Clinical Features and Pathology of PLA2R and THSD7A-Associated Membranous Nephropathy: A Single-Center Study from China

Objective

Serum-specific antibodies as a non-invasive means to effectively diagnose idiopathic membranous nephropathy and assess clinicopathology.

Methods

Immunofluorescence of anti-PLA2R and THSD7A antibodies and kidney tissue PLA2R, THSD7A and IgG4 expression in IMN and non-IMN (2020-2021) was detected to assess the efficacy of diagnosing IMN. IMN patients were divided into two groups, anti-PLA2R antibody positive (161 cases) and negative (26 cases), and two groups, kidney tissue PLA2R (40 cases) and PLA2R+THSD7A (6 cases), to compare the clinical and pathological features, and to carry out a prognostic analysis of THSD7A-positive patients, with a focus on correlation with malignancy.

Results

The positive rate of anti-PLA2R antibodies was significantly higher in IMN (P<0.05); anti-PLA2R antibodies, kidney tissue PLA2R and IgG4 and THSD7A had some diagnostic value. Anti-PLA2R antibodies correlated with proteinuria levels in IMN patients, and their levels were negatively correlated with blood albumin (r=-0.146, P=0.042); correlated with pathological stage and C3 and IgG4 immunodeposition; there was no significant difference in clinical pathology between kidney tissue THSD7A+PLA2R positive compared to kidney tissue PLA2R positive patients, but the probability of achieving complete remission was low and time longer, and no malignancy events were detected during follow-up.

Conclusion

Anti-PLA2R antibodies, kidney tissue PLA2R, THSD7A and IgG4 have high diagnostic efficacy for IMN; anti-PLA2R antibodies can be used as diagnostic markers to assist in the assessment of clinical and pathological features; co-expression of kidney tissue PLA2R and THSD7A is not significantly different from kidney tissue PLA2R in assessing the clinical features, pathological manifestations and prognosis, but requires long-term. However, long-term follow-up is needed to monitor the potential risk, and a larger multicentre study with long-term follow-up is expected to be conducted to comprehensively assess IMN characteristics.

The Clinical Profile and Long-Term Outcome of Children with Membranous Nephropathy, and the Evaluation of Anti-Phospholipase A2 Receptor Antibody Immunohistochemistry in Kidney Biopsy

Introduction

Idiopathic membranous nephropathy (iMN) is a rare cause of nephrotic syndrome in children (1%-7%). Anti-phospholipase A2 receptor (PLA2R) antibody positivity in kidney biopsy is observed in 52%-78% of adults and 45% of children with iMN. The objectives of the study are to analyze the clinical profile and outcome of membranous nephropathy in children, to assess the prevalence of anti-PLA2R immunohistochemistry (IHC) in kidney biopsy, and to correlate their presence with disease characteristics.

Methods

We are reporting a single-center retrospective study conducted in pediatric nephrology division. Clinical data and outcome parameters of children with membranous nephropathy were analyzed. PLA2R IHC was performed in kidney biopsy specimens retrospectively.

Results

We analyzed 43 children with membranous nephropathy (MN) from a single center. 18 (42%) had idiopathic MN (iMN). PLA2R IHC was performed in kidney biopsy specimens in 14/18 (78%) patients with iMN and 7/9 (78%) non-lupus secondary membranous nephropathy (SMN) patients. The most common cause of SMN was lupus nephritis in 16 patients (64%). The mean estimated glomerular filtration rate (eGFR) at onset was 156 ± 81 ml/min/1.73m2. The sensitivity and specificity of PLA2R IHC in diagnosing pediatric MN was 50% and 57%, respectively; positive and negative predictive values were 70% and 36%, respectively. At the final follow-up, chronic kidney disease stage 5 (CKD 5) developed in 2/14 (14.3%) iMN patients.

Conclusions

IHC PLA2R staining of glomerular tissue is a useful diagnostic marker of IMN. Though PLA2R prevalence is lower in children, its role in guiding treatment needs further exploration.

Challenges and dilemmas in pediatric hepatic Wilson's disease

Wilson disease is an autosomal recessive disorder affecting the ATP7B gene located on chromosome 13q. This leads to copper deposition in various organs, most importantly in the liver and brain. The genetic mutations are vast, well reported in the West but poorly documented in developing countries. Hence the diagnosis is made with a constellation of clinico-laboratory parameters which have significant overlap with other liver diseases and often pose a significant dilemma for clinicians. Diagnostic scoring systems are not fool-proof. The availability and affordability of chelators in developing countries impact the drug compliance of patients. While D-penicillamine is a potent drug, its side effects lead to drug discontinuation. Trientine is cost-prohibitive in developing countries. There is no single test to assess the adequacy of chelation. Exchangeable urinary copper is an essential upcoming diagnostic and prognostic tool. In the presence of cirrhosis, hypersplenism clouds the assessment of myelosuppression of drugs. Similarly, it may be difficult to distinguish disease tubulopathy from drug-induced glomerulonephritis. Neurological worsening due to chelators may appear similar to disease progression. Presentation as fulminant hepatic failure requires rapid workup. There is a limited window of opportunity to salvage these patients with the help of plasmapheresis and other liver-assisted devices. This review addresses the challenges and clinical dilemmas faced at beside in developing countries.

Anti-PLA2R Antibody Levels and Clinical Risk Factors for Treatment Nonresponse in Membranous Nephropathy

BACKGROUND

The 2021 Kidney Disease Improving Global Outcomes (KDIGO) guidelines recommend following anti-phospholipase A2 receptor (PLA2R) antibody levels as a marker of treatment response in membranous nephropathy; however, the optimal timing to evaluate antibody levels and how to combine them with other clinical variables are currently unknown.

METHODS

We used a cohort of 85 patients from the Membranous Nephropathy Trial Of Rituximab (MENTOR) with anti-PLA2R antibodies ≥14 RU/ml to identify risk factors for not experiencing proteinuria remission after 12 months of treatment with cyclosporine or rituximab. Three landmark times were considered: at baseline and after 3 and 6 months of treatment. Logistic regression model performance was evaluated using C-statistics and model fit (Akaike information criterion [AIC], R 2 ).

RESULTS

The model at baseline that best predicted no remission included anti-PLA2R antibodies >323 RU/ml and creatinine clearance; the best model after 3 months included the change from baseline in both antibody and albumin levels; and the best model after 6 months included antibody levels >14 RU/ml, creatinine clearance, and the change from baseline in albumin. Compared with the model at baseline, the model at 3 months had better model fit (AIC 70.9 versus 96.4, R 2 51.8% versus 30.1%) and higher C-statistic (0.93 versus 0.83, P = 0.008). The model at 6 months had no difference in performance compared with the model at 3 months (AIC 68.6, R 2 53.0%, C-statistic 0.94, P = 0.67).

CONCLUSIONS

In patients with membranous nephropathy treated with cyclosporine or rituximab in the MENTOR trial, we found that the optimal method to evaluate risk factors for the probability of treatment response was to use anti-PLA2R antibody levels combined with albumin levels after 3 months of treatment, which was significantly better than using antibody levels alone or risk factor evaluation at baseline, with no added benefit of waiting until 6 months of treatment.

PODCAST

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/CJASN/2023_10_09_CJN0000000000000237.mp3.

Diagnostic utility of serum and urine biomarkers in idiopathic membranous nephropathy: a systematic review and meta-analysis

BACKGROUND

Membranous nephropathy is an autoimmune nephropathy that is one of the most common pathological types of nephrotic syndrome. It is important to find and apply specific biomarkers for the noninvasive diagnosis of idiopathic membranous nephropathy (IMN). However, there are limited data about their diagnostic value. Therefore, an overall meta-analysis helps to identify effective biomarkers for the clinical diagnosis of IMN.

METHODS

A systematic literature search was carried out in PubMed, Embase, Cochrane and Web of Science from inception until December 31, 2020. Two researchers searched for studies that met the inclusion criteria. The results of the joint study were expressed in terms of sensitivity and specificity.

RESULTS

The meta-analysis included 24 studies with biomarkers for the clinical diagnosis of IMN, including antibody against phospholipase A2 receptor (PLA2R-AB), antibody against thrombospondin type I domain-containing 7A (THSD7A-AB), lysosome membrane protein-2 (LIMP-2) and circular RNAs. The diagnostic efficiency of PLA2R-AB for IMN had a combined sensitivity of 60% and a combined specificity of 100%. The diagnostic efficiency of THSD7A-AB for IMN had a combined sensitivity of 3% and a combined specificity of 99%. The diagnostic efficiency of urinary LIMP-2 for IMN was 100%, and the specificity was 100%. The diagnostic efficiency of exosomal circRNAs for IMN was 100%, and the specificity was 100%.

CONCLUSIONS

This meta-analysis shows that PLA2R-AB and THSD7A-AB are of important diagnostic value for IMN. More studies are needed in the future to reveal the diagnostic value of LIMP-2 and circRNAs for IMN.

