Recurrent Membranous Nephropathy After Kidney Transplantation Associated With Phospholipase A2 Receptor and Successfully Treated With Rituximab: A Case Report

Primary membranous nephropathy (MN) is an organ-specific autoimmune disease mainly caused by autoantibodies acting against the podocyte antigen M-type phospholipase A2 receptor 1 (PLA2R). Herein we present the clinical and histologic findings, including PLA2R staining, of early recurrent MN after kidney transplantation that was successfully treated with rituximab.A 60-year-old Japanese man had end-stage renal failure due to steroid-resistant primary MN and underwent ABO-incompatible living donor kidney transplantation. At 1 month after transplantation, a protocol biopsy revealed positive granular staining of IgG, C4d, and PLA2R on glomerular capillaries (GCs) without any abnormalities on light microscopy (LM). Although the patient had low-level proteinuria, recurrent MN was suspected based on the positive PLA2R staining; he was treated with an angiotensin receptor blocker and a single dose of 200 mg rituximab. However, proteinuria gradually increased to 877 mg/d. At 21 months after transplantation, a graft biopsy revealed spikes along the outer aspects of GC on LM, with stronger staining for PLA2R than that at 1 month after transplantation. A single dose of 500 mg rituximab was added, which effectively reduced proteinuria, and clinical remission continued until 3 years after transplantation. The latest graft biopsy showed reduced staining of PLA2R. The disease activity and therapeutic effect were well-reflected in the intensity of PLA2R staining.An approach intending an early diagnosis by protocol biopsy using PLA2R immunostaining is made and early treatment with rituximab will help reduce the risk of kidney graft loss due to recurrent primary MN.     

Pre‐transplant phospholipase A2 receptor autoantibody concentration is associated with clinically significant recurrence of membranous nephropathy post‐kidney transplantation

Previous studies that have assessed the association of pre‐transplant antiphospholipase A2 receptor autoantibody (PLA2R‐Ab) concentration with a recurrence of membranous nephropathy (rMN) post‐kidney transplant have yielded variable results. We tested 16 consecutive transplant patients with a history of iMN for pre‐transplant PLA2R‐Ab. Enzyme‐linked immunosorbent assay titers (Euroimmun, NJ, USA) >14 RU/mL were considered positive. A receiver operating characteristic (ROC) analysis was performed after combining data from Quintana et al. (n = 21; Transplantation February 2015) to determine a PLA2R‐Ab concentration which could predict rMN. Six of 16 (37%) patients had biopsy‐proven rMN at a median of 3.2 yr post‐transplant. Of these, five of six (83%) had a positive PLA2R‐Ab pre‐transplant with a median of 82 RU/mL (range = 31–1500). The only patient who had rMN with negative PLA2R‐Ab was later diagnosed with B‐cell lymphoma. One hundred percent (n = 10) of patients with no evidence of rMN (median follow‐up = five yr) had negative pre‐transplant PLA2R‐Ab. In a combined ROC analysis (n = 37), a pre‐transplant PLA2R‐Ab > 29 RU/mL predicted rMN with a sensitivity of 85% and a specificity of 92%. Pre‐transplant PLA2R‐Ab could be a useful tool for the prediction of rMN. Patients with rMN in the absence of PLA2R‐Ab should be screened for occult malignancy and/or alternate antigens.     

Recent advances and prognosis in idiopathic membranous nephropathy

Idiopathic membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome. Recently, progress has been made in understanding the pathogenesis of idiopathic MN with the finding of M-type phospholipase A2 receptor (PLA2R) antibodies in the serum and immune complexes of glomeruli in the majority of adult idiopathic MN patients. In the future, the detection of M-type PLA2R antibodies may help distinguish patients with primary MN who require aggressive immunosuppressive therapy from those with secondary disease. Levels of circulating antibody to this receptor may help in monitoring disease activity and in gauging response to therapy, as changes in antibody levels may precede changes in proteinuria. The degree of renal dysfunction or change in renal function over time and the level of persistent proteinuria are key prognostic factors in the decision to initiate therapy in idiopathic MN patients. Although spontaneous remissions occur in ~30% of patients, partial and complete remissions help to define the clinical course of an individual patient.     

