Anti-glomerular basement membrane autoantibodies against different target antigens are associated with disease severity

Coexistence of anti-glomerular basement membrane disease and IgA nephropathy: an illustrative case and comprehensive literature review

Anti-glomerular basement membrane (GBM) disease is a rare autoimmune condition characterized by the presence of positive anti-GBM autoantibodies, linear deposition of immunoglobulin G (IgG) along the GBM and severe kidney injury. In a limited number of cases, the association of anti-GBM disease with other glomerulonephritis has been reported. Herein, we present the case of a 66-year-old female patient with progressive worsen kidney function and decreased urine output. A renal biopsy revealed crescent glomerulonephritis with lineal IgG deposition along the GBM and mesangial IgA deposition, which supported the diagnosis of concurrent anti-GBM disease and IgA nephropathy (IgAN). In an extensive literature review, we identified a total of thirty-nine patients were reported anti-GBM disease combined with IgAN. The clinical characteristics of these patients demonstrate that the anti-GBM disease combined with IgAN tends to be milder with a more indolent course and a better prognosis than the classic anti-GBM disease, and its potential pathogenesis deserves to be further explored.

Denovo glomerulonephritis associated with IgA anti-GBM alloantibodies after kidney transplantation in Alport syndrome: A case report with diagnostic implications

Alport syndrome (AS) is a hereditary disorder caused by pathogenic variants in COL4A3, COL4A4, or COL4A5 genes expressing α3, α4, and α5 chains of basement membrane type IV collagen (COL4). The triple-helical α3α4α5(IV) protomer is a major component of the mature glomerular basement membrane (GBM) whose defective formation in AS leads to structural GBM disruption and kidney dysfunction, often resulting in kidney replacement therapy. A genetically intact renal graft exposes the immune system to a non-tolerized α3α4α5(IV) component and an alloimmune response eventually ensues. So far, only IgG alloantibodies reacting against COL4 have been reported in AS alloimmune responses. Here, we report alloimmune glomerulonephritis mediated by IgA antibodies against the non-collagenous C-terminal domain 1 of the α5(IV) chain in a patient with autosomal recessive AS following a second kidney transplantation. The patient presented a not previously described biallelic variant in the COL4A4 gene. Immunological, diagnostic, and clinical implications are discussed.

Atypical anti-glomerular basement membrane disease with membranous hyperplasia: diagnostic challenges and treatment variability

This case report presents a detailed analysis of a 31-year-old male patient who presented with a complex array of clinical symptoms, including proteinuria, hematuria, edema, and kidney insufficiency. Despite undergoing multiple tests, the results for anti-glomerular basement membrane antibodies yielded negative findings. Subsequently, kidney biopsy pathology revealed a distinct diagnosis of atypical anti-glomerular basement membrane (anti-GBM) disease with membrane hyperplasia. Treatment was initiated with a comprehensive approach involving high doses of corticosteroids therapy and cyclophosphamide (CTX). However, contrary to expectations, the patient's kidney function exhibited rapid deterioration following this therapeutic regimen. The culmination of these complications necessitated a pivotal transition to maintenance hemodialysis. This case underscores the intricate challenges associated with diagnosing and managing rare and atypical presentations of kidney disorders. The negative anti-GBM antibody results and subsequent identification of atypical anti-GBM nephropathy highlight the need for tailored diagnostic strategies to discern subtle nuances within complex clinical scenarios. Additionally, the unexpected response to the treatment regimen emphasizes the potential variability in individual patient responses, underlining the necessity for vigilant monitoring and adaptable treatment strategies. This case report contributes to the evolving understanding of atypical kidney pathologies and the complexities involved in their management.

Using imlifidase to elucidate the characteristics and importance of anti-GBM antibodies produced after start of treatment

BACKGROUND

Autoantibodies are common in glomerulonephritis, but the clinical benefit of rapid elimination has not been determined, even in anti-glomerular basement membrane (GBM) disease. Even less is known about the importance of autoantibody characteristics, including epitope specificity and immunoglobulin G (IgG) subclass distribution. We aimed to address this by characterizing the autoantibody profile in anti-GBM patients: we utilized samples from the GOOD-IDES-01 (treating GOODpasture's disease with Imunoglobulin G Degrading Enzyme of Streptococcus pyogenous) (ClinicalTrials.gov identifier: NCT03157037) trial , where imlifidase, which cleaves all IgG in vivo within hours, was given to 15 anti-GBM patients.

METHODS

In the GOOD-IDES-01 trial, plasmapheresis was (re)started if anti-GBM antibodies rebounded. Serum samples were collected prospectively for 6 months and analyzed for anti-GBM epitope specificity using recombinant constructs of the EA and EB epitopes, IgG subclass using monoclonal antibodies, and anti-neutrophil cytoplasmic antibodies (ANCA). The results were correlated with clinical data.

RESULTS

Patients with a rebound (n = 10) tended to have lower eGFR at 6 months (11 vs 34 mL/min/1.73 m2, P = .055), and patients with dialysis at 6 months had a higher EB/EA ratio at rebound (0.8 vs 0.5, P = .047). Moreover, two patients demonstrated increasing epitope restriction and several patients displayed a shift in subclass distribution at rebound. Six patients were double positive for ANCA. ANCA rebound was seen in 50% of patients; only one patient remained ANCA positive at 6 months.

CONCLUSIONS

In this study, rebound of anti-GBM antibodies, especially if directed against the EB epitope, was associated with a worse outcome. This supports the notion that all means should be used to eliminate anti-GBM antibodies. In this study ANCA was removed early and long-term by imlifidase and cyclophosphamide.

Autoantibodies against laminin-521 are pathogenic in anti-glomerular basement membrane disease

Anti-glomerular basement membrane (anti-GBM) disease is an organ-specific autoimmune disorder characterized by autoantibodies against GBM components. Evidence from human inherited kidney diseases and animal models suggests that the α, β, and γ chains of laminin-521 are all essential for maintaining the glomerular filtration barrier. We previously demonstrated that laminin-521 is a novel autoantigen within the GBM and that autoantibodies to laminin-521 are present in about one-third of patients. In the present study, we investigated the pathogenicity of autoantibodies against laminin-521 with clinical and animal studies. Herein, a rare case of anti-GBM disease was reported with circulating autoantibodies binding to laminin-521 but not to the NC1 domains of α1-α5(IV) collagen. Immunoblot identified circulating IgG from this patient bound laminin α5 and γ1 chains. A decrease in antibody levels was associated with improved clinical presentation after plasmapheresis and immunosuppressive treatments. Furthermore, immunization with laminin-521 in female Wistar-Kyoto rats induced crescentic glomerulonephritis with linear IgG deposits along the GBM, complement activation along with infiltration of T cells and macrophages. Lung hemorrhage occurred in 75.0% of the rats and was identified by the presence of erythrocyte infiltrates and hemosiderin-laden macrophages in the lung tissue. Sera and kidney-eluted antibodies from rats immunized with laminin-521 demonstrated specific IgG binding to laminin-521 but not to human α3(IV)NC1, while the opposite was observed in human α3(IV)NC1-immunized rats. Thus, our patient data and animal studies imply a possible independent pathogenic role of autoantibodies against laminin-521 in the development of anti-GBM disease.

