Immunology of membranous nephropathy: from animal models to humans

A comparative urinary proteomic and metabolomic analysis between renal aa amyloidosis and membranous nephropathy with clinicopathologic correlations

Urinary omics has become a powerful tool for elucidating pathophysiology of glomerular diseases. However, no urinary omics analysis has been performed yet on renal AA amyloidosis. Here, we performed a comparative urine proteomic and metabolomic analysis between recently diagnosed renal AA amyloidosis (AA) and membranous nephropathy (MN) patients. Urine samples of 22 (8 AA, 8 MN and 6 healthy control) patients were analyzed with nLC-MS/MS and GC/MS for proteomic and metabolomic studies, respectively. Pathological specimens were scored for glomerulosclerosis and tubulointerstitial fibrosis grades. Functional enrichment analysis between AA and control groups showed enrichment in cell adhesion related sub-domains. Uromodulin (UMOD) was lower, whereas ribonuclease 1 (RNase1) and α-1-microglobulin/bikunin precursor (AMBP) were higher in AA compared to MN group. Correlations were demonstrated between UMOD-proteinuria (r = -0.48, p = 0.03) and AMBP-eGFR (r = -0.69, p = 0.003) variables. Metabolomic analysis showed myo-inositol and urate were higher in AA compared to MN group. A positive correlation was detected between RNase1 and urate independent of eGFR values (r = 0.63, p = 0.01). Enrichment in cell adhesion related domains suggested a possible increased urinary shear stress due to amyloid fibrils. UMOD, AMBP and myo-inositol were related with tubulointerstitial damage, whereas RNase1 and urate were believed to be related with systemic inflammation in AA amyloidosis. SIGNIFICANCE: Urinary omics studies have become a standard tool for biomarker studies. However, no urinary omics analysis has been performed yet on renal AA amyloidosis. Here, we performed a comparative urinary omics analysis between recently diagnosed renal AA amyloidosis (AA), membranous nephropathy (MN) patients and healthy controls. Pathological specimens were scored with glomerulosclerosis (G) and tubulointerstitial fibrosis (IF) grades to consolidate the results of the omics studies and correlation analyzes. Functional enrichment analysis showed enrichment in cell adhesion related sub-domains due to downregulation of cadherins; which could be related with increased urinary shear stress due to amyloid deposition and disruption of tissue micro-architecture. In comparative proteomic analyzes UMOD was lower, whereas RNase1 and AMBP were higher in AA compared to MN group. Whereas in metabolomic analyzes; myo-inositol, urate and maltose were higher in AA compared to MN group. Correlations were demonstrated between UMOD-proteinuria (r = -0.48, p = 0.03), AMBP-eGFR (r = -0.69, p = 0.003) and between RNase1-Urate independent of eGFR values (r = 0.63, p = 0.01). This study is the first comprehensive urinary omics analysis focusing on renal AA Amyloidosis to the best of our knowledge. Based on physiologic roles and clinicopathologic correlations of the molecules; UMOD, AMBP and myo-inositol were related with tubulointerstitial damage, whereas RNase1 and urate were believed to be increased with systemic inflammation and endothelial damage in AA amyloidosis.

Machine learning model to estimate probability of remission in patients with idiopathic membranous nephropathy

BACKGROUND

Idiopathic membranous nephropathy (IMN) is a type of nephrotic syndrome and the leading cause of chronic kidney disease. As far as we know, no predictive model for assessing the prognosis of IMN is currently available. This study aims to establish a nomogram to predict remission probability in patients with IMN and assists clinicians to make treatment decisions.

METHODS

A total of 266 patients with histopathology-proven IMN were included in this study. Least absolute shrinkage and selection operator regression was utilized to identify the most important variables. Subsequently, multivariate Cox regression analysis was conducted to construct a nomogram, and bootstrap resampling was employed for internal validation. Receiver operating characteristic and calibration curves and decision curve analysis (DCA) were utilized to assess the performance and clinical utility of the developed model.

RESULTS

A prognostic nomogram was established, which incorporated creatinine, glomerular_basement_membrane_thickening, gender, IgG_deposition, low-density lipoprotein cholesterol, and fibrinogen. The areas under the curves of the 3-, 12-, 24-month were 0.751, 0.725, and 0.830 in the training set, and 0.729, 0.730, and 0.948 in the validation set respectively. These results and calibration curves demonstrated the good discrimination and calibration of the nomogram in the training and validation sets. Additionally, DCA indicated that the nomogram was useful for remission prediction in clinical settings.

CONCLUSION

The nomogram was useful for clinicians to evaluate the prognosis of patients with IMN in early stage.

Large B-cell Lymphoma-Associated Membranous Nephropathy With Positive PLA2R on Kidney Biopsy

Large B-cell lymphoma associated with membranous nephropathy (MN) is a rare and complex medical condition that involves the simultaneous presence of two distinct diseases: a malignant lymphoma and a kidney disorder called membranous nephropathy. In this case, there is an additional element of interest, which is the presence of positive Phospholipase A2 Receptor (PLA2R) in the kidney. The case involves a 53-year-old Caucasian male with a three-week history of lower leg edema and a past medical history of recurrent upper respiratory infections. The upper respiratory infections were characterized by symptoms of fever, sore throat, and headache, and they required multiple rounds of antibiotics for treatment, including Augmentin and Keflex. A diagnosis of nephrotic syndrome was made based on proteinuria of fourteen grams with no RBC cast on urinalysis. Kidney biopsy stained positive for antiposophlipase A2 receptor on a frozen section. Thrombospondin type 1 domain-containing 7A (THSD7A) was not detected.  Given his biopsy and absence of clinical symptoms, he was treated as a case of primary membranous nephropathy with angiotensin-converting enzyme (ACE) inhibitors, steroids, and immunosuppressive. Three months following the treatment, his condition deteriorated, and after a thorough investigation, he appeared to have large B-cell lymphoma as a secondary cause of membranous glomerulopathy (MGN). When large B-cell lymphoma is associated with membranous nephropathy, it presents a unique clinical challenge. The interaction between these two conditions is not fully understood, but it is believed that the lymphoma may provoke an immune response that leads to the development of membranous nephropathy. Moreover, the presence of positive PLA2R in the kidney indicates a specific mechanism at play in this complex disease scenario. Treatment for this condition typically involves addressing both the lymphoma and the kidney disorder. This may include chemotherapy or other treatments to target the lymphoma and immunosuppressive therapy to manage the autoimmune response causing membranous nephropathy. Close monitoring and coordination between oncologists and nephrologists are essential for the best possible outcome in managing this rare and challenging condition.

Physiological Replication of the Human Glomerulus Using a Triple Culture Microphysiological System

The function of the glomerulus depends on the complex cell-cell/matrix interactions and replication of this in vitro would aid biological understanding in both health and disease. Previous models do not fully reflect all cell types and interactions present as they overlook mesangial cells within their 3D matrix. Herein, the development of a microphysiological system that contains all resident renal cell types in an anatomically relevant manner is presented. A detailed transcriptomic analysis of the contributing biology of each cell type, as well as functionally appropriate albumin retention in the system, is demonstrated. The important role of mesangial cells is shown in promoting the health and maturity of the other cell types. Additionally, a comparison of the incremental advances that each individual cell type brings to the phenotype of the others demonstrates that glomerular cells in simple 2D culture exhibit a state more reflective of the dysfunction observed in human disease than previously recognized. This in vitro model will expand the capability to investigate glomerular biology in a more translatable manner by the inclusion of the important mesangial cell compartment.

A nomogram prediction model for treatment failure in primary membranous nephropathy

BACKGROUND

Primary membranous nephropathy (PMN) has a heterogeneous natural course. Immunosuppressive therapy is recommended for PMN patients at moderate or high risk of renal function deterioration. Prediction models for the treatment failure of PMN have rarely been reported.

METHODS

This study retrospectively studied patients diagnosed as PMN by renal biopsy at Sichuan Provincial People's Hospital from January 2017 to December 2020. Information on clinical characteristics, laboratory test results, pathological examination, and treatment was collected. The outcome was treatment failure, defined as the lack of complete or partial remission at the end of 12 months. Simple logistic regression was used to identify candidate predictive variables. Forced-entry stepwise multivariable logistic regression was used to develop the prediction model, and performance was evaluated using C-statistic, calibration plot, and decision curve analysis. Internal validation was performed by bootstrapping.