Membranous nephropathy with light chain restricted deposits

The literature on membranous nephropathy (MN) with monoclonal deposits on immunofluorescence (IF) and their outcome is very scarce. We report our experience of managing five patients with this clinical entity. The mean age of the patients was 33.2 ± 6.55 years. The mean proteinuria, serum albumin and serum creatinine was 5.73 ± 2.17 g/day, 2.86 ± 0.51 g/dL and 1.34 ± 1.19 mg/dL, respectively. None of the patients had a lymphoproliferative disorder. Only one patient had an elevated free light chain ratio. Four (80%) patients were M‐type phospholipase A2 receptor (PLA2R) negative (tissue and serum), and one (20%) was PLA2R related. Three (60%) cases had monoclonal IgG3/k, one IgG3/λ, whereas one patient with PLA2R positivity had an IgG3/IgG4k subtype. Two (67%) patients treated with cyclical cyclophosphamide and steroids (cCYC/GC) achieved complete remission and one patient (33%) with elevated baseline creatinine had a reduction in serum creatinine with persistent proteinuria at the end of the 12th month of follow‐up. One patient with PLA2R positive MN was treated with Rituximab and is in complete remission. The patient with an elevated free light chain at baseline was treated with Bortezomib/Thalidomide/Dexamethasone, had complete remission at 12 months, however, had a progressive rise in creatinine over the next 40 months of follow‐up. The current series, though limited by numbers, documents the efficacy of conventional therapies in non‐malignant associated MN with monoclonal deposits on IF.     

Anti-Phospholipase A2 Receptor Antibody Titer Predicts Post-Rituximab Outcome of Membranous Nephropathy

Rituximab induces nephrotic syndrome (NS) remission in two-thirds of patients with primary membranous nephropathy (MN), even after other treatments have failed. To assess the relationships among treatment effect, circulating nephritogenic anti-phospholipase A₂ receptor (anti-PLA₂R) autoantibodies and genetic polymorphisms predisposing to antibody production we serially monitored 24-hour proteinuria and antibody titer in patients with primary MN and long-lasting NS consenting to rituximab (375 mg/m²) therapy and genetic analyses. Over a median (range) follow-up of 30.8 (6.0–145.4) months, 84 of 132 rituximab-treated patients achieved complete or partial NS remission (primary end point), and 25 relapsed after remission. Outcomes of patients with or without detectable anti-PLA₂R antibodies at baseline were similar. Among the 81 patients with antibodies, lower anti-PLA₂R antibody titer at baseline (P=0.001) and full antibody depletion 6 months post-rituximab (hazard ratio [HR], 7.90; 95% confidence interval [95% CI], 2.54 to 24.60; P<0.001) strongly predicted remission. All 25 complete remissions were preceded by complete anti-PLA₂R antibody depletion. On average, 50% anti-PLA₂R titer reduction preceded equivalent proteinuria reduction by 10 months. Re-emergence of circulating antibodies predicted disease relapse (HR, 6.54; 95% CI, 1.57 to 27.40; P=0.01), whereas initial complete remission protected from the event (HR, 6.63; 95% CI, 2.37 to 18.53; P<0.001). Eighteen patients achieved persistent antibody depletion and complete remission and never relapsed. Outcome was independent of PLA2R1 and HLA-DQA1 polymorphisms and of previous immunosuppressive treatment. Therefore, assessing circulating anti-PLA₂R autoantibodies and proteinuria may help in monitoring disease activity and guiding personalized rituximab therapy in nephrotic patients with primary MN.     

Rituximab-induced depletion of anti-PLA2R autoantibodies predicts response in membranous nephropathy

Autoantibodies to the M-type phospholipase A(2) receptor (PLA(2)R) are sensitive and specific for idiopathic membranous nephropathy. The anti-B cell agent rituximab is a promising therapy for this disease, but biomarkers of early response to treatment currently do not exist. Here, we investigated whether levels of anti-PLA(2)R correlate with the immunological activity of membranous nephropathy, potentially exhibiting a more rapid response to treatment than clinical parameters such as proteinuria. We measured the amount of anti-PLA(2)R using Western blot immunoassay in serial serum samples from a total of 35 patients treated with rituximab for membranous nephropathy in two distinct cohorts. Pretreatment samples from 25 of 35 (71%) patients contained anti-PLA(2)R, and these autoantibodies declined or disappeared in 17 (68%) of these patients within 12 months after rituximab. Those who demonstrated this immunologic response fared better clinically: 59% and 88% attained complete or partial remission by 12 and 24 months, respectively, compared with 0% and 33% among those with persistent anti-PLA(2)R levels. Changes in antibody levels preceded changes in proteinuria. One subject who relapsed during follow-up had a concomitant return of anti-PLA(2)R. In summary, measuring anti-PLA(2)R levels by immunoassay may be a method to follow and predict response to treatment with rituximab in membranous nephropathy.     