The Sensitivity and Specificity of Serum Phospholipase A2 Receptor Antibodies in Diagnosing Primary Membranous Nephropathy in Patients with Adult Nephrotic Syndrome and its Correlation with Serum Phospholipase A2 Receptor Staining in Kidney Biopsies

Membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome (NS) in nondiabetic adults, with about 70%-80% of cases of MN being primary MN (pMN). Many studies have shown that serum phospholipase A2 receptor (PLA2R) antibodies are a diagnostic and prognostic biomarker for pMN, with a pooled diagnostic sensitivity and specificity of 54%-82% and 89%-100%, respectively, resulting in PLA2R staining and serum PLA2R antibodies being incorporated in the management algorithms of MN. We studied the sensitivity and specificity of serum PLA2R antibodies for diagnosing pMN and its correlation with PLA2R staining in kidney biopsies in a prospective observational study of 58 adult NS subjects undergoing a kidney biopsy. Serum PLA2R antibodies were determined by indirect immunofluorescence (IF) before the biopsy. Kidney biopsies were sent for light microscopy and IF examinations. Biopsy samples with MN histology were stained for PLA2R antigens. Out of the 58 adult NS subjects, 28 were diagnosed with pMN and one with secondary MN. Serum PLA2R antibodies were positive in 12 subjects with pMN, and one had focal segmental glomerulosclerosis not otherwise specified, giving a sensitivity of 42.8% and specificity of 96.7% for diagnosing pMN. There was a significant association between glomerular staining for PLA2R (24 of 28 subjects) and a diagnosis of pMN by kidney biopsy, with a sensitivity of 82.8%. Cohen's kappa agreement between glomerular staining for PLA2R and a diagnosis of MN was 0.83 (0.57-1.08).

[Clinical significance of the determination of antibodies to thrombospondin type 1 containing domain 7A (THSD7A) in membranous nephropathy]

BACKGROUND

Membranous nephropathy (MN) is an immunocomplex glomerular disease, which is the most common cause of nephrotic syndrome in adults. Numerous studies have established that autoantibodies against the target podocyte autoantigens, including the thrombospondin type 1 domain containing 7A (THSD7A), play a leading role in the development of idiopathic MN.

AIM

To evaluate the prevalence of anti-THSD7A autoantibodies (anti-THSD7A AB) in a group of Russian patients with MN.

MATERIALS AND METHODS

Serum titers of anti-THSD7A AB were tested in 61 patients with biopsy-proven MN and 12 healthy controls.

RESULTS

The prevalence of anti-THSD7A AB was not differing significantly in patients with MN and in the control group (110.9 [71.63; 210.62] and 159.25 [125.64; 231.97] pg/ml, respectively; p=0.111). When comparing subgroups of anti-PLA2R-negative patients and patients who did not receive immunosuppressive therapy with the control group, there were also no statistically significant differences in the Anti-THSD7A AB levels (p>0.05). In the MN group, 1 (1.6%) patient was anti-THSD7A-positive: a 60-year-old man with anti-PLA2R-negative MN and the presence of hormonally inactive adenomas of both adrenal glands and colon polyps (villous adenoma with focal moderate dysplasia, tubulo-villous and tubular adenoma with focal moderate severe dysplasia).

CONCLUSION

THSD7-associated MN is a rare variant of MN and is usually detected in PLA2R-negative patients. Screening for malignancies in THSD7A-positive MN patients is proposed.

Diagnostic Usefulness of Antibodies Against M-type Phospholipase A2 Receptor (aPLA2R) in Primary Membranous Nephropathy in the Mexican Population

OBJECTIVE

This study aimed to determine the frequency and diagnostic performance of antibodies against M-type phospholipase A2 receptors (aPLA2R) in subjects with idiopathic membranous nephropathy (IMN).

MATERIALS AND METHODS

A diagnostic test study was conducted in a cohort of 160 patients from the nephrology outpatient clinic over a period of eight years. Serum samples were taken and analyzed from patients with a histological diagnosis of IMN with proteinuria greater than and less than 1 g in 24 hours and other glomerular diseases other than IMN with aPLA2R measurement by enzyme-linked immunosorbent assay (ELISA) (Euroimmun, Luebeck, Germany).

RESULTS

In 22 of 160 patients, an aPLA2R concentration >9 RU/mL was found, and all these cases had IMN. The prevalence of seropositivity in cases with active IMN was 78% (21/27). All these correlations were statistically significant with a p<0.001. The area under the receiver operating characteristic (ROC) curve (AB-ROC) of aPLA2R was 0.87 (95%, CI: 78-0.96).

CONCLUSIONS

The aPLA2R has adequate diagnostic usefulness to diagnose IMN in the selected population, especially in subjects with proteinuria greater than 1 gr/day, with a sensitivity of 78% and a specificity of 99%.

PLA2R Antibody Does Not Outperform Conventional Clinical Markers in Predicting Outcomes in Membranous Nephropathy

Introduction

The prognostic value of PLA2R antibody (Ab) test in clinical practice remains unclear. We aimed to evaluate its ability in predicting hard outcomes in primary membranous nephropathy (PMN) after adjustments to conventional markers of disease activity.

Methods

A total of 222 patients diagnosed with PMN from January 2003 to July 2019 having had a serum PLA2R Ab test, were included from 3 centers in the north of England. Baseline conventional markers, PLA2R-Ab-status (positive vs. negative), Ab-titer (high vs. low), and time of testing (pre-PLA2R era vs. PLA2R era) were evaluated for association with outcomes. Primary outcome was time to progression (composite of doubling of creatinine, stage 5 chronic kidney disease, or death). Secondary outcomes were time to partial remission (PR) and time to immunosuppression. Cox proportional hazard testing was used.

Results

During a median follow-up of 5.26 years, progression was seen in 65 (29.3%) and PR in 179 of 222 patients (80.6%). There was a clear association of estimated glomerular filtration rate (eGFR) (standardized hazard ratio [HRZ] = 0.767, P < 0.05) and urine protein-to-creatinine ratio (uPCR) (HRZ = 1.44, P < 0.005) with time to progression among all patients, and eGFR (HRZ = 0.606, P < 0.005) in Ab-positive patients. Baseline Ab-positivity was not associated with time to progression (adjusted hazard ratio [aHR] = 0.93, P = 0.71) or time to PR (aHR = 0.84, P = 0.13). Similarly, baseline high Ab-titer was not associated with time to progression (aHR = 1.07, P = 0.77) or time to PR (aHR = 0.794, P = 0.08).

Conclusion

Once adjusted to conventional markers of disease activity, baseline PLA2R Ab-positivity or Ab-titer do not predict disease progression or time to PR. Further studies are needed to harness the utility of PLA2R Ab test in prognostication in PMN.

Clinicopathological features and prognosis of primary membranous nephropathy in combination with crescent

OBJECTIVE

The incidence of primary membranous nephropathy with crescentic bodies is low, but the specificity of its clinical presentation, pathology and prognosis is of great interest. In this study, we retrospectively analyzed the clinicopathological and prognostic characteristics of patients with crescentic MN in our hospital over the past 4 years.

METHODS

Ten patients with combined crescentic primary membranous nephropathy diagnosed by renal biopsy at our hospital from 2018 to 2021 were retrospectively analysed and compared with 39 patients with PMN (simple random sample) during the same period for clinicopathological and prognostic comparisons.

RESULTS

The 10 patients had higher 24 h urine protein quantification, creatinine levels on renal biopsy, interstitial fibrosis and tubular atrophy, and interstitial inflammatory cell infiltration than the control group (P < 0.05); there were no significant differences in anti-PLA2R antibodies and PLA2R staining of renal tissue (P > 0.05); At follow-up, the poor outcome of crescentic MN treatment and the low clinical remission rate were found, with the percentage of crescentic bodies being a factor in patient prognosis (P < 0.05).

CONCLUSION

Crescentic MN has a low prevalence and maybe a specific type of PMN; it has more severe clinical symptoms and pathology than PMN, and the crescentic proportion is strongly associated with renal prognosis. Intensive treatment is recommended for these patients.

Determination of Anti-Phospholipase A2 and Anti-Thrombospondin Type 1 Domain-Containing Protein 7A in Latin Patients with Membranous Nephropathy

Primary membranous nephropathy (MN) is caused by antibodies against podocyte antigens, especially the type M receptor of phospholipase A2 (PLA2R) and thrombospondin type-1 domain containing 7 A (THSD7A). This study's aim was the determination of anti-PLA2R, anti-THSD7A serum antibodies, and anti-PLA2R renal tissue staining prevalence in a Latin population with MN, as well as evaluating their role as biomarkers for disease activity. The performance of the two anti-PLA2R serum diagnostic methods-ELISA and indirect immunofluorescence (IFI)-was evaluated for the diagnosis of MN. Fifty-nine patients, including 29 with MN, 18 with lupus membranous nephropathy (LMN) and 12 with focal and segmental glomerulosclerosis (FSGS), were evaluated for serum antibodies. Renal biopsies were also evaluated for the presence of anti-PLA2R staining. Twenty-one patients with MN were followed for 1 year. Patients with LMN and FSGS were negative for both antibodies. All 29 MN patients were negative for anti-THSD7A; 16 MN patients were positive for anti-PLA2R by ELISA and/or IFI, and 3 MN patients were positive for anti-PLA2R only by IFI. Thus, the anti-PLA2R ELISA test demonstrated 45% sensitivity and 97% specificity, while the IFI test showed, respectively, 55% and 100% in our MN patients. Among the 28 MN renal biopsies, 20 presented anti-PLA2R positive staining, corresponding to a 72% sensitivity. Positive correlations were observed between the anti-PLA2R ELISA titer and proteinuria. In conclusion, determination of anti-PLA2R antibodies in the MN Latin population showed similar rates to those reported for other populations. The anti-PLA2R serum levels correlated with MN disease activity.

