Anti-neutrophil cytoplasmic antibody-associated glomerulonephritis with detection of myeloperoxidase and phospholipase A2 receptor in membranous nephropathy-lesions: report of two patients with microscopic polyangiitis

Myeloperoxidase-Associated Membranous Nephropathy in Antineutrophil Cytoplasmic Antibody-Associated Glomerulonephritis

Introduction

Antineutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (GN) is characterized by pauci-immune crescentic GN. Myeloperoxidase ANCA-associated GN (MPO-ANCA GN) with membranous nephropathy (MN), where bright granular capillary MPO and IgG staining along the glomerular basement membrane (GBM) is present, has been reported; however, its clinicopathological features remain unclear.

Methods

We investigated 7 MPO-ANCA GN with MN and 11 control cases (6 MPO-ANCA GN and 5 primary MN cases). Proteomics of laser microdissected glomeruli followed by immunohistochemical analysis was performed to identify causal antigens in MPO-ANCA GN with MN. We described the clinicopathological features of MPO-associated MN compared with those of MPO-ANCA GN and primary MN.

Results

We detected proteomic MPO and granular capillary MPO deposits in all MPO-ANCA GN with MN cases. Confocal microscopy revealed MPO and IgG colocalization along the GBM. MPO-associated MN clinicopathological features include greater proteinuria, a higher fibrous crescent rate, and a lower MPO-ANCA titer than MPO-ANCA GN. The estimated glomerular filtration rate (eGFR) and urinary protein excretion were lower in MPO-associated MN than in primary MN.

Conclusion

MPO-associated MN, a unique type of secondary MN where MPO serves as the causal antigen, is a subset of MPO-ANCA GN with MN. Prolonged periods of MPO-ANCA GN and a low MPO-ANCA titer might be related to MPO-associated MN development.

The Prevalence, Characteristics, and Putative Mechanisms of Dual Antigen-Positive Membranous Nephropathy: The Underestimated Condition

Following the discovery of podocyte phospholipase A2 receptor and thrombospondin type-1 domain-containing 7A, various potential target antigens for membranous nephropathy (MN) have been reported one after another. MN target antigens have now been identified in a significant proportion of patients, and a new classification framework classifies patients with MN based on the detected antigen and associated disease phenotype. A serology-based approach that does not require a histological diagnosis for patients suspected of having MN has also been proposed. However, there have been cases in which dual positivity for MN antigens and/or corresponding antibodies has been shown. Importantly, some of them showed a transition of the affected patient's immune responses to MN antigens, suggesting that serological diagnosis changes depending on the timing of the analysis. In this review, we provide detailed information on these cases and present an overview of our recent understanding of their putative mechanisms involved in these cases. Greater awareness is required to adequately recognize and develop appropriate therapeutic strategies for this condition.

Rare case of exostosin 1/exostosin 2-related membranous lupus nephritis concomitant with dual ANCA- and anti-GBM antibody-associated crescentic glomerulonephritis effectively diagnosed by mass spectrometry: a case report

BACKGROUND

Recent developments in mass spectrometry (MS) have revealed target antigens for membranous nephropathy (MN), including phospholipase A2 receptor and exostosin 1/exostosin 2 (EXT1/2). EXT1/2 are known antigens of autoimmune disease-related MN, especially membranous lupus nephritis. We describe the case of an elderly man who developed nephrotic syndrome followed by progressive renal dysfunction.

CASE PRESENTATION

A 78-year-old man presented with rapidly progressive renal dysfunction with proteinuria and hematuria. Three years previously, he had developed leg edema but did not receive any treatment. Laboratory tests showed elevated anti-nuclear antibody (Ab), anti-dsDNA Ab titer, and hypocomplementemia, indicating systemic lupus erythematous. Myeloperoxidase anti-neutrophil cytoplasmic Ab (ANCA) and anti-glomerular basement membrane (GBM) Ab were also detected. The renal pathologic findings were compatible with crescentic glomerulonephritis (GN), whereas non-crescentic glomeruli exhibited MN without remarkable endocapillary or mesangial proliferative change. Immunofluorescence microscopy revealed glomerular IgG, C3, and C1q deposition. All IgG subclasses were positive in glomeruli. Anti-PLA2R Ab in serum was negative. MS analysis was performed to detect the antigens of MN, and EXT1/2 was detected in glomeruli. Therefore, we reached a diagnosis of membranous lupus nephritis concurrent with both ANCA-associated vasculitis and anti-GBM-GN. The simultaneous occurrence of these three diseases is extremely rare.