Posttransplant nephrotic syndrome resulting from NELL1-positive membranous nephropathy

Membranous nephropathy (MN) constitutes a major cause of nephrotic syndrome (NS) in adults. After kidney transplantation (KTx), both recurrent and de novo MN has been reported. In addition to PLA2R and THSD7A, recent identification of neural EGFL-like-1 protein, NELL1, as a potential disease antigen has enriched our understanding of MN pathogenesis. To date, NELL1-positive MN has only been described in native kidneys, but never been diagnosed in renal allografts. We here report on a 56-year-old male kidney transplant recipient suffering from amyotrophic lateral sclerosis (ALS), who developed NS 25 years after KTx. Allograft biopsy revealed NELL1-positive MN. Using specifically established immunoblotting techniques, we detected new-onset NELL1-IgG1, IgG3, and IgG4 antibodies in the patient´s serum correlating with the course of proteinuria. While primary renal disease was undetermined, MN recurrence seemed unlikely given the long-time span since KTx. By clinical investigation of de novo etiologies, we did not detect an underlying malignancy. However, previous self-medication with dimercaptopropane sulfonate (DMPS) and alpha lipoic acid (ALA) represented a potential trigger and cessation associated with partial remission of proteinuria. This report illustrates the first case of posttransplant NS due to NELL1-positive MN. Monitoring NELL1 antibodies in the serum promise to be a non-invasive diagnostic tool guiding disease management.     

Autoantibodies against phospholipase A2 receptor in Brazilian patients with glomerular diseases

Background

Recently, great progress has been made in understanding the pathogenesis of membranous nephropathy (MN) with the discovery of autoantibodies (Abs) to M-type phospholipase A2 receptor (PLA2R) in serum and in immunocomplexes deposited in glomerulus in most adult patients with primary MN.

Objective

To evaluate the diagnostic performance of anti-PLA2R in Brazilian patients with MN, as well as to verify the possible association of anti-PLA2R serum levels with disease activity.

Methods

117 patients with glomerular diseases confirmed by renal biopsy underwent routinely clinical and laboratory evaluation (serum creatinine and albumin, 24-h proteinuria, urinalysis, tests for etiological investigation) and determination of serum anti-PLA2R by ELISA.

Results

67.5% of the patients had MN, 9.4% focal segmental glomerulosclerosis, 7.7% lupus nephritis class V and 15.4%, other proteinuric glomerular diseases. The mean level of glomerular filtration rate (estimated by the CKD-EPI formula) was 79.43 mL/min (12.00–151.20 mL/min), 24 h proteinuria of 2.89 g (0–14.90 g), serum albumin of 3.79 g/dL (1.20–4.80 g/dL). Anti-PLA2R was detected in 27 patients, all with active MN, being 26 primary and 1 secondary MN. Sensitivity and specificity rates for the test were 60.5–94.7%, and positive (PPV) and negative (NPV) predictive values were 92.9 and 67.9%, respectively.

Conclusions

Anti-PLA2R showed high specificity and PPV for the diagnosis of primary MN in Brazilian patients. There was a strong correlation between disease activity and positive anti-PLA2R. This biomarker represents an important diagnostic tool for primary MN and may contribute to the monitoring of disease activity in such patients.

     

Recurrent Membranous Nephropathy in an Allograft Caused by IgG3κ Targeting the PLA2 Receptor