Antiglomerular basement membrane antibody type rapidly progressive glomerulonephritis with seizures: Two cases and literature review

BACKGROUND

Rapidly progressive glomerulonephritis (RPGN) is clinically manifestations as a rapidly progressive renal failure and pathologically as crescentic and necrotizing lesions with infiltration of inflammatory cells in the glomeruli. Uremic encephalopathy (UE) usually develops in patients who are suffering from acute or chronic renal failure.

OBJECTIVE

The purpose of this article is to provide reference for clinical diagnosis and treatment of renal disease complicated with seizures. Patients Two cases of anti-glomerular basement membrane type rapidly progressive glomerulonephritis complicated with seizures were reported.

MATERIALS & METHODS

In case 1, a 40-year-old woman was hospitalized for the treatment of nausea, anorexia, and fever. On admission, she presented with elevated serum inflammatory indicators, moderate anemia, and advanced acute kidney injury requiring hemodialysis. Her anti-glomerular basement membrane (GBM) antibody in serum and renal tissues was found to be extremely high. She was finally diagnosed with anti-GBM disease. She was treated with a combination of corticosteroid pulse therapy, oral cyclophosphamide and prednisolone, and plasma exchange, while continued to require maintenance hemodialysis for end-stage kidney disease. During treatment, she suddenly suffered blindness, seizure, and consciousness disturbance. She was diagnosed as posterior reversible leukoencephalopathy syndrome by magnetic resonance imaging (MRI). The posterior reversible leukoencephalopathy syndrome subsided quickly after control of her hypertension and reinforcement of immunosuppressive treatment. In case 2, the patient also developed epileptic symptoms on the basis of GBM disease, and was given treatment similar to that of Case 1, so that the epileptic symptoms were controlled.

RESULT

Reversible posterior leukoencephalopathy syndrome, especially when accompanied by cerebral hemorrhage, may lead to irreversible and lethal neurological abnormalities, and nephrologists should, therefore, be aware of the potential risk of reversible posterior leukoencephalopathy syndrome in patients with anti-GBM disease. We can discuss the current two cases in the light of the previous literature.

Demonstration of equivocal anti-glomerular basement membrane antibody positivity as a non-specific reaction through multiple immunologic assays in a case of pediatric asymptomatic hematuria

BACKGROUND

Anti-glomerular basement membrane (anti-GBM) antibody is essential for the diagnosis of anti-GBM disease. The major epitope consists of the α3 subunits of type IV collagen non-collagenous domain (α 3(IV)NC1). There have been only a few reports of patients false-positive for anti-GBM antibody.

CASE REPORT

We experienced an 8-year-old boy who presented with asymptomatic hematuria followed by positivity for anti-GBM antibody as evaluated by a commercially available chemiluminescent enzyme immunoassay (CLEIA). While his condition remained stable other than continuing hematuria, his anti-GBM antibody titer increased. Further examination of another anti-GBM antibody assay (fluoroenzyme immunoassay) showed negative results. Thus, evaluation of the accuracy of his positivity for anti-GBM antibody was required. We conducted the following examinations: A) enzyme-linked immunosorbent assay, B) immunoblotting for recombinant α 1-5(IV)NC1, and C) immunohistochemical analysis of normal kidney tissue sections. Specimens used for the analysis were sera in A and IgG from the patient in B and C, respectively. As a result, no anti-GBM antibody was detected in A. In B, no band specific to α 1-5(IV)NC1 was observed. In C, the kidney tissue was not stained. Taken together, these results led us to judge the positive anti-GBM result in CLEIA of our patient to be a non-specific reaction.

CONCLUSION

The commercial assays for anti-GBM antibody can lead to false-positive results. We recommend confirmation of anti-GBM antibody positivity through the use of multiple assays in patients demonstrating an atypical clinical course for anti-GBM disease.

Risk Stratification to Predict Renal Survival in Anti-Glomerular Basement Membrane Disease

SIGNIFICANCE STATEMENT

Most patients with anti-glomerular basement membrane (GBM) disease present with rapidly progressive glomerulonephritis, and more than half develop ESKD. Currently, no tools are available to aid in the prognostication or management of this rare disease. In one of the largest assembled cohorts of patients with anti-GBM disease (with 174 patients included in the final analysis), the authors demonstrated that the renal risk score for ANCA-associated vasculitis is transferable to anti-GBM disease and the renal histology is strongly predictive of renal survival and recovery. Stratifying patients according to the percentage of normal glomeruli in the kidney biopsy and the need for RRT at the time of diagnosis improves outcome prediction. Such stratification may assist in the management of anti-GBM disease.

BACKGROUND

Prospective randomized trials investigating treatments and outcomes in anti-glomerular basement membrane (anti-GBM) disease are sparse, and validated tools to aid prognostication or management are lacking.

METHODS

In a retrospective, multicenter, international cohort study, we investigated clinical and histologic parameters predicting kidney outcome and sought to identify patients who benefit from rescue immunosuppressive therapy. We also explored applying the concept of the renal risk score (RRS), currently used to predict renal outcomes in ANCA-associated vasculitis, to anti-GBM disease.

RESULTS

The final analysis included 174 patients (out of a total of 191). Using Cox and Kaplan-Meier methods, we found that the RRS was a strong predictor for ESKD. The 36-month renal survival was 100%, 62.4%, and 20.7% in the low-risk, moderate-risk, and high-risk groups, respectively. The need for renal replacement therapy (RRT) at diagnosis and the percentage of normal glomeruli in the biopsy were independent predictors of ESKD. The best predictor for renal recovery was the percentage of normal glomeruli, with a cut point of 10% normal glomeruli providing good stratification. A model with the predictors RRT and normal glomeruli ( N ) achieved superior discrimination for significant differences in renal survival. Dividing patients into four risk groups led to a 36-month renal survival of 96.4% (no RRT, N ≥10%), 74.0% (no RRT, N <10%), 42.3% (RRT, N ≥10%), and 14.1% (RRT, N <10%), respectively.

CONCLUSIONS

These findings demonstrate that the RRS concept is transferrable to anti-GBM disease. Stratifying patients according to the need for RRT at diagnosis and renal histology improves prediction, highlighting the importance of normal glomeruli. Such stratification may assist in the management of anti-GBM disease.

PODCAST

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/JASN/2023_02_27_JASN0000000000000060.mp3.

Combination of anti-C1qA08 and anti-mCRP a.a.35-47 antibodies is associated with renal prognosis of patients with lupus nephritis

Objective

The aim of this study is to explore the prevalence and clinicopathological associations between anti-C1qA08 antibodies and anti-monomeric CRP (mCRP) a.a.35-47 antibodies and to explore the interaction between C1q and mCRP.

Methods

Ninety patients with biopsy-proven lupus nephritis were included from a Chinese cohort. Plasma samples collected on the day of renal biopsy were tested for anti-C1qA08 antibodies and anti-mCRP a.a.35-47 antibodies. The associations between these two autoantibodies and clinicopathologic features and long-term prognosis were analyzed. The interaction between C1q and mCRP was further investigated by ELISA, and the key linear epitopes of the combination of cholesterol binding sequence (CBS; a.a.35-47) and C1qA08 were tested by competitive inhibition assays. The surface plasmon resonance (SPR) was used to further verify the results.