CONCLUSIONS

This is the first report of EXT1/2-related membranous lupus nephritis concurrent with ANCA-associated vasculitis and anti-GBM-GN. This case demonstrates the usefulness of MS in diagnosing complicated cases of MN.

Anti-PLA2R Antibody Development During NELL1-Associated Membranous Glomerulonephritis Treatment: A Case Report

A Japanese man in his early 70s was referred to our hospital because of massive proteinuria. Analysis of his kidney biopsy demonstrated glomerular subepithelial immune deposits containing immunoglobulin (Ig)G, which was dominant for the IgG1 subclass. Immunoperoxidase staining for neural epidermal growth factor-like 1 protein (NELL1) was positive on the glomerular capillary walls, whereas neither serum anti-phospholipase A2 receptor (PLA₂R) antibodies nor immunofluorescence staining for PLA₂R was positive. Detailed investigation revealed no associated conditions, including underlying malignancies, and thus he was diagnosed as having NELL1-associated idiopathic membranous nephropathy (MN). The patient was treated with steroids, which substantially improved his nephrotic syndrome. Interestingly, serum anti-NELL1 as well as anti-PLA₂R antibodies became positive during his clinical course. Serology-based approaches are currently proposed for the treatment of patients suspected of having MN; however, an accurate diagnosis of the present patient would have been difficult if such an approach was performed only at a later phase of the disease. Several target antigens for the glomerular immune deposits observed in patients with MN have recently been identified, and dual positivity of antibodies to these antigens reportedly occurs in some patients. Further accumulation and analyses of such patients are needed to establish more appropriate diagnostic approaches for MN.

Crescentic Glomerulonephritis and Membranous Nephropathy: A Rare Overlap

Background

Membranous nephropathy (MN) is a disease that affects the basement membrane of the glomeruli of the kidney resulting in proteinuria. The concurrent incidence of vasculitic glomerulonephritis and MN in the same patient is unusual. Herein, we report a case with this unusual combination.

Case

Our patient is a 53-year-old Hispanic male with a medical history of tobacco use, type 2 diabetes mellitus, and hypertension who presented with hematuria and was found to have nephrotic range proteinuria and renal impairment. Blood workup revealed positive ANCA serology, which led to a renal biopsy that showed crescentic vasculitis in addition to membranous nephropathy. The patient was started on intermittent hemodialysis (HD) and treated initially with intravenous (IV) pulse steroids; subsequently, oral prednisolone and IV cyclophosphamide were initiated. The patient remained HD dependent at the time of discharge with the resolution of hematuria. A follow-up with an outpatient nephrology clinic was arranged.

Conclusion

Membranous nephropathy complicated by crescentic glomerulonephritis has a more aggressive clinical course and decline in renal function compared to MN alone which can lead to initiating renal replacement therapy. However, immunosuppressive drugs can result in significant improvement of renal function if started early enough.

Anti-Neuronal IgG4 Autoimmune Diseases and IgG4-Related Diseases May Not Be Part of the Same Spectrum: A Comparative Study

Background

IgG4 is associated with two emerging groups of rare diseases: 1) IgG4 autoimmune diseases (IgG4-AID) and 2) IgG4-related diseases (IgG4-RLD). Anti-neuronal IgG4-AID include MuSK myasthenia gravis, LGI1- and Caspr2-encephalitis and autoimmune nodo-/paranodopathies (CNTN1/Caspr1 or NF155 antibodies). IgG4-RLD is a multiorgan disease hallmarked by tissue-destructive fibrotic lesions with lymphocyte and IgG4 plasma cell infiltrates and increased serum IgG4 concentrations. It is unclear whether IgG4-AID and IgG4-RLD share relevant clinical and immunopathological features.