RESULTS

In total, 310 patients were recruited for this study. 116 patients achieved the outcome. Forced-entry stepwise multivariable logistic regression indicated that PLA2Rab titer (OR = 1.002, 95% CI: 1.001-1.004, p = 0.003), inflammatory cells infiltration (OR = 2.753, 95% CI: 1.468-5.370, p = 0.002) and C3 deposition on immunofluorescence (OR = 0.217, 95% CI: 0.041-0.964, p = 0.049) were the three independent risk factors for treatment failure of PMN. The final prediction model had a C-statistic (95% CI) of 0.653 (0.590-0.717) and a net benefit of 23%-77%.

CONCLUSIONS

PLA2R antibody, renal interstitial inflammation infiltration, and C3 deposition on immunofluorescence were the three independent risk factors for treatment failure in PMN. Our prediction model might help identify patients at risk of treatment failure; however, the performance awaits improvement.

Ferroptosis is involved in passive Heymann nephritis in rats

Ferroptosis is found to be involved in some experimental models of kidney diseases, but its role in membrane nephropathy (MN) is still unclear. The purpose of this study is to explore whether ferroptosis occurred in MN, and the role of ferritinophagy. In this study, passive Heymann nephritis (PHN) rats were induced by single tail vein injection of anti-Fx1A serum, and normal rats were used as control. The changes of 24 h urinary protein, serum biochemical parameters, renal pathological damage, iron content, lipid peroxidation parameters, ferroptosis markers, and ferritinophagy markers were evaluated in the two groups. Compared with the control group, PHN rats showed obvious proteinuria, hypoproteinemia, and hyperlipidemia. Besides, more severe renal pathological damage and higher Fe2+ levels were observed in PHN rats, and the levels of malondialdehyde (MDA) increased significantly, while the levels of superoxide Dismutase (SOD) and glutathione (GSH) decreased. In addition, the expression of glutathione peroxidase 4 (GPX4) in renal tissues of PHN rats decreased significantly, while the expression of transferrin receptor (TFR) and acyl-CoA synthetase long-chain family member 4 (ACSL4) increased. The expression of microtubule associated protein 1 light chain 3 (LC3) II/LC3I and nuclear receptor coactivator 4 (NCOA4) increased significantly. Therefore, our study shows that ferroptosis is involved in the pathological damage of MN, and companied by activation of ferritinophagy.

The cutoff value and prognosis of anti-PLA2R antibody for idiopathic membranous nephropathy: a single-center retrospective study in China

Serum anti-phospholipase A2 receptor (anti-PLA2R) antibody is used for the noninvasive diagnosis of idiopathic membranous nephropathy (IMN). However, the cutoff value of anti-PLA2R antibodies in IMN patients is debatable. This study aimed to investigate the cutoff value of anti-PLA2R antibodies for diagnosing IMN and the correlation of anti-PLA2R antibodies with clinical parameters and prognosis. A total of 252 IMN patients and 521 non-IMN patients with both renal biopsy and serum anti-PLA2R antibody data from April 2017 to November 2019 were enrolled. Anti-PLA2R antibody was detected by an enzyme-linked immunosorbent assay. The anti-PLA2R antibody titer was higher in the IMN group than in the non-IMN group (153.1 ± 22.4 vs. 2.0 ± 0.2 RU/mL, p < 0.001). The optimal anti-PLA2R antibody cutoff value for diagnosing IMN was 2.5 RU/mL, with a sensitivity, specificity, and Youden index of 85.7%, 88.3%, and 0.740, respectively. There was a significant positive correlation between anti-PLA2R antibody and 24-h urinary protein levels (r = 0.341, p < 0.001), and a significant negative correlation between anti-PLA2R antibody and serum albumin levels (r=-0.274, p < 0.001) in patients with IMN. The remission rates positively correlated with the immunosuppressive usage rates and increased from the low- to the high-titer subgroup. Multivariable Cox regression analysis showed that immunosuppressive therapy (adjusted HR = 4.656; 95% confidence interval [CI], 1.461-14.839; p = 0.009) was associated with a higher remission rate in patients with IMN. The optimal Anti-PLA2R antibody cutoff value for diagnosing IMN was 2.5 RU/mL, which was much lower than that indicated by the manufacturer. If IMN is actively treated, patients can have much better prognoses.Trial registration: retrospectively registered.

Myostatin silencing inhibits podocyte apoptosis in membranous nephropathy through Smad3/PKA/NOX4 signaling pathway

This article focuses on deciphering the effect of myostatin (MSTN) on podocyte apoptosis in membranous nephropathy (MN) and fathoming out its underlying mechanism. Rats received the intravenous injection of cationized-bovine serum albumin to induce MN in vivo, while angiotensin II (Ang II) was exposed to AB8/13 cells to induce MN model in vitro. The mRNA expression of MSTN was detected by qRT-PCR. The effects of MSTN silencing on MN model rats and cells were assessed by cell counting kit-8 assay, flow cytometry, hematoxylin and eosin staining, and TUNEL assay. The expressions of proteins related to apoptosis and Smad3/protein kinase A (PKA)/NADPH oxidase 4 (NOX4) signaling pathway were examined by western blot. As a result, MSTN was highly expressed in MN cell and rat models. Besides, knockdown of MSTN elevated the MN cell viability and dwindled apoptosis rate, as well as attenuated kidney injury in MN rats. Meanwhile, MSTN silencing lessened the expressions of phosphorylated (p)-Smad3 and Nox4, while boosting the p-PKA expression in MN rats and cells. Additionally, Smad3 overexpression reversed the above effects of MSTN silencing on Ang II-induced podocytes. In conclusion, MSTN knockdown restrains the podocyte apoptosis through regulating Smad3/PKA/NOX4 signaling pathway.

Computer-aided diagnosis of primary membranous nephropathy using expert system

BACKGROUND

The diagnosis of primary membranous nephropathy (PMN) often depends on invasive renal biopsy, and the diagnosis based on clinical manifestations and target antigens may not be completely reliable as it could be affected by uncertain factors. Moreover, different experts could even have different diagnosis results due to their different experiences, which could further impact the reliability of the diagnosis. Therefore, how to properly integrate the knowledge of different experts to provide more reliable and comprehensive PMN diagnosis has become an urgent issue.

METHODS

This paper develops a belief rule-based system for PMN diagnosis. The belief rule base is constructed based on the knowledge of the experts, with 9 biochemical indicators selected as the input variables. The belief rule-based system is developed of three layers: (1) input layer; (2) belief rule base layer; and (3) output layer, where 9 biochemical indicators are selected as the input variables and the diagnosis result is provided as the conclusion. The belief rule base layer is constructed based on the knowledge of the experts. The final validation was held with gold pattern clinical cases, i.e., with known and clinically confirmed diagnoses.

RESULTS

134 patients are used in this study, and the proposed method is defined by its sensitivity, specificity, accuracy and area under curve (AUC), which are 98.0%, 96.9%, 97.8% and 0.93, respectively. The results of this study present a novel and effective way for PMN diagnosis without the requirement of renal biopsy.

CONCLUSIONS

Through analysis of the diagnosis results and comparisons with other methods, it can be concluded that the developed system could help diagnose PMN based on biochemical indicators with relatively high accuracy.

Lectin Complement Pathway Activation is Associated with Massive Proteinuria in PLA2R-Positive Membranous Nephropathy: A Retrospective Study

Introduction

Complement activation is highly involved in membranous nephropathy. Identifying the mechanism of the complement activation pathway carries crucial therapeutic implications yet remains controversial. This study explored lectin complement pathway activation in PLA2R-associated membranous nephropathy (MN).

Methods

One hundred and seventy-six patients with biopsy-proven PLA2R-associated MN were enrolled in the retrospective study and divided into the remission group (24-hour urine protein <0.75g and serum albumin >35 g/L) and the nephrotic syndrome group. The clinical manifestation and C3, C4d, C1q, MBL, and B factor in renal biopsy tissues and C3, C4, and immunoglobulins in serum were evaluated.

Results

Deposition of glomerular C3, C4d, and mannose-binding lectin (MBL) was significantly higher in the activated state than in the remission state in PLA2R-associated MN. MBL deposition was the risk factor for no remission. During follow-up, the persistent non-remission patients have significantly lower serum C3 levels.

Conclusion

Activation of the lectin complement pathway in PLA2R-associated MN may contribute to proteinuria progression and disease activity.