Results

The prevalence of anti-C1qA08 antibodies and anti-mCRP a.a.35-47 antibodies were 50/90 (61.1%) and 45/90 (50.0%), respectively. Levels of anti-C1qA08 antibodies and anti-mCRP a.a.35-47 antibodies were negatively correlated with serum C3 concentrations ((0.5(0.22-1.19) g/L vs. 0.39(0.15-1.38) g/L, P=0.002) and (0.48(0.44-0.88) g/L vs. 0.41(0.15-1.38) g/L, P=0.028), respectively. Levels of anti-C1qA08 antibodies were correlated with the score of fibrous crescents and tubular atrophy (r=-0.256, P=0.014 and r=-0.25, P=0.016, respectively). The patients with double positive antibodies showed worse renal prognosis than that of the double negative group (HR 0.899 (95% CI: 0.739-1.059), P=0.0336). The binding of mCRP to C1q was confirmed by ELISA. The key linear epitopes of the combination were a.a.35-47 and C1qA08, which were confirmed by competitive inhibition experiments and SPR.

Conclusion

The combination of anti-C1qA08 and anti-mCRP a.a.35-47 autoantibodies could predict a poor renal outcome. The key linear epitopes of the combination of C1q and mCRP were C1qA08 and a.a.35-47. A08 was an important epitope for the classical pathway complement activation and a.a.35-47 could inhibit this process.

Autoimmunity in Anti-Glomerular Basement Membrane Disease: A Review of Mechanisms and Prospects for Immunotherapy

Anti-glomerular basement membrane (anti-GBM) disease is an organ-specific autoimmune disorder characterized by autoantibodies against the glomerular and alveolar basement membranes, leading to rapidly progressive glomerulonephritis and severe alveolar hemorrhage. The noncollagenous domain of the α3 chain of type IV collagen, α3(IV)NC1, contains the main target autoantigen in this disease. Epitope mapping studies of α3(IV)NC1 have identified several nephritogenic epitopes and critical residues that bind to autoantibodies and trigger anti-GBM disease. The discovery of novel target antigens has revealed the heterogeneous nature of this disease. In addition, both epitope spreading and mimicry have been implicated in the pathogenesis of anti-GBM disease. Epitope spreading refers to the development of autoimmunity to new autoepitopes, thus worsening disease progression, whereas epitope mimicry, which occurs via sharing of critical residues with microbial peptides, can initiate autoimmunity. An understanding of these autoimmune responses may open opportunities to explore potential new therapeutic approaches for this disease. We review how current advances in epitope mapping, identification of novel autoantigens, and the phenomena of epitope spreading and mimicry have heightened the understanding of autoimmunity in the pathogenesis of anti-GBM disease, and we discuss prospects for immunotherapy.

Predictors of Kidney Outcomes of Anti-Glomerular Basement Membrane Disease in a Large Chinese Cohort

INTRODUCTION

Anti-glomerular basement membrane (GBM) disease is a rare but the most aggressive form of glomerulonephritis. To dissect the prognostic factors, we retrospectively analyzed the clinical features of a large cohort and compared the clinical features and prognosis during decades.

METHODS

Data on clinical manifestation, treatment, and prognosis were collected. Cox models and receiver operating characteristic (ROC) curve were used to investigate the predictors for outcomes. The Kaplan-Meier curve and log-rank test were used to compare kidney and patient survival.

RESULTS

A total of 448 patients were enrolled. Patient survival and kidney survival at 1 year was 69.4% and 37.7%, respectively. During the past 3 decades, mortality at 3 months and 1 year significantly dropped from 37.5% and 57.1% in 1991-2000 to 2.8% and 6.9% in 2011-2020 (p < 0.001), respectively; kidney prognosis showed a tendency of improvement as well. Serum creatinine (Scr) on diagnosis (HR, 1.16; 95% CI, 1.05-1.29) and crescent percentage (HR, 1.73; 95% CI, 1.34-2.24) were independent predictors for end-stage kidney disease. ROC curve showed that the optimal cutoff point of Scr on diagnosis for prediction of dialysis dependency at 1 year was 536.4 μmol/L (sensitivity 88.3% and specificity 80.8%). Antineutrophil cytoplasmic antibodies (ANCAs) positivity (HR, 4.43; 95% CI, 1.72-11.38) was a predictor for mortality. Plasma exchange was associated with a better patient prognosis (HR, 0.40; 95% CI 0.16-0.95).

CONCLUSION

Scr on diagnosis and percentage of crescents were predictors for kidney outcomes. Positive ANCA was a predictor for mortality. Overall patient prognosis of anti-GBM disease was improved during the past 3 decades.

Anti-glomerular basement membrane disease (Goodpasture disease): From pathogenesis to plasma exchange to IdeS

Anti-glomerular basement membrane (GBM) disease (Goodpasture disease) often presents with severe kidney failure and pulmonary hemorrhage. Anti-GBM antibodies are pathogenic, and other autoantibodies such as laminin-521 have been identified recently, potentially indicating a subset with a more severe disease phenotype and poor prognosis. Around 30%-40% of patients are also anti-neutrophil cytoplasmatic antibody (ANCA)-positive and this subset combines features of anti-GBM disease and ANCA-associated vasculitis, with particular impact on long-term treatment. A combination of therapeutic plasma exchange (or immunoadsorption), cyclophosphamide, and glucocorticoids is considered standard of care management, but despite early initiation, patients with poor prognostic factors often remain dialysis dependent. Imlifidase (IdeS), capable to cleave IgG within hours, has been tested in a phase II trial. Among 15 patients, 10 with poor prognosis at baseline (eGFR <15 ml/min/1.73 m² ) were dialysis independent at 6 months. Further developments are needed to refine treatment approaches in anti-GBM disease.

Laminin-521 is a Novel Target of Autoantibodies Associated with Lung Hemorrhage in Anti-GBM Disease

BACKGROUND

Antiglomerular basement membrane (anti-GBM) disease is characterized by GN and often pulmonary hemorrhage, mediated by autoantibodies that typically recognize cryptic epitopes within α345(IV) collagen-a major component of the glomerular and alveolar basement membranes. Laminin-521 is another major GBM component and a proven target of pathogenic antibodies mediating GN in animal models. Whether laminin-521 is a target of autoimmunity in human anti-GBM disease is not yet known.

METHODS

A retrospective study of circulating autoantibodies from 101 patients with anti-GBM/Goodpasture's disease and 85 controls used a solid-phase immunoassay to measure IgG binding to human recombinant laminin-521 with native-like structure and activity.

RESULTS

Circulating IgG autoantibodies binding to laminin-521 were found in about one third of patients with anti-GBM antibody GN, but were not detected in healthy controls or in patients with other glomerular diseases. Autoreactivity toward laminin-521 was significantly more common in patients with anti-GBM GN and lung hemorrhage, compared with those with kidney-limited disease (51.5% versus 23.5%, P=0.005). Antilaminin-521 autoantibodies were predominantly of IgG1 and IgG4 subclasses and significantly associated with lung hemorrhage (P=0.005), hemoptysis (P=0.008), and smoking (P=0.01), although not with proteinuria or serum creatinine at diagnosis.

CONCLUSIONS

Besides α345(IV) collagen, laminin-521 is another major autoantigen targeted in anti-GBM disease. Autoantibodies to laminin-521 may have the potential to promote lung injury in anti-GBM disease by increasing the total amount of IgG bound to the alveolar basement membranes.

