Interaction between PLA2R1 and HLA-DQA1 variants associates with anti-PLA2R antibodies and membranous nephropathy

Association of Exposure to Fine-Particulate Air Pollution and Acidic Gases with Incidence of Nephrotic Syndrome

Background: Air pollution has been associated with autoimmune diseases. Nephrotic syndrome is a clinical manifestation of immune-mediated glomerulopathy. However, the association between nephrotic syndrome and air pollution constituents remains unknown. We conducted this nationwide retrospective study to investigate the association between PM_2.5 and nephrotic syndrome. Methods: We used the Longitudinal Health Insurance Database (LHID) and the Taiwan Air Quality-Monitoring Database (TAQMD). We combined and stratified the LHID and the TAQMD data by residential areas of insurants linked to nearby air quality-monitoring stations. Air pollutant concentrations were grouped into four levels based on quartile. Univariable and multivariable Cox proportional hazard regression models were applied. Findings: Relative to Q1-level SO₂, subjects exposed to the Q4 level were associated with a 2.00-fold higher risk of nephrotic syndrome (adjusted HR = 2.00, 95% CI = 1.66⁻2.41). In NOx, relative to Q1 NOx concentrations, the adjusted HRs of nephrotic syndrome risk were 1.53 (95% CI = 1.23⁻1.91), 1.30 (95% CI = 1.03⁻1.65), and 2.08 (95% CI = 1.69⁻2.56) for Q2, Q3, and Q4 levels, respectively. The results revealed an increasing trend for nephrotic syndrome risk correlating with increasing levels of NO, NO₂, and PM_2.5 concentrations. Interpretation: High concentrations of PM_2.5, NO, NO₂, and SO₂ are associated with increased risk of nephrotic syndrome.

Analysis of the relationship between Oxford classification, IgM deposition and multiple indexes and the adverse prognosis of patients with primary IgA nephropathy and related risk factors

The risk and influencing factors of prognosis in patients with primary IgA nephropathy (IgAN) were explored. One hundred and twenty-four patients who were diagnosed with IgA nephropathy in West China Hospital of Sichuan University were selected as the study subjects. The baseline data were recorded. All patients were followed up for 3 years. Patients with poor prognosis were defined as poor prognosis group, and the patient with no adverse prognosis was defined as a good prognosis group during the follow-up period. The risk factors that may affect the prognosis of patients with IgAN were analyzed by single factor analysis. The influence of all factors that were statistically significant on the prognosis of the patients was further evaluated by multifactor Cox regression. The single factor analysis and multivariate Cox proportional hazard model showed that patients with 24 h urinary protein, pathological type, Oxford classification (T1+T2), Lee (grade IV) and mesangial IgM deposition were independent factors of patients, and the difference was statistically significant, their P-values were 0.041, 0.046, 0.037, 0.043, and 0.028, respectively. Patients with 24 h urinary protein, pathological type, Oxford classification (T1+T2), Lee (grade IV) and mesangial IgM deposition can be used as independent factors affecting poor prognosis in primary IgAN patients. It provides evidence for early detection of high-risk IgA nephropathy.

Association between the HLA-DQA1 rs2187668 polymorphism and risk of idiopathic membranous nephropathy: A PRISMA-compliant meta-analysis

OBJECTIVE

Numerous studies have evaluated the association between the rs2187668 polymorphism in the human leucocyte antigen (HLA) complex class II HLA-DQ a-chain 1 (HLA-DQA1) gene and idiopathic membranous nephropathy (iMN) risk, which provided new insight into potential new targets for the treatment of iMN. However, this relationship remains inconclusive. Our aim was to evaluate the relationship between this polymorphism and iMN susceptibility by performing a meta-analysis.

METHODS

Articles were identified in the PubMed, Google Scholar, EMBASE, Cochran Library databases. Meta-analyses were performed for rs2187668 allele frequency, genotypes, and the association with iMN susceptibility. Subgroup analyses, publication bias and sensitivity analyses were also conducted.