Idiopathic membranous nephropathy with renal amyloidosis: A case report

Background

Immunoglobulin light chain amyloidosis is a clonal, non-proliferative plasma cell disorder, in which fragments of immunoglobulin light chain are deposited in tissues. Clinical features depend on organs involved but can include restrictive cardiomyopathy, nephrotic syndrome, hepatic failure, peripheral/autonomic neuropathy, and atypical multiple myeloma. Membranous nephropathy (MN) is a group of diseases characterized by deposition of immune complexes under the epithelial cells of glomerular basement and diffuse thickening of the basement membrane. Most patients with idiopathic MN (IMN) have been exposed to phospholipase A2 receptor (PLA2R) antigen, and anti-PLA2R antibodies that attack podocytes can be detected in their blood. IMN combined with amyloidosis nephropathy without secondary factors is rare. The present study describes a patient with IMN combined with immunoglobulin light chain amyloidosis nephropathy.

Case report

A 39-year-old man was admitted to our hospital because of weight loss and edema. His clinical manifestation was nephrotic syndrome. Renal pathology revealed MN. A positive Congo red staining and the pathognomonic apple-green birefringence under cross-polarized light were considered to be associated with amyloid nephropathy. Immunofluorescence showed that λ light chain was positive. Heavy chain deposition disease and amyloid-associated protein amyloidosis were excluded by immunofluorescence and immunohistochemistry, respectively. Subsequent examinations showed that his serum was negative for antibodies against the PLA2R, but PLA2R was present in renal tissue. The final diagnosis was IMN with light chain amyloid nephropathy.

Conclusion

Renal amyloidosis accompanied by IMN is uncommon. Attention should be paid to the subtype of the disease and the exclusion of secondary factors. Perfect clinical and pathological examination are helpful for the classification and staging of the disease. Congo red staining, light microscopy, immunofluorescence, immunohistochemistry, electron microscopic examination, pathological tissue staining for PLA2R antigen and testing for anti-PLA2R antibody in serum are helpful.

Membranous nephropathy: Systems biology-based novel mechanism and traditional Chinese medicine therapy

Membranous nephropathy (MN) is a renal-limited non-inflammatory autoimmune disease in the glomerulus, which is the second or third main cause of end-stage kidney diseases in patients with primary glomerulonephritis. Substantial achievements have increased our understanding of the aetiology and pathogenesis of murine and human MN. The identification of nephritogenic autoantibodies against neutral endopeptidase, phospholipase A₂ receptor (PLA₂R) and thrombospondin type-1 domain-containing 7A (THSD7A) antigens provide more specific concept-driven intervention strategies for treatments by specific B cell-targeting monoclonal antibodies to inhibit antibody production and antibody-antigen immune complex deposition. Furthermore, additional antibody specificities for antigens have been discovered, but their pathogenic effects are uncertain. Although anti-PLA₂R and anti-THSD7A antibodies as a diagnostic marker is widely used in MN patients, many questions including autoimmune response development, antigenic epitopes, and podocyte damage signalling pathways remain unresolved. This review describes the current available evidence regarding both established and novel molecular mechanisms based on systems biology approaches (gut microbiota, long non-coding RNAs, metabolite biomarkers and DNA methylation) in MN, with an emphasis on clinical findings. This review further summarizes the applications of traditional Chinese medicines such as Tripterygium wilfordii and Astragalus membranaceus for MN treatment. Lastly, this review considers how the identification of novel antibodies/antigens and unresolved questions and future challenges reveal the pathogenesis of MN.

Analysis of glomerular PLA2R efficacy in evaluating the prognosis of idiopathic membranous nephropathy in the background of different serum anti-PLA2R levels

OBJECTIVE

To verify glomerular PLA2R antigen and serum PLA2R antibody expression in membranous nephropathy as well as to explore glomerular PLA2R efficacy in evaluating the prognosis of idiopathic membranous nephropathy (IMN) in the background of different serum anti-PLA2R levels.

METHODS

We retrospectively analyzed 155 patients who were diagnosed with IMN by kidney biopsy. Patients were divided into six groups according to their serum PLA2R antibody or glomerular PLA2R antigen positiveness and the level of serum anti-PLA2R titer. Both clinical features and pathological characteristics were recorded, and the remission time was compared among groups. Correlation between clinical figures and the anti-PLA2R titer or semi-quantity of glomerular PLA2R antigen was detected.

RESULTS

A positive correlation between time to partial remission and serum anti-PLA2R titer was found. Among patients with serum anti-PLA2R titer <150 RU/ml, there were shorter remission time in negative glomerular PLA2R antigen group compared with positive glomerular PLA2R antigen, and a positive correlation between time to complete remission and semi-quantity of glomerular PLA2R antigen was found.

CONCLUSION

Both glomerular PLA2R antigen and serum anti-PLA2R play a role in disease presentation and prognosis in primary membranous nephropathy. Glomerular PLA2R antigen has a major role on disease prognosis when serum anti-PLA2R titer is less than 150RU/ml, while serum anti-PLA2R has predominant role in IMN prognosis when serum anti-PLA2R titer is above 150RU/ml.

Definition of IgG Subclass-Specific Glycopatterns in Idiopathic Membranous Nephropathy: Aberrant IgG Glycoforms in Blood

The podocyte injury, and consequent proteinuria, that characterize the pathology of idiopathic membranous nephropathy (IMN) is mediated by an autoimmune reaction against podocyte antigens. In particular, the activation of pathways leading to abundant renal deposits of complement is likely to involve the binding of mannose-binding lectin (MBL) to aberrant glycans on immunoglobulins. To obtain a landscape of circulatory IgG Fc glycosylation characterizing this disease, we conducted a systematic N-glycan profiling study of IgG1, 2, and 4 by mass spectrometry. The cohort included 57 IMN patients, a pathological control group with nephrotic syndrome (PN) (n = 20), and 88 healthy control subjects. The effect of sex and age was assessed in all groups and controlled by rigorous matching. Several IgG Fc glycan traits were found to be associated with IMN. Interestingly, among them, only IgG4-related results were specific for IMN and not for PN. Hypo-galactosylation of IgG4, already shown for IMN, was observed to occur in the absence of core fucose, in line with a probable increase of pro-inflammatory IgG. In addition, elevated levels of fucosylated IgG4, along with low levels of hybrid-type glycans, were detected. Some of these IgG4 alterations are likely to be more pronounced in high PLA2R (phospholipase A2 receptor) patients. IgG Fc glycosylation patterns associated with IMN warrant further studies of their role in disease mechanisms and may eventually enrich the diagnostic spectrum regarding patient stratification.

Association Between Urinary Protein-to-Creatinine Ratio and Chronic Kidney Disease Progression: A Secondary Analysis of a Prospective Cohort Study

Objective

Studies on the association between urinary protein-to-creatinine ratio (UPCR) and chronic kidney disease (CKD) progression are limited. This study aimed to investigate the relationship between UPCR and CKD progression in a Japanese population.

Methods

The present research was a secondary analysis of a prospective cohort study. Eight hundred and ninety-six subjects from the research of CKD-ROUTE in Japan were included. All the patients were new visitors or first referred to the participating centers of nephrology between October 2010 and December 2011. The target-independent variable was UPCR measured at baseline. The dependent variable was CKD progression and the estimated glomerular filtration rate (eGFR) changes during follow-up. We used Cox proportional hazards regression to investigate the association between UPCR and CKD progression risk. To address UPCR and CKD progression's non-linearity, a multivariate Cox proportional hazards regression analysis with cubic spline functions model and smooth curve fitting (penalized spline method) were conducted. We further used a generalized linear mixed model to explore the relationship between UPCR and the changes of eGFR.

Result

The mean age of the included patients was 67.2 ± 13.4 years old. Two hundred and thirty-four people occurred CKD progression during follow-up. The present study showed that UPCR was independently associated with CKD progression in the multivariate analysis [HR = 1.164, 95% CI (1.116, 1.215)]. The non-linear relationship between UPCR and CKD progression was explored in a dose-dependent manner, with an obvious inflection point of 1.699. Furthermore, our findings indicated that the tendency of the effect sizes on both the left and right sides of the inflection point was not consistent [left HR: 4.377, 95% CI (2.956, 6.483); right HR: 1.100, 95% CI (1.049–1.153)]. Using the linear mixed-effects regression model, we found that UPCR was an independent predictor of the longitudinal changes in eGFR (p < 0.001 for the interaction term with time).

Conclusion

This study demonstrates a nonlinear positive relationship between UPCR and CKD progression in the Japanese population. UPCR is also an independent predictor of the longitudinal changes in eGFR.

