidney function requiring renal replacement therapy. Kidney biopsy revealed small-vessel vasculitis with glomerular crescents. Serologic studies were negative for antineutrophil cytoplasmic antibody antibodies and other causes of acute GN. Plasmapheresis, immunosuppressive, and anticoagulant therapies were prescribed. Absence of other apparent end-organ involvement with vasculitis pointed toward renal-limited small-vessel vasculitis, yet presence of unprovoked DVT argues for systemic vascular inflammation. This case illustrates that venous thrombosis can be the presenting manifestation in patients with vasculitis and silent, severe end-organ involvement. The epidemiology and pathophysiology of venous thromboembolism in small-vessel vasculitis are discussed in this report.

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.

The Plasma Soluble Urokinase Plasminogen Activator Receptor Is Related to Disease Activity of Patients with ANCA-Associated Vasculitis

Objective

The soluble urokinase plasminogen activator receptor (suPAR) is associated with kidney diseases and is used as a prognostic factor of renal function progression. The aim of this study was to explore whether circulating suPAR was associated with antineutrophil cytoplasmic autoantibody- (ANCA-) associated vasculitis (AAV) disease activity.

Methods

We evaluated 90 AAV patients with follow-up data and 35 normal controls; their plasma suPAR and C-reactive protein (CRP) levels were measured by ELISA. Associations between these levels, clinical parameters, and prognosis were analyzed.

Results

Plasma suPAR levels in AAV patients were significantly higher than in healthy controls (5,920.08 ± 3,447.17 vs. 1,441.97 ± 835.04 pg/mL, P < 0.001). Furthermore, suPAR was significantly elevated in AAV patients in active stage compared to those in partial remissions (6,492.19 ± 3,689.48 vs. 5,031.86 ± 2,489.01 pg/mL, P = 0.039). Correlation analyses demonstrated that suPAR levels positively correlated with initial serum creatinine, BVAS, CRP, and procalcitonin concentration, and negatively correlated with eGFR and C3 circulating levels. In a Kaplan-Meier survival analysis, patients with plasma suPAR levels >5683.3 pg/mL showed poorer survival than patients with lower levels (log-rank, P = 0.001). Besides, multivariate analyses confirmed that plasma suPAR levels were an independent adverse prognostic factor for a composite outcome of end-stage renal disease (ESRD) or death, after adjusting for age and gender (HR 1.05, 95% CI = 1.01 − 1.11, P = 0.043). Receiver operating characteristic curves showed a suPAR cutoff value >6662.2 pg/mL for composite outcome with 68% sensitivity and 88% specificity, with an AUC = 0.82, (95% CI = 0.68 − 0.96, P < 0.001).

Conclusion

Circulating suPAR levels might be a marker of activity correlated with disease activity in AAV patients, and, to some extent, could be a factor of poor prognosis.

Unique case of ANCA-negative pauci-immune necrotizing glomerulonephritis with diffuse alveolar hemorrhage, potentially associated with midostaurin

We present a 61-year-old male with FLT3-mutated acute myeloid leukemia treated with midostaurin who developed acute kidney injury requiring hemodialysis and pulmonary renal syndrome. Antibodies to proteinase-3, myeloperoxidase, and glomerular basement membrane were negative. Renal biopsy confirmed acute pauci-immune focal necrotizing glomerulonephritis (GN) with fibrin crescents indicating rapidly progressing glomerulonephritis. He improved with pulse methylprednisolone, intravenous cyclophosphamide, and plasma exchange with resolution of hemoptysis. This case highlights the importance of prompt renal biopsy to guide early initiation of life-saving therapies. To our knowledge, this is the first reported case of ANCA-negative pauci-immune necrotizing GN likely secondary to midostaurin.

Individualised Homeopathic Therapy in ANCA Negative Rapidly Progressive Necrotising Crescentic Glomerulonephritis with Severe Renal Insufficiency - A Case Report

Anti-Neutrophil Cytoplasmic Antibody (ANCA)-negative Rapidly Progressive Glomerulonephritis (RPGN) is a severe form of autoimmune renal injury with a bleak prognosis.

A 60-year-old Indian woman was treated with classical homeopathy for ANCA-negative RPGN, and after one year of treatment, serum creatinine and other parameters indicating renal injury dropped steadily despite the withdrawal of immunosuppressive drugs; renal dialysis, which was conducted twice a week initially, was made rarer and stopped after one year.