RESULTS

11 eligible studies (3209 cases and 7358 controls) from 7 articles were included. Statistical analyses were carried out using Stata 12.0, combining data from all the relevant studies. The pooled odds ratios (ORs) regarding the association between the HLA-DQA1 rs2187668 polymorphism and iMN risk were statistically significant [A vs G: OR = 3.34, 95% confidence interval (CI) = 2.70-4.13; AA vs GA + GG: OR = 8.69, 95% CI = 6.64-11.36; GG vs GA + AA: OR = 0.25, 95% CI = 0.19-0.33;AA vs GG: OR = 12.61, 95% CI = 8.02-19.81; GA vs GG: OR = 3.45, 95% CI = 2.79-4.25].

CONCLUSIONS

Our pooled analysis showed a significant association between rs2187668-(A) allele and iMN susceptibility, and the intervention of this mutation might bring new therapeutic strategy for iMN. However, further studies should be performed to confirm this finding.

Identification of a two-SNP PLA2R1 Haplotype and HLA-DRB1 Alleles as Primary Risk Associations in Idiopathic Membranous Nephropathy

The associations of single nucleotide polymorphisms (SNPs) in PLA2R1 and HLA-DQA1, as well as HLA-DRB1*15:01-DQB1*06:02 haplotype with idiopathic membranous nephropathy (IMN) is well known. However, the primary associations of these loci still need to be determined. We used Japanese-specific SNP genotyping array and imputation using 2,048 sequenced Japanese samples to fine-map PLA2R1 region in 98 patients and 413 controls. The most significant SNPs were replicated in a separate sample set of 130 patients and 288 controls. A two-SNP haplotype of intronic and missense SNPs showed the strongest association. The intronic SNP is strongly associated with PLA2R1 expression in the Genotype-Tissue Expression (GTEx) database, and the missense SNP is predicted to alter peptide binding with HLA-DRB1*15:01 by the Immune Epitope Database (IEDB). In HLA region, we performed relative predispositional effect (RPE) tests and identified additional risk alleles in both HLA-DRB1 and HLA-DQB1. We collapsed the risk alleles in each of HLA-DRB1 and HLA-DQB1 into single risk alleles. Reciprocal conditioning of these collapsed risk alleles showed more residual significance for HLA-DRB1 collapsed risk than HLA-DQB1 collapsed risk. These results indicate that changes in the expression levels of structurally different PLA2R protein confer risk for IMN in the presence of risk HLA-DRB1 alleles.

Characteristics of patients with coexisting IgA nephropathy and membranous nephropathy

BACKGROUND

Coexistence of IgA nephropathy (IgAN) and membranous nephropathy (MN) in the same patient is rare. Few studies have reported the clinical and pathological features of patients with combined IgAN and MN (IgAN-MN).

METHODS

The clinico-pathological features, levels of galactose-deficient IgA1 (Gd-IgA1) and autoantibodies against M-type transmembrane phospholipase A₂ receptor (anti-PLA₂R) in sera were compared among IgAN-MN, IgAN, and MN patients.

RESULTS

Twenty-six patients with biopsy-proven IgAN-MN were enrolled. The mean age at biopsy was 43.6 ± 15.9 years, and 65.4% were male. Proteinuria and estimated glomerular filtration rate (eGFR) levels in patients with IgAN-MN were similar to that of MN patients. Compared with the IgAN patients, IgAN-MN patients showed a higher median proteinuria level (4.3 vs. 1.2 g/day, p < .001), and a higher mean eGFR level (101.8 ± 25.4 vs. 78.6 ± 26.9 mL/min/1.73 m², p < .001). IgAN-MN patients presented with milder pathological lesions than IgAN patients according to the Oxford Classification. IgAN-MN patients had comparable serum levels of Gd-IgA1 with those of IgAN patients (353.4 ± 95.5 vs. 347.0 ± 109.6 U/mL, p = .801). Percentage of IgAN-MN patients with detectable serum levels of anti-PLA₂R was lower than that of MN patients (38.5% vs. 68.6%, p = .011).