Methods

We collected and analyzed clinical, serological, and histopathological data in 50 patients with anti-neuronal IgG4-AID and 19 patients with IgG4-RLD.

Results

A significantly higher proportion of IgG4-RLD patients had serum IgG4 elevation when compared to IgG4-AID patients (52.63% vs. 16%, p = .004). Moreover, those IgG4-AID patients with elevated IgG4 did not meet the diagnostic criteria of IgG4-RLD, and their autoantibody titers did not correlate with their serum IgG4 concentrations. In addition, patients with IgG4-RLD were negative for anti-neuronal/neuromuscular autoantibodies and among these patients, men showed a significantly higher propensity for IgG4 elevation, when compared to women (p = .005). Last, a kidney biopsy from a patient with autoimmune paranodopathy due to CNTN1/Caspr1-complex IgG4 autoantibodies and concomitant nephrotic syndrome did not show fibrosis or IgG4+ plasma cells, which are diagnostic hallmarks of IgG4-RLD.

Conclusion

Our observations suggest that anti-neuronal IgG4-AID and IgG4-RLD are most likely distinct disease entities.

Membranous Nephropathy With Monoclonal IgM Lambda Deposits in a Patient With IgM Monoclonal Gammopathy: A Case Report

We report a case of membranous nephropathy with monoclonal immunoglobulin (Ig)M lambda deposits in a patient with IgM monoclonal gammopathy, in whom histological changes were observed on repeat renal biopsy. A 72-year-old Japanese woman was referred to our hospital because of massive proteinuria. A prominent increase in monoclonal IgM lambda level was identified, and she was diagnosed as having IgM monoclonal gammopathy of undetermined significance. Renal biopsy showed glomerular subepithelial electron-dense deposits that were found to be granular deposits of IgM lambda but not kappa or IgG by immunofluorescence staining, resulting in a diagnosis of membranous nephropathy with monoclonal IgM deposits. The second biopsy, which was performed 2 years later because of exacerbation of her nephrotic syndrome, demonstrated less immunofluorescence staining of IgM, and dominant IgG2 deposition without light chain restriction. Interestingly, immunostaining for thrombospondin-type-1-domain-containing-7A was positive in both renal biopsy tissues, although the second biopsy showed clearly stronger immunoreactivity. The effect of steroid therapy was limited; however, rituximab treatment improved both the hematological and renal abnormalities. Solitary deposition of IgM in membranous nephropathy is a quite rare condition. To our knowledge, this is the first case of monoclonal gammopathy of renal significance presenting as membranous nephropathy with monoclonal IgM deposits, in which chronological immunohistochemical changes were observed and rituximab therapy was effective.

Autoantibodies in the Diagnosis, Monitoring, and Treatment of Membranous Nephropathy

The discovery of anti-podocyte antibodies in primary membranous nephropathy (MN) has revolutionized our approach toward the diagnosis and treatment of this disease. Evaluation of serum levels of anti-podocyte antibodies paved the way for non-invasive diagnosis and helped distinguish between primary and secondary MN although the relationship between anti-podocyte antibodies and cancer remains to be elucidated. Serum levels of anti-PLA2R antibodies directed against the major podocyte autoantigen are related to MN activity and the decrease in serum levels of anti-PLA2R antibodies in response to treatment (immunologic remission) also serves as an early indicator of the later putative proteinuric remission, enabling personalization of the treatment. The serum levels of anti-podocyte antibodies also enable the prediction of renal outcomes in terms of both remission and the risk of progression to end-stage renal disease. The positivity of anti-PLA2R antibodies before renal transplantation is associated with the risk of recurrence of MN. It remains to be established if all these relations observed in patients with anti-PLA2R antibodies are also valid for expanding spectrum of antibodies directed against recently discovered minor antigens (e.g., THSD7A, NELL-1, semaphorin 3B).

A Target Antigen-Based Approach to the Classification of Membranous Nephropathy

OBJECTIVE

To describe the clinical and pathological phenotype of membranous nephropathy (MN) associated with M-type-phospholipase-A₂-receptor (PLA₂R), thrombospondin-type-1-domain-containing-7A (THSD7A), semaphorin 3B (SEMA3B), neural-epidermal-growth-factor-like-1-protein (NELL-1), protocadherin 7 (PCDH7), exostosin 1/exostosin 2 (EXT1/EXT2) and neural cell adhesion molecule 1 (NCAM-1) as target antigens.