Classical homeopathy may be considered a potential therapeutic modality in severe pathologies. Controlled studies are required to establish further the extent to which classical homeopathy may relieve patients from procedures such as dialysis that cause considerable physical and economic discomfort.

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.

Renal outcomes in primary IgA nephropathy patients with segmental glomerular necrosis: a case-control study

The renal prognosis and treatment of primary IgA nephropathy (IgAN) patients with segmental glomerular necrosis (SGN) remain controversial. Patients with primary IgAN confirmed by renal biopsy were enrolled. Patients with SGN on renal biopsy were selected as the necrosis group, and a propensity score matching method was used to match a control group according to age, gender, weight, height and follow-up time. A total of 825 IgAN patients were enrolled in the present study. Seventy-three (8.8%) patients with SGN were selected as the necrosis group, and 292 patients without SGN were matched as the control group. Compared to the control group, a significantly increased serum fibrinogen level (3.97 g/L vs 3.54 g/L, P=.002) and proportion of patients with macroscopic hematuria (35.6% vs 14.7%, P<.001) was observed in the necrosis group. According to the new IgA pathological classification system, crescent formation was more pronounced in the necrosis group (P=.001). The average estimated glomerular filtration rate was obviously higher in the necrosis group and decreased more slowly during follow-up. However, the time-averaged urine protein-to-creatinine ratio remained low in the necrotic group, whereas it gradually increased in the control group. SGN suggests an active renal inflammatory state, but it was not an independent risk factor for a poor renal outcome in patients treated with immunosuppressive therapy. Furthermore, patients with SGN had a more stable renal function and low urinary protein excretion during follow-up, which may be attributable to aggressive immunotherapy.

Pathophysiology of ANCA-associated Vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis is characterized as inflammation of small-sized to medium-sized blood vessels and encompasses several clinicopathologic entities including granulomatosis with polyangiitis, microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis, and renal-limited ANCA-associated vasculitis. Over the past several decades, significant progress has been made in understanding the pathophysiology of ANCA-associated vasculitis. Although neutrophils contain a multitude of granular proteins, clinically significant autoantibodies are only recognized against myeloperoxidase and proteinase 3, both of which are present in the azurophilic granules. The propensity to develop these antibodies depends on a variety of predisposing factors such as microbial infection, genetic factors, environmental agents, and therapeutic drugs among others. These factors are usually associated with production of proinflammatory cytokines with capacity to prime the neutrophils. As a result a high proportion of neutrophils in circulation may be primed resulting in exposure of cytoplasmic proteins including myeloperoxidase and proteinase 3 on the surface of the neutrophils. Primed neutrophils are activated by interaction with ANCA in circulation. Activated neutrophils attach to and transmigrate through endothelium and accumulate within the vessel wall. These neutrophils degranulate and produce reactive oxygen radicals and ultimately die, causing tissue injury. Endothelial injury results in leakage of serum proteins and coagulation factors causing fibrinoid necrosis. B cells produce ANCAs, as well as neutrophil abnormalities and imbalances in different T-cell subtypes with excess of Th17, which perpetuate the inflammatory process.

Update on systemic vasculitides

Management of systemic vasculitis has been revolutionised over the last decade with the introduction of targeted biological agents. With an increase in both the prevalence and the recognition of vasculitis as well as the high cost of these agents, it is important to ensure their most optimal utilisation. The goals of vasculitis therapy include the induction and maintenance of remissions, preventing relapses, reducing the toxicity of therapy with the aim of reducing morbidity and mortality as well as improving the quality of life of those afflicted. This review focuses on the recent advances in the diagnosis, surveillance and treatment of these conditions.

Gut microbiome and kidney disease: a bidirectional relationship

Recent technological advances and efforts, including powerful metagenomic and metatranscriptomic analyses, have led to a tremendous growth in our understanding of microbial communities. Changes in microbial abundance or composition of human microbial communities impact human health or disease state. However, explorations into the mechanisms underlying host-microbe interactions in health and disease are still in their infancy. Although changes in the gut microbiota have been described in patients with kidney disease, the relationships between pathogenesis, mechanisms of disease progression, and the gut microbiome are still evolving. Here, we review changes in the host-microbiome symbiotic relationship in an attempt to explore the bidirectional relationship in which alterations in the microbiome affect kidney disease progression and how kidney disease may disrupt a balanced microbiome. We also discuss potential targeted interventions that may help re-establish this symbiosis and propose more effective ways to deploy traditional treatments in patients with kidney disease.