Association of serum mannose-binding lectin, anti-phospholipase A2 receptor antibody and renal outcomes in idiopathic membranous nephropathy and atypical membranous nephropathy: a single center retrospective cohort study

Objectives

Idiopathic membranous nephropathy (iMN) is a major cause of nephrotic syndrome. Atypical membranous nephropathy (aMN) is a new type of nephropathy in China, characterized by a ‘full-house’ on immunofluorescent examination, that is IgG, IgA, IgM, C3, C1q positive, but without clinical evidence of a secondary cause. Phospholipase A2 receptor (PLA2R) was the major target antigens in iMN patients. Activation of the mannose-binding lectin (MBL) pathway plays a vital role in the development of MN. Our objective was to investigate the role of PLA2R and MBL in the pathogenesis of iMN and aMN.

Methods

We conducted a retrospective observational study using propensity score matching by age, gender, and eGFR. All clinical, laboratory data, and follow-up data of the patients were collected. Serum levels of anti-PLA2R antibodies and MBL were tested.

Results

Finally, 30 iMN patients and 30 aMN patients were included, and 20 healthy controls were retrospectively collected in this study. The 24 h proteinuria level was higher and serum albumin was lower in anti-PLA2R (+) patients than in anti-PLA2R (−) patients in both iMN and aMN groups. In aMN patients, MBL levels were significantly higher in anti-PLA2R (+) patients than in anti-PLA2R (−) patients (p = .045). The serum level of anti-PLA2R positively correlated with no-remission in both iMN and aMN groups.

Conclusions

The complement lectin pathway has an association with the development of MN, especially in patients with positive anti-PLA2R antibodies. Serum MBL cannot differentiate between the two diseases. Serum MBL levels are not associated with clinical manifestations, nor with prognosis.

Nell1 as Target Antigen for Mercury Related Membranous Nephropathy: A Case Report

Membranous nephropathy constitutes 30% of adult nephrotic syndrome. Of all cases of membranous nephropathy, primary membranous nephropathy is commonest. Mercury is known to be a cause of secondary membranous nephropathy. There is no human data on the pathophysiology of mercury-related membranous nephropathy, but animal studies suggested an autoimmune mechanism behind it. There is no data to the best of our knowledge about target antigen for mercury-related membranous nephropathy. We are reporting a case of NELL-1 positive mercury-related membranous nephropathy that started resolving after stopping siddha medication and taking antiproteinuric. There was also concomitant euthyroid lymphocytic thyroiditis with anti-TPO positive, which started after exposure to siddha medication, which suggests systemic autoimmune phenomenon due to mercury exposure.

Acute chest pain and dyspnoea as clinical presentation of primary membranous nephropathy. A case report and literature review

Membranous nephropathy (MN) is the commonest cause of nephrotic syndrome (NS) in adult male patients worldwide. Most of the cases (80%) are idiopathic (primary MN, PMN), whereas about 20% are associated with autoimmune diseases, malignancies or exposures (secondary MN). PMN is a kidney-specific autoimmune glomerular disease mediated by antibodies to the M-type phospholipase A2 receptor (anti-PLA2R) (85%), thrombospondin type 1 domain containing 7A (THSD7A) (3-5%), or by other still unidentified mechanisms (10%). Most of the patients with PMN present with NS (80%). Clinical course of PMN is characterised by spontaneous remissions (40%) and relapses (15-30%). One third develop end-stage renal disease (ESRD) within 5 to 15 years from the onset. Anti-PLA2R/THSD7A antibodies levels correlate with proteinuria, clinical course, and outcomes. The treatment still remains matter of debate. Hypertension, proteinuria, and hyperlipidaemia must be treated in all patients. Immunosuppressive therapy is indicated in patients with elevated anti-PLA2R/THSD7A levels and proteinuria >3.5 g/d at diagnosis. With proper management, only 10% or less will develop ESRD over the subsequent 10 years. Here we report a case of a 34-year-old male patient with a ten-year history of asymptomatic PMN, treated with ACE-inhibitors, who presented to our emergency room for acute chest pain and exertional dyspnoea due to ESRD that required urgent dialysis. (www.actabiomedica.it).

Sanqi Oral Solution Mitigates Proteinuria in Rat Passive Heymann Nephritis and Blocks Podocyte Apoptosis via Nrf2/HO-1 Pathway

Idiopathic membranous nephropathy (IMN) is the most common pathological type in adult nephrotic syndrome where podocyte apoptosis was found to mediate the development of proteinuria. Sanqi oral solution (SQ), an effective Chinese herbal preparation clinically used in treatment of IMN for decades, plays an important role in reducing proteinuria, but the underlying mechanisms have not been fully elucidated yet. The current study tested the hypothesis that SQ directly lessens proteinuria in IMN by reducing podocyte apoptosis. To investigate the effects of SQ, we established the experimental passive Heymann nephritis (PHN) rat model induced by anti-Fx1A antiserum in vivo and doxorubicin hydrochloride (ADR)-injured apoptotic podocyte model in vitro. SQ intervention dramatically reduced the level of proteinuria, together with the rat anti-rabbit IgG antibodies, complement C3, and C5b-9 deposition in glomerulus of PHN rats, accompanied by an elevation of serum albumin. Protein expression of synaptopodin, marker of podocyte injury, restored after SQ administration, whereas the electron microscopic analysis indicated that fusion of foot processes, and the pachynsis of glomerular basement membrane was markedly diminished. Further studies showed that SQ treatment could significantly inhibit podocyte apoptosis in PHN rats and ADR-injured podocytes, and protein levels of Cleaved Caspase-3 or the ratio of Bax/Bcl-2 were significantly decreased with SQ treatment in vivo or in vitro. Moreover, we found that the nuclear factor erythroid 2–related factor-2/heme oxygenase 1 (Nrf2/HO-1) pathway mediated the anti-apoptosis effective of SQ in podocyte. Thus, SQ mitigates podocyte apoptosis and proteinuria in PHN rats via the Nrf2/HO-1 pathway.

How Times Have Changed! A Cornucopia of Antigens for Membranous Nephropathy

The identification of the major target antigen phospholipase A2 receptor (PLA2R) in the majority of primary (idiopathic) cases of membranous nephropathy (MN) has been followed by the rapid identification of numerous minor antigens that appear to define phenotypically distinct forms of disease. This article serves to review all the known antigens that have been shown to localize to subepithelial deposits in MN, as well as the distinctive characteristics associated with each subtype of MN. We will also shed light on the novel proteomic approaches that have allowed identification of the most recent antigens. The paradigm of an antigen normally expressed on the podocyte cell surface leading to in-situ immune complex formation, complement activation, and subsequent podocyte injury will be discussed and challenged in light of the current repertoire of multiple MN antigens. Since disease phenotypes associated with each individual target antigens can often blur the distinction between primary and secondary disease, we encourage the use of antigen-based classification of membranous nephropathy.

Advances in antigens associated with Idiopathic Membranous Nephropathy

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Idiopathic MN (IMN), one of the forms of MN, usually has an unknown etiology. IMN is described as an autoimmune disease, and its pathogenesis is quite complex. The discovery of the M-type phospholipase A₂ receptor (PLA₂R) plays an important role in promoting our understanding of IMN, although the exact mechanisms of its occurrence and development are still not completely clear. Other target antigens have been discovered one after another, as considerable progress has been made in the molecular pathomechanisms of IMN. Here, we review the findings about the target antigens associated with IMN in recent years. It is hoped that this article can provide researchers with some scientific issues or innovative ideas for future studies of IMN, which will provide clinicians with more knowledge about further improving their abilities to provide better medical care for IMN patients.

Mechanisms of Primary Membranous Nephropathy

Membranous nephropathy (MN) is an autoimmune disease of the kidney glomerulus and one of the leading causes of nephrotic syndrome. The disease exhibits heterogenous outcomes with approximately 30% of cases progressing to end-stage renal disease. The clinical management of MN has steadily advanced owing to the identification of autoantibodies to the phospholipase A2 receptor (PLA2R) in 2009 and thrombospondin domain-containing 7A (THSD7A) in 2014 on the podocyte surface. Approximately 50–80% and 3–5% of primary MN (PMN) cases are associated with either anti-PLA2R or anti-THSD7A antibodies, respectively. The presence of these autoantibodies is used for MN diagnosis; antibody levels correlate with disease severity and possess significant biomarker values in monitoring disease progression and treatment response. Importantly, both autoantibodies are causative to MN. Additionally, evidence is emerging that NELL-1 is associated with 5–10% of PMN cases that are PLA2R- and THSD7A-negative, which moves us one step closer to mapping out the full spectrum of PMN antigens. Recent developments suggest exostosin 1 (EXT1), EXT2, NELL-1, and contactin 1 (CNTN1) are associated with MN. Genetic factors and other mechanisms are in place to regulate these factors and may contribute to MN pathogenesis. This review will discuss recent developments over the past 5 years.