Up to 80% of patients with idiopathic membranous nephropathy have non–complement-fixing IgG4 autoantibodies to the phospholipase A2 receptor (PLA2R). Membranous nephropathy recurs in approximately 40% of patients after kidney transplantation, but the mechanism is unknown. Here, we describe a patient with recurrent membranous nephropathy 13 days after kidney transplantation whose graft biopsy specimen showed granular staining for C3, C5b-9, C1q, and IgG3κ; electron microscopy revealed subepithelial nonorganized deposits. A search for hematologic disorders was negative. Retrospective evaluation of a biopsy sample from the native kidney revealed a similar pattern: monotypic IgG3κ deposits together with C3, C1q, and C5b-9. Glomerular deposits contained PLA2R in both the graft and the native kidney, suggesting that the recurrence was the result of circulating anti-PLA2R antibodies binding to PLA2R antigen expressed on donor podocytes. Confocal analysis of anti-PLA2R and antihuman IgG3 showed co-localization, and the patient had IgG3κ-restricted circulating anti-PLA2R antibodies. Treatment with rituximab stabilized both proteinuria and serum creatinine, and circulating anti-PLA2R became undetectable. In summary, this case of recurrent membranous nephropathy in a graft suggests that circulating monoclonal anti-PLA2R IgG3κ caused the disease and activated complement by the classic pathway.Membranous nephropathy (MN) is one of the more common causes of nephrotic syndrome in the adult population, accounting for about 20% of cases. It can be idiopathic, without identified cause (70%–80%), or secondary to various clinical conditions, including infections (hepatitis B, syphilis), systemic lupus erythematosus, cancers, and drug intoxications.¹MN is an immunologically mediated disease defined by immune complex deposition in the subepithelial space that causes a membrane-like thickening. The immune deposits consist of IgG, antigens that have long eluded identification, and the membrane attack complex of complement C5b-9. IgG4 is the most prominent deposited subclass in idiopathic MN, although variable amounts of IgG1 are usually associated; in secondary MN, IgG1, IgG2, and IgG3 exceed IgG4.^2,3 The formation of subepithelial immune deposits and complement activation are presumably responsible for functional impairment of the glomerular capillary wall, causing proteinuria. Evidence now suggests that MN is triggered by antibodies directed against podocyte proteins. Two major antigens, both membrane glycoproteins, have been identified. The first is neutral endopeptidase, the alloantigen involved in rare neonatal cases of MN that occur in newborns from neutral endopeptidase–deficient mothers.⁴ The disease could be transferred to rabbits injected with immunoglobulin purified from the infant’s mother’s serum but not from the father’s serum.⁵ The second antigen is the M-type phospholipase A2 receptor (PLA2R), the first antigen identified in idiopathic MN in adults, which is considered an autoimmune disease.⁶Although anti-PLA2R antibodies are found in about 70% of patients with idiopathic MN^6–9 and seem to correlate with disease activity and proteinuria,^6,10,11 there is no definitive proof that these antibodies are pathogenic. First, PLA2R-related MN could not be induced by transfer of patients’ serum or IgG to mouse, rat, or rabbit because these species do not express PLA2R antigen in glomeruli. Second, as yet there is no animal model of PLA2R-related MN that could phenocopy Heymann nephritis, a reliable form of MN in the rat in which the target antigen, megalin, is also located at the podocyte surface.^12,13 Third, anti-PLA2R antibodies can occasionally be found in patients with idiopathic MN but without PLA2R antigen in subepithelial immune deposits, a finding suggesting that at least some anti-PLA2R antibodies might not be pathogenic.¹⁴ Fourth, although PLA2R-related MN can recur in the kidney graft, sometimes after only a few days,^15–17 some patients with high-titer anti-PLA2R antibodies at the time of transplantation will not have clinical or histologic recurrence.¹⁶ In those cases, however, differences between donor and recipient PLA2R sequence variants might account for the lack of recurrence.Here we report an exceptional case of recurrent PLA2R-related MN with monotypic IgG3κ deposits and circulating anti-PLA2R antibodies restricted to IgG3κ, which provides an argument favoring the pathogenicity of anti-PLA2R antibodies, at least in this particular situation.A kidney allograft biopsy was performed 13 days after transplantation because of delayed graft function (plasma creatinine, 2.82 mg/dl) and proteinuria (1.85 g/d) in a 52-year-old man in whom MN had been diagnosed 13 years earlier and who has been receiving hemodialysis for the last 6 years. Pretransplantation assessment of the glomerulopathy failed to identify a cause, thereby suggesting idiopathic MN. The biopsy revealed early recurrence of MN, characterized by abundant granular deposits of IgG on the outer aspect of the glomerular basement membrane (Figure 1A). These deposits did not show any organization by electron microscopy (Figure 1B). We performed a subclass and light-chain isotype analysis of deposited IgG, which exclusively stained for IgG3κ (Figure 1C). Biopsy specimen also contained C3, C1q, and C5b-9 in deposits but no mannose-binding lectin (MBL) (Figure 1D). The positive control for MBL staining is shown in Supplemental Figure 1.Open in a separate windowFigure 1.Characterization of immune deposits in kidney biopsy specimens from grafted (A–D) and native (E) kidneys. (A) Immunofluorescence study showing early recurrence of the MN (day 13) characterized by granular deposits of IgG. (B) Representative segment of the capillary wall analyzed by electron microscopy. Electron-dense deposits seen on the outer aspect of the glomerular basement membrane do not show any organization. (C) Immunostaining for IgG subclasses and light-chain isotypes showing the presence of monotypic IgG3κ. (D) Complement components, including C3, C1q and C5b-9, detected in the absence of MBL. (E) Kidney biopsy specimen from native kidney stained for IgG3 and light-chain isotype. The specimens shown in E are paraffin sections, whereas those shown in A, C, and D are cryostat sections. Original magnification for A, C, D, and E x400; for B x40,000.The finding of monotypic IgG3κ deposits prompted an extensive search for a hematologic disorder. Electrophoresis and immunofixation of serum proteins did not disclose any qualitative anomaly. Serum κ and λ free light-chain levels and immunoglobulin classes were normal, except for IgG, which was moderately decreased. Blood lymphocyte immunophenotyping was unremarkable. Positron emission tomography did not reveal hyperfixation, and the bone marrow biopsy specimen was normal, revealing rare, polytypic plasma cells.We then asked whether deposits in the native kidney biopsy specimen were also monotypic. The pathologic report described granular deposits of IgG, C3, and C1q, but there was no information on light-chain isotype. Because of the lack of frozen kidney biopsy specimen, we developed a new technique to perform subclass and isotype analysis in paraffin-embedded sections. The deposits stained for IgG3 and κ but did not stain for the λ isotype (Figure 1E).PLA2R antigen was detected in a granular pattern typical of subepithelial immune deposits in the native and kidney graft biopsy specimens (Figure 2, A and B). Co-localization with IgG3 was established by confocal microscopy (Figure 2, C–F).Open in a separate windowFigure 2.Detection of PLA2R in glomerular immune deposits. Immunofluorescence analysis of paraffin kidney biopsy specimens shows PLA2R in (A) native and (B) grafted kidney. (C–E) Positively stained glomeruli in a biopsy specimen from grafted kidney that has been double-labeled with anti-PLA2R (C) and anti-human IgG3 antibodies (D); E shows the merged image of boxed areas in C and D. (F) Quantitative analysis of the fluorescence recorded across sections of a representative capillary loop (arrowheads). Note superimposition of the two signals, which indicates that subepithelial immune deposits are composed of PLA2R (red) and IgG3 (green). Original magnification for A, B, C, D, and E x400.Because both the native and kidney graft biopsy specimens featured monotypic IgG3κ deposits in the absence of IgG4, we reasoned that the circulating anti-PLA2R antibodies could also be monotypic. Using the indirect immunofluorescence test (Euroimmun AG, Lübeck, Germany), we first showed that in patient’s serum anti-PLA2R antibodies were present at the time of transplantation (Figure 3). Next, using subclass- and light-chain isotype–specific revealing antibodies, we found that anti-PLA2R antibodies were restricted to IgG3κ, which is the immunoglobulin isotype detected in glomerular deposits (Figure 2).Open in a separate windowFigure 3.Detection and isotyping of circulating anti-PLA2R antibodies in patient’s serum using immunofluorescence test (Euroimmun). The serum sample after transplantation before rituximab treatment contains anti-PLA2R antibodies that are restricted to IgG3κ. Neg, negative; Rtx, rituximab; TX, transplantation.On the basis of these findings, the patient received four injections of rituximab (375 mg/m²) at 2-week intervals. Six months later, proteinuria had decreased dramatically (from 5.1 g/d before rituximab to 0.4 g/d), kidney graft function had stabilized (serum creatinine, 2.72 mg/dl before rituximab versus 2.56 mg/dl), and anti-PLA2R antibodies had disappeared (Figure 3).     