CONCLUSIONS

IgAN-MN patients display similar clinical features to MN patients and milder pathological lesions than IgAN patients. IgAN-MN patients have similar levels of Gd-IgA1 to those of IgAN patients, and a lower proportion of anti-PLA₂R than MN patients.

Genetics of membranous nephropathy

An HLA-DR3 association with membranous nephropathy (MN) was described in 1979 and additional evidence for a genetic component to MN was suggested in 1984 in reports of familial MN. In 2009, a pathogenic autoantibody was identified against the phospholipase A2 receptor 1 (PLA2R1). Here we discuss the genetic studies that have proven the association of human leucocyte antigen class II and PLA2R1 variants and disease in MN. The common variants in PLA2R1 form a haplotype that is associated with disease incidence. The combination of the variants in both genes significantly increases the risk of disease by 78.5-fold. There are important genetic ethnic differences in MN. Disease outcome is difficult to predict and attempts to correlate the genetic association to outcome have so far not been helpful in a reproducible manner. The role of genetic variants may not only extend beyond the risk of disease development, but can also help us understand the underlying molecular biology of the PLA2R1 and its resultant pathogenicity. The genetic variants identified thus far have an association with disease and could therefore become useful biomarkers to stratify disease risk, as well as possibly identifying novel drug targets in the near future.

HLA class II alleles differing by a single amino acid associate with clinical phenotype and outcome in patients with primary membranous nephropathy

Genome-wide associations and HLA genotyping have revealed associations between HLA alleles and susceptibility to primary membranous nephropathy. However, associations with clinical phenotypes and kidney outcome are poorly defined. We previously identified DRB1*1501 and DRB1*0301 as independent risk alleles for primary membranous nephropathy. Here, we investigated HLA associations with demographic characteristics, anti-phospholipase A2 receptor (PLA2R) antibody, treatment response and kidney outcome after a median follow-up of 52 months in 258 patients. DRB1*0301, but not DRB1*1501, was associated with a significantly higher level of PLA2R antibody (odds ratio 1.58, 95% confidence interval 1.13-2.22). Although DRB1*1502, which differs from DRB1*1501 by a single amino acid, was not a risk allele for primary membranous nephropathy (odds ratio 1.01), it was associated with significantly lower estimated glomerular filtration rates both at baseline (1.79, 1.18-2.72) and at last follow-up (1.72, 1.17-2.53), a significantly worse renal outcome by Kaplan-Meier analysis and a significantly higher risk of end-stage renal disease by Cox regression analysis (hazard ratio 4.52, 1.22-16.74). Nevertheless, the absence of remission remained the only independent risk factor for end-stage renal disease by multivariate analysis. DRB1*1502 was also associated with a significantly higher median PLA2R antibody level [161.4 vs. 36.3 U/mL] and showed interaction with DRB1*0301 for this variable. Thus, HLA genes control PLA2R antibody production and primary membranous nephropathy severity and outcome. Additionally, DRB1*1502 behaves like a modifier gene with a strong predictor value when associated with HLA risk alleles. Other modifier genes need further investigations in larger cohorts.

The Genetic and Environmental Factors of Primary Membranous Nephropathy: An Overview from China

Background

Primary membranous nephropathy (pMN) is the most common cause of nephrotic syndrome in adults. The discovery of the 2 autoantigens, M-type phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A), has defined pMN as an autoimmune disease. A remarkable increase in the frequency of pMN in primary glomerular disease was witnessed in China. The genetic and environmental contributors to disease susceptibility have been investigated in these patients.