Neonatal Fc receptor in human immunity: Function and role in therapeutic intervention

The humoral immune response provides specific, long-lived protection against invading pathogens, via immunoglobulin production and other memory functions. IgG, the most abundant immunoglobulin isotype, has the longest half-life and protects against bacterial and viral infections. The neonatal Fc receptor (FcRn) transports IgG across barriers, for example, the placenta, enhancing fetal humoral immunity to levels similar to their mothers'. Importantly, FcRn, by protecting IgG from intracellular degradation, results in an approximately 21-day circulating IgG half-life and high plasma levels; similarly, FcRn recycles albumin and is the portal of entry for enteric cytopathic human orphan (echo) virus infection. Dysregulated immune responses may lead to antibodies against self-antigens (autoantibodies), resulting in organ-specific or systemic autoimmune diseases. Autoantibody-mediated diseases have been treated by nonspecific immunoglobulin-lowering/modulating therapies, including immunoadsorption, plasma exchange, and high-dose intravenous immunoglobulin. However, targeting FcRn with specific inhibitors results in reduction in only IgG levels. The effectiveness of FcRn inhibitors in autoimmune diseases, including myasthenia gravis and immune thrombocytopenia, provides further evidence that IgG is a primary driver in these autoantibody-mediated diseases. We describe the role of FcRn in human biology, including insights that clinical testing of FcRn inhibitors have provided into FcRn biology and autoimmune disease mechanisms, allowing fact-based speculation on their therapeutic potential.

The Potential Role of Regulatory B Cells in Idiopathic Membranous Nephropathy

Regulatory B cells (Breg) are widely regarded as immunomodulatory cells which play an immunosuppressive role. Breg inhibits pathological autoimmune response by secreting interleukin-10 (IL-10), transforming growth factor-β (TGF-β), and adenosine and through other ways to prevent T cells and other immune cells from expanding. Recent studies have shown that different inflammatory environments induce different types of Breg cells, and these different Breg cells have different functions. For example, Br1 cells can secrete IgG4 to block autoantigens. Idiopathic membranous nephropathy (IMN) is an autoimmune disease in which the humoral immune response is dominant and the cellular immune response is impaired. However, only a handful of studies have been done on the role of Bregs in this regard. In this review, we provide a brief overview of the types and functions of Breg found in human body, as well as the abnormal pathological and immunological phenomena in IMN, and propose the hypothesis that Breg is activated in IMN patients and the proportion of Br1 can be increased. Our review aims at highlighting the correlation between Breg and IMN and proposes potential mechanisms, which can provide a new direction for the discovery of the pathogenesis of IMN, thus providing a new strategy for the prevention and early treatment of IMN.

Clusterin Deficiency Predisposes C57BL/6j Mice to Cationic Bovine Serum Albumin-Induced Glomerular Inflammation

Background

Membranous nephropathy (MN) is a specific entity of glomerulonephritis, and its glomerular inflammation is characterized by the deposition of immune complexes in the glomerular basement membrane and proteinuria. However, the molecular mechanisms underlying the glomerular inflammation of MN are not fully understood. This study was designed to investigate the role of clusterin (CLU) in the development of MN using a mouse model of cationic bovine serum albumin (cBSA)-induced MN.

Methods

Both wild-type C57BL/6j (WT) and CLU-knockout C57BL/6j (CLU-KO) mice were immunized with cBSA. The kidney function was determined by the levels of serum creatinine (SCr), blood urea nitrogen (BUN) and urinary protein. MN and glomerular deposits of CLU, complement C3 and immunoglobulins (Igs) were determined by histological analyses. Serum proteins were analyzed by the enzyme-linked immunosorbent assay, Western blot and liquid chromatography-mass spectrometry.

Results

Here, we showed that after cBSA immunization, SCr and proteinuria were increased in CLU-KO mice but not in WT mice. Similarly, severe glomerular atrophy and mesangial expansion along with C3 deposit were only found in the kidneys of CLU-KO mice but not in WT mice. However, there were no differences of serum IgG and complement 3 levels between CLU-KO and WT mice. In the serum of WT mice, CLU bound to anti-cBSA IgG, complements (eg, C8), proteinase/protease inhibitors and antioxidative proteins to form a complex, and incubation with WT serum reduced the complement-dependent lysis of podocytes in cultures.

Conclusion

Our data suggest that a CLU deficiency induces cBSA-initiated glomerular inflammation of MN in a disease-resistant strain of mice, suggesting an anti-glomerular inflammatory function of CLU in the resistance to MN development. This function may be at least in part due to the formation of CLU-anti-cBSA Igs complex that prevents glomerular inflammation or injury in the disease-resistant mice.

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.

Myeloid-Derived Suppressor Cells Promote the Progression of Primary Membranous Nephropathy by Enhancing Th17 Response

Several studies have confirmed that the myeloid-derived suppressor cells (MDSCs) are closely associated with autoimmune diseases, but their exact role in these processes remains largely unclear. Here, we investigated the role MDSCs in patients with primary membranous nephropathy (PMN). Compared to healthy controls (HCs), PMN patients showed significantly increased number of HLA-DR^-CD11b⁺CD33⁺ MDSCs in the peripheral blood, including both CD14⁺CD66b^- monocytic and CD14^-CD66b⁺ granulocytic MDSCs. The frequency of MDSCs was positively correlated with the level of serum anti-phospholipase A2 receptor (anti-PLA2R), 24-h urine protein quantification, and disease activity in PMN patients. Consistently, enhanced T helper 2 (Th2) and T helper 17 (Th17) immune responses were positively associated with plasma anti-PLA2R levels, 24-h urine protein quantification, and the disease activity in PMN patients. Moreover, compared to HCs, MDSCs from PMN patients exhibited significantly elevated arginase-1 (ARG-1) production and increased potential to promote Th17 differentiation in vitro in an ARG-1-dependent manner. This study directly demonstrates a pathogenic role for MDSCs in human PMN and provides a molecular mechanism for the pathogenesis of PMN. Our data show that MDSCs may promote PMN disease progression mainly by enhancing Th17 response. Therefore, MDSCs may be an important diagnostic, therapeutic, and prognostic marker for PMN diseases.

Urinary ERdj3 and mesencephalic astrocyte-derived neutrophic factor identify endoplasmic reticulum stress in glomerular disease

Podocyte injury and endoplasmic reticulum (ER) stress have been implicated in the pathogenesis of various glomerular diseases. ERdj3 (DNAJB11) and mesencephalic astrocyte-derived neurotrophic factor (MANF) are ER chaperones lacking the KDEL motif, and may be secreted extracellularly. Since podocytes reside in the urinary space, we examined if podocyte injury is associated with secretion of KDEL-free ER chaperones from these cells into the urine, and if chaperones in the urine reflect ER stress in glomerulonephritis. In cultured podocytes, ER stress increased ERdj3 and MANF intracellularly and in culture medium, whereas GRP94 (KDEL chaperone) increased only intracellularly. ERdj3 and MANF secretion was blocked by the secretory trafficking inhibitor, brefeldin A. Urinary ERdj3 and MANF increased in rats injected with tunicamycin (in the absence of proteinuria). After induction of passive Heymann nephritis (PHN) and puromycin aminonucleoside nephrosis (PAN), there was an increase in glomerular ER stress, and appearance of ERdj3 and MANF in the urine, coinciding with the onset of proteinuria. Rats with PHN were treated with the chemical chaperone, 4-phenyl butyrate (PBA), starting at the time of disease induction, or after disease was established. In both protocols, 4-PBA reduced proteinuria and urinary ER chaperone secretion, compared with PHN rats treated with saline (control). In conclusion, urinary ERdj3 and MANF reflect glomerular ER stress. 4-PBA protected against complement-mediated podocyte injury and the therapeutic response could be monitored by urinary ERdj3 and MANF.

