Primary Membranous Nephropathy With Enhanced Staining of Exostosin 1/Exostosin 2 in the Glomeruli: A Report of 2 Cases.

Technological advances have allowed the discovery of 6 subtypes of membranous nephropathy based on target antigens: M-type phospholipase A2 receptor (PLA2R), thrombospondin type 1 domain-containing 7A (THSD7A), neural epidermal growth factor-like 1 protein, semaphorin 3B, exostosin 1 (EXT1), and EXT2. EXT1/EXT2 are thought to be associated with secondary (autoimmune) membranous nephropathy. Although it has been reported that PLA2R- and THSD7A-associated membranous nephropathy have rarely been detected concomitantly, there have been no previous reports demonstrating PLA2R- or THSD7A-associated membranous nephropathy with enhanced glomerular staining of EXT1/EXT2. We describe 2 cases of primary membranous nephropathy with enhanced glomerular staining of EXT1/EXT2. Patient 1 was diagnosed with PLA2R-associated primary membranous nephropathy, and patient 2 was diagnosed with THSD7A-associated primary membranous nephropathy. Both patients achieved clinical remission in response to immunosuppressive therapy. Neither patient demonstrated signs of autoimmune diseases, and antinuclear antibodies were absent in their sera. Based on these 2 cases, enhanced staining of EXT1/EXT2 in glomeruli, although rare, can be detected in primary membranous nephropathy without autoimmune diseases.

Iwakura T ，Ema C ，Sato T ，Isobe S ，Fujikura T ，Ohashi N ，Kato A ，Yasuda H ... -  《-》

Exostosin 1/Exostosin 2-Associated Membranous Nephropathy.

In membranous nephropathy (MN), which is characterized by deposition of immune complexes along the glomerular basement membrane (GBM), phospholipase A2 receptor (PLA2R) and thrombospondin type 1 domain-containing 7A are target antigens in approximately 70% and 1%-5% of cases of primary MN, respectively. In other cases of primary MN and in secondary MN, the target antigens are unknown. We studied 224 cases of biopsy-proven PLA2R-negative MN and 102 controls (including 47 cases of PLA2R-associated MN) in pilot and discovery cohorts. We also evaluated 48 cases of PLA2R-negative presumed primary MN and lupus MN in a validation cohort. We used laser microdissection and mass spectrometry to identify new antigens, which were localized by immunohistochemistry. Mass spectrometry detected exostosin 1 (EXT1) and exostosin 2 (EXT2) in 21 cases of PLA2R-negative MN, but not in PLA2R-associated MN and control cases. Immunohistochemistry staining revealed bright granular GBM staining for EXT1 and EXT2. Clinical and biopsy findings showed features of autoimmune disease, including lupus, in 80.7% of the 26 EXT1/EXT2-associated MN cases we identified. In the validation cohort, we confirmed that EXT1/EXT2 staining was detected in pure class 5 lupus nephritis (eight of 18 patients) and in presumed primary MN associated with signs of autoimmunity (three of 16 patients); only one of the 14 cases of mixed class 5 and 3/4 lupus nephritis was positive for EXT1/EXT2. Tests in seven patients with EXT1/EXT2-associated MN found no circulating anti-exostosin antibodies. A subset of MN is associated with accumulation of EXT1 and EXT2 in the GBM. Autoimmune disease is common in this group of patients.

Sethi S ，Madden BJ ，Debiec H ，Charlesworth MC ，Gross L ，Ravindran A ，Hummel AM ，Specks U ，Fervenza FC ，Ronco P ... -  《-》

Prevalence of neural epidermal growth factor-like 1- and exostosin 1/exostosin 2-associated membranous nephropathy: a single-center retrospective study in Japan.

Membranous nephropathy (MN) is the leading cause of nephrotic syndrome in adults. We previously reported that the prevalence of phospholipase A2 receptor (PLA2R)- and thrombospondin type 1 domain containing 7A (THSD7A)-associated MN patients in Japan is 52.7% and 9.1%, respectively. In addition to PLA2R and THSD7A, we assessed the presence of newly discovered target antigens, neural epidermal growth factor-like 1 (NELL-1), semaphorin 3B (SEMA3B), and exostosin 1/exostosin 2 (Ext1/Ext2), in renal specimens from patients with primary and secondary MN by immunohistochemistry. We found enhanced glomerular staining of PLA2R, THSD7A, NELL-1, and Ext1/Ext2 in 53.6%, 8.7%, 1.5%, and 13.0% of the renal samples, respectively, in patients with primary MN. None of the patient specimens showed enhanced staining of SEMA3B. Enhanced glomerular staining of PLA2R, NELL-1, and Ext1/Ext2 was detected in 5.7%, 8.6%, and 22.9% of the patients with secondary MN, respectively. Based on our findings, we recommend the assessment of PLA2R, THSD7A and NELL-1 in addition to clinical information and IgG4 staining to differentiate between primary and secondary MN. This would aid in distinguishing secondary MN patients from primary MN patients who coincidentally have some secondary characteristics.