Critical evaluation of cancer risks in glomerular disease

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The increased cancer incidence in patients with glomerular disease can be secondary to an intrinsic immune dysfunction associated with the disease or/and extrinsic factors, especially immunosuppressants.

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Paraneoplastic glomerulopathy is sometimes misdiagnosed as primary glomerulopathy.

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The treatment for paraneoplastic glomerulopathy is different from primary glomerular disease.

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In membranous nephropathy, serum circulating autoantibodies against PLA2R and THSD7A, immunohistochemical tissue markers for glomerular PLA2R, THSD7A and specific types of immunoglobulin G (IgG) may be used for identifying underlying malignancies.

•

A scheme of screening of cancers frequently reported in the setting of glomerular disease is important.

The increased cancer incidence in patients with glomerular disease can be secondary to an intrinsic immune dysfunction associated with the disease or/and extrinsic factors, especially immunosuppressants. The treatment for paraneoplastic glomerulopathy is different from primary glomerular disease. Immunosuppressive therapy often used for primary glomerulopathy may aggravate concomitant cancers in patients with paraneoplastic glomerulopathy. In membranous nephropathy (MN), measurement of serum circulating autoantibodies against podocyte transmembrane glycoprotein M-type phospholipase A2 receptor (PLA2R) and thrombospondin type 1 domain-containing 7A (THSD7A), immunohistochemical staining of kidney tissue for glomerular PLA2R, THSD7A, neural epidermal growth factor-like 1 protein (NELL-1) and specific types of immunoglobulin G (IgG) may be useful adjuncts when screening for underlying malignancies. This review addresses overall cancer risks in individuals with glomerular diseases and employment of biomarkers available for MN. We propose a scheme of screening of cancers frequently reported in the setting of glomerular disease.

Membranous nephropathy: new pathogenic mechanisms and their clinical implications

Membranous nephropathy (MN) is characterized histomorphologically by the presence of immune deposits in the subepithelial space of the glomerular filtration barrier; its clinical hallmarks are nephrotic range proteinuria with oedema. In patients with primary MN, autoimmunity is driven by circulating autoantibodies that bind to one or more antigens on the surface of glomerular podocytes. Compared with other autoimmune kidney diseases, the understanding of the pathogenesis of MN has substantially improved in the past decade, thanks to the discovery of pathogenic circulating autoantibodies against phospholipase A₂ receptor 1 (PLA₂R1) and thrombospondin type 1 domain-containing protein 7A (THSD7A). The subsequent identification of more proteins associated with MN, some of which are also endogenous podocyte antigens, might further advance the clinical characterization of MN, including its diagnosis, treatment and prognosis. Insights from studies in patients with MN, combined with the development of novel in vivo and in vitro experimental models, have potential to improve the management of patients with MN. Characterizing the interaction between autoimmunity and local glomerular lesions provides an opportunity to develop more specific, pathogenesis-based treatments.

Revisiting immunological and clinical aspects of membranous nephropathy

Idiopathic or primary membranous nephropathy (IMN) is one of the most frequent causes of nephrotic syndrome in adults and the elderly. It is characterized by a thickening of the wall of the glomerular capillaries due to the presence of immune complex deposits. 85% of membranous nephropathy cases are classified as primary or idiopathic (IMN). The rest are of secondary origin (SMN), caused by autoimmune conditions or malignant tumors as lung cancer, colon and melanomas. It is an organ-specific autoimmune disease in which the complement system plays an important role with the formation of the membrane attack complex (MAC; C5b-9), which produces an alteration of the podocyte structure. The antigen responsible for 70-80% of IMN is a podocyte protein called M-type phospholipase A2 receptor (PLA2R). More recently, another podocyte antigen has been identified, the "Thrombospondin type-1 domain-containing 7A" (THSD7A), which is responsible for 10% of the cases of negative IMN for anti- PLA2R.

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.

Biomarkers in pediatric glomerulonephritis and nephrotic syndrome

Glomerular diseases are often chronic or recurring and thus associated with a tremendous physical, psychological, and economic burden. Their etiologies are often unknown, and their pathogeneses are frequently poorly understood. The diagnoses and management of these diseases are therefore based on clinical features, traditional laboratory markers, and, often, kidney pathology. However, the clinical presentation can be highly variable, the kidney pathology may not establish a definitive diagnosis, and the therapeutic responses and resulting clinical outcomes are often unpredictable. To try to address these challenges, significant research efforts have been made over the last decade to identify potential biomarkers that can help clinicians optimize the diagnosis and prognosis at clinical presentation, as well as help predict long-term outcomes. Unfortunately, these efforts have to date only identified a single biomarker for glomerular disease that has been fully validated and developed for widespread clinical use (anti-PLA2R antibodies to diagnose membranous nephropathy). In this manuscript, we review the definitions and development of biomarkers, as well as the current knowledge on both historical and novel candidate biomarkers of glomerular disease, with an emphasis on those associated with idiopathic nephrotic syndrome.

Renal manifestations of syphilis

Syphilis is a sexually transmitted disease caused by spirochaete Treponema pallidum. The incidence of syphilis is rising across the globe. It has been described in the literature as a great imitator due to the vast range of clinical manifestations that can occur in the disease. Renal manifestations are rare but a feature of secondary syphilis. It can cause glomerulopathies, tubular pathology and vasculitic lesions in the kidney. Membranous nephropathy is the most commonly reported glomerular lesion associated with syphilis. With two recent cases of secondary membranous nephropathy due to syphilis, it is timely to review the current state of knowledge, and discuss the different renal manifestation of syphilis, its pathology and treatment options.

A novel time-resolved fluoroimmunoassay based on magnetic microspheres method for detecting antibodies against the phospholipase A2 receptor

BACKGROUND

the level of serum antibodies against the M-type phospholipase A2 receptor (anti-PLA2R-IgG) is closely related to the disease activity of idiopathic membranous nephropathy (IMN). Therefore, the establishment of a sensitive and rapid method for detecting anti-PLA2R-IgG will be beneficial for the differential diagnosis of IMN.

METHODS

magnetic microspheres coupled with the PLA2R antigen were used to capture anti-PLA2R-IgG in serum samples, and europium-labeled goat anti-human IgG antibodies were used for tracking. An anti-PLA2R-IgG-time-resolved fluoroimmunoassay (TRFIA) based on magnetic microspheres using an indirect method was established and analyzed. Various indicators of this method were evaluated.

RESULTS

the sensitivity of the anti-PLA2R-IgG-TRFIA based on magnetic microspheres was 0.51 RU mL^-1, and the linear detection range was 0.51-1000 RU mL^-1. The average intra- and inter-assay coefficients of variation (CVs) were 3.62% and 4.45%, respectively, and the average recovery was 95.60%. No cross-reactivity with IgA was observed. The median (interquartile range) concentration of anti-PLA2R-IgG in patients with IMN was 40.37 RU mL^-1 (11.33 to 83.05 RU mL^-1). The cut-off values of the anti-PLA2R-IgG concentration for healthy volunteers and those with other kidney diseases were determined to be 8.06 RU mL^-1 and 13.23 RU mL^-1, respectively. Additionally, the positive rates of anti-PLA2R-IgG in patients with IMN corresponding to the above cut-off values were 91.07% and 71.32%, respectively. The correlation coefficient between the magnetic microsphere-based anti-PLA2R-TRFIA and the PLA2R-ELISA kit for detecting anti-PLA2R-IgG was 0.944.

CONCLUSION

a highly sensitive and rapid magnetic microsphere-based anti-PLA2R-IgG-TRFIA was successfully established to detect the concentrations of anti-PLA2R-IgG in the sera of patients with IMN.

Outcomes of primary membranous nephropathy based on serum anti-phospholipase A2 receptor antibodies and glomerular phospholipase A2 receptor antigen status: a retrospective cohort study

Introduction

Primary membranous nephropathy (PMN) is associated with the anti-phospholipase A2 receptor (anti-PLA2R) antibody in 70% of cases. Some anti-PLA2R-negative patients have the PLA2R antigen in renal tissue. This study examined the prognosis of patients with PMN according to their serum anti-PLA2R antibody (SAb) and glomerular PLA2R antigen (GAg) status.

Methods

Patients diagnosed with PMN were included retrospectively. Patients were grouped according to their PLA2R status into the SAb−/GAg−, SAb−/GAg+, and SAb+/GAg + groups. Baseline data, renal biopsy results, treatment, and clinical data were compared among the groups. Cox univariable and multivariable analyses examined the factors related to complete remission (CR).