LAMP-2 is required for incorporating syntaxin-17 into autophagosomes and for their fusion with lysosomes

Autophagy is an evolutionarily conserved process used for removing surplus and damaged proteins and organelles from the cytoplasm. The unwanted material is incorporated into autophagosomes that eventually fuse with lysosomes, leading to the degradation of their cargo. The fusion event is mediated by the interaction between the Qa-SNARE syntaxin-17 (STX17) on autophagosomes and the R-SNARE VAMP8 on lysosomes. Cells deficient in lysosome membrane-associated protein-2 (LAMP-2) have increased numbers of autophagosomes but the underlying mechanism is poorly understood. By transfecting LAMP-2-deficient and LAMP-1/2­-double-deficient mouse embryonic fibroblasts (MEFs) with a tandem fluorescent-tagged LC3 we observed a failure of fusion between the autophagosomes and the lysosomes that could be rescued by complementation with LAMP-2A. Although we observed no change in expression and localization of VAMP8, its interacting partner STX17 was absent from autophagosomes of LAMP-2-deficient cells. Thus, LAMP-2 is essential for STX17 expression by the autophagosomes and this absence is sufficient to explain their failure to fuse with lysosomes. The results have clear implications for situations associated with a reduction of LAMP-2 expression.

Summary: LAMP-2 is required for autophagosome-lysosome fusion. Its absence does not affect the lysosomal SNARE VAMP8 while its interacting partner STX17 is absent from the autophagosomes providing a molecular explanation for this fusion failure.

Recent advances in anti-neutrophil cytoplasmic antibody-associated vasculitis

Anti-neutrophil cytoplasmic antibody-associated vasculitis is an uncommon inflammatory disease of small to medium-sized vessels that frequently presents with rapidly progressive glomerulonephritis and renal failure though it can affect any organ system. If untreated, the vast majority of patients will die within a year. Current treatments improve prognosis but affected patients remain at a substantially higher risk of death and adverse outcomes. We review the classification of the disease, our understanding of the pathogenesis and epidemiology, and propose future directions for research. We also evaluate the evidence supporting established treatment regimens and the progress of clinical trials for newer treatments to inform the design of future studies.

Can antineutrophil cytoplasmic antibody levels be used to inform treatment of pauci-immune vasculitis?

PURPOSE OF REVIEW

The role of serial antineutrophil cytoplasmic antibody (ANCA) measurements to guide immunosuppressive therapy in pauci-immune vasculitis is an area of ongoing controversy. Evidence elucidating the relationship between ANCA levels and disease activity continues to grow.

RECENT FINDINGS

The finding that proteinase 3-ANCA and myeloperoxidase-ANCA-associated diseases differ genetically has challenged the traditional classification and study of pauci-immune vasculitis. Multiple studies have also found that the clinical features and course of disease differ by ANCA antigen specificity more than clinical diagnosis. Advances in diagnostic assays and new techniques for the evaluation of ANCA levels over time have yielded improved assay performance in specific subsets of patients. In addition, increasing use of rituximab has added to our understanding of the relationship of ANCA levels to B-cell counts and disease relapse, which may differ by treatment regimen.

SUMMARY

The relationship between ANCA levels and disease activity is impacted by multiple factors, including antigen specificity, disease manifestations, clinical assay, and therapeutic regimen. Each of these must be taken into account when determining the significance of ANCA levels during long-term follow-up of pauci-immune vasculitis.

Working Intricately with Moh Daha

Moh Daha has been instrumental for initiating and coordinating many European consortia in the area of immunopathogenesis of glomerulonephritis including a number with the author. This review provides a personal history of these developments, ending with INTRICATE, an FP7 medium scale project investigating ANCA-associated vasculitis (AAV). The current status of this research and recent insight in the autoimmune reactions and autoantigens in AAV are briefly summarized.

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

PURPOSE OF REVIEW

Antineutrophil cytoplasmic antibodies (ANCAs) remain central to our current understanding of the pathogenesis of ANCA-associated vasculitis (AAV), and this review considers recent developments in the context of four key questions: are there targets for ANCA beyond myeloperoxidase (MPO) and proteinase 3 (PR3); are all ANCA pathogenic; how are ANCAs generated; and how do ANCA cause disease?