Temporal IgG Subtype Changes in Recurrent Idiopathic Membranous Nephropathy

Determination of the IgG subtypes within the immune deposits in membranous nephropathy (MN) may be helpful in the differential diagnosis. IgG4 is the predominant subtype in idiopathic MN and recurrent MN, while IgG1, IgG2, and IgG3 subtypes are more common in secondary MN and de novo disease in the allograft. The temporal change of IgG subclasses in individual patients and its correlation with clinical variables have not been studied. We reviewed all posttransplantation protocol and indication biopsies (49) in 18 patients with recurrent MN who underwent transplantation at our center between 1998 and 2013 and performed IgG subtyping (IgG1–4). We tested serum for M‐type phospholipase A₂ receptor (PLA₂R) autoantibodies or performed PLA₂R antigen staining on the kidney biopsy. IgG4 was the (co)dominant IgG subtype in 10 of 14 biopsies at the diagnosis of recurrence regardless of PLA₂R association. In 8 of 12 transplantations with serial biopsies, the (co)dominant subtype did not change over time. There was a trend toward IgG1 and IgG3 (co)dominance in biopsies >1 year from recurrence and more IgG1 (co)dominant subtyping in the setting of more‐advanced EM deposits. Treatment with rituximab did not affect the IgG subtype. In conclusion, the dominant IgG subtype did not change over time in recurrent MN.     

Immunoadsorbtion and rituximab therapy in a second living-related kidney transplant patient with recurrent focal segmental glomerulosclerosis

A 29-year-old patient with focal segmental glomerulosclerosis (FSGS) and recurrence of the disease in a living donor kidney transplant received a second living-related kidney graft. She received pre- and postoperative immunoadsorptions and immunosuppression with tacrolimus, mycophenolate mofetil, basiliximab and steroids. Serum creatinine returned to normal values and only minor proteinuria was detected post-transplant (400 mg/24 h). However, recurrence of proteinuria with up to 3.3 g/24 h occurred 2 months after transplantation and the patient underwent intermediate immunoadsorption sessions with immediate reduction of proteinuria for the following year. She then received three doses of rituximab (600 mg, 375 mg/m(2)) that caused immediate reduction of proteinuria with only minimal increase in the following 12 months. Graft function is excellent 2 years after transplantation. These findings suggest that intermittent immunoadsorption combined with B-cell depletion by rituximab treatment induced prolonged reduction of proteinuria in a high-risk patient for recurrence of FSGS in the graft.     

Anti-phospholipase A2 receptor antibody in membranous nephropathy

The M-type phospholipase A2 receptor (PLA2R) is a target autoantigen in adult idiopathic membranous nephropathy (MN), but the prevalence of autoantibodies against PLA2R is unknown among Chinese patients with MN. Here, we measured anti-PLA2R antibody in the serum of 60 patients with idiopathic MN, 20 with lupus-associated MN, 16 with hepatitis B (HBV)-associated MN, and 10 with tumor-associated MN. Among patients with idiopathic MN, 49 (82%) had detectable anti-PLA2R autoantibodies using a Western blot assay; an assay with greater sensitivity detected very low titers of anti-PLA2R in 10 of the remaining 11 patients. Using the standard assay, we detected anti-PLA2R antibody in only 1 patient with lupus, 1 with HBV, and 3 with cancer, producing an overall specificity of 89% in this cohort limited to patients with secondary MN. The enhanced assay detected low titers of anti-PLA2R in only 2 additional samples of HBV-associated MN. In summary, these results suggest that PLA2R is a major target antigen in Chinese idiopathic MN and that detection of anti-PLA2R is a sensitive test for idiopathic MN.     

特发性膜性肾病的分子发病机制

特发性膜性肾病( IMN)是国内外常见的引起成人肾病综合征的病理类型之一。在中国人群中,近年来特发性膜性肾病在原发性肾小球疾病中所占比例明显升高。由于病因及发病机制仍不清楚,以及缺乏预测疾病活动性的生物学标志物,因此目前治疗所带来的经济负担以及药物毒性仍具有争议和挑战。IMN是一种器官特异性的自身免疫性疾病,非炎症性自身抗体与足细胞上的靶抗原结合,在基底膜外侧上皮下形成原位免疫复合物,激活补体,从而引起足细胞损伤和蛋白尿。Heymann肾炎模型是经典的膜性肾病动物模型,然而其靶抗原Megalin并不是人类膜性肾病发生的原因。之后,中性肽链内切酶(NEP)被证实为母胎同种异体产前膜性肾病的靶抗原。直到2009年,磷脂酶A2受体(PLA2R)被证实为IMN的靶抗原。在IMN患者血浆中检测到抗PLA2R-IgG4,其特异性高达100%,敏感性约为70%～80%。抗PLA2R-IgG4滴度可以预测疾病的活动性,其与PLA2R抗原结合形成原位免疫复合物,激活补体凝集素途径,形成C5b-9膜攻击复合物沉积在足细胞上,引起足细胞损伤,导致蛋白尿形成。HLA-DQA1与PLA2R基因多态性均与IMN的发病相关,二者的风险基因具有叠加效应。综上所述,IMN的发生是多种因素共同作用的结果,包括易感基因、靶抗原、自身抗体、补体等,这些研究进展对于IMN的诊断和治疗具有重要意义。     

Successful treatment of recurrent focal segmental glomerulosclerosis with a low dose rituximab in a kidney transplant recipient

Recurrence of focal segmental glomerulosclerosis (FSGS) is a major therapeutic challenge in kidney transplantation (KT). Although intensive plasmapheresis and high-dose rituximab have been introduced to treat recurrent FSGS, the most effective dosage and regimen of rituximab have not been determined. Herein we reported the first case of successful treatment of recurrent FSGS with a low-dose rituximab. The patient showed marked proteinuria (3.5?g/d) and oliguria 2?d after KT. Two courses of plasmapheresis and immunoglobulin were applied to the patient, however, nephrotic range proteinuria persisted and creatinine level increased to 3.56?mg/dL. Five months post-transplant, the patient received injection with only one dose of rituximab 100?mg, without further plasmapheresis, which resulted in immediate reduction of serum creatinine and full remission of proteinuria during the following 18 months. This case suggested that recurrent FSGS, which frequently relapses after plasmapheresis, could be treated successfully with a low-dose rituximab even without plasmapheresis.     

Anti‐Phospholipase A2 Receptor Antibodies in Recurrent Membranous Nephropathy

About 70% of patients with primary membranous nephropathy (MN) have circulating anti‐phospholipase A₂ receptor (PLA₂R) antibodies that correlate with disease activity, but their predictive value in post‐transplant (Tx) recurrent MN is uncertain. We evaluated 26 patients, 18 with recurrent MN and 8 without recurrence, with serial post‐Tx serum samples and renal biopsies to determine if patients with pre‐Tx anti‐PLA₂R are at increased risk of recurrence as compared to seronegative patients and to determine if post‐Tx changes in anti‐PLA₂R correspond to the clinical course. In the recurrent group, 10/17 patients had anti‐PLA₂R at the time of Tx versus 2/7 patients in the nonrecurrent group. The positive predictive value of pre‐Tx anti‐PLA₂R for recurrence was 83%, while the negative predictive value was 42%. Persistence or reappearance of post‐Tx anti‐PLA₂R was associated with increasing proteinuria and resistant disease in 6/18 cases; little or no proteinuria occurred in cases with pre‐Tx anti‐PLA₂R and biopsy evidence of recurrence in which the antibodies resolved with standard immunosuppression. Some cases with positive pre‐Tx anti‐PLA₂R were seronegative at the time of recurrence. In conclusion, patients with positive pre‐Tx anti‐PLA₂R should be monitored closely for recurrent MN. Persistence or reappearance of antibody post‐Tx may indicate a more resistant disease.     

Rituximab treatment for posttransplant lymphoproliferative disorder (PTLD) induces complete remission of recurrent nephrotic syndrome

A 12-year-old Japanese boy who underwent kidney transplantation with a kidney from his mother developed severe proteinuria immediately after the operation. Because his original disease was nephrotic syndrome (focal segmental glomerulosclerosis, or FSGS) and electron microscopic examination of the renal biopsy showed foot process fusion, we diagnosed this as a recurrence of nephrotic syndrome to the transplanted kidney. Four months after the transplantation, posttransplant lymphoproliferative disorder (PTLD) developed, which was pathologically diagnosed as diffuse large B cell lymphoma. Treatment consisting of a reduction in immunosuppression resulted in improvement in PTLD a month after the start of treatment. However, relapse occurred 2 months after the first onset of PTLD, which we treated with rituximab (CD-20 monoclonal antibody 375 mg/m²) once weekly for a total of four doses. The PTLD resolved immediately after the rituximab treatment was started, and, interestingly, urinary protein levels also improved at the same time. Three years later, the boy shows no signs of PTLD, and no proteinuria has been detected. These findings suggest that rituximab may be an effective treatment for recurrence of nephrotic syndrome after transplantation and that activated B cells may play a pivotal role in the recurrence of nephrosis after renal transplantation.     

New ‘Antigens’ in Membranous Nephropathy

Membranous nephropathy (MN) occurs due to deposition of immune complexes along the subepithelial region of glomerular basement membrane. Two previously identified target antigens for the immune complexes, PLA2R (identified in 2009) and THSD7A (in 2014), account for approximately 60% of all MN, both primary and secondary. In the remaining MN, target antigens were unknown. Use of laser microdissection and mass spectrometry enabled identification of new “antigens.” This approach led to the identification of four novel types of MN: exotosin 1 (EXT1)– and exotosin 2 (EXT2)–associated MN, NELL1-associated MN, Sema3B-associated MN, and PCDH7-associated MN. Each of these represents a distinct disease entity, with different clinical and pathologic findings. In this review, the structure of the proteins and the clinical and pathologic findings of the new types of MN are discussed. The role of mass spectrometry for accurate diagnosis of MN cannot be overemphasized. Finally, any classification of MN should be made on the basis of the antigens that are detected. Further studies are required to understand the pathophysiology, response to treatment, and outcomes of these new MNs.     

Treatment of focal segmental glomerular sclerosis with rituximab: 2 case reports

BACKGROUND: Primary focal segmental glomerular sclerosis (FSGS) recurs in 20 - 40% of patients after kidney transplantation. Rituximab has been used to treat several glomerular diseases. PATIENTS AND RESULTS: We treated two renal-transplant patients with recurrence of FSGS with rituximab. Despite a prophylactic perioperative therapy of plasmapheresis (PE) and i.v. cyclosporine A, Patient 1 developed significant proteinuria, at 1 day after his first kidney transplantation. After two infusions of rituximab (375 mg/m2) he had complete remission. A second relapse, which occurred on Day 40, was also successfully treated by PE and one additional infusion of rituximab. 10 months after transplantation, he still has complete remission from recurrent nephrotic syndrome. Patient 2 also developed significant proteinuria, but 1 day after a second kidney transplantation. Nephrotic syndrome persisted despite 27 sessions of PE and cyclophosphamide therapy. At 13 months after transplantation, he received four infusions of rituximab (375 mg/m(2)), but this was ineffective. CONCLUSION: There is a need to demonstrate whether or not rituximab therapy is of interest to prevent and to treat nephritic syndrome in renal-transplant patients who suffer from FSGS.     

Recurrence of nephrotic proteinuria in children with focal segmental glomerulosclerosis after renal transplantation treated with plasmapheresis and immunoadsorption: case reports

Idiopathic focal segmental glomerulosclerosis (FSGS) is believed to be caused by a circulating permeability factor. FSGS recurrence is common after transplantation. The treatment is still a matter of debate; plasmapheresis (PE) and immunoadsorption (IA) are often used. We report on PE and IA in the treatment of two children with recurrent nephrotic proteinuria. Patient 1 was a 16-year-old girl who had recurrence of nephrotic proteinuria on the first day after transplantation (proteinuria-19 g/d). Primary immunosuppressive therapy was changed to high-dose cyclosporine and cyclophosphamide; plasmapheresis was started on day 4. Altogether we performed 53 PE and 38 IA procedures. During the first month, PE procedures were performed with no more than a 2-day interval between sessions, and the girl achieved partial remission (proteinuria 3 g/d). PE was then stopped. After 2 months, a relapse of heavy proteinuria occurred. This relapse was successfully treated again with intensified PE treatment. After achieving remission, a chronic PE regimen was started (PE once a week), similar to the previous series. The child remained in partial remission. Seven months after renal transplantation, she was switched from PE to IA, because of severe hypoproteinemia. Graft biopsy performed at 4 months showed effacement of the foot processes. At the present time she has a good graft function and 3 g/d proteinuria. Patient 2 was a 13-year-old girl with FSGS since 9 years. On the second day after renal transplantation she developed nephrotic proteinuria (proteinuria-14 g/d), which was treated with 39 PE and 16 IA treatments. She went into complete remission on the intensified PE regimen, had one relapse, and was switched to chronic IA. Graft biopsy performed at 2 weeks after transplantation showed effacement of the foot processes. At the present time she has good graft function and low proteinuria (0.3 g/d). In conclusion, intensified PE or IA treatments induced remission of recurrent nephrotic range proteinuria. Chronic PE or IA can maintain patients with frequent relapses in long-term remission.     

乙型肝炎病毒相关膜性肾病患者抗血清磷脂酶A2受体-IgG特点及其相关因素的临床研究

目的研究乙型肝炎病毒相关膜性肾病(HBV-MN)患者血清抗磷脂酶A2受体(PLA2R)-IgG阳性率,分析与PLA2R-IgG滴度相关的因素。 方法本研究纳入经肾穿刺活检确诊的HBV-MN患者108例,检测血清PLA2R－IgG滴度、肌酐、白蛋白和24 h尿蛋白定量等,计算肾小球滤过率,分别统计患者肾活检组织中PLA2R及免疫荧光IgG、C3、C1q及IgG亚型阳性率,分析年龄、性别、蛋白尿与血清中和肾活检组织中PLA2R-IgG检测结果的关系。 结果108例HBV-MN患者中,血清PLA2R-IgG阳性率为37%,肾组织PLA2R阳性率54.6%,血清PLA2R-IgG的阳性率和滴度与年龄、性别无统计学相关性(P>0.05),与尿蛋白水平相关(χ²＝9.159,P＝0.010;χ²＝11.327,P＝0.004);尿蛋白>3.5 g/d组患者PLA2R－IgG阳性率显著高于尿蛋白<1g/d及1～3.5 g/d组(Z＝2.863,P＝0.012和Z＝2.356,P＝0.049)。 结论HBV-MN患者中PLA2R-IgG阳性率较高,阳性率及滴度均与蛋白尿水平相关,尿蛋白越多,阳性率和滴度也随之升高。