Clinicopathological features and prognosis in patients with idiopathic membranous nephropathy with hypertension

The present study analyzed the clinicopathological features and prognosis in patients with idiopathic membranous nephropathy (IMN) with hypertension. In the hypertension group, significant differences were found in the age, hypertension history, systolic blood pressure, diastolic blood pressure (DBP), mean arterial pressure, albumin, serum creatinine, low-density lipoprotein, 24 h urine protein levels, calculated estimated glomerular filtration rate (e-GFR), glomerular sclerosis, segmental sclerosis, ischemic sclerosis, interstitial fibrosis, tubular atrophy and vascular lesion compared with the non-hypertension group (P<0.05). The average follow-up time was 35.70 months (5.10-103.77 months). In total, 54 patients reported a 50% decline in e-GFR, eight patients reported progression of disease to end-stage renal disease (ESRD) and nine cases of mortality were reported. Survival analysis results suggested that patients with hypertension had a lower cumulative renal survival rate than those without hypertension (P=0.034). Multivariate Cox hazards regression analysis results suggested that DBP [hazard ratio (H), 5.160; CI, 0.865-0.989; P=0.023], age (H, 4.839; CI, 1.008-1.142; P=0.028), sex (H, 5.680; CI, 0.031-0.714; P=0.017), serum creatinine (H, 20.920; CI, 1.035-1.089; P<0.001), uric acid (H, 4.783; CI, 0.982-0.0.999; P=0.029), 24 h urine protein (H, 6.318; CI, 1.079-1.850; P=0.012), e-GFR (H, 4.008; CI, 1.001-1.062; P=0.045) and glomerular sclerosis (H, 8.722; CI, 1.860-21.559; P=0.003), segmental sclerosis (H, 7.737; CI, 7.770-13.219; P=0.005), percentage of ischemic sclerosis (H, 4.729; CI, 1.444-11.945; P=0.030), crescents (H, 5.938; CI, 0.003-0.526; P=0.015), interstitial fibrosis and tubular atrophy (H, 8.128; CI, 0.005-1.052; P=0.043), and vascular lesion (H, 4.049; CI, 1.030-9.766; P=0.044) were risk factors for the development of IMN into ESRD. The results suggested that DBP may be an independent risk factor for the development of IMN with hypertension.

Co-delivery of p38α MAPK and p65 siRNA by novel liposomal glomerulus-targeting nano carriers for effective immunoglobulin a nephropathy treatment

Glomerulonephritis related renal failure is a frequent cause of end-stage renal disease, and immunoglobulin A nephropathy (IgAN) is the most frequent type of primary glomerulonephritis. As damage induced by IgAN mostly attributes to inflammation responses, inhibiting inflammation in glomerulus can protect normal renal function and delay the onset of renal failure. Hence, reducing levels of p38 MAPK and p65 which are essential regulators in p38 MAPK and NF-κB related inflammation responses could be effective against IgAN. Here, we rationally designed and constructed size- and surface charge- dependent glomerulus-targeting liposomal nanoparticles which are loaded with both p38α MAPK and p65 siRNA. Experiments show that our nanoparticles successfully crossed fenestrated endothelium, accumulated in mesangial cells and endothelial cells, efficiently silenced p38α MAPK and p65 genes, and eventually alleviated proteinuria, inflammation and excessive extracellular matrix deposition in mouse IgAN models. This siRNA co-delivery system thus represents a promising treatment option for IgAN and offers a versatile platform for other glomerular problems. Our work also highlights a novel strategy of glomerulus-targeting and an encouraging therapeutic route for other inflammatory diseases.

Immunological Pathogenesis of Membranous Nephropathy: Focus on PLA2R1 and Its Role

Membranous nephropathy (MN) is the major cause of nephrotic syndrome with special pathological features, caused by the formation of immune complexes in the space between podocytes and the glomerular basement membrane. In idiopathic membranous nephropathy (IMN) the immune complexes are formed by circulating antibodies binding mainly to one of two naturally-expressed podocyte antigens: the M-type receptor for secretory phospholipase A2 (PLA2R1) and the Thrombospondin type-1 domain-containing 7A (THSD7A). Formation of antibodies against PLA2R1 is much more common, accounting for 70-80% of IMN. However, the mechanism of anti-podocyte antibody production in IMN is still unclear. In this review, we emphasize that the exposure of PLA2R1 is critical for triggering the pathogenesis of PLA2R1-associated MN, and propose the potential association between inflammation, pollution and PLA2R1. Our review aims to clarify the current research of these precipitating factors in a way that may suggest future directions for discovering the pathogenesis of MN, leading to additional therapeutic targets and strategies for the prevention and early treatment of MN.

Genetic determinants of the development and course of membranous nephropathy

Membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in adults and is classified as either primary (idiopatic) or secondary MN according to underlying etiology (the later result from some known disease such as systemic autoimmune diseases, infections, malignancies, drugs, etc). In recent years, phospholipase A2 receptor 1 (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) were identified as two major podocytic antigens involved in the pathogenesis of idiopatic MN (IMN). And the discovery of circulating antibodies specific for these target antigens has transformed the diagnostic workup and significally improved management of IMN. However why do such antibodies develop is not conclusively established. The role of underlying genetic factors is discussed. The review presents the results of recent studies, that have shown significant associations of specific genetic factors (particularly human leucocyte antigen class II and PLA2R1 genes) with IMN.

Clinical significance of C4d deposition in renal tissues from patients with primary Sjögren's syndrome-a preliminary study

Background

To evaluate renal expression of C4d, a complement component in the classical/mannose binding lectin (MBL) pathway, in patients with primary Sjögren’s syndrome (pSS)-associated renal impairments.

Methods

We retrospectively reviewed the clinical and pathological data from 39 patients with pSS presenting with renal impairments. C4d was examined in paraffin-embedded biopsy tissues using immunohistochemistry. Glomerular C4d positive was defined when > 75% glomeruli were globally stained. Tubulointerstitial C4d (TI-C4d) were scored semi-quantitatively as 0 (absent), 1 (spotty or weak), 2 (patchy) and 3 (diffuse). A TI-C4d score ≥ 2 was considered TI-C4d positive and included in the TI-C4d⁺ group and vice versa. Peritubular capillary (PTC) C4d was scored as 0 (absent), 1 (0~10%, minimal), 2 (10%~ 50%, focal), and 3 (> 50%, diffuse).

Results

Glomerular C4d deposition was observed in all 8 patients with pSS-related membranous nephropathy (MN) without obvious C1q deposition. Two of 5 patients with mesangial proliferative glomerulonephritis and 1 of 2 patients with IgA nephropathy had mild mesangial C4d deposition. Sixteen patients (6 glomerular dominant and 10 tubulointerstitial dominant) presented TI-C4d score ≥ 2. Patients in the TI-C4d⁺ group exhibited a higher serum creatinine level at the time of renal biopsy (TI-C4d⁺ 132.5 [89.7, 165.5] vs. TI-C4d⁻ 83.0 [70.7, 102.0] μmol/L, P = 0.008). PTC C4d was observed in 12 patients, with each of minimal, focal and diffuse staining being noted in 4 patients.

Conclusions

The MBL pathway of complement activation was potentially involved in pSS-related MN. Tubulointerstitial C4d might be a pathological marker of severe renal injury in patients with pSS-related renal impairments.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1341-y) contains supplementary material, which is available to authorized users.

Combined Plasmatic and Tissue Approach to Membranous Nephropathy-Proposal of a Diagnostic Algorithm Including Immunogold Labelling: Changing the Paradigm of a Serum-based Approach

Membranous nephropathy represents the most frequent cause of nephrotic syndrome in the adult, leading to end-stage renal disease in one third of all the patients. In the last years, the discovery of circulating autoantibodies against phospholipase A2 receptor 1 (PLA2R) and thrombospondin type-1 containing 7A domain (THSD7A), shed light on the pathogenesis of idiopathic forms, being responsible for 70% and 3% of all the cases, respectively. These identifications allowed the development of serological and histologic tests to detect autoantibodies and relative targets for diagnostic and prognostic purposes. Rising evidences suggest that serum titer correlates with disease activity and response to therapy. For these reasons, for patients with nephrotic syndrome, a serum-based approach has been proposed, reserving renal biopsy only in cases with doubtful/negative serology. However, the recent introduction of useful criteria for the interpretation of PLA2R/THSD7A immunohistochemistry could lead to high values of sensitivity and specificity for the in situ detection of target antigens. The present multicentric study on a series of membranous nephropathy cases with available serum/histologic correlation will show the importance of the crosstalk among the different techniques, recovering the possible role of electron microscopy in challenging situations.