RECENT FINDINGS

B-cell epitope mapping raises the possibility that only a subset of ANCA may be pathogenic. Anti-lysosomal-associated membrane protein 2 autoantibodies have recently emerged as a novel form of ANCA and can be found in anti-MPO and anti-PR3 negative disease. These also provide recent evidence for molecular mimicry in the pathogenesis of AAV, but a definitive proof in human AAV remains elusive. Neutrophil extracellular traps may represent an important mechanism by which MPO and PR3 are taken up by dendritic cells for presentation to the adaptive immune system, and the role of the alternative pathway of complement in AAV has recently been emphasized, with therapeutic implications.

SUMMARY

Our current understanding of the pathogenesis of AAV not only reinforces the central role of neutrophils but also provides a sound rationale for B-cell and complement-directed therapies.

Infectious triggers for vasculitis

PURPOSE OF REVIEW

Infections have been suggested to contribute to disease induction and reactivation in many of the idiopathic vasculitides. This review describes and evaluates the evidence that microbes are involved in the etiopathogenesis of these diseases.

RECENT FINDINGS

Large-vessel vasculitis has recently been associated with two specific bacteria. Mycobacterium tuberculosis is thought to have an inducing role in Takayasu arteritis and a Burkholderia bacterium might be involved in giant cell arteritis. Hepatitis B and C viruses have been linked to polyarteritis nodosa. In antineutrophil cytoplasmic autoantibody-associated vasculitis, and more specifically granulomatosis with polyangiitis (GPA), Staphylococcus aureus has been the focus of many studies. Chronic nasal carriage of S. aureus is related to endonasal activity and disease relapses in GPA patients. Moreover, antibacterial treatment is known to reduce the risk for disease relapses. If and how pathogens trigger vasculitis is still unclear, but several potential mechanisms have been suggested and are briefly reviewed here.

SUMMARY

Although many observations suggest a link between infections and the development of vasculitis, no direct proof exists. Transcriptomic and proteomic studies of the pathogens involved could aid in identifying specific or common traits of pathogens that are relevant for the development and reactivation of vasculitis.

Recent pathogenetic advances in ANCA-associated vasculitis

Since the discovery of anti-neutrophil cytoplasmic autoantibodies (ANCA), great strides have been made in elucidating the etiology and pathogenesis of disease. In this article, we review recent published key breakthroughs in understanding the pathogenesis of ANCA vasculitis, including some that may lead to novel therapeutics. These breakthroughs have occurred in multiple areas of investigation. A European genome-wide association study (GWAS) revealed the importance of the genetic contribution of proteinase 3 (PR3) and its endogenous inhibitor, alpha (1)-antitrypsin as well as HLA risk. Epigenetic modification of autoantigen genes appears to contribute to perpetuation of disease and possibly relapse risk. Autoantigen excision, a novel method to detect autoantibody epitopes using mass spectrometry, not only revealed pathogenic epitopes in myeloperoxidase (MPO)-ANCA vasculitis and identified unique MPO-ANCA responsible for the majority of ANCA-negative small vessel vasculitis, but has vast applicability to other autoantibody-mediated diseases. An explosion of biomarker studies has revealed circulating cytokines and alternative complement pathway products that may predict active disease. Interestingly, alternative complement pathway blockade in the murine model of disease is protective and a clinical trial in humans using an oral alternative complement pathway inhibitor is underway. Increasing clarity of the role of B and T cells in disease pathogenesis is ongoing. B cell depleting agents have shown great utility in remission induction and maintenance, and monitoring specific B cell subsets during the disease course may have predictive power for remission maintenance. Despite these substantial advances, more research is needed including, but not limited to, validation of existing discoveries. As additional novel discoveries emerge, so will novel therapies, and it is with great hope that these collective insights will ultimately lead to prevention and cure.