METHODS

A retrospective cohort of 270 adult patients with biopsy-proven MN diagnosed between January 2015 and April 2020 was classified as PLA₂R-, THSD7A-, SEMA3B-, NELL-1-, PCDH7-, EXT1/EXT2-, NCAM-1-associated or septuple-negative MN using serologic tests, immunostaining, and/or mass spectrometry. Clinical, biochemical, pathologic, and follow-up data were systematically abstracted from the medical records, including disease activity of conditions traditionally associated with MN and occurring within 5 years of MN diagnosis.

RESULTS

Patients with PLA₂R-associated MN were predominantly middle-aged white men without associated disease. The presence of associated disease did not affect the clinical and pathologic characteristics of PLA₂R-associated MN, suggesting that they were coincidental rather than causally linked. THSD7A-, NELL-1-, PCDH7-, and NCAM-1-associated MN were rare and SEMA3B-associated MN was not discovered in our cohort. EXT1/EXT2-associated MN was primarily diagnosed in younger women with active systemic autoimmunity. A significant proportion of septuple-negative patients had associated malignancy or systemic autoimmunity.

CONCLUSION

The widely used distinction between primary and secondary MN has limitations. We propose a refined terminology that combines the target antigen and associated disease to better classify MN and guide clinical decision making.

Membranous Nephropathy with Proteinase 3-ANCA-associated Vasculitis Successfully Treated with Rituximab

Membranous nephropathy (MN) with anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (ANCA-GN) is seen infrequently. Previous reports of patients with ANCA-GN with MN showed that the most frequent ANCA subtype was myeloperoxidase-ANCA. We herein present a 73-year-old woman with scleritis, hematuria, proteinuria, and positive serum proteinase 3 (PR3)-ANCA. She underwent a renal biopsy and was diagnosed with MN and ANCA-GN. Immunofluorescence staining for PR3 colocalized with IgG along the glomerular basement membrane were observed. Oral prednisolone and intravenous rituximab therapy immediately improved her symptoms and urinalysis abnormalities. PR3-ANCA may be involved in the pathogenesis of MN via the formation of immune complexes.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.

Membranous Glomerulonephritis With Crescents

Introduction

Membranous glomerulonephritis (MGN) is rarely associated with necrotizing and crescentic glomerulonephritis (NCGN).

Methods

We report the clinical and pathologic findings in 15 patients with MGN and NCGN associated with anti-neutrophil cytoplasm antibodies (ANCAs), anti-glomerular basement membrane (GBM), or anti-phospholipase A2 receptor (PLA2R) antibodies.

Results

The cohort consisted of 15 patients: 7 males and 8 females with a median age of 63 years (range: 18-79). In 12 of 15 patients, MGN and NCGN were diagnosed at the time of the biopsy, and in 3 cases, MGN predated the NCGN. ANCA was positive in 7 cases (6 MPO myeloperoxidase (MPO)-ANCA and 1 PR3-ANCA), anti-GBM antibodies were detected in 5 cases, and anti-PLA2R antibodies were found in 2 cases. One case was negative for all antibodies. Microscopic hematuria was present in all but one patient who was anuric, and median urinary protein-to-creatinine ratio was 819.5 mg/mmol (range: 88-5600). Pathologic evaluation revealed MGN and NCGN with crescents involving 28% of glomeruli (median; range: 5%-100%). Follow-up was available for all 15 patients; all were treated with steroids; 10 with cyclophosphamide, and 6 also received rituximab. At a median follow-up of 72 months, 9 had stabilization or improvement of renal function, 6 had progressed to end-stage renal disease, and 4 died during the follow-up period.

Conclusion

MGN with crescents associated with ANCAs or anti-GBM antibodies is a rare dual glomerulopathy. Patients present with heavy proteinuria, microscopic hematuria, and acute kidney injury and should be treated for a rapidly progressive glomerulonephritis. Prognosis is variable, and 40% of patients progress to end-stage renal disease.