Definition of a new cut-off for the anti-phospholipase A2 receptor (PLA2R) autoantibody immunoassay in patients affected by idiopathic membranous nephropathy

Autoantibodies against phospholipase A2 receptor (PLA2R) are a sensitive and specific marker for idiopathic membranous nephropathy (IMN). The aim of our study was to redefine the cut-off value for the measurement of anti-PLA2R autoantibody levels by an automated enzyme immunoassay, in a large single-center cohort of Italian IMN patients at the time of diagnosis. Sixty-seven consecutive incident patients, with biopsy-proven IMN, were recruited. All patients were naïve to preceding immunosuppressive therapeutic regimens. The patient population had a mean age of 57 years and included 48 males and 19 females. Also, 200 patients with other renal diseases and 36 healthy subjects were studied as controls. The anti-PLA2R autoantibody levels were measured using the commercial enzyme-linked immunosorbent assay kit at the time of renal biopsy. At a cut-off value of 2.7 RU/ml (significantly lower than the manufacturer's recommended value of 14 RU/ml), calculated by receiver operating characteristic curves, the sensitivity and specificity of anti-PLA2R autoantibodies in the diagnosis of IMN was 88.1 and 96% respectively. The adapted cut-off value of 2.7 UI/ml increased sensitivity without affecting the specificity and it should be the recommended value for this method. Additionally our study confirmed the correlation, at baseline, between anti-PLA2R autoantibody levels and other biomarkers of disease activity.

Role of melatonin receptor 1A and pituitary homeobox-1 coexpression in protecting tubular epithelial cells in membranous nephropathy

Membranous nephropathy (MN), a type of glomerular nephritis, is one of the most common causes of nephrotic syndrome in adults. Although it is known that melatonin plays a protective role in MN, the role of melatonin receptors in the pathophysiology of MN is unclear. Using an experimental MN model and clinical MN specimens, we studied melatonin receptor expression and found that melatonin receptor 1A (MTNR1A) expression was significantly downregulated in renal tubular epithelial cells. Molecular studies showed that the transcription factor pituitary homeobox-1 (PITX1) promoted MTNR1A expression via direct binding to its promoter. Treatment of a human tubular cell line with albumin to induce injury resulted in the stable reduction in MTNR1A and PITX1 expression. PITX1 levels were significantly downregulated in tubular epithelial cells from mice MN kidneys and MN renal specimens. Knockdown of MTNR1A, PITX1, or cyclic adenosine monophosphate-responsive element-binding protein (CREB) decreased E-cadherin (CDH1) expression, but upregulated Per2 and α-smooth muscle actin (αSMA) expression. Blockade of the MTNR1A receptor with luzindole in MN mice further impaired renal function; this was accompanied by CDH1 downregulation and Per2 and αSMA upregulation. Together, our results suggest that in injured tissue, decreased PITX1 expression at the MTNR1A promoter regions leads to decreased levels of MTNR1A in renal tubular epithelial cells, which increases the future risk of MN.

A pilot and comparative study between pathological and serological levels of immunoglobulin and complement among three kinds of primary glomerulonephritis

Background

Immunoglobulin A nephropathy (IgAN), membranous nephropathy (MN) and minimal-change disease (MCD) are three common types of glomerulonephritis in China. Pathological diagnosis based on renal biopsy is the criterion and the golden standard for diagnosing the sub-types of primary or secondary glomerulonephritis. Immunoglobulin and complements might be used in the differential diagnosis of glomerulonephritis without renal biopsies. However, the relationship between IF intensities of immune proteins and the corresponding serum levels remained unclear, and seldom studies combine histopathological examination results and blood tests together for a predictive purpose. This study was considered as a pilot study for integrating histopathological indicators into serum parameters for exploring the relationship of IF intensity and serum values of immunoglobulin and complement, and for screening and investigating effective indicators inIgAN, MN and MCD.

Methods

Renal tissue immunofluorescence (IF) intensity grades and serum levels of immunoglobulin and complements (IgG, IgA, IgM, C3 and C4) were retrospectively analyzed in 236 cases with IgAN, MN or MCD. IF grades were grouped as negative (−), positive (+) or strong positive (++) with both high and low magnification of microscope. Other serum indicators such as urea nitrogen (BUN), creatinine (Crea) and estimated glomerular filtration rate (eGFR) were also evaluated among the groups.

Results

There were difference in IgA, IgG and C3 IF intensity grades among IgAN, MN and MCD groups (p = 9.82E-43, 4.60E-39, 7.45E-15, respectively). Serum values of BUN, Crea, eGFR, IgG, IgA, IgM and C4 showed difference in three groups (BUN: p = 0.045, Crea: p = 3.45E-5, eGFR: p = 0.005, IgG: p = 1.68E-14, IgA: p = 9.14E-9, IgM: p = 0.014, C4: p = 0.026). eGFR had the trend to decrease with enhanced IgA IF positive grades (p = 8.99E-4); Crea had trends to decrease with both enhanced IgA and IgG IF intensity grades (p = 2.06E-6, 2.94E-5, respectively). In all subjects, serum IgA levels was inversely correlated with eGFR(r = − 0.216, p = 0.001) and correlated with Crea levels(r = 0.189, p = 0.004); serum IgG and Crea showed no correlation which were discordance with inverse correlation of IgG IF grade and Crea(r = 0.058,p = 0.379). IgG serum level was inverse correlated with its IF grades (p = 3.54E-5, p = 7.08E-6, respectively); C3 serum levels had significantly difference between Neg and positive (+) group (p = 0.0003). IgA serum level was positive correlated with its IF grades (Neg-(+): p = 0.0001; (+)-(++): p = 0.022; Neg-(++): p = 2.01E-10). After matching comparison among C3 groups, C3 Neg. group and C3 ++ group had difference (*p = 0.017). C4 had all negative IF expression in all pathological groups. In IgAN subjects, there were statistical differences of serum C3 levels between its pathological Neg and positive (+) group(p = 0.026), and serum IgA levels showed difference between IgA pathological positive(+) and (++)(p = 0.007). In MN subjects, sIgG levels showed difference between IgG pathological IF grade positive (+) and (++)(p = 0.044); serum C3 levels showed difference between C3 pathological IF grade Neg and positive(+)(p = 0.005); and serum IgA levels showed difference between Neg and positive(+)(p = 0.040). In IgAN, eGFR showed serum IgA levels had significant differences among groups (p = 0.007) and had increasing trend with enhanced its IF grades(P_trend = 0.016). There were also difference between IgG group Neg and positive (+) (p = 0.005, P_trend = 0.007) in IgAN. In MN, serum IgG levels had significant differences among IF groups (p = 0.034) and had decreasing trend with its enhanced IF grades (P_trend = 0.014). Serum C3 concentrations also were found distinctive among IF groups (p = 0.016) and had in inverse correlation with its enhanced IF grades (P_trend = 0.004).

Discussion

Our research cross contrasts several immunoprotein IF intensities and relevant serum levels in three kinds of primary glomerular nephritis, and finally acquired helpful results for understanding the relationships between pathological presentation and serological presentation of immunoproteins in kidney diseases. Furthermore, this pilot study is offering a possible method for the analysis of combination of pathology and serology.

Conclusion

Different pathological types of nephritis presented different expression patterns of immunoglobulin and complement, especially IgA and IgG, which suggested different pathogenesis involved in the development of IgAN and MN. Furthermore, either in tissue or in serum, increased IgA level was closely related with renal function in all of the patients.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0254-z) contains supplementary material, which is available to authorized users.

The role of the immune system in kidney disease

The immune system and the kidneys are closely linked. In health the kidneys contribute to immune homeostasis, while components of the immune system mediate many acute forms of renal disease and play a central role in progression of chronic kidney disease. A dysregulated immune system can have either direct or indirect renal effects. Direct immune-mediated kidney diseases are usually a consequence of autoantibodies directed against a constituent renal antigen, such as collagen IV in anti-glomerular basement membrane disease. Indirect immune-mediated renal disease often follows systemic autoimmunity with immune complex formation, but can also be due to uncontrolled activation of the complement pathways. Although the range of mechanisms of immune dysregulation leading to renal disease is broad, the pathways leading to injury are similar. Loss of immune homeostasis in renal disease results in perpetual immune cell recruitment and worsening damage to the kidney. Uncoordinated attempts at tissue repair, after immune-mediated disease or non-immune mediated injury, result in fibrosis of structures important for renal function, leading eventually to kidney failure. As renal disease often manifests clinically only when substantial damage has already occurred, new diagnostic methods and indeed treatments must be identified to inhibit further progression and promote appropriate tissue repair. Studying cases in which immune homeostasis is re-established may reveal new treatment possibilities.

Urine proteomics of primary membranous nephropathy using nanoscale liquid chromatography tandem mass spectrometry analysis

Background

Primary membranous nephropathy (PMN) is an important cause of nephrotic syndrome in adults. Urine proteome may provide important clues of pathophysiological mechanisms in PMN. In the current study, we analyzed and compared the proteome of urine from patients with PMN and normal controls.