The Influence and Role of Microbial Factors in Autoimmune Kidney Diseases: A Systematic Review

A better understanding of the pathophysiology of autoimmune disorders is desired to allow tailored interventions. Despite increased scientific interest a direct pathogenic factor in autoimmune renal disease has been described only in a minority like membranous nephropathy or ANCA-associated vasculitis. Nonetheless the initial step leading to the formation of these antibodies is still obscure. In this review we will focus on the possible role of microbial factors in this context. Staphylococcus aureus may be a direct pathogenetic factor in granulomatosis with polyangiitis (GPA). Chronic bacterial colonization or chronic infections of the upper respiratory tract have been proposed as trigger of IgA vasculitis and IgA nephropathy. Interventions to remove major lymphoid organs, such as tonsillectomy, have shown conflicting results but may be an option in IgA vasculitis. Interestingly no clear clinical benefit despite similar local colonization with bacterial strains has been detected in patients with IgA nephropathy. In systemic lupus erythematosus injection of bacterial lipopolysaccharide induced progressive lupus nephritis in mouse models. The aim of this review is to discuss and summarize the knowledge of microbial antigens in autoimmune renal disease. Novel methods may provide insight into the involvement of microbial antigens in the onset, progression, and prognosis of autoimmune kidney disorders.

The kidneys and ANCA-associated vasculitis: from pathogenesis to diagnosis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) are a group of pauci-immune small vessel vasculitides that often affect the kidneys manifesting as rapidly progressive glomerulonephritis. Although the exact pathogenesis of AAV is not fully known, evidence from in vitro, in vivo and clinical studies all point to the involvement of ANCA in the pathogenesis of AAV. In this review, we highlight the contributory roles played by various factors (e.g. genetics, environment, B and T-regulatory cells, toll-like receptors, etc.) in the pathogenesis of AAV. Furthermore, we discuss renal involvement in AAV in terms of clinical features and the various histopathological classification patterns, which are also known to be of prognostic importance. We also present information on useful imaging techniques for localizing kidney and other organ system involvement in AAV, and also on novel laboratory methods and assays useful for rapid and more specific determination of patients' ANCA status. Finally, we demonstrate evidence on novel serum biomarkers that have been shown to correlate with disease activity in AAV.

Innovative human-specific investigational approaches to autoimmune disease

An organ-on-chip disease model approach, including “pre-clinical trial-on-chip” is introduced for understanding of human autoimmune disease pathophysiology and drug development.

Infections and antineutrophil cytoplasmic antibodies: triggering mechanisms

The precise cause of the antineutrophil cytoplasmic antibodies (ANCA) autoimmunity is not known and is likely to be multifactorial. Infections may trigger formation of ANCA and a fraction of the patients with infection-triggered ANCA develop ANCA-associated vasculitis. Here we discuss some of the proposed mechanisms of ANCA formation during the course of infection. They include initiation of autoimmune response by microbial peptides that are complementary to autoantigens; epigenetic silencing and antigen complementarity leading to upregulation of autoantigen genes; molecular mimicry between bacterial and self-antigens; formation of neutrophil extracellular traps that stimulate immune processes including production of ANCA; and interaction of bacterial components with Toll-like receptors, which leads to formation of mediators affecting the immune responses to infections and can trigger ANCA production. Further work is needed to clarify these mechanisms and develop preventive measures and therapeutic interventions.

B cell-mediated pathogenesis of ANCA-mediated vasculitis

B cells and their progeny that produce and release anti-neutrophil cytoplasmic autoantibodies (ANCA) are the primary cause for an aggressive form of necrotizing small vessel vasculitis. Cytoplasmic ANCA antigens are released at the surface and in the microenvironment of cytokine-primed neutrophils. Binding of ANCA to ANCA antigens activates neutrophils by both Fc receptor engagement and direct Fab'2 binding to antigen on the cell surface. ANCA-activated neutrophils release factors that induce alternative complement pathway activation, which establishes a potent inflammatory amplification loop that causes severe necrotizing vascular inflammation. The origin of the ANCA autoimmune response is unknown but appears to involve genetically determined HLA specificities that allow the autoimmune response to develop. One putative immunogenic mechanism begins with an immune response to a peptide that is complementary to the autoantigen and evolves through an anti-idiotypic network to produce autoantibodies to the autoantigen. Another putative immunogenic mechanism begins with an immune response to a microbe-derived molecular mimic of the autoantigen resulting in antibodies that cross-react with the autoantigen. Release of neutrophil extracellular traps, apoptosis, and increased granule protein expression of ANCA antigens may facilitate the initiation of an ANCA autoimmune response, augment established pathogenic ANCA production, or both. The ANCA B cell autoimmune response is facilitated by quantitatively and qualitatively impaired T cell and B cell suppression and by release from activated neutrophils of B cell-activating factors that enhance B cell proliferation and retard B cell apoptosis.