Summary

We reviewed recent publications in genetic and environmental studies of pMN, focusing mainly on those undertaken in China. Following a genome-wide association study, the gene-gene interaction between the 2 most significant risk factors, PLA2R1 and DQA1, was validated in Chinese patients with MN. Fine mapping on human leukocyte antigen (HLA) locus found that DRB1*1501 and DRB1*0301 were risk alleles. Three amino acid residues on positions 13 and 71 of HLA-DRβ1 chain may confer the susceptibility to pMN by presenting T-cell epitopes on PLA2R. Another study found that DRB3*0202 was the most likely culprit allele for the signal at DRB1*0301. One environmental risk factor for pMN has been identified as the long-term exposure to high levels of PM_2.5 in Chinese patients with MN. Each 10 μg/m³ increase in PM_2.5 concentration was associated with 14% higher odds for pMN in the regions with PM_2.5 above 70 μg/m³.

Key Message

A gene-environment interaction is suspected as an underlying mechanism for the increasing trend of pMN in China.

A New Classification System for IgG4 Autoantibodies

IgG4 autoimmune diseases are characterized by the presence of antigen-specific autoantibodies of the IgG4 subclass and contain well-characterized diseases such as muscle-specific kinase myasthenia gravis, pemphigus, and thrombotic thrombocytopenic purpura. In recent years, several new diseases were identified, and by now 14 antigens targeted by IgG4 autoantibodies have been described. The IgG4 subclass is considered immunologically inert and functionally monovalent due to structural differences compared to other IgG subclasses. IgG4 usually arises after chronic exposure to antigen and competes with other antibody species, thus "blocking" their pathogenic effector mechanisms. Accordingly, in the context of IgG4 autoimmunity, the pathogenicity of IgG4 is associated with blocking of enzymatic activity or protein-protein interactions of the target antigen. Pathogenicity of IgG4 autoantibodies has not yet been systematically analyzed in IgG4 autoimmune diseases. Here, we establish a modified classification system based on Witebsky's postulates to determine IgG4 pathogenicity in IgG4 autoimmune diseases, review characteristics and pathogenic mechanisms of IgG4 in these disorders, and also investigate the contribution of other antibody entities to pathophysiology by additional mechanisms. As a result, three classes of IgG4 autoimmune diseases emerge: class I where IgG4 pathogenicity is validated by the use of subclass-specific autoantibodies in animal models and/or in vitro models of pathogenicity; class II where IgG4 pathogenicity is highly suspected but lack validation by the use of subclass specific antibodies in in vitro models of pathogenicity or animal models; and class III with insufficient data or a pathogenic mechanism associated with multivalent antigen binding. Five out of the 14 IgG4 antigens were validated as class I, five as class II, and four as class III. Antibodies of other IgG subclasses or immunoglobulin classes were present in several diseases and could contribute additional pathogenic mechanisms.

Biomarkers to detect membranous nephropathy in Chinese patients

Anti-M-type phospholipase A₂ receptor (anti-PLA₂R) is a widely accepted biomarker for clinical idiopathic membranous neurophathy (IMN). However, its ability to differentiate between IMN and secondary MN (SMN) is controversial. The objective of this study was to assess clinical MN biomarkers in blood, tissue and urine samples from Chinese patients. In total, 195 MN patients and 70 patients with other glomerular diseases were prospectively enrolled in the study. Participants were followed up for average of 17 months (range 3-39 months). Anti-PLA₂R and anti-THSD7A (thrombospondin type-1 domain-containing 7A) were detected only in MN patient sera and not in controls. Serum anti-THSD7A and THSD7A-positive biopsies were detected in 1/18 and 2/18 PLA₂R-negative MN cases, respectively. PLA₂R and THSD7A were detected in 72.27% and 40% of SMN cases, respectively. While serum positivity for both anti-PLA₂R and anti-THSD7A at the time of renal biopsy was specific to MN patients, neither antigen could discriminate between primary and secondary MN. We also found that high urinary levels of retinol binding protein (RBP) predicted poor proteinuria outcomes in study participants. Patients with low or medium urinary RBP levels achieved remission more frequently than those with high RBP.