Early onset calciphylaxis following acute kidney injury secondary to anti-glomerular basement membrane antibody disease

Calciphylaxis is commonly associated with end-stage renal disease (ESRD) and renal transplant. We present a rare case of early onset calciphylaxis in a patient presenting with acute kidney injury (AKI) secondary to anti-glomerular basement membrane (anti-GBM) antibody disease. A 65-year-old obese Caucasian woman with type 2 diabetes mellitus and hypertension presented with a 1-month history of painless gross haematuria and worsening lower extremity oedema. Laboratory results indicated AKI and nephrotic-range proteinuria. Anti-glomerular antibodies were elevated. Renal biopsy revealed focal crescentic glomerulonephritis with linear capillary immunoglobulin G staining consistent with anti-GBM antibody disease. She was treated with haemodialysis, plasmapheresis, steroids, bumetanide and cyclophosphamide. Two months later, she developed necrotic lesions on bilateral thighs. Wound biopsy was consistent with calciphylaxis. This case highlights that calciphylaxis, usually seen in patients with chronic kidney disease or ESRD, can manifest in patients with AKI as well.

Absence of Anti-Glomerular Basement Membrane Antibodies in 200 Patients With Systemic Lupus Erythematosus With or Without Lupus Nephritis: Results of the GOODLUPUS Study

Introduction

Anti-glomerular basement membrane (GBM) antibodies are pathogenic antibodies first detected in renal-limited anti-GBM disease and in Goodpasture disease, the latter characterized by rapidly progressive crescentic glomerulonephritis combined with intra-alveolar hemorrhage. Studies have suggested that anti-GBM antibody positivity may be of interest in lupus nephritis (LN). Moreover, severe anti-GBM vasculitis cases in patients with systemic lupus erythematosus (SLE) have been described in the literature, but few studies have assessed the incidence of anti-GBM antibodies in SLE patients.

Objective

The main study objective was to determine if positive anti-GBM antibodies were present in the serum of SLE patients with or without proliferative renal damage and compared to a healthy control group.

Methodology

This retrospective study was performed on SLE patients’ sera from a Franco-German European biobank, developed between 2011 and 2014, from 17 hospital centers in the Haut-Rhin region. Patients were selected according to their renal involvement, and matched by age and gender. The serum from healthy voluntary blood donors was also tested. Anti-GBM were screened by fluorescence enzyme immunoassay (FEIA), and then by indirect immunofluorescence (IIF) in case of low reactivity detection (titer >6 U/ml).

Results

The cohort was composed of 100 SLE patients with proliferative LN (27% with class III, 67% with class IV, and 6% with class V), compared to 100 SLE patients without LN and 100 controls. Patients were mostly Caucasian and met the ACR 1997 criteria and/or the SLICC 2012 criteria. Among the 300 tested sera, no significant levels of anti-GBM antibodies were detected (>10 U/ml) by the automated technique, three sera were found “ambivalent” (>7 U/ml): one in the SLE with LN group and two in the SLE without LN group. Subsequent IIF assays did not detect anti-GBM antibodies.

Conclusion

Anti-GBM antibodies were not detected in the serum of Caucasian patients with SLE, even in case of renal involvement, a situation favoring the antigenic exposure of glomerular basement membranes. Our results reaffirm the central role of anti-GBM antibodies as a specific diagnostic biomarker for Goodpasture vasculitis and therefore confirm that anti-GBM antibody must not be carried out in patients with SLE (with or without LN) in the absence of disease-suggestive symptoms.

Anti-glomerular basement membrane antibody disease complicated by posterior reversible encephalopathy syndrome

Anti-glomerular basement membrane (anti-GBM) antibody disease is a rare type of small-vessel vasculitis. Posterior reversible encephalopathy syndrome (PRES) is a syndrome of heterogeneous aetiologies grouped together based on similar neuroimaging findings. We report a rare case of a patient who received treatment for anti-GBM antibody disease who developed PRES. A 33-year-old woman presented with severe generalised oedema, proteinuria, haematuria, and cylindruria. She was diagnosed with anti-GBM antibody disease based on positive findings for anti-GBM antibodies and urinalysis. Haemodialysis was eventually required. She received steroid therapy, plasma exchange therapy, and intravenous cyclophosphamide, along with a red blood cell transfusion for progressive anaemia. After the transfusion, she experienced nausea, severe headache, visual hallucinations, and agitation followed by seizures and a rapid increase in blood pressure. Imaging studies led to a diagnosis of PRES. Renal failure improved with the decrease in anti-GBM antibodies, and haemodialysis was discontinued. Phenytoin was administered, and seizures disappeared. Although we cannot rule out the possibility that the treatment this patient underwent for anti-GBM antibody disease led to the development of PRES, we speculate that endothelial dysfunction leading to the development of PRES is caused not only by known risk factors such as cytotoxic agents, blood transfusions, or renal failure, but also by immunological abnormalities and subsequent inflammatory reactions due to anti-GBM antibody disease. These factors may be shared pathophysiologic mechanisms of PRES and anti-GBM antibody disease.

Diagnostic and management challenges in Goodpasture's (anti-glomerular basement membrane) disease

Goodpasture's or anti-glomerular basement membrane (GBM) disease is classically characterized by the presence of circulating autoantibodies directed against the non-collagenous domain of the α3 chain of type IV collagen, targeting glomerular and alveolar basement membranes, and associated with rapidly progressive crescentic glomerulonephritis, with alveolar haemorrhage in over half the patients. However, there are increasing examples of variants or atypical presentations of this disease, and novel therapeutic options have been proposed, which nephrologists should be aware of. The pathophysiology of this condition has been understood through molecular analysis of the antibody-antigen interactions and the use of human leucocyte antigen-transgenic animals, while the association of anti-GBM antibodies with anti-neutrophil cytoplasm antibodies and their combined impact on disease phenotype is increasingly recognized, providing some insights into the basis of glomerular damage and autoimmunity.

Fever and prodromal infections in anti-glomerular basement membrane disease

AIM

Anti-glomerular basement membrane (GBM) disease is an autoimmune disorder with rapidly progressive glomerulonephritis and alveolar haemorrhage. Fever symptoms and prodromal infections have been reported in many cases, but still not been elucidated.

METHODS

Our study enrolled 140 consecutive patients with anti-GBM disease and retrospectively analyzed the characteristics of fever symptoms and the possible reasons.

RESULTS

Among the 140 patients, 94 (67.1%) patients presented with fever (over 37.5°C) prior to admission or within 48 h of hospitalization. Among those with fever, 74 (78.7%) patients had infections, 15 (16.0%) patients had positive serum anti-neutrophil cytoplasmic antibodies, all towards myeloperoxidase, which was comparable to the patients without fever (17.4%, P = 0.830). There were 93/140 patients suffered from infections, with 47.3% in lungs and 31.2% on upper respiratory tract. In some cases, we identified the microbes of infections, including Candida albicans, Escherichia coli, Acinetobacter baumannii, Enterococcus faecalis, Klebsiella pneumoniae, Hemolytic staphylococci, Pseudomonas aeruginosa and Citrobacter braakii. Patients with fever had higher levels of serum anti-GBM antibodies (154.9 ± 58.4 vs. 106.0 ± 63.2 IU/mL, P < 0.001), higher serum creatinine (733.4 ± 402.5 vs. 580.6 ± 368.1 μmol/L, P = 0.032), higher percentage of crescents (87.0 ± 15.6 vs. 67.4 ± 37.6%, P = 0.021), and higher frequency of progression to end stage renal disease (ESRD) (80.9% vs. 60.9%, P = 0.011).

CONCLUSION

We concluded that fever is a common symptom in anti-GBM disease and associates with more severe glomerulonephritis. The majority of patients at presentation had fever with respiratory tract infections, which needs further investigation to reveal their role in the pathogenesis of anti-GBM disease.