Results

A total of 114 patients were enrolled; 10 (9%) in the SAb−/GAg−, 23 (20%) in the SAb−/GAg+, and 81 (71%) in the SAb+/GAg+ groups. Cumulative CR rate showed a significant difference between the SAb−/GAg − and SAb+/GAg+ groups (log-rank p = 0.003). The multivariable Cox proportional hazard analysis showed that age (HR = 0.968; 95%CI = 0.946–0.990; p = 0.005), SAb+/GAg+ versus SAb−/GAg− (HR = 0.387; 95%CI = 0.190–0.788; p = 0.009), SAb−/GAg+ versus SAb−/GAg− (HR = 0.398; 95%CI = 0.169, 0.939; p = 0.035), total renal chronicity score ≥2 (HR = 0.461, 95%CI: 0.277–0.766, p = 0.003), and IgA deposition (HR = 2.596; 95%CI = 1.227–5.492; p = 0.013) were all independently related (p < 0.05) to CR.

Conclusions

The SAb and GAg status was an indicator of PMN prognosis. The patients with SAb−/GAg − had an increased likelihood of achieving CR than those with SAb−/GAg+ and SAb+/GAg+.

Rapid, quantitative, and high-sensitivity detection of anti-phospholipase A2 receptor antibodies using a novel CdSe/ZnS-based fluorescence immunosorbent assay

Autoantibodies against M-type phospholipase A2 receptor (PLA2R) serve as specific biomarkers for idiopathic membranous nephropathy (IMN), and its quantification helps monitor disease activity. In this study, we describe a rapid and highly sensitive quantum dots-based immunochromatography assay (QD-ICA) for quantifying PLA2R autoantibodies. Serum samples from 135 biopsy-confirmed patients with nephrotic syndrome were analyzed for PLA2R autoantibodies using the novel QD-ICA as well as commercialized enzyme-linked immunosorbent assay (ELISA). Areas under the receiver operating characteristic curve (AUC-ROC) of QD-ICA were significantly greater than those of ELISA (91.1% [95% CI 85.9-96.3%] and 83.9% [95% CI 76.5-91.2%] respectively; p < 0.01). The detection sensitivity and specificity of QD-ICA (80.9% [95% CI 69.2-89.0%] and 100% [95% CI 93.2-100.0%], respectively) exceeded those of ELISA (72.1% [95% CI 59.7-81.9%] and 98.5% [95% CI 90.9-100.0%], respectively). The optimum cut-off value of QD-ICA was 18.18 relative units (RU)/mL, and the limit of detection was 2.86 RU/mL. The novel QD-ICA outperforms ELISA in detecting PLA2R autoantibodies, with shorter detection time, fewer steps, smaller equipment size, and broader testing application, suggesting its capability to improve IMN diagnosis and monitor patient response to treatment.

Comparison of 3 anti-PLA2R inmmunoassaysfor the diagnosis of idiopathic membranous nephropathy in an european population. A pilot study

Membranous nephropathy (MN) is one of the most frequent causes of nephrotic syndrome. Renal biopsy is nowadays the gold standard for the diagnosis of MN. The presence of circulating PLA2R antibody is a very specific tool for the diagnosis of this disease, especially associated with primary or idiopathic MN (IMN), even though it can be also found in a small proportion of patients with secondary MN (SMN). This pilot study compares three different techniques for the detection of anti-PLA2R autoantibodies (immunofluorescence, ELISA immunoassay, and multiplex laser bead technology). Serum of 12 IMN and 9 SMN patients was obtained at diagnosis. Additionally, we employed serum samples of 15 healthy volunteers. From our patient cohort, we obtained a 7.75 RU/ml cut-off for the ELISA and 3104 MFI for the Luminex assays. The agreement between the three techniques improved considerably when applying the new cut-off points. As several authors have suggested, cut-offs may be calculated for each specific population instead of establishing global cut-off points. Patients with IMN showed significantly lower serum albumin levels and higher 24 h proteinuria compared to those with SMN. Analysis of ROC curves suggests that ELISA and LUMINEX assays are more useful than biochemical variables to differentiate patients with IMN and SMN. This pilot study contributes to confirming that the combination of ELISA and Luminex assays provide excellent sensitivity and specificity for the identification of IMN.

Perspectives in membranous nephropathy

The identification of the phospholipase A2 receptor 1 (PLA2R) and thrombospondin type-1 domain-containing protein 7A (THSD7A) as podocyte antigens in adult patients with membranous nephropathy (MN) has strongly impacted both experimental and clinical research on this disease. Evidence has been furnished that podocyte-directed autoantibodies can cause MN, and novel PLA2R- and THSD7A-specific animal models have been developed. Today, measurement of serum autoantibody levels and staining of kidney biopsies for the target antigens guides MN diagnosis and treatment worldwide. Additionally, anti-PLA2R antibodies have been proven to be valuable prognostic biomarkers in MN. Despite these impressive advances, a variety of questions regarding the disease pathomechanisms, clinical use of antibody measurement, and future treatments remain unanswered. In this review, we will outline recent advances made in the field of MN and discuss open questions and perspectives with a focus on novel antigen identification, mechanisms of podocyte injury, clinical use of antibody measurement to guide diagnosis and treatment, and the potential of innovative, pathogenesis-based treatment strategies.

Serum Antibody and Glomerular Antigen of Antiphospholipase A2 Receptor in Chinese Patients with Idiopathic Membranous Nephropathy

Background

M-type phospholipase A2 receptor (PLA2R) is the first autoantigen responsible for idiopathic membranous nephropathy (IMN). However, serum PLA2R antibody (PLA2R-Ab) can be inaccurate in distinguishing between IMN and secondary membranous nephropathy, while renal PLA2R antigen (PLA2R-Ag) emerges as an ancillary diagnostic. The present study is aimed at examining the associations between PLA2R-Ab in sera and PLA2R-Ag in kidneys in IMN patients.

Methods

A total of 93 patients with IMN were retrospectively identified. Their serum PLA2R-Ab and renal PLA2R-Ag expression levels were determined, and the clinical correlations between these parameters and clinical features were examined.

Results

The sensitivities of serum PLA2R-Ab and renal PLA2R-Ag for diagnosing IMN were 74.2% and 88.2%, respectively (P < 0.001), with poor consistency. Higher serum PLA2R-Ab levels were correlated to stronger renal PLA2R-Ag expression (P = 0.048). Patients with positive PLA2R-Ab significantly differed from those with negative levels, in terms of proteinuric levels over 24 hours (4.54 vs. 3.46 g/day, P = 0.015) and serum albumin (23.28 vs. 27.95 g/L, P = 0.038). Among patients with positive renal PLA2R-Ag, patients with positive PLA2R-Ab had significantly higher 24-hour proteinuria, when compared to patients with negative PLA2R-Ab (4.57 vs. 3.08 g/day, P = 0.005). Among those with positive PLA2R-Ab in sera, their PLA2R-Ab levels were correlated with the estimated glomerular filtration and serum creatinine.

Conclusion

Serum PLA2R-Ab exhibits a closer correlation with proteinuric severity and renal function, when compared to renal PLA2R-Ag.

A New Chemiluminescence Immunoassay for Phospholipase A2 Receptor 1 Autoantibodies Allows Early Identification of Autoantibody Recurrence in Patients With Membranous Nephropathy

Background

Circulating autoantibodies against the M-type phospholipase A₂ receptor 1 (PLA₂R1) are important biomarkers in membranous nephropathy (MN), supporting the diagnosis and the clinical monitoring of patients. Standardized recombinant cell-based indirect immunofluorescence assay (RC-IFA) and enzyme-linked immunosorbent assay (ELISA) are widely established for the detection of anti-PLA₂R1 autoantibodies (PLA₂R1-ab). The RC-IFA provides higher sensitivity than the ELISA, but lacks exact graduated quantification of antibody levels. In this study, we evaluated the diagnostic performance of a novel PLA₂R1-ab immunoassay based on chemiluminescence (ChLIA) by comparing it to RC-IFA and ELISA in samples from patients with MN with different diagnostic scenarios.

Methods

Serum samples from patients with biopsy-proven MN and disease controls were analyzed for PLA₂R1-ab by ChLIA, ELISA, and RC-IFA.

Results

The ChLIA demonstrated almost perfect agreement with RC-IFA for the identification of patients with PLA₂R1-associated MN, while additionally allowing fine-graduated quantification of PLA₂R1-ab levels. In patients with a relapse of MN, the ChLIA allowed an earlier detection of PLA₂R1-ab recurrence by at least 3 months in 63% of cases compared with the ELISA.

Conclusions

The PLA₂R1-ab ChLIA had the same excellent diagnostic performance as the RC-IFA and outperformed the ELISA in the diagnosis of MN and the early identification of relapses. It thus presents a favorable tool for accurate PLA₂R1-ab assessment in routine diagnostic settings, while enabling fast processing and fully automated random-access implementation.

Diagnostic accuracy of anti-phospholipase A2 receptor (PLA2R) antibodies in idiopathic membranous nephropathy: an Italian experience

Background

Autoantibodies against-phospholipase A2 receptor (PLA2R) are specific markers of idiopathic membranous nephropathy (iMN). Enzyme-linked immunosorbent assay (ELISA) is becoming the preferred method in many laboratories for the determination of anti-PLA2R antibodies, because it provides quantitative results, and is not prone to subjective interpretation, as is the case with indirect immunofluorescence assay.