Methods

We performed two technical replicates (TMT1 and TMT2) to analyze and compare the urine proteome from patients with PMN and normal controls by tandem mass tag (TMT) technology coupled with nanoscale liquid chromatography tandem mass spectrometry analysis (LC–MS/MS). Gene ontology (GO) enrichment analysis was performed to analyse general characterization of the proteins. The proteins were also matched against the database of Kyoto Encyclopedia of Genes and Genomes (KEGG). For validation, Western blot was used to analyze the selected proteins.

Results

A total of 509 proteins and 411 proteins were identified in TMT1 and TMT2, respectively. 249 proteins were both identified in two technical replicates. GO analysis and KEGG analysis revealed immunization and coagulation were predominantly involved. Among the differential protein, the overexcretion of alpha-1-antitrypsin (A1AT) and afamin (AFM) were validated by Western blot analysis.

Conclusions

Our data showed the important role of immunologic mechanism in the development of PMN, and the value of urinary A1AT and AFM in biomarker discovery of patients with PMN. The discovery of the overexcretion of A1AT and AFM in the urine can help to further elucidate pathogenetic mechanisms involved in PMN.

Electronic supplementary material

The online version of this article (10.1186/s12014-018-9183-3) contains supplementary material, which is available to authorized users.

IgG4-mediated autoimmune diseases: a niche of antibody-mediated disorders

Immunoglobulin 4 (IgG4) is one of four human IgG subclasses and has several unique functional characteristics. It exhibits low affinity for complement and for most Fc receptors. It furthermore has generally high affinity for its antigen, with binding occurring in a monovalent fashion, as IgG4 can exchange Fab-arms with other IgG4 molecules. Because of these characteristics, IgG4 is believed to block its targets and prevent inflammation, which, depending on the setting, can have a protective or pathogenic effect. One example of IgG4 pathogenicity is muscle-specific kinase (MuSK) myasthenia gravis (MG), in which patients develop IgG4 MuSK autoantibodies, resulting in muscle weakness. As a consequence of the distinct IgG4 characteristics, the pathomechanism of MuSK MG is very different from IgG1-and IgG3-mediated autoimmune diseases, such as acetylcholine receptor MG. In recent years, new autoantibodies in a spectrum of autoimmune diseases have been discovered. Interestingly, some were found to be predominantly IgG4. These IgG4-mediated autoimmune diseases share many pathomechanistic aspects with MuSK MG, suggesting that IgG4-mediated autoimmunity forms a separate niche among the antibody-mediated disorders. In this review, we summarize the group of IgG4-mediated autoimmune diseases, discuss the role of IgG4 in MuSK MG, and highlight interesting future research questions for IgG4-mediated autoimmunity.

Serum anti-PLA2R antibody as a diagnostic biomarker of idiopathic membranous nephropathy: The optimal cut-off value for Chinese patients

BACKGROUND

The M-type phospholipase A2 receptor (PLA2R) is a specific target autoantigen identified in idiopathic membranous nephropathy (IMN). The autoantibody against PLA2R (anti-PLA2R) may be used to diagnose IMN. However, the appropriate diagnosis cut-off value for Chinese patients with IMN has not been established.

METHODS

In total, 119 patients who underwent renal biopsy (57 patients with IMN and 62 patients with non-IMN glomerulonephritis) and 22 healthy individuals were recruited for our observation study from Qianfoshan Hospital between September 2011 and March 2016. The serum concentration of anti-PLA2R was measured using a quantitative enzyme-linked immunosorbent assay (ELISA). The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and receiver operating characteristic (ROC) curve of anti-PLA2R in diagnosing IMN were analysed based on the ELISA detection.

RESULTS

The sensitivity, specificity, PPV, and NPV of anti-PLA2R in the diagnosis of IMN in the Chinese patients were 82.5, 75, 69.1, and 86.3% for the 2RU/ml cut-off value; 78.9, 91.7, 86.5, and 86.5% for the 2.6RU/ml cut-off value; 59.6, 95.2, 89.5, and 77.7% for the 14RU/ml cut-off value; 50.9, 96.4, 90.6, and 74.3% for the 20RU/ml cut-off value; and 47.4, 97.6, 93.1, and 73.2% for the 40RU/ml cut-off value, respectively. The area under the ROC curve was 0.879.

CONCLUSIONS

The cut-off value of 2.6RU/ml is recommended for the use of anti-PLA2R for the diagnosis of IMN in Chinese patients based on the ELISA.

Diagnostic specificity of autoantibodies to M-type phospholipase A2 receptor (PLA2R) in differentiating idiopathic membranous nephropathy (IMN) from secondary forms and other glomerular diseases

Autoantibody against phospholipase A2 receptor (anti-PLA2R) is a sensitive and specific biomarker of idiopathic membranous nephropathy (iMN), being found in approximately 70% of iMN patients and only occasionally in other glomerular diseases. However, whereas its diagnostic specificity vs. normal controls and other glomerulonephritides (GN) has been firmly established, its specificity vs. membranous nephropathy associated with various diseases (sMN) has given inconsistent results. The aim of our study was to evaluate the prevalence of anti-PLA2R antibodies in iMN in comparison with various control groups, including sMN. A total of 252 consecutive iMN patients, 184 pathological and 43 healthy controls were tested for anti-PLA2R antibody using indirect immunofluorescence (PLA2R IIFT, Euroimmun). Anti-PLA2R autoantibodies were detectable in 178/252 iMN patients, 1/80 primary GN, 0/72 secondary GN, 9/32 sMN and 0/43 healthy controls, with a diagnostic sensitivity of 70.6%. The diagnostic specificity of anti-PLA2R antibody vs. normal and pathological controls was 100 and 94.6% respectively. However, when the diagnostic specificity was calculated only vs. secondary forms of MN, it decreased considerably to 71.9%. Interestingly enough, 9 out of 10 anti-PLA2R positive patients in the disease control groups had membranous nephropathy associated with various diseases (7 cancer, 1 Crohn's disease, 1 scleroderma). In conclusion, anti-PLA2R positivity in a patient with MN, should not be considered sufficient to abstain from seeking a secondary cause, especially in patients with risk factors for neoplasia. The causal relationship between tumors and anti-PLA2R-induced MN remains to be established, as well as the possible mechanisms through which malignancies provoke autoimmunity.

[Immunological principles of IgG4 related diseases]

In contrast to the other IgG subclasses, IgG4 does not bind to low affinity Fc receptors or activate the classical complement pathway. In addition, it is unstable and can dissociate into two hemimolecules; therefore, IgG4 most likely has an immunosuppressive role. On the other hand, there a few examples of an immunostimulatory role of IgG4 antibodies; therefore, the function of IgG4 in IgG4 related diseases is not yet entirely clear. The trigger factors of IgG4 related diseases (allergic or autoimmune) are still under debate. The activation of T helper (Th) 2 and regulatory T cells has been shown to be important in the pathophysiology of IgG4 related diseases as they produce cytokines which contribute to the formation of IgG4 and to fibrosis of various tissues.

Primary Membranous Nephropathy

Membranous nephropathy (MN) is a unique glomerular lesion that is the most common cause of idiopathic nephrotic syndrome in nondiabetic white adults. About 80% of cases are renal limited (primary MN, PMN) and 20% are associated with other systemic diseases or exposures (secondary MN). This review focuses only on PMN. Most cases of PMN have circulating IgG4 autoantibody to the podocyte membrane antigen PLA2R (70%), biopsy evidence PLA2R staining indicating recent immunologic disease activity despite negative serum antibody levels (15%), or serum anti-THSD7A (3%-5%). The remaining 10% without demonstrable anti-PLA2R/THSd7A antibody or antigen likely have PMN probably secondary to a different, still unidentified, anti-podocyte antibody. Considerable clinical and experimental data now suggests these antibodies are pathogenic. Clinically, 80% of patients with PMN present with nephrotic syndrome and 20% with non-nephrotic proteinuria. Untreated, about one third undergo spontaneous remission, especially those with absent or low anti-PLA2R levels, one-third progress to ESRD over 10 years, and the remainder develop nonprogressive CKD. Proteinuria can persist for months after circulating anti-PLA2R/THSD7A antibody is no longer detectable (immunologic remission). All patients with PMN should be treated with supportive care from the time of diagnosis to minimize protein excretion. Patients with elevated anti-PLA2R/THSD7A levels and proteinuria >3.5 g/d at diagnosis, and those who fail to reduce proteinuria to <3.5 g after 6 months of supportive care or have complications of nephrotic syndrome, should be considered for immunosuppressive therapy. Accepted regimens include steroids/cyclophosphamide, calcineurin inhibitors, and B cell depletion. With proper management, only 10% or less will develop ESRD over the subsequent 10 years.