T cell responses to peptides of Goodpasture autoantigen in patients with anti-glomerular basement membrane disease

AIM

Cell-mediated autoimmunity, especially autoreactive T cells, is crucial in the initiation of anti-glomerular membrane (GBM) disease. Epitopes for T cells on Goodpasture autoantigen are not fully defined. This study investigated T cell epitopes in anti-GBM patients, aiming to identify the epitopes and their clinical significance.

METHODS

Peripheral blood mononuclear cells (PBMC) were collected from 13 patients with anti-GBM disease. Twenty-four overlapping linear peptides were synthesized covering the whole sequence of human α3(IV)NC1. PBMC response to each peptide was detected by proliferation assay. Their associations with clinical features were further analyzed.

RESULTS

Peripheral blood mononuclear cells proliferative responses to linear peptides on α3(IV)NC1 could be detected in all patients. Five major epitopes were identified as stimulatory in over half of the patients: α3(IV)NC1_127-148 (P14) (69.2%), α3(IV)NC1_159-178 (77.8%), α3(IV)NC1_179-198 (55.6%), α3(IV)NC1_189-208 (P19) (75.0%) and α3(IV)NC1_141-154 (57.1%). P14 and P19 were highly recognized in patients comparing with healthy controls (69.2% vs. 0.0%, P = 0.011; 75.0% vs. 0.0%, P = 0.021, respectively).

CONCLUSION

T cell proliferation to linear epitopes was detected in human anti-GBM disease. α3_127-148 was a mutual T and B cell epitope, implying its initial role in epitope spreading process.

Coexistence of Anti-Glomerular Basement Membrane Glomerulonephritis and Membranous Nephropathy in a Female Patient with Preserved Renal Function

Renal prognosis for anti-glomerular basement membrane (GBM) glomerulonephritis is poor. The greater the amount of anti-GBM antibody binding the antigen (type IV collagen of the glomerular basement membrane), the greater the number of crescents that develop in glomeruli, resulting in progression of renal impairment. Immunofluorescence staining reveals linear IgG depositions on glomerular capillary walls. Membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in middle-aged to elderly patients. Immune complex is deposited in the sub-epithelial space of the glomerulus resulting in the development of a membranous lesion. Immunofluorescence staining reveals granular IgG depositions on glomerular capillary walls. Coexisting anti-GBM glomerulonephritis and MN are rare and, here we report a case of coexisting anti-GBM glomerulonephritis and MN with preserved renal function. There are some cases of coexisting anti-GBM glomerulonephritis and MN do not show severely decreased renal function. A 76-year-old Japanese woman presented with nephrotic syndrome, microscopic hematuria, and was positive for anti-GBM antibody. Kidney biopsy revealed linear and granular IgG depositions in glomerular capillary walls, crescent formations, and electron-dense deposits in the sub-epithelial space. She was diagnosed with anti-GBM glomerulonephritis and MN. Steroid and cyclosporine therapy achieved complete remission, and kidney function was preserved. In conclusion, coexisting anti-GBM glomerulonephritis and MN can have preserved renal function. IgG subclass of deposited anti-GBM antibody may be associated with the severity of anti-GBM glomerulonephritis. In addition, in the case of nephrotic syndrome with hematuria, we should consider the possibility of coexisting anti-GBM glomerulonephritis and MN.

Goodpasture's autoimmune disease - A collagen IV disorder

Goodpasture's (GP) disease is an autoimmune disorder characterized by the deposition of pathogenic autoantibodies in basement membranes of kidney and lung eliciting rapidly progressive glomerulonephritis and pulmonary hemorrhage. The principal autoantigen is the α345 network of collagen IV, which expression is restricted to target tissues. Recent discoveries include a key role of chloride and bromide for network assembly, a novel posttranslational modification of the antigen, a sulfilimine bond that crosslinks the antigen, and the mechanistic role of HLA in genetic susceptibility and resistance to GP disease. These advances provide further insights into molecular mechanisms of initiation and progression of GP disease and serve as a basis for developing of novel diagnostic tools and therapies for treatment of Goodpasture's disease.

The Clinical and Immunologic Features of Patients With Combined Anti-GBM Disease and Castleman Disease

Patients with both anti-glomerular basement membrane (anti-GBM) disease and Castleman disease have been rarely reported. In this study, we report 3 patients with this combination. They had immunologic features similar to patients with classic anti-GBM disease. Sera from the 3 patients recognized the noncollagenous (NC) domain of the α3 chain of type IV collagen (α3(IV)NC1) and its 2 major epitopes, EA and EB. All 4 immunogloblin G (IgG) subclasses against α3(IV)NC1 were detectable, with predominance of IgG1. In one patient with lymph node biopsy specimens available, sporadic plasma cells producing α3(IV)NC1-IgG were found, suggesting a causal relationship between the 2 diseases. One patient, who achieved remission with antibody clearance and normalization of serum creatinine and interleukin 6 concentrations after plasma exchange and 3 cycles of chemotherapy, experienced recurrence of anti-GBM antibodies and an increase in interleukin 6 concentration after chemotherapy discontinuation because of adverse effects, but both returned to normal after another cycle of chemotherapy. This clinical course and the pathologic findings support the hypothesis that the Castleman disease-associated tumor cells are the source of the anti-GBM autoantibodies.

[Antiglomerular basement disease in children: Literature review and therapeutic options]

Antiglomerular basement membrane glomerulonephritis is a rare autoimmune disease characterized by rapidly progressive glomerulonephritis that may be associated with pulmonary hemorrhage (Goodpasture syndrome). The disease is caused by autoantibodies (classically IgGs) directed against the α3 subunit of type IV collagen. This is a rare disease in the adult population and extremely rare in children, with a reported cumulative annual incidence at 1/10⁶ people/year. Among scarce reported pediatric cases (n=31), most are girls (M/F sex ratio, 1:4), and the mean age at diagnoses is 9.2±4.6 years. A medical diagnosis is an emergency and is based on the identification of specific antibodies in the serum, and pathognomonic linear fixation of IgGs along the glomerular basement membrane. Without appropriate treatment, the disease is generally fulminant, and patient and kidney survival is poor. Indeed, glomerular function strongly correlates with histological lesions. The current guidelines recommend the use of plasma exchanges and immunosuppressive drugs. For the past few years, alternative therapeutics such as specific anti-B-cell antibodies (rituximab) or specific extrarenal cleansing such as immunoadsorption have been successfully used in adults. Immunoadsorptions (IAs) can remove pathogenic IgGs from the circulation and do not require plasma infusions, contrary to plasma exchanges. In this review, we discuss the key points of antiglomerular basement membrane glomerulonephritis diagnosis and conventional or alternative therapeutics.

Different Outcome of Goodpasture Syndrome

Goodpasture syndrome is a rare autoimmune disease, with significant morbidity and mortality in young people and otherwise healthy population. Complete disease remission is possible with prompt diagnosis and treatment. We report 3 cases with Goodpasture syndrome treated at the Department of Nephrology, University Clinic of Nephrology, with different outcome. All of the patients were with similar clinical feature, with renal failure that needed treatment with hemodialysis. But results of the treatment with plasmapheresis indicate that this procedure reduces morbidity in patients with Goodpasture syndrome. The clinical course and the outcome of the disease were different. The disease is unpredictable, and the early diagnosis and start with the treatment is important for the remission.

The pathogenicity of T cell epitopes on human Goodpasture antigen and its critical amino acid motif

Goodpasture antigen, the non‐collagenous domain of α3 chain of type IV collagen [α3(IV)NC1], is the target antigen of anti‐glomerular basement membrane (GBM) antibodies. The pathogenicity of T cell epitopes is not elucidated clearly. In this study, we aim to define the nephritogenic T cell epitopes and its critical amino acid residues. Twenty‐four overlapping linear peptides were synthesized covering the whole sequence of human α3(IV)NC1. Wistar–Kyoto rats were immunized with linear peptides, and experimental autoimmune glomerulonephritis was evaluated. Critical amino acid was identified by the loss of nephritogenic function after each amino acid substitution by alanine. Of the 24 peptides, P14 (α3_127‐148) could induce 90.5% (19/21) of WKY rats developing anti‐GBM glomerulonephritis with proteinuria, elevated serum urea and creatinine, IgG linear deposit on GBM and substantial (in average 82.4 ± 5.6%) crescent formation in glomeruli. Lymphocytes of immunized rats proliferated in response to α3_127‐148 and α3(IV)NC1 in vitro. Sera of these rats recognized α3_127‐148 and later on together with intact human α3(IV)NC1. Antibodies towards α3_127‐148 and intact α3(IV)NC1 could also be detected from the kidney elutes. These antibodies showed no cross‐reaction with each other, which implies intramolecular epitope spreading during disease progress. After sequential amino acid substitution, the α3_127‐148 with substitution of tryptophan₁₃₆, isoleucine₁₃₇, leucine₁₃₉ or tryptophan₁₄₀ lost its nephritogenicity. Human α3_127‐148 is a nephritogenic T cell epitope in WKY rats, with the critical amino acids as W₁₃₆I₁₃₇xL₁₃₉W₁₄₀. These findings might facilitate future investigation on microbial aetiology and potential specific immunotherapy of anti‐GBM disease.

Deglycosylation of myeloperoxidase uncovers its novel antigenicity

Myeloperoxidase (MPO) is a common target antigen of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis and is recognized in one-third of patients with anti-glomerular basement membrane (GBM) disease. Our previous study identified over 60% of patients with anti-GBM disease recognizing linear peptides of MPO heavy chain. Here we tested whether aberrant glycosylation alters MPO antigenicity through exposure of neo-epitopes on MPO molecules. Atypical glycosylated MPO molecules, including all possible glycosylation types, were prepared by exoglycosidase and endoglycosidase treatments. Antibodies were detected from the sera of 40 patients with anti-GBM disease without the coexistence of MPO-ANCA. Circulating antibodies against aberrant glycosylated MPO existed in 21 of these patients. Non-glycan MPO and MPO with only N-acetylglucosamine had high frequencies of recognition (16 and 15 patients, respectively). Antibodies binding to aberrant glycosylated MPO could not be inhibited by intact MPO or GBM antigen. When applied to ethanol-fixed neutrophils from normal individuals, these antibodies yielded a typical cytoplasmic staining pattern (c-ANCA). Antigen specificity was detected in 90% of the antibodies using five peptides containing one of the five N-glycosylation sites each, mostly on N323, N355, and N391. The antibodies were restricted to IgG1 subclass, could activate complement, and induce neutrophil degranulation in vitro. Thus, aberrant glycosylated MPO exposed neo-epitopes and was recognized by half of the patients with anti-GBM disease. Their antibodies possessed pathogenic characteristics and may be associated with kidney injury.

Primary glomerulonephritides

Most glomerulonephritides, even the more common types, are rare diseases. They are nevertheless important since they frequently affect young people, often cannot be cured, and can lead to chronic kidney disease, including end-stage renal failure, with associated morbidity and cost. For example, in young adults, IgA nephropathy is the most common cause of end-stage renal disease. In this Seminar, we summarise existing knowledge of clinical signs, pathogenesis, prognosis, and treatment of glomerulonephritides, with a particular focus on data published between 2008 and 2015, and the most common European glomerulonephritis types, namely IgA nephropathy, membranous glomerulonephritis, minimal change disease, focal segmental glomerulosclerosis, membranoproliferative glomerulonephritis, and the rare complement-associated glomerulonephritides such as dense deposit disease and C3 glomerulonephritis.

Antibodies to α5 chain of collagen IV are pathogenic in Goodpasture's disease

Autoantibody against glomerular basement membrane (GBM) plays a direct role in the initiation and development of Goodpasture's (GP) disease. The principal autoantigen is the non-collagenous domain 1 (NC1) of α3 chain of collagen IV, with two immunodominant epitopes, EA-α3 and EB-α3. We recently demonstrated that antibodies targeting α5NC1 are bound to kidneys in GP patients, suggesting their pathogenic relevance. In the present study, we sought to assess the pathogenicity of the α5 autoantibody with clinical and animal studies. Herein, we present a special case of GP disease with circulating autoantibody reactive exclusively to the α5NC1 domain. This autoantibody reacted with conformational epitopes within GBM collagen IV hexamer and produced a linear IgG staining on frozen sections of human kidney. The antibody binds to the two regions within α5NC1 domain, EA and EB, and inhibition ELISA indicates that they are targeted by distinct sub-populations of autoantibodies. Sequence analysis highlights five residues that determine specificity of antibody targeting EA and EB epitopes of α5NC1 over homologous regions in α3NC1. Furthermore, immunization with recombinant α5NC1 domain induced crescentic glomerulonephritis and alveolar hemorrhage in Wistar-Kyoto rats. Thus, patient data and animal studies together reveal the pathogenicity of α5 antibodies. Given previously documented cases of GP disease with antibodies selectively targeting α3NC1 domain, our data presents a conundrum of why α3-specific antibodies developing in majority of GP patients, with α5-specific antibodies emerged in isolated cases, the answer for which is critical for understanding of etiology and progression of the GP disease.

Autoantibodies against Linear Epitopes of Myeloperoxidase in Anti-Glomerular Basement Membrane Disease

BACKGROUND AND OBJECTIVES

Approximately 20%-30% of patients with anti-glomerular basement membrane disease present coexisting anti-myeloperoxidase (MPO) autoantibodies. We previously showed the recognition of a linear fragment of the MPO heavy chain N-terminus ((1)H, MPO279-409) in plasma from most double-positive patients. Herein, we investigated the frequency of autoantibodies against overlapping (1)H-derived linear peptides in plasma from patients with anti-glomerular basement membrane disease.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We synthesized 13 overlapping linear peptides ((1)H-1 to (1)H-13) covering MPO279-409. We retrospectively collected plasma samples from 67 patients with anti-glomerular basement membrane disease from 1996 to 2012, and we screened them for IgG autoantibodies by ELISA using intact human MPO and the overlapping peptides as antigens, and we further investigated the clinical significance. Autoantibody binding to the linear MPO structure was confirmed by Western blotting.

RESULTS

We followed up the 67 patients until 2015, with a median follow-up time of 10.0 (2.3-36.0) months, and 56 ESRD events occurred among the 67 patients with follow-up data. Plasma from 23.9% (16) of the patients recognized intact human MPO, whereas 62.7% (42) plasma samples recognized MPO279-409 linear peptides. Of the 13 linear peptides, (1)H-4 (44.8%, 30 patients) and (1)H-12 (40.3%, 27 patients) exhibited the highest recognition frequencies. Patients with autoantibodies against (1)H-11 or (1)H-12 (MPO371-400) were older (46.1±18.8 versus 34.1±16.6 years; P<0.01), had higher serum creatinine upon diagnosis (median 7.8 mg/dl, interquartile range 4.9-12.6 mg/dl versus median 5.4 mg/dl, interquartile range 2.4-7.3 mg/dl; P=0.02), and had a higher probability of progressing to ESRD; however, multivariate Cox regression analysis showed that (1)H-11 or 12 reaction was not an independent risk factor for renal failure (hazard ratio, 1.2; 95% confidence interval, 0.8 to 2.8; P=0.19).

CONCLUSIONS

Autoantibodies against linear peptides of MPO can be detected in the majority of patients with anti-glomerular basement membrane disease, and several are associated with disease severity. The potential common pathogenic mechanism between anti-glomerular basement membrane antibodies and anti-MPO autoantibodies in anti-glomerular basement membrane disease requires further investigation.

Anti-C1q autoantibodies from active lupus nephritis patients could inhibit the clearance of apoptotic cells and complement classical pathway activation mediated by C1q in vitro

Anti-C1q antibodies are prevalent in patients with active lupus nephritis and were found to be closely associated with renal involvement and predictive for a flare of nephritis. However, the pathogenesis of anti-C1q antibodies involved in human lupus nephritis remains unclear. C1q, which plays a key role in apoptotic cell and immune complex removal, is a very important functional molecule in the pathogenesis of SLE. The aim of this study was to investigate the influence of anti-C1q autoantibodies from active lupus nephritis patients on the bio-functions of C1q in vitro. We purified IgG autoantibodies against C1q from lupus nephritis patients, and found that they could recognize C1q bound on early apoptotic cells at 30 μg/ml, and could significantly decrease the phagocytosis by macrophages of early apoptotic cells opsonized by 50 μg/ml C1q in comparison with normal IgG. Levels of circulating immune complexes of the ten patients were measured by a circulating immune complexes (CIC)-C1q Enzyme Immunoassay Kit. Anti-C1q autoantibodies affinity purified by microtiter plates could significantly inhibit the deposition of C3c on CIC-C1q in a dose dependent manner in comparison with IgG from 10 healthy blood donors. The binding of opsonized immune complexes to RBCs was significantly inhibited by anti-C1q autoantibodies purified by microtiter plates in a dose dependent manner. Our observations suggest that serum anti-C1q autoantibodies from active lupus nephritis patients could interfere with some biological function of C1q in vitro.

Detection of autoantibodies in a point-of-care rheumatology setting

Autoimmune rheumatic diseases are common and confront society with serious medical, social, and financial burdens imposed by their debilitating nature. Many autoimmune diseases are associated with a particular set of autoantibodies, which have emerged as highly useful to define and classify disease, predict flares, or monitor efficacy of therapy. However, current practice for monitoring autoantibodies is protracted, labor-intensive, and expensive. This review provides an overview on the value of point-of-care (POC) biosensor technology in the diagnosis and management of patients with autoimmune rheumatic diseases. Real-time measurement of autoantibodies will clearly benefit the rheumatology practice in emergency and urgent care settings, where definitive diagnosis is essential for initiation of correct critical care therapy. Immediate serological information in clinic will provide considerable value for long-term patient care and an opportunity for an instant, result-deduced therapeutic action, avoiding delays and improving compliance, especially in field-based and remote areas. We describe the particular autoantibodies that are useful disease and activity markers and would, therefore, be attractive to POC applications. Already existing biosensors and platforms that show promise for autoantibody testing are summarized and comparatively evaluated. As POC assessment is gaining momentum in several areas of patient care, we propose that rheumatology is poised to benefit from this innovative and affordable technology.

The HLA-DRB1*15:01-restricted Goodpasture's T cell epitope induces GN

Human anti-glomerular basement membrane (GBM) disease strongly associates with HLA-DRB1*15:01. The target autoantigen in this disease is the noncollagenous domain of the α3 chain of type IV collagen, α3(IV)NC1, but critical early T cell epitopes presented by this human MHC class II molecule are unknown. Here, by immunizing HLA-DRB1*15:01 transgenic mice with whole recombinant α3(IV)NC1 and with overlapping α3(IV)NC1 peptides, we defined a HLA-DRB1*15:01-restricted α3(IV)NC1 T cell epitope (α3136-146) with four critical residues. This peptide was not immunogenic in HLA-DRB1*01:01 transgenic or C57BL/6 mice. The T cell epitope is naturally processed from α3(IV)NC1. CD4(+) T cell clones, generated from HLA-DRB1*15:01 transgenic mice and specific for α3136-146, transferred disease into naive HLA-DRB1*15:01 transgenic mice, evidenced by the development of necrotizing crescentic GN, albuminuria, renal impairment, and accumulation of CD4(+) T cells and macrophages in glomeruli. Because Fcγ receptors are implicated in disease susceptibility, we crossed HLA transgenic mice onto an FcγRIIb-deficient background. Immunization with either α3136-146 or α3(IV)NC1 induced GN in HLA-DRB1*15:01 transgenic FcγRIIb-deficient mice, but HLA-DRB1*01:01 transgenic FcγRIIb-deficient mice were unaffected. Taken together, these results demonstrate that the HLA-DRB1*15:01-restricted T cell epitope α3136-146 can induce T cell responses and injury in anti-GBM GN.

Association of epitope spreading of antiglomerular basement membrane antibodies and kidney injury

BACKGROUND AND OBJECTIVES

Antiglomerular basement membrane autoantibodies are pathogenic in antiglomerular basement membrane disease with two major epitopes, E(A) and E(B), on α3 chain of type IV collagen. This study investigated the epitope spectrum of antiglomerular basement membrane autoantibodies, aiming to identify the association between epitope specificity and kidney injury.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

All 108 patients with antiglomerular basement membrane disease and complete clinical data were divided into three groups according to renal dysfunction: mild group (n=20) with serum creatitine≤1.5 mg/dl; moderate group (n=22) with serum creatinine=1.5-6.8 mg/dl; severe group (n=66) with serum creatitine≥6.8 mg/dl. Epitope spectrums of antibodies were determined by ELISA, and their associations with kidney damage were analyzed. Sequential serum samples in 40 patients were examined during disease courses.

RESULTS

E(A) and E(B) were recognized in 79.6% and 72.2% of patients, respectively. E(A) and E(B) reactions were the lowest in the mild group and higher in the moderate group (E(A): 35.0% versus 81.8%, P=0.002; E(B): 15.0% versus 68.2%, P=0.001). They were the highest in the severe group (E(A): 92.4%, P=0.31; E(B): 90.9%, P=0.02). Close association was observed between renal injury and E(A) and E(B) reactions. Multivariate Cox regression analysis showed that E(B) reaction was an independent risk factor for renal failure (hazard ratio=6.91, P=0.02). The recognition for non-E(AB) remained low among groups. No augmentation of epitope spectrum was shown in serial serum samples.

CONCLUSIONS

Intramolecular epitope spreading might occur before the onset of human antiglomerular basement membrane disease. The autoimmunity to E(A) and E(B), especially E(B), was crucial for kidney dysfunction.

Antibodies against linear epitopes on the Goodpasture autoantigen and kidney injury

BACKGROUND AND OBJECTIVES

Linear epitopes on the Goodpasture autoantigen involved in human anti-glomerular basement membrane (GBM) disease are not fully defined. This study investigated the linear epitopes recognized by circulating antibodies in anti-GBM patients, aiming to identify the potential nephrogenic linear epitopes and their clinical significance.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Sixty-eight patients with anti-GBM disease were enrolled. Twenty-four overlapping linear peptides were synthesized across the whole sequence of the human Goodpasture autoantigen. ELISA detected circulating antibodies against linear epitopes. Their associations with clinical features were further analyzed.

RESULTS

Antibodies against linear peptides were detected in sera from 55 patients (80.9%). Three major epitopes with high frequencies were identified: P14 (41%), P16 (36.8%), and P18 (57%). P14, a formerly defined T cell epitope, was a mutual B cell epitope. Antibodies against P14 were frequently detected in patients with positive antineutrophil cytoplasmic antibodies (39.3% versus 12.5%; P=0.01). Patients with anti-P16 antibodies presented with higher serum creatinine on diagnosis (665.5±227.2 versus 443.7±296.8 μmol/L; P=0.001) and worse renal outcome during follow-up (hazard ratio, 2.10; 95% confidence interval, 1.10-3.90; P=0.02). The level of anti-P18 antibodies positively correlated with the percentage of crescents in glomeruli (r=0.54; P=0.008). Recognition of P22 was an independent predictor for patient death (hazard ratio, 3.02; 95% confidence interval, 1.20-7.57; P=0.02).

CONCLUSIONS

Antibodies against linear epitopes on the Goodpasture autoantigen could be detected in human anti-GBM disease and were associated with kidney injury. P14 was a mutual T and B cell epitope, implying its nephrogenic role in disease initiation.

Performance evaluation of a novel chemiluminescence assay for detection of anti-GBM antibodies: an international multicenter study

BACKGROUND

Autoantibodies to the non-collagen region (NC1) of the alpha-3 subunit of collagen IV represent a serological hallmark in the diagnosis of Goodpasture's syndrome (GPS). The objective of our study was to carefully analyze the performance characteristics of a novel anti-glomerular basement membrane (GBM) chemiluminescence immunoassay (CIA).

METHODS

Sera from patients with GPS (n = 90) were collected from four clinical centers. Samples from different disease groups (n = 397) and healthy individuals (n = 400) were used as controls. All samples were tested for anti-GBM antibodies by a rapid, random access CIA (QUANTA Flash™ GBM). Most of the samples were also tested using other methods including different commercial anti-GBM IgG assays and research assays for anti-GBM IgA and IgM.

RESULTS

The sensitivity and specificity of the novel CIA was 95.6% [95% confidence interval (CI) 89.0-98.8%] and 99.6% (95% CI 98.9-99.9%), respectively. Receiver operating characteristic analysis showed good discrimination between GPS patients and controls. The area under the curve was 0.98 (CI 0.96-1.0). The three anti-GBM antibody-positive samples from the control group were from two healthy individuals and one human immunodeficiency virus (HIV)-infected patient. All three individuals had low levels of anti-GBM antibodies [20, 24 and 25 chemiluminescent unit (CU), cutoff 20 CU]. When the results of the new CIA were compared to other methods, good agreement was observed: 95.8% (kappa = 0.92) versus EliA™ GBM, 97.4% (kappa = 0.95) versus both BINDAZYME™ Anti-GBM and QUANTA Lite® GBM. Anti-GBM IgA was detectable in low concentrations in patients with GPS and was associated with anti-GBM IgG but was less useful in discriminating GPS patients and controls. No discrimination was found for anti-GBM IgM.

CONCLUSION

The novel QUANTA Flash™ GBM CIA demonstrated good sensitivity and specificity and had good agreement with other methods. Our data confirm that ∼5% of patients with GPS do not have detectable levels of anti-GBM antibodies.

Autoantibodies as prognostic markers in autoimmune liver disease

Certain autoantibodies in autoimmune liver disease have prognostic implications that are under-utilized and under-developed. The goals of this review are to indicate progress in characterizing the autoantibodies with prognostic connotations and to indicate the feasibility and importance of discovering other markers. Prime source and review articles in English were selected by a Medline search through 2010. Antibodies to soluble liver antigen, actin, liver cytosol type 1, asialoglycoprotein receptor, chromatin, cyclic citrullinated peptide, and uridine glucuronosyltransferases have been associated with the occurrence, severity, and progression of autoimmune hepatitis, and antibodies to Sp100, gp210, and centromere have had similar implications in primary biliary cirrhosis. Antibodies to soluble liver antigen have shown the most promise in autoimmune hepatitis as they have been associated with severe histological changes, long durations of treatment, relapse after drug withdrawal, and high frequency of liver failure. Antibodies to the nuclear rim pore protein, gp210, have shown the most promise in primary biliary cirrhosis as they have been associated with severe interface hepatitis, lobular inflammation, and progression to liver failure. The major limitations of the autoantibodies have been their lack of standardized assays, low negative predictabilities, and fluctuating levels. Performance parameters will improve as critical pathogenic pathways, comprehensive testing batteries, and standardized assays through international exchange workshops are developed. Progress has been made in identifying the serological markers of prognosis in autoimmune liver disease, and they promise to reflect critical disease mechanisms and enhance patient management.

Molecular architecture of the Goodpasture autoantigen in anti-GBM nephritis

BACKGROUND

In Goodpasture's disease, circulating autoantibodies bind to the noncollagenous-1 (NC1) domain of type IV collagen in the glomerular basement membrane (GBM). The specificity and molecular architecture of epitopes of tissue-bound autoantibodies are unknown. Alport's post-transplantation nephritis, which is mediated by alloantibodies against the GBM, occurs after kidney transplantation in some patients with Alport's syndrome. We compared the conformations of the antibody epitopes in Goodpasture's disease and Alport's post-transplantation nephritis with the intention of finding clues to the pathogenesis of anti-GBM glomerulonephritis.

METHODS

We used an enzyme-linked immunosorbent assay to determine the specificity of circulating autoantibodies and kidney-bound antibodies to NC1 domains. Circulating antibodies were analyzed in 57 patients with Goodpasture's disease, and kidney-bound antibodies were analyzed in 14 patients with Goodpasture's disease and 2 patients with Alport's post-transplantation nephritis. The molecular architecture of key epitope regions was deduced with the use of chimeric molecules and a three-dimensional model of the alpha345NC1 hexamer.

RESULTS

In patients with Goodpasture's disease, both autoantibodies to the alpha3NC1 monomer and antibodies to the alpha5NC1 monomer (and fewer to the alpha4NC1 monomer) were bound in the kidneys and lungs, indicating roles for the alpha3NC1 and alpha5NC1 monomers as autoantigens. High antibody titers at diagnosis of anti-GBM disease were associated with ultimate loss of renal function. The antibodies bound to distinct epitopes encompassing region E(A) in the alpha5NC1 monomer and regions E(A) and E(B) in the alpha3NC1 monomer, but they did not bind to the native cross-linked alpha345NC1 hexamer. In contrast, in patients with Alport's post-transplantation nephritis, alloantibodies bound to the E(A) region of the alpha5NC1 subunit in the intact hexamer, and binding decreased on dissociation.

CONCLUSIONS

The development of Goodpasture's disease may be considered an autoimmune "conformeropathy" that involves perturbation of the quaternary structure of the alpha345NC1 hexamer, inducing a pathogenic conformational change in the alpha3NC1 and alpha5NC1 subunits, which in turn elicits an autoimmune response. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases.)