Lessons from CKD-Related Genetic Association Studies-Moving Forward

Over the past decade, genetic association studies have uncovered numerous determinants of kidney function in the general, diabetic, hypertensive, CKD, ESRD, and GN-based study populations (e.g., IgA nephropathy, membranous nephropathy, FSGS). These studies have led to numerous novel and unanticipated findings, which are helping improve our understanding of factors and pathways affecting both normal and pathologic kidney function. In this review, we report on major discoveries and advances resulting from this rapidly progressing research domain. We also predict some of the next steps the nephrology community should embrace to accelerate the identification of genetic and molecular processes leading to kidney dysfunction, pathophysiologically based disease subgroups, and specific therapeutic targets, as we attempt to transition toward a more precision-based medicine approach.

Renal Phospholipase A2 Receptor and the Clinical Features of Idiopathic Membranous Nephropathy

Background:

According to the renal phospholipase A2 receptor (PLA2R) immunohistochemistry, idiopathic membranous nephropathy (iMN) could be categorized into PLA2R-associated and non-PLA2R-associated iMN. This study aimed to examine whether the non-PLA2R-associated iMN had any difference in clinical features compared with PLA2R-associated iMN.

Methods:

A total of 231 adult patients diagnosed as iMN were recruited to this retrospective study. Renal PLA2R expression was examined by immunofluorescence. Among these patients, 186 (80.5%) with complete baseline clinical data were used for further study. Urinary protein excretion, serum albumin, and creatinine were analyzed. For those patients with follow-up longer than 1 year, the relationship between PLA2R and response to immunosuppressants were analyzed. The t-test was used for parametric analysis and the Mann-Whitney U-test was used for nonparametric analysis. Categorical variables were described as frequencies or percentages, and the data were analyzed with Pearson's Chi-square test or Fisher's exact test.

Results:

Of the 231 iMN patients, 189 showed renal detectable PLA2R expression (81.8%). The baseline serum creatinine, serum albumin, and urine protein excretion were not significantly different between PLA2R-associated (n = 145) and non-PLA2R-associated iMN patients (n = 41). However, about 1/3 of the non-PLA2R-associated iMN had abnormal serological tests, significantly more common than PLA2R-associated iMN (31.7% vs. 8.3%, P = 0.000). The non-PLA2R-associated iMN had lower C4 levels compared with PLA2R-associated iMN (P = 0.004). The non-PLA2R-associated iMN patients also showed a better response to immunosuppressants (complete remission [CR] 42.9%; partial remission [PR] 14.3%) compared with PLA2R-associated iMN (CR 3.2%; PR 48.4%, P = 0.004) at the 3^rd month.

Conclusions:

There were no significant differences in serum creatinine, albumin, and urine protein excretion between PLA2R-associated and non-PLA2R-associated iMN, while the non-PLA2R-associated iMN patients showed more abnormal serological tests. The non-PLA2R-associated iMN seemed to respond more quickly to the immunosuppressive therapy compared with PLA2R-associated iMN.

Recent Progress in Deciphering the Etiopathogenesis of Primary Membranous Nephropathy

Primary membranous nephropathy (MN) is the leading cause of nephrotic syndrome in adults. Discovery of several antibodies has contributed to an increased understanding of MN. Antibodies against the M-type phospholipase A2 receptor (PLA2R) are present in 50-100% with primary MN and are associated with a lower frequency of spontaneous remission. High levels are linked with a higher probability of treatment resistance, higher proteinuria, and impaired renal function, as well as a more rapid decline of kidney function during follow-up. Immunologic remission precedes reduction of proteinuria by months. Pretransplant evaluation of PLA2R antibodies is warranted to predict recurrence of disease following renal transplantation. Several risk alleles related to the PLA2R1 gene and within the HLA loci have been identified, whereas epitope spreading of PLA2R may predict treatment response. More recently, thrombospondin type 1 domain-containing 7A (THSD7A) antibodies have been discovered in primary MN. Several other rare antigens have been described, including antibodies against neutral endopeptidase as a cause of antenatal MN and circulating cationic bovine serum albumin as an antigen with implications in childhood MN. This review focuses on the progress with a special focus on diagnostic accuracy, predictive value, and treatment implications of the established and proposed antigens.

Urine anti-PLA2R antibody is a novel biomarker of idiