Accuracy of Anti-GBM Antibodies in Diagnosing Anti-Glomerular Basement Membrane Disease: A Systematic Review and Meta-Analysis.

BACKGROUND: The sensitivity and specificity of anti-glomerular basement membrane (GBM) antibodies have not been systematically analyzed. In this systematic review, we aimed to evaluate the diagnostic accuracy of anti-GBM antibodies for anti-GBM disease. SUMMARY: Potential studies were searched using MEDLINE, Embase, the Cochrane Library, and the International Clinical Trials Registry Platform based on the index test and target condition. The inclusion criteria were prospective or retrospective cohort studies or case-control studies assessing the sensitivity and specificity of anti-GBM antibodies, and the reference standard was clinical diagnosis including biopsy results. The exclusion criteria were review articles, case reports, animal studies, and in vitro studies. Quality assessment was conducted based on the Quality Assessment of Diagnostic Accuracy Studies-2. The pooled estimates of sensitivity and specificity were calculated using a bivariate random-effects model. The overall quality was evaluated using the Grades of Recommendation, Assessment, Development, and Evaluation. Six studies (1,691 patients) and 11 index tests were included in our systematic review. A high risk of bias and concerns regarding the applicability of patient selection were noted because of the case-control design in 67% of the included studies. The pooled sensitivity and specificity were 93% (95% CI: 84-97%) and 97% (95% CI: 94-99%), respectively. The certainty of evidence was low because of the high risk of bias and indirectness. Key Messages: Anti-GBM antibodies may exhibit high sensitivity and specificity in the diagnosis of anti-GBM disease. Further cohort studies are needed to confirm their precise diagnostic accuracy and compare diagnostic accuracies among different immunoassays.

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.

Atypical anti-glomerular basement membrane disease with anti-GBM antibody negativity and ANCA positivity: a case report.

BACKGROUND: Anti-glomerular basement membrane (anti-GBM) disease is an organ-specific autoimmune disease that involves the lung and kidneys and leads to rapid glomerulonephritis progression, with or without diffuse alveolar hemorrhage, and even respiratory failure. Classic cases of anti-GBM disease are diagnosed based on the presence of the anti-GBM antibody in serum samples and kidney or lung biopsy tissue samples. However, atypical cases of anti-GBM disease are also seen in clinical practice. CASE PRESENTATION: We herein report the rare case of a patient with atypical anti-GBM disease whose serum was negative for the anti-GBM antibody but positive for the myeloperoxidase (MPO) anti-neutrophil cytoplasmic antibody (p-ANCA) and another atypical ANCA. Laboratory test results showed severe renal insufficiency with a creatinine level of 385 µmol/L. Renal biopsy specimen analysis revealed 100% glomeruli with crescents; immunofluorescence showed immunoglobulin G (IgG) linearly deposited alongside the GBM. Finally, the patient was discharged successfully after treatment with plasmapheresis, methylprednisolone and prednisone. CONCLUSION: This patient, whose serum was negative for the anti-GBM antibody but positive for p-ANCA and another atypical ANCA, had a rare case of anti-GBM disease. Insights from this unusual case might help physicians diagnose rare forms of glomerulonephritis and treat affected patients in a timely manner.

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.

[Benefit of Howell-Jolly bodies detection: finding of an acquired hyposplenism in a patient with Goodpasture syndrome]. / Intérêt de la détection des corps de Howell-Jolly : hyposplénisme acquis dans le cadre d'un syndrome de Goodpasture.

Howell-Jolly bodies are intraerythrocytic inclusions corresponding to a small portion of chromatin. Red blood cells that contain these nuclear remnants are removed from the circulation by the spleen. In most cases, presence of Howell-Jolly bodies on a blood smear is the result of functional asplenia and splenectomy. Observation. We report incidental finding of numerous Howell-Jolly bodies in a patient followed by the nephrology department. This microscopic observation of blood smear led to a diagnostic imaging and to the evidence of a reduced spleen, possibly favoured by a history of Goodpasture syndrome in this renal transplant patient without splenectomy. Vaccination and antibioprophylaxy were proposed to prevent infectious risk linked to this splenic hypoplasia. Conclusion. Seeking of Howell-Jolly bodies could be made in every condition associated with a risk of splenic hypoplasia to prevent infectious risk.

Comparison of the performance of a chemiluminescence assay and an ELISA for detection of anti-GBM antibodies.

Objective: Autoantibodies to the α3 chain noncollagen 1 domain of type IV collagen (α3(IV)NC1) are a serological hallmark in the diagnosis of anti-glomerular basement membrane (GBM) disease. The objective of our study was to compare the performance of anti-glomerular basement membrane (GBM) antibody detection by chemiluminescence immunoassay (CIA) and by enzyme-linked immunosorbent assays (ELISAs).Methods: Sera from outpatients who were suspected to have anti-GBM disease and 31 patients with biopsy-proven anti-GBM disease were collected. Thirty normal controls were also included. All samples were tested for anti-GBM antibodies by CIA and commercial ELISA. The anti-GBM antibody-positive samples were confirmed by a homemade ELISA coated with recombinant human α3(IV)NC1.Results: Compared with detection of anti-GBM antibodies with ELISA, detection of anti-GBM antibodies with CIA showed a positivity agreement of 70% and a negativity agreement of 98.6%. Among the 4 patients with different results, the anti-GBM antibody detection by CIA was in agreement with the homemade ELISA coated with recombinant human α3(IV)NC1 and the clinical diagnosis. In 31 patients with anti-GBM disease, good agreement was achieved in the detection of anti-GBM antibodies with CIA, commercial ELISA and the homemade ELISA (100%, 100%). The AUC for CIA and commercial ELISA was 0.987 and 0.966, respectively.Conclusions: The detection of anti-GBM antibodies with CIA demonstrated good sensitivity and specificity and was in good agreement with our homemade ELISA, which seems better than the commercial ELISA in suspected anti-GBM disease patients. The three assays performed in parallel in the diagnosis of anti-GBM disease patients.

Rituximab in treatment of anti-GBM antibody glomerulonephritis: A case report and literature review.

RATIONALE: Anti-glomerular basement membrane (GBM) disease is a T cell-mediated disease that has a poor prognosis with conventional therapy. We tested rituximab as a primary therapy to reduce anti-GBM antibody produced by B cells. PATIENT CONCERNS: A 53-year old woman with complaints of a fever, headache and abdominal discomfort showed renal failure with elevated anti-GBM antibody, and renal biopsy revealed crescentic necrotizing glomerulonephritis with linear immunoglobulin G (IgG) 1 deposition along GBM. DIAGNOSES: The patient's plasma contained autoantibodies against Goodpasture antigen, which is the NC domain of collagen IVα3, and CD4-positive helper T cells were found surrounding crescent glomeruli with the coexistence CD20-positive B cells. INTERVENTIONS: Rituximab with steroid and plasma exchange. OUTCOMES: The levels of autoantibody for Goodpasture antigen were reduced, and the patient was able to temporarily withdraw from hemodialysis. LESSONS: B cell depletion with rituximab is effective as an initial therapy for anti-GBM disease.

A "double-seropositive" Vasculitis for antiglomerular basement membrane antibodies and antineutrophil cytoplasmic antibody, and multiple myeloma, all three with simultaneous diagnosis of renal involvement, common pathophysiology, or pure coincidence? first case in the World.

The combination of Goodpasture's disease and antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis is not exceptional. However, to the best of our knowledge, their association with multiple myeloma (MM) with kidney involvemen thas not been described. We report probably the first case of double-seropositive vasculitis for antiglomerular basement membrane (GBM) antibodies and ANCA associated with MM with renal involvement. A 60- year-old-female presented with severe acute kidney injury. Three months earlier, she had a history of bone pain. Blood workup found a creatinine of 1100 µmol/L and a C-reactive protein of 60 mg/L. Anti-GBM antibodies returned positive at 400 U/mL and pANCA positive at 380 U/mL. Plasma protein immunofixation found a monoclonal immunoglobulin G (IgG) KAPPA peak; the myelogram found a 10% plasmocytosis. On the day 4 of hospitalization, the patient presented with alveolar hemorrhage. The renal biopsy showed diffuse crescentic glomerulo-nephritis with linear glomerular deposits of IgG, with kappa light chain cast nephropathy. The association between vasculitis and malignant blood disease is very rare; the pathophysiology of this association remains unclear. It would seem interesting to look for possible ANCA or anti- GBM activity carried by the monoclonal immunoglobulin.

ANCA associated vasculitis: experience of a tertiary care referral center / Vasculite associada a ANCA: experiência de um centro de referência de atendimento terciário

ABSTRACT Background and objectives: Anti-neutrophil cytoplasmic autoantibodies (ANCA) associated vasculitis is a small vessel vasculitis with insufficient epidemiologic estimates in the United States. We aimed to determine demographic and clinical features of ANCA associated vasculitis patients presenting to a large tertiary care referral center in Upstate New York. Design, setting, participants, and measurements: A retrospective analysis of cases with pauci-immune GN on renal biopsy and clinical diagnosis of ANCA vasculitis presenting over 11 years was conducted. Outcomes of interest were: demographics, ANCA antibody positivity, patient and renal survival, and regional trends. Results: 986 biopsies were reviewed, 41 cases met the criteria for inclusion: 18 GPA, 19 MPA, and 4 double positive (anti-GBM disease plus ANCA vasculitis). Mean age at presentation was 52.4 years (SD 23.7), 23 (56%) were male and median creatinine was 2.6 mg/dL. The median patient follow up was 77 weeks (IQR 10 - 263 weeks), with a 3-month mortality rate of 5.7% and a 1-year estimated mortality rate of 12%. Thirteen patients required hemodialysis at the time of diagnosis; 7 patients came off dialysis, with median time to renal recovery of 4.86 weeks (IQR 1.57 - 23.85 weeks). C-ANCA positivity (p < 0.001) and C-ANCA plus PR3 antibody pairing (p = 0.005) was statistically significant in GPA versus MPA. P-ANCA positivity was observed in MPA versus GPA (p = 0.02) and double positive versus GPA (p = 0.002), with P-ANCA and MPO antibody pairing in MPA versus GPA (p = 0.044). Thirty-seven of the 41 cases were referred locally, 16 cases were from within a 15-mile radius of Albany, Schenectady, and Saratoga counties. Conclusions: ANCA vasculitis is associated with end stage renal disease and increased mortality. Our study suggests the possibility of higher regional incidence of pauci-immune GN in Upstate New York. Further studies should investigate the causes of clustering of cases to specific regions.

RESUMO Introdução e objetivos: A vasculite associada a anticorpos anticitoplasma de neutrófilo (ANCA) é uma vasculite de pequenos vasos com estimativas epidemiológicas insuficientes nos Estados Unidos. Nosso objetivo foi determinar características demográficas e clínicas de pacientes com vasculite associada à ANCA, apresentando-se a um grande centro de referência de atendimento terciário em Upstate New York. Formato, cenário, participantes e medidas: Foi realizada uma análise retrospectiva dos casos de GN pauci-imune em biópsias renais e diagnóstico clínico de vasculite ANCA por mais de 11 anos. Os resultados de interesse foram: dados demográficos, positividade de anticorpos ANCA, sobrevidas renal e de pacientes e tendências regionais. Resultados: 986 biópsias foram revisadas, 41 casos preencheram os critérios de inclusão: 18 GPA, 19 PAM, e 4 duplo-positivos (doença anti-MBG com vasculite ANCA). A média de idade na apresentação foi de 52,4 anos (DP 23,7), 23 (56%) eram do sexo masculino e mediana de creatinina de 2,6 mg/dL. O acompanhamento mediano dos pacientes foi de 77 semanas (IQR 10 - 263 semanas), com uma taxa de mortalidade de 3 meses de 5,7% e uma taxa de mortalidade estimada em 1 ano de 12%. Treze pacientes necessitaram de hemodiálise no momento do diagnóstico; 7 pacientes saíram da diálise, com tempo médio para recuperação renal de 4,86 semanas (IQR 1,57 - 23,85 semanas). A positividade para C-ANCA (p < 0,001) e o pareamento de anticorpos C-ANCA mais PR3 (p = 0,005) foram estatisticamente significantes em GPA versus PAM. A positividade de P-ANCA foi observada em PAM versus GPA (p = 0,02) e duplo positivo versus GPA (p = 0,002), com pareamento de anticorpos P-ANCA e MPO em PAM versus GPA (p = 0,044). Trinta e sete dos 41 casos foram encaminhados localmente, 16 casos foram de dentro de um raio de 15 milhas dos condados de Albany, Schenectady e Saratoga. Conclusões: A vasculite por ANCA está associada à doença renal terminal e aumento da mortalidade. Nosso estudo sugere a possibilidade de maior incidência regional de GN pauci-imune no norte do estado de Nova York. Novos estudos devem investigar as causas do acúmulo de casos em regiões específicas.

ANCA associated vasculitis: experience of a tertiary care referral center.

BACKGROUND AND OBJECTIVES: Anti-neutrophil cytoplasmic autoantibodies (ANCA) associated vasculitis is a small vessel vasculitis with insufficient epidemiologic estimates in the United States. We aimed to determine demographic and clinical features of ANCA associated vasculitis patients presenting to a large tertiary care referral center in Upstate New York. Design, setting, participants, and measurements: A retrospective analysis of cases with pauci-immune GN on renal biopsy and clinical diagnosis of ANCA vasculitis presenting over 11 years was conducted. Outcomes of interest were: demographics, ANCA antibody positivity, patient and renal survival, and regional trends. RESULTS: 986 biopsies were reviewed, 41 cases met the criteria for inclusion: 18 GPA, 19 MPA, and 4 double positive (anti-GBM disease plus ANCA vasculitis). Mean age at presentation was 52.4 years (SD 23.7), 23 (56%) were male and median creatinine was 2.6 mg/dL. The median patient follow up was 77 weeks (IQR 10 - 263 weeks), with a 3-month mortality rate of 5.7% and a 1-year estimated mortality rate of 12%. Thirteen patients required hemodialysis at the time of diagnosis; 7 patients came off dialysis, with median time to renal recovery of 4.86 weeks (IQR 1.57 - 23.85 weeks). C-ANCA positivity (p < 0.001) and C-ANCA plus PR3 antibody pairing (p = 0.005) was statistically significant in GPA versus MPA. P-ANCA positivity was observed in MPA versus GPA (p = 0.02) and double positive versus GPA (p = 0.002), with P-ANCA and MPO antibody pairing in MPA versus GPA (p = 0.044). Thirty-seven of the 41 cases were referred locally, 16 cases were from within a 15-mile radius of Albany, Schenectady, and Saratoga counties. CONCLUSIONS: ANCA vasculitis is associated with end stage renal disease and increased mortality. Our study suggests the possibility of higher regional incidence of pauci-immune GN in Upstate New York. Further studies should investigate the causes of clustering of cases to specific regions.

Use of rituximab as an induction therapy in anti-glomerular basement-membrane disease.

BACKGROUND: Anti-glomerular basement-membrane (anti-GBM) disease (or Goodpasture disease) is characterized by severe kidney and lung involvement. Prognoses have improved with treatments that combine plasma exchange and immunosuppressive drugs. However, patients with severe renal involvement can have poor renal outcomes and cyclophosphamide can cause significant complications. Anti-GBM antibodies have a direct pathogenic effect on the disease: thus, therapeutics that can decrease their production, such as rituximab, could be a good alternative. METHODS: The medical files of five patients that had received rituximab as a first-line therapy (instead of cyclophosphamide), plus plasma exchange and steroids, were reviewed. All patients had severe disease manifestations. RESULTS: Four patients required dialysis at diagnosis and remained dialysis-dependent over the mean follow-up of 15 months. Three patients had pulmonary involvement, but recovered even though mechanical ventilation was required. Anti-GBM antibodies became rapidly undetectable in all patients. One infectious and two hematological complications were observed. CONCLUSIONS: We report the outcomes of five patients with Goodpasture disease and treated with rituximab as a first-line treatment. This strategy was effective at treating pulmonary manifestations and was associated with a good biological response with no major serious adverse events. However, renal outcomes were not significantly improved.

The treatment of ANCA-associated rapidly-progressive glomerulonephritis and Goodpasture syndrome with therapeutic apheresis.

Therapeutic plasma aphresis (plasmapheresis) is one form of treatment that is frequently used in practice of Nephrology. Plasmapheresis is the most important part of the therapies for Goodpasture's syndrome and anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis which are causes of rapidly progressive glomerulonephritis. The reason why the effectiveness of plasmapheresis therapy cannot be clearly demonstrated in renal involvement in these diseases is that it does not appear to be possible to recruit an adequate number of patients and plasmapheresis is not effective in advanced disease if early treatment is not initiated.

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)NC1127-148 (P14) (69.2%), α3(IV)NC1159-178 (77.8%), α3(IV)NC1179-198 (55.6%), α3(IV)NC1189-208 (P19) (75.0%) and α3(IV)NC1141-154 (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. α3127-148 was a mutual T and B cell epitope, implying its initial role in epitope spreading process.

Patients double-seropositive for ANCA and anti-GBM antibodies have varied renal survival, frequency of relapse, and outcomes compared to single-seropositive patients.

Co-presentation with both ANCA and anti-GBM antibodies is thought to be relatively rare. Current studies of such 'double-positive' cases report small numbers and variable outcomes. To study this further we retrospectively analyzed clinical features and long-term outcomes of a large cohort of 568 contemporary patients with ANCA-associated vasculitis, 41 patients with anti-GBM disease, and 37 double-positive patients with ANCA and anti-GBM disease from four European centers. Double-positive patients shared characteristics of ANCA-associated vasculitis (AAV), such as older age distribution and longer symptom duration before diagnosis, and features of anti-GBM disease, such as severe renal disease and high frequency of lung hemorrhage at presentation. Despite having more evidence of chronic injury on renal biopsy compared to patients with anti-GBM disease, double-positive patients had a greater tendency to recover from being dialysis-dependent after treatment and had intermediate long-term renal survival compared to the single-positive patients. However, overall patient survival was similar in all three groups. Predictors of poor patient survival included advanced age, severe renal failure, and lung hemorrhage at presentation. No single-positive anti-GBM patients experienced disease relapse, whereas approximately half of surviving patients with AAV and double-positive patients had recurrent disease during a median follow-up of 4.8 years. Thus, double-positive patients have a truly hybrid disease phenotype, requiring aggressive early treatment for anti-GBM disease, and careful long-term follow-up and consideration for maintenance immunosuppression for AAV. Since double-positivity appears common, further work is required to define the underlying mechanisms of this association and define optimum treatment strategies.

Plasma from patients with anti-glomerular basement membrane disease could recognize microbial peptides.

Infection has long been suspected as a trigger of autoimmune diseases, and molecular mimicry mechanism was hypothesized in this study. Microbe originated peptides were searched from the Uniprot database based on a previous defined critical amino acid motif within α3129-150, isoleucine137, tryptophan140, glycine142, phenylalanine 143 and phenylalanine 145. 23826 microbial peptides were identified using our searching strategy, among which seven were related with human infections. Circulating IgG and IgM antibodies against the seven microbial peptides were detected using ELISA in 76 patients with anti-GBM disease. Four peptides were recognized by both IgG and IgM antibodies, and one peptide was recognized by IgG antibodies only. Peptides from Bacteroides, Saccharomyces cerevisiae, and Bifidobacterium thermophilum possessed the highest recognition frequency with the prevalence of 73.7%, 61.8% and 67.1% for IgG, 56.6%, 44.7% and 67.1% for IgM in anti-GBM patients. Patients with antibodies against these microbial peptides showed more severe kidney injury, including higher serum creatinine and higher percentage of crescent formation. In conclusion, antibodies against microbial peptides were identified in the circulation of anti-GBM patients, implying its etiological role in eliciting autoimmune response against α3(IV)NC1 through molecular mimicry.

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 (α3127-148 ) 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 α3127-148 and α3(IV)NC1 in vitro. Sera of these rats recognized α3127-148 and later on together with intact human α3(IV)NC1. Antibodies towards α3127-148 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 α3127-148 with substitution of tryptophan136 , isoleucine137 , leucine139 or tryptophan140 lost its nephritogenicity. Human α3127-148 is a nephritogenic T cell epitope in WKY rats, with the critical amino acids as W136 I137 xL139 W140 . These findings might facilitate future investigation on microbial aetiology and potential specific immunotherapy of anti-GBM disease.