Iwakura T ，Ema C ，Isobe S ，Fujikura T ，Ohashi N ，Kato A ，Yasuda H ... -  《Scientific Reports》

Lupus-like membranous nephropathy during the postpartum period expressing glomerular antigens exostosin 1/exostosin 2 and phospholipase A2 receptor: a case report.

Recently, several target antigens of membranous nephropathy (MN), such as phospholipase A2 receptor (PLA2R) and exostosin 1/exostosin 2 (EXT1/2), have been discovered. A 30-year-old woman was referred to our hospital with nephrotic range proteinuria and microscopic hematuria. She was first noted to have proteinuria before pregnancy, and her proteinuria worsened in the postpartum period. A renal biopsy showed MN. Immunofluorescence microscopy showed IgG, IgA, IgM, C3, C4, and C1q depositions in the mesangial area and glomerular capillary walls (GCWs). Regarding the IgG subclass, IgG1 and IgG3 were detected on glomeruli. Electron microscopy showed subepithelial electron-dense deposits (EDDs). EDDs were also detected in paramesangial and subendothelial areas. The diagnosis of membranous lupus nephritis (MLN) was suspected, but she did not fulfill the criteria for systemic lupus erythematosus. Neither anti-nuclear antibody nor hypocomplementemia were detected. We further evaluated glomerular EXT1/2 expressions, which were evident on GCWs. In addition, PLA2R was also detected on GCWs, although serum antibody for PLA2R was negative. She responded to immunosuppressive therapy with decreased proteinuria. In the present case, glomerular PLA2R expression implied the possibility of primary MN. However, pathological findings with a full-house staining pattern and glomerular EXT1/2 expressions were very similar to those of lupus-associated MN. Glomerular PLA2R expression appeared not to reflect immunocomplexes of PLA2R and autoantibody when considering the results for glomerular IgG subclass and the absence of serum anti-PLA2R antibody. Collectively, it is plausible that this was a case of a relatively young postpartum female who developed latent MLN rather than primary MN.

Miyasaka R ，Wada Y ，Takeuchi K ，Abe T ，Uchitsubo R ，Kawamura S ，Sakurabayashi S ，Naito S ，Aoyama T ，Shimizu A ，Takeuchi Y ... -  《-》

Distribution spectrum and clinical significance of glomerular exostosin (EXT1) deposits in PLA2R-positive membranous nephropathy.

The discovery of antigen phospholipase A2 receptor (PLA2R) in 2009 ushered in the antigen-based study of membranous nephropathy. The further putative antigen exostosin 1/2 (EXT1/2) was described in 2019. However, the distribution spectrum of glomerular EXT1 deposits in membranous nephropathy has not been fully elucidated. We conducted a retrospective cohort study of biopsy-proven membranous nephropathy patients. Patients with complete baseline data and adequate tissue specimens were included in this study. Tests for glomerular expression of PLA2R and EXT1 and circulating anti-PLA2R antibodies were performed. Clinicopathological and outcome data were reviewed. We included 626 patients, namely, 487 (77.8%) PLA2R-positive patients and 54 (8.6%) EXT1-positive patients; 32 (5.1%) patients were dual-positive for PLA2R and EXT1 (PLA2R + /EXT1 +). A higher percentage of dual-positive patients had low C3 levels (P < 0.001) and were more likely to have autoimmune diseases (P = 0.013) than PLA2R-positive and EXT1-negative (PLA2R + /EXT1-) patients. Kidney biopsy findings revealed that there was a higher percentage of glomerular IgG1, IgG2, IgA, C4, and C1q deposits (P < 0.05), "full-house" staining (P < 0.001), and stronger intensity of C1q staining (P = 0.002) in PLA2R + /EXT1 + patients. Based on Kaplan-Meier analysis, a higher percentage of PLA2R + /EXT1 + patients exhibited partial or complete remission of proteinuria. Furthermore, EXT1-positive expression was a favourable predictor for proteinuria remission, whereas interstitial fibrosis/tubular atrophy was an unfavourable predictor. A complement C3 level  < 0.79 g/L was independently associated with EXT1 positivity in PLA2R-positive membranous nephropathy. We describe a subgroup of PLA2R and EXT1 dual-positive patients. Patients in this subset exhibited more signs of autoimmunity and more frequent clinical remission. In PLA2R-positive membranous nephropathy, a complement C3 level  < 0.79 g/L was independently associated with EXT1 positivity, which was a favourable predictor for proteinuria remission.

Liu Z ，Wan C ，Cao Y ，Liu S ，Xu Z ，Zhang C ，Su H ... -  《-》