Methods

The purpose of our study was to determine the diagnostic performance of serum PLA2R antibodies detected by commercially available ELISA in a large Italian multicenter cohort of patients with biopsy-proven iMN and in patients with other renal diseases, with special focus on evaluating the optimal cut-off value to discriminate positive and negative results. A total of 495 consecutive patients were recruited. Renal biopsies were performed in all patients, and blood samples were taken before the initiation of immunosuppressive treatment.

Results

According to the clinical diagnosis and to kidney biopsy, 126 patients were diagnosed with iMN and 369 had other non-membranous nephropathies. Anti-PLA2R autoantibodies were detected using a commercial anti-PLA2R ELISA. At a cut-off value of 20 relative units (RU)/ml indicated by the manufacturer for positive classification, sensitivity was 61.1% and specificity 99.7%. At a cut-off value of 14 RU/ml indicated by the manufacturer for borderline results, sensitivity was 63.5% and specificity remained the same (99.7%). At a cut-off of 2.7 RU/ml, selected as the optimal cut-off on the basis of ROC curve analysis, sensitivity was 83.3% and specificity 95.1%. The best overall efficiency of the test was observed at 2.7 RU/ml; however, the highest positive likelihood ratio and diagnostic odds ratio were achieved at 14 RU/ml. A cut-off threshold higher than 14 RU/ml or lower than 2.7 RU/ml entailed worse test performance.

Conclusion

Depending on the clinical use (early diagnosis or as a support to confirm clinical diagnosis), nephrologists may take advantage of this evidence by choosing the most convenient cut-off. However, renal biopsy remains mandatory for the definitive diagnosis of iMN and for the assessment of disease severity.

sPLA2-IB Level Correlates with Hyperlipidemia and the Prognosis of Idiopathic Membranous Nephropathy

Recent studies suggested that serum secretory phospholipase A2 group IB (sPLA2-IB) was increased in idiopathic membranous nephropathy (IMN). However, the interference of high lipemia on the sPLA2-IB levels was not taken into account in these studies. The present study aimed to investigate the correlation between sPLA2-IB and lipemia, and the clinical merit of sPLA2-IB in the prediction of prognosis of IMN patients. A total of 64 IMN patients, 39 immunoglobulin A nephropathy (IgAN) patients and 64 healthy controls were included in the study. The levels of serum sPLA2-IB, lipemia and proteinuria were measured. Fifty IMN patients were followed up for 6 months. Pathologic stages were made for all IgAN and IMN patients. The results showed that the levels of serum sPLA2-IB, cholesterol and low-density lipoprotein cholesterol (LDL-C) were significantly higher, and the levels of albumin and high-density lipoprotein cholesterol (HDL-C) were significantly lower in IMN patients than in healthy controls and IgAN patients. Serum sPLA2-IB levels were also found to be higher in IgAN patients than in heathy controls, but the association of serum sPLA2-IB levels with proteinuria, cholesterol and albumin was only shown in IMN patients. Antibody against M-type receptor for secretory phospholipase A2 (PLA2R1) was positive in 81.3% IMN patients. Glomerular sPLA2-IB deposition, podocyte fused processes, and density deposition on thickened basement membrane were seen in IMN patients, but not in IgAN patients. IMN patients with lower sPLA2-IB and proteinuria levels were found to have better outcome after the 6-month follow-up. In IMN patients, sPLA2-IB levels were significantly increased in both serum and renal tissue. In conclusion, serum sPLA2-IB was closely correlated with proteinuria, albumin and cholesterol, and IMN patients with lower sPLA2-IB levels were more likely to achieve a better outcome.

The association of anti-PLA2R with clinical manifestations and outcomes in idiopathic membranous nephropathy: a meta-analysis

PURPOSE

The meta-analysis aims to investigate the relationship between anti-phospholipase A2 receptor autoantibody (anti-PLA2R) and clinical characteristics and adverse outcomes of idiopathic membranous nephropathy (IMN).

METHODS

Related studies published before February 2020 were systematically retrieved from foreign and domestic databases, RevMan5.3 software was used for meta-analysis and subgroup analysis, and STATA 15.0 statistical software was used for its heterogeneity and testing publication bias.

RESULTS

Twenty studies were included, involving 2224 patients with IMN. Our results showed that a significant correlation existed between the expression of serum anti-PLA2R and age (MD = 2.91, 95% CI = 2.15-3.67, P < 0.00001), total serum cholesterol (MD = 35.52, 95% CI = 9.52-61.52, P = 0.007), urine protein by creatinine ratio (UPCR) (MD = 2.15, 95% CI = 1.86-2.44, P<0.00001), serum albumin (MD = -0.40, 95% CI = -0.56 to -0.23, P < 0.00001), eGFR (MD = -10.44, 95% CI = -12.19 to -8.68, P < 0.00001), unremission rate (RR = 1.76, 95% CI = 1.37-2.27, P < 0.0001). In addition, the high titer in seropositive group was closely correlated with serum albumin (MD = -0.40, 95% CI = -0.74 to -0.05, P = 0.03), eGFR (MD = -12.40, 95% CI = -16.29 to -8.52, P < 0.00001) and unremission rate (RR = 2.52, 95% CI = 1.79-3.55, P < 0.00001). No significant correlation was found between glomerular anti-PLA2R and clinical manifestations except for serum cholesterol (MD = 0.81, 95% CI = 0.21-1.41, P = 0.008). However, in terms of prognosis, glomerular anti-PLA2R showed a significant relevance to recurrence rate (RR = 2.25, 95% CI = 1.07-4.72, P = 0.03).

CONCLUSION

Compared with glomerular anti-PLA2R, serum anti-PLA2R may better reflect the activities of IMN disease, while the glomerular anti-PLA2R might be connected with the recurrence of the disease.

Retrospective study: clinicopathological features and prognosis of idiopathic membranous nephropathy with seronegative anti-phospholipase A2 receptor antibody

Background

To discuss the clinicopathological features and prognosis of patients with idiopathic membranous nephropathy (IMN) who are serum-negative for the anti-PLA2R antibody.

Method

Overall, 229 IMN patients were retrospectively collected in this study and classified into anti-PLA2R antibody-negative (PLA2R−, 59 cases) and antibody-positive (PLA2R+, 170 cases) groups. The clinical and pathological features of the PLA2R− group were analyzed; 162 patients in both groups were followed up, and the PLA2R antigen was detected in renal biopsies from the PLA2R− group. Kaplan-Meier and survival analyses were used to compare differences in prognosis.

Results

Serum albumin levels were higher and 24-hour urine protein, creatinine, and beta 2-microglobulin (BMG) levels were lower in the PLA2R− group than in the PLA2R+ group; the proportion of acute and chronic tubular lesions was also significantly lower in the PLA2R− group than in in the PLA2R+ group. After treatment, the remission rate was significantly higher in the negative group than in the positive group (93.02% vs 74.78%,), especially the rate of complete remission (51.16% vs 23.47%). Furthermore, the PLA2R antigen-positive staining rate of 43 patients in the PLA2R− group was 62.79%. Although not significant, the survival rate was higher in the PLA2R− group than in the PLA2R+ group. BMG, 24-hour urine protein and acute and chronic tubular lesions were risk factors for kidney death, and 24-hour urine protein was an independent risk factor for kidney death.

Conclusions

Compared with the PLA2R+ group, the PLA2R− group had mild clinical manifestations and pathological damage and a higher clinical treatment remission rate. Renal tissue PLA2R antigen testing can be considered for patients with seronegative IMN to increase the diagnostic rate.

Novel ELISA for thrombospondin type 1 domain-containing 7A autoantibodies in membranous nephropathy

Autoantibodies against phospholipase A2 receptor 1 (PLA2R1) and thrombospondin type 1 domain-containing 7A (THSD7A) are emerging as biomarkers to classify membranous nephropathy (MN) and to predict outcome or response to treatment. Anti-THSD7A autoantibodies are detected by Western blot and indirect immunofluorescence test (IIFT). Here, we developed a sensitive enzyme-linked immunosorbent assay (ELISA) optimized for quantitative detection of anti-THSD7A autoantibodies. Among 1012 biopsy-proven MN patients from 6 cohorts, 28 THSD7A-positive patients were identified by ELISA, indicating a prevalence of 2.8%. By screening additional patients, mostly referred because of PLA2R1-unrelated MN, we identified 21 more cases, establishing a cohort of 49 THSD7A-positive patients. Twenty-eight patients (57%) were male, and male patients were older than female patients (67 versus 49 years). Eight patients had a history of malignancy, but only 3 were diagnosed with malignancy within 2 years of MN diagnosis. We compared the results of ELISA, IIFT, Western blot, and biopsy staining, and found a significant correlation between ELISA and IIFT titers. Anti-THSD7A autoantibodies were predominantly IgG4 in all patients. Eight patients were double positive for THSD7A and PLA2R1. Levels of anti-THSD7A autoantibodies correlated with disease activity and with response to treatment. Patients with high titer at baseline had poor clinical outcome. In a subgroup of patients with serial titers, persistently elevated anti-THSD7A autoantibodies were observed in patients who did not respond to treatment or did not achieve remission. We conclude that the novel anti-THSD7A ELISA can be used to identify patients with THSD7A-associated MN and to monitor autoantibody titers during treatment.

Membranous nephropathy: A ten-year journey of discoveries

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Over the last decade important research discoveries have revealed that most "idiopathic" cases are caused by autoantibodies to podocyte antigens including phospholipase A2 receptor (PLA2R) and thrombospondin type 1 domain containing 7A (THSD7A). In this review, we will discuss the histopathology of primary MN, recent revelations regarding pathogenesis, and ancillary tests.

Receptor autoimmunity: diagnostic and therapeutic implications

Receptor autoimmunity is one of the ways in which autoimmune diseases appear in humans. Graves' disease, myasthenia gravis, idiopathic membranous nephropathy, and autoimmune acute encephalitis are the major autoimmune diseases belonging to this particular group. Receptor autoimmune disease are dependent on the presence of autoantibodies directed against cell-surface antigens, namely TSH receptor in thyrocytes, acetylcholine receptor in neuromuscular junction, phospholipase 2 receptor in podocytes, and NMDA receptor in cortical neurons. In this article we outline the distinctive features of receptor autoimmunity and the specific relationship between the autoimmunology laboratory and the presence/concentration of autoantibodies. Some immunological features distinguish receptor autoimmunity. Anti-receptor autoantibody pathologies are considered T cell-dependent, B-cell-mediated autoimmune disorders: the knowledge about the presence of circulating and/or localized autoantibodies to target organs and identification of autoantigens involved in the autoimmune reaction is of paramount importance. Due to the close correlation between the concentration of anti-receptor autoantibodies, the autoimmune target of some cell-surface receptors and the intensity of symptoms, the measurement of these immunoglobulins has become central to diagnose autoimmune diseases in all affected patients, not just in clinically dubious cases. The measurement of autoantibodies is also relevant for differential diagnosis of autoimmune and non-autoimmune forms with similar symptoms. From the methodological point of view, quantitative immunoassay methods of measurement should be preferred over semi-quantitative ones, for the capacity of the first class of methods to define precisely the reference ranges and decision levels overcoming the measurement uncertainty of semi-quantitative methods.

Anti-Phospholipase A2 Receptor (Anti-PLA2R) Antibody in Diagnosis and Treatment of Idiopathic Membranous Nephropathy: A Single-Center Observational Study in China

Background

The aim of this study was to observe the concentration of serum anti-PLA2R antibody in idiopathic membranous nephropathy (IMN) patients and analyze its relationship with clinical and laboratory parameters.

Material/Methods

We treated 72 patients with idiopathic membranous nephropathy diagnosed by renal biopsy; all these patients who presented nephrotic syndrome were enrolled for investigation, and then underwent combination therapy with prednisone and cyclosporine A for 6 months. We collected data on 24-h total proteinuria (TUpro), creatinine clearance rate (Ccr), and serum albumin (Alb) levels before and after immunosuppressive treatment. Serum anti-PLA2R antibody was measured by enzyme-linked immunosorbent assay (ELISA).

Results

Fifty-six out of 72 IMN patients presented positive serum anti-PLA2R antibody. The titer of anti-PLA2R antibody was significantly correlated with both TUpro and serum Alb levels of pre- and post-therapeutic values in IMN (P<0.05), but did not have a relationship with Ccr (P>0.05). In comparison with the anti-PLA2R antibody-negative group, there were significantly higher TUpro and lower Alb levels in the anti-PLA2R antibody-positive group (P<0.05). However, Ccr was comparatively lower in the anti-PLA2R antibody-positive group, but the difference was not statistically significant (P>0.05). There were 24 patients with negative anti-PLA2R antibody and 14 patients had complete remission in the positive anti-PLA2R antibody group, while anti-PLA2R antibody of all 14 patients became negative. Eight out of 16 patients without anti-PLA2R antibody went into complete remission.

Conclusions

Serum anti-PLA2R antibody, as determined by non-invasive technique, is a specific biomarker for diagnosis of IMN. Our results suggest that serum anti-PLA2R antibody has great potential to guide clinical diagnosis and treatment, as well as prognosis determination, in IMN patients.

Relationship between renal tissues phospholipase A2 receptor and its serum antibody and clinical condition and prognosis of idiopathic membranous nephropathy: a meta-analysis

Objective

To investigate the correlation of M-type phospholipase A2 receptor (PLA2R) expression and serum anti-PLA2R antibody with the clinical parameters and prognosis of patients with idiopathic membranous nephropathy (IMN).

Methods

A literature search for relevant original articles published between January 2009 and October 2019 was conducted on domestic and foreign databases. RevMan 5.3 software was used for meta-analysis.

Results

Eighteen studies were included in this meta-analysis. There were 1235 anti-PLA2R antibody-positive and PLA2R-positive patients, and 407 serum anti-PLA2R antibody-negative and PLA2R-negative patients. Compared with negative group, patients in the serum PLA2R antibody -positive group had lower serum albumin [SMD = -1.11, 95% CI (− 1.82, − 0.40), P < 0.00001], higher age [MD = 2.71, 95% CI (1.94, 3.48), P < 0.00001], and lower estimated glomerular filtration rate (eGFR) [MD = -10.34, 95% CI (− 12.09, − 8.60), P < 0.00001]; no significant between-group difference was observed with respect to 24-h urine protein and serum creatinine. However, no significant difference was observed between renal tissues PLA2R -positive and -negative groups with respect to serum albumin, eGFR, serum creatinine, and 24-h urine protein. Remission rate in the serum anti-PLA2R antibody -positive group was lower than that in the -negative group [OR = 0.41, 95% CI (0.28, 0.61),P < 0.00001]; however, no significant between-group difference in this respect was observed between the renal tissue PLA2R-positive and -negative groups. In the serum anti-PLA2R antibody -positive group, the higher titer subgroup had lower remission rate [OR = 0.19, 95% CI (0.07, 0.55),P = 0.002]. No significant difference was observed between anti-PLA2R antibody -positive and -negative groups with respect to adverse events. Serum anti-PLA2R antibody titer did not affect the adverse event rate.

Conclusion

As compared to PLA2R, serum anti-PLA2R antibody is more closely related with IMN disease progression.

Secretion of secretory phospholipase A2 into Spodoptera exigua larval midgut lumen and its role in lipid digestion

In insects, lipid digestion is controversial because insects have no bile salts to solubilize dietary lipids. One hypothesis is that a secretory type of phospholipase A₂ (sPLA₂ ) provides lysophospholipid (LPL) from dietary phospholipids (PLs). We identified a sPLA₂ , Se-sPLA₂ , in beet armyworm, Spodoptera exigua, that hydrolyses PLs at sn-2. Our goal was to investigate its role in lipid digestion. Se-sPLA₂ was expressed in the entire alimentary canal. Incubating the isolated midgut in a cell culture medium led to secretion of Se-sPLA₂ and other proteins. Ex vivo RNA interference (RNAi) of Se-sPLA₂ expression in isolated midgut culture led to significantly decreased Se-sPLA₂ secretion into the medium. Feeding double-stranded RNA specific to Se-sPLA₂ to larvae suppressed sPLA₂ activity in gut contents. A recombinant Se-sPLA₂ was susceptible to benzylideneacetone (BZA), a specific PLA₂ inhibitor. After feeding BZA to larvae, we recorded significant decreases in gut content sPLA₂ activity, body growth and total haemolymph lipid contents. RNAi against Se-sPLA₂ resulted in reduced digestibility. Addition of a specific LPL, 1-palmitoyl-sn-glycero-3-phosphocholine, to BZA-treated larvae rescued digestibility and larval growth. These results strongly bolster our hypothesis that Se-sPLA₂ secreted from the midgut acts in lipid digestion by providing necessary LPL to solubilize dietary neutral lipids.

Development of a Standardized Chemiluminescence Immunoassay for the Detection of Autoantibodies Against Human M-Type Phospholipase A2 Receptor in Primary Membranous Nephropathy

Introduction

Autoantibodies against the M-type phospholipase A2 receptor (PLA2R) are important markers in the diagnosis and monitoring of primary membranous nephropathy (pMN). For the detection of anti-PLA2R autoantibodies, a standardized recombinant cell-based indirect immunofluorescence assay (RC-IFA) and enzyme-linked immunosorbent assay (ELISA) are widely used, the former providing higher sensitivity but lacking a finely graduated quantification of antibody titers. In this study, we evaluated the diagnostic performance characteristics of a novel standardized chemiluminescence immunoassay (ChLIA) by comparison with the established anti-PLA2R test systems.

Methods

Sera from 155 patients with biopsy-proven pMN and 154 disease controls were analyzed for autoantibodies against PLA2R by the novel ChLIA as well as by ELISA and RC-IFA.

Results

The clinical sensitivity of the ChLIA (83.9%) was higher compared with ELISA (73.5%) and equaled that of RC-IFA (83.2%), at similar specificities (≥99.4%). Among ELISA-negative pMN samples, ChLIA and RC-IFA yielded positive results in 39.0% and 36.6%, respectively. The qualitative agreement amounted to 94.5% (ChLIA vs. ELISA) and 99.4% (ChLIA vs. RC-IFA).

Conclusion

The novel anti-PLA2R ChLIA outperforms the ELISA in detecting patients with pMN and demonstrates almost perfect agreement with RC-IFA. It thus presents a promising alternative tool for accurate anti-PLA2R testing, with the advantage of rapid turnaround times and fully automated random-access processing.

Diagnostic efficacy of serum anti-phospholipase A2 receptor antibodies for idiopathic membranous nephropathy in patients with diabetic kidney disease

AIM

Serum anti-phospholipase A2 receptor (anti-PLA2R) antibodies are highly accurate in diagnosing idiopathic membranous nephropathy (IMN) in populations with kidney disease. However, the diagnostic value of anti-PLA2R antibodies for IMN in diabetic kidney disease (DKD) is unclear. The objective of this study is to determine the diagnostic efficacy and the optimal cut-off value of this marker in populations with DKD.

METHODS

This study included 227 patients with type 2 diabetes who were admitted to the Department of Nephrology of the Chinese People's Liberation Army General Hospital from May 2016 to January 2018 and underwent pathological diagnosis by renal biopsy. Anti-PLA2R antibodies were detected by enzyme-linked immunosorbent assay in this population. According to the pathological results, the participants were divided into an IMN group and non-membranous nephropathy (non-MN) group. The clinical characteristics were analyzed, the diagnostic ability of anti-PLA2R antibodies was evaluated, and the receiver operating characteristic (ROC) curve was constructed to obtain the optimal cut-off value.

RESULTS

There were 45 patients in the IMN group, accounting for 19.8% of the study sample. The patients in this group were older at the time of renal biopsy than the non-MN group and presented a shorter duration of diabetes, better glycemic control, lower blood pressure and uric acid, and better renal function; in addition, their clinical symptoms indicated nephrotic syndrome. The optimal cut-off value for anti-PLA2R antibodies for the diagnosis of IMN in DKD was 2.71 Ru/ml, sensitivity was 0.800, specificity was 0.951, positive predictive value was 0.800, negative predictive value was 0.951, accuracy was 0.921, and the Yoden index was 0.750. The area under the ROC curve was 0.87 (95% CI, 0.788-0.952) (p < 0.001).

CONCLUSIONS

Patients in the IMN group were older, had better renal function and general condition, and the clinical symptoms indicated nephrotic syndrome. Anti-PLA2R antibodies had a good diagnostic performance for IMN in the population with DKD, and the optimal cut-off value was 2.71.

Serum Levels of BAFF and APRIL Predict Clinical Response in Anti-PLA2R-Positive Primary Membranous Nephropathy

Primary membranous nephropathy (PMN) is a renal-specific autoimmune disease caused by circulating autoantibodies that target glomerular podocyte antigens (PLA2R/THSD7A). However, very little is known on the molecular mechanisms controlling B cell response in this nephropathy. The present study was aimed at correlating the serum levels of B cell activators BAFF/BLyS and APRIL with the presence of anti-PLA2R antibodies in PMN patients and with long-term clinical outcome. To this aim, 51 patients with anti-PLA2R-positive biopsy-proven PMN and nephrotic range proteinuria (>3.5 g/24 hours) were enrolled between January 2009 and December 2015 and treated with conventional 6-month immunosuppressive therapy. After 6 months, 29 patients (56.9%) cleared circulating anti-PLA2R, while in remaining 22 (43.1%), they persisted. Intriguingly, in the first group, baseline serum levels of BAFF/BLyS and APRIL were significantly lower than those in the second one. Moreover, after 6 months of immunosuppressive therapy, an overall reduction in both cytokine serum levels was observed. However, in PMN patients with anti-PLA2R clearance, this reduction was more prominent, as compared with those with anti-PLA2R persistence. When related to clinical outcome, lower baseline BAFF/BLyS (<6.05 ng/mL) and APRIL (<4.20 ng/mL) serum levels were associated with significantly higher probability to achieve complete or partial remission after 24-month follow-up. After dividing the entire study cohort into three groups depending on both cytokine baseline serum levels, patients with both BAFF/BLyS and APRIL below the cut-off showed a significantly higher rate of complete or partial remission as compared with patients with only one cytokine above the cut-off, while the composite endpoint was achieved in a very low rate of patients with both cytokines above the cut-off. Taken together, these results provide new insights into the role of BAFF/BLyS and APRIL in both the pathogenesis of anti-PLA2R-positive PMN and the response to immunosuppressive therapy.

Comprehensive RNA-Sequencing Analysis in Peripheral Blood Cells Reveals Differential Expression Signatures with Biomarker Potential for Idiopathic Membranous Nephropathy

To date, the clinical course of idiopathic membranous nephropathy (iMN) remains unclear and lacks direct and effective diagnostic methods. To better understand the host gene expression changes involved in the iMN process and identify the potential signatures for clinical diagnosis, we performed a whole genome-wide transcriptome profile of peripheral blood cells (PBC) from patients with iMN and healthy controls (HCs). A total of 188 differentially expressed genes (DEGs) were detected in patients with iMN versus HCs. Gene ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that these DEGs were mainly correlated with protein targeting, ion homeostasis GO terms, and ribosome and phagosome pathways. The top 10 differentially expressed protein-coding genes with >2-fold changes and high expression levels were validated using quantitative real-time PCR, and showed high consistency with the high-throughput sequencing results. HLA-C, S100A8, and FTH1 genes were selected for further validation and showed the most significant difference between the iMN and HC group, indicating that they could be used as potential clinical diagnostic biomarkers. Our results provide novel potential diagnostic signatures for iMN and have important implications for better understanding the pathogenesis of iMN.

Serum anti-phospholipase A2 receptor (PLA2R) antibody detected at diagnosis as a predictor for clinical remission in patients with primary membranous nephropathy: a meta-analysis

BACKGROUND

The diagnostic value of serum M-type phospholipase A2 receptor antibody (sPLA2R-ab) expression in patients with primary membranous nephropathy (PMN) has been established. However, the association between sPLA2R-ab and clinical remission remains uncertain.

METHODS

We systematically searched the literature for clinical trials regarding the correlation between sPLA2R-ab expression and clinical remission of PMN patients. Meta-analysis was performed to determine this association. Subgroup analysis, funnel plots, and sensitivity analysis were also performed to investigate heterogeneity or bias.

RESULTS

A total of 11 trials involving 824 patients were included. Patients with positive sPLA2R-ab had a poor clinical remission rate (RR = 0.76, 95%CI 0.68-0.86, P < 0.0001; I² = 39%), a higher titer of sPLA2R-ab had a lower chance of clinical remission (RR = 0.72, 95%CI 0.59-0.87, P = 0.0006; I² = 42%),and a higher risk of renal failure (RR = 4.85, 95% CI, 1.83-12.85, P = 0.002; I² = 0%), without affecting relapse (RR = 0.97, 95% CI, 0.55-1.70; P = 0.92, I² = 0%). Subgroup analysis by treatment strategies, assay methods, ethnicity, gender, renal function, the approach of ruling out SMN, and the ratio of patients with nephrotic-range proteinuria at baseline showed no significant association between these factors with the prognostic value of sPLA2R-ab for PMN patients. No significant publication bias was found.

CONCLUSION

This meta-analysis adds to the evidence for current guidelines that sPLA2R-ab acts as not only a diagnostic marker but also a pivotal predictor for clinical remission. Therefore, sPLA2R-ab can be considered as a prognostic factor for stratifying PMN patients.

Role of phospholipase A2 receptor 1 antibody level at diagnosis for long-term renal outcome in membranous nephropathy

Background

Membranous nephropathy (MN) is an autoimmune disease induced by circulating antibodies against the podocyte protein phospholipase A₂ receptor 1 (PLA₂R1-ab) in 80% of patients and represents the leading cause of nephrotic syndrome in adults. PLA₂R1-ab levels correlate with disease activity and treatment response. However, their predictive role for long-term renal outcome is not clear.

Methods

The aim of this prospective observational multicenter study was to investigate the predictive role of PLA₂R1-ab levels at the time of diagnosis for long-term outcome in a cohort of 243 patients with newly diagnosed biopsy-proven PLA₂R1-associated MN. Statistical analyses included Cox proportional hazard models. The primary study endpoint was defined prior to data collection as doubling of serum creatinine or development of end-stage renal disease.

Results

During the median follow-up time of 48 months, 36 (15%) patients reached the study endpoint. Independent predictors for reaching the study endpoint were baseline PLA₂R1-ab levels (HR = 1.36, 95%CI 1.11–1.66, p = 0.01), percentage of tubular atrophy and interstitial fibrosis (HR = 1.32, 95%CI 1.03–1.68, p = 0.03), PLA₂R1-ab relapse during follow-up (HR = 3.22, 95%CI 1.36–7.60, p = 0.01), and relapse of proteinuria (HR = 2.60, 95%CI 1.17–5.79, p = 0.02). Fifty-four (22%) patients received no immunosuppressive treatment during the study, in 41 (76%) of them PLA₂R1-ab spontaneously disappeared during follow-up, 29 (54%) patients had a complete remission of proteinuria, and 19 (35%) had a partial remission. Patients not treated with immunosuppression were more often females and had lower PLA₂R1-ab levels, proteinuria, and serum creatinine at baseline compared to patients receiving immunosuppression. However, no conclusion on the efficacy of immunosuppressive therapies can be made, since this was not a randomized controlled study and treatment decisions were not made per-protocol.

Conclusions

PLA₂R1-ab levels are, in addition to pre-existing renal damage, predictive factors for long-term outcome and should therefore be considered when deciding the treatment of patients with MN.

High-Dose Rituximab and Early Remission in PLA2R1-Related Membranous Nephropathy

BACKGROUND AND OBJECTIVES

Different rituximab protocols are used to treat membranous nephropathy. We compared two rituximab protocols in patients with membranous nephropathy.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Twenty-eight participants from the NICE cohort received two infusions of 1-g rituximab at 2-week intervals, whereas 27 participants from the Prospective Randomized Multicentric Open Label Study to Evaluate Rituximab Treatment for Membranous Nephropathy (GEMRITUX) cohort received two infusions of 375 mg/m² at 1-week interval. We measured serum rituximab levels and compared remission at month 6 and before any treatment modification and analyzed factors associated with remission and relapses.

RESULTS

Remissions occurred in 18 (64%) versus eight (30%) from the NICE and GEMRITUX cohort (P=0.02) at month 6, respectively, and in 24 (86%) versus 18 (67%) participants (P=0.12) before treatment modification, respectively. Median time to remission was 3 [interquartile range (IQR), 3-9] and 9 [IQR, 6-12] months for NICE and GEMRITUX cohorts respectively (P=0.01). Participants from the NICE cohort had higher circulating level of rituximab and lower CD19 counts (3.3 µg/L [IQR, 0.0-10.8] versus 0.0 [IQR, 0.0-0.0] P<0.001 and 0.0 [IQR, 0.0-2.0] versus 16.5 [IQR, 2.5-31.0] P<0.001) at month 3, lower level of anti-PLA2R1 antibodies at month 6 (0.0 [IQR, 0.0-8.0] versus 8.3 [IQR, 0.0-73.5] P=0.03). In the combined study population, lower epitope spreading at diagnosis and higher rituximab levels at month 3 were associated with remissions at month 6 (13/26 (50%) versus 22/29 (76%) P=0.05 and 2.2 µg/ml [IQR, 0.0-10.9] versus 0.0 µg/ml [IQR, 0.0-0.0] P<0.001 respectively). All non-spreaders entered into remission whatever the protocol. Eight of the 41 participants who reached remission had relapses. Epitope spreading at diagnosis (8/8 (100%) versus 16/33 (48%) P=0.01) and incomplete depletion of anti-PLA2R1 antibodies at month 6 (4/8 (50%) versus 5/33 (9%) P=0.05) were associated with relapses.

CONCLUSIONS

Our work suggests that higher dose rituximab protocol is more effective on depletion of B-cells and lack of epitope spreading is associated with remission of membranous nephropathy.

Phospholipase A2 Receptor Antibody IgG4 Subclass Improves Sensitivity and Specificity in the Diagnosis of Idiopathic Membranous Nephropathy

AIMS

The aim of this study was to develop a new method for detecting anti-phospholipase A2 receptor-IgG4 to improve the sensitivity and specificity in the diagnosis of idiopathic membranous nephropathy (IMN).

METHODS

A highly sensitive quantitative assay was developed for the detection of serum anti-phospholipase A2 receptor-IgG4 with europium chelation by time-resolved fluoroimmunoassay (TRFIA), and a mouse anti-human IgG4 tracer was prepared using europium chelation for detection. The specificity and sensitivity of anti-phospholipase A2 receptor-IgG4 in the diagnosis of IMN were further assessed in patients with different kidney diseases.

RESULTS

The detection limit of anti-PLA2R-IgG4 was 0.69 ng/mL. The measurement range of anti-PLA2R-IgG4 TRFIA was 0.69-2,500 ng/mL. Mean serum anti-PLA2R-IgG4 was 21.27 ± 15.15 ng/mL in 45 healthy volunteers, 31.08 ± 18.17 ng/mL in 29 IgA nephropathy patients, 49.10 ± 34.32 ng/mL in 8 lupus nephropathy patients, and 10,324.11 ± 17,030.40 ng/mL in 30 IMN patients. The anti-PLA2R-IgG4 cutoff concentration was >161.2 ng/mL with the sensitivity of 90.0% and specificity of 100% in the diagnosis of IMN. However, the cutoff for other kidney diseases was lower than 161.2 ng/mL.

CONCLUSION

The serum anti-phospholipase A2 receptor IgG4 detected with the method developed in this study has higher sensitivity and higher specificity than total IgG in the diagnosis of IMN.

Membranous Nephropathy (MN) Recurrence After Renal Transplantation

Primary membranous nephropathy (MN) is a frequent cause of NS in adults. In native kidneys the disease may progress to ESRD in the long term, in some 40–50% of untreated patients. The identification of the pathogenic role of anti-podocyte autoantibodies and the development of new therapeutic options has achieved an amelioration in the prognosis of this disease. MN may also develop in renal allograft as a recurrent or a de novo disease. Since the de novo MN may have some different pathogenetic and morphologic features compared to recurrent MN, in the present paper we will deal only with the recurrent disease. The true incidence of the recurrent form is difficult to assess. This is mainly due to the variable graft biopsy policies in kidney transplantation, among the different transplant centers. Anti-phospholipase A2 receptor (PLA2R) autoantibodies are detected in 70–80% of patients. The knowledge of anti-PLA2R status before transplant is useful in predicting the risk of recurrence. In addition, the serial survey of the anti-PLA2R titers is important to assess the rate of disease progression and the response to treatment. Currently, there are no established guidelines for prevention and treatment of recurrent MN. Symptomatic therapy may help to reduce the signs and symptoms related to the nephrotic syndrome. Anecdotal cases of response to cyclical therapy with steroids and cyclophosphamide have been published. Promising results have been reported with rituximab in both prophylaxis and treatment of recurrence. However, these results are based on observational data, and prospective controlled trials are still missing.

Clinicopathological characteristics of thrombospondin type 1 domain-containing 7A-associated membranous nephropathy

Thrombospondin type 1 domain-containing 7A (THSD7A) is a recently identified target antigen of idiopathic membranous nephropathy (iMN). The clinicopathological characteristics of THSD7A-associated MN are poorly characterised due to low prevalence among MN patients. Among 469 consecutive cases of pathologically confirmed MN diagnosed at four centres in Japan, 14 cases were confirmed positive for THSD7A by immunohistochemistry (3.0%). The prevalence of THSD7A-associated MN tended to be higher in northern Japan. Most cases demonstrated nephrotic-range proteinuria (12/14 cases, 86%). In two patients, cancer was detected at the time of renal biopsy (small-cell carcinoma of the lung and prostatic adenocarcinoma with neuroendocrine differentiation). Both tumours were negative for THSD7A. Four patients had concurrent or previous incidence of allergic diseases, including one patient with Kimura’s disease. Pathological analysis of kidney biopsy tissue revealed slight mesangial cell proliferation in three cases and spike formation in one case. Immunofluorescence studies demonstrated that IgG subclass was mainly IgG4-dominant/codominant (12/13, 92% cases), while the case with prostatic cancer had an IgG2-dominant distribution. The immunostaining profile for components of the lectin complement pathways was not significant in three cases including two patients with malignancy. One case was dual positive for THSD7A and PLA2R. Of 10 cases with known clinical follow-up data, 6 demonstrated reduced serum creatinine and 8 presented reduced proteinuria. In summary, although the major IgG phenotype was usually IgG4-dominant/codominant, clinical background was otherwise heterogeneous. Further investigation of regional differences in THSD7A-associated MN prevalence may reveal genetic and environmental risk factor and associated pathogenic mechanisms.

[Membranous glomerulonephritis : An example of individualized medicine in nephrology]

BACKGROUND

Membranous glomerulonephritis (MGN) is the most frequent cause of a nephrotic syndrome in adults. It is an autoimmune disease caused by binding of autoantibodies to endogenous proteins expressed on glomerular podocytes. Antibody binding and activation of inflammatory mediators result in the onset of proteinuria. Recently, two endogenous podocytic target antigens in MGN have been characterized and their clinical role is a main focus of research in nephrology.

OBJECTIVE

The discovery that antibodies against phospholipase A2 receptor 1 (PLA₂R1) and thrombospondin type 1 domain containing 7A (THSD7A) mediate the pathogenesis of MGN leads to the question of what clinical role these antibodies have in patients with MGN.

MATERIAL AND METHODS

Evidence published in recent years on the role of the described antigens is analyzed and critically discussed. The clinical conclusions derived for patients with MGN are presented.

RESULTS

Antibodies against PLA₂R1 are detectable in approximately 80% of patients with MGN, while 2-3% of patients have antibodies against THSD7A. Serum analyses of antibodies and immunohistological staining in kidney biopsies enable an almost 100% certain diagnosis of PLA₂R1 and THSD7A-mediated MGN. Serum levels of PLA₂R1 antibodies are predictors for the response to therapy, determine the prognosis and allow an exact individualized monitoring of treatment. The THSD7A antibodies are associated with an increased prevalence of malignant tumors and play a pathogenetic role in the genesis of this secondary form of MGN.

CONCLUSION

The characterization of the antibodies responsible for the development of MGN is an example of precision medicine in nephrology and the foundation for the development of new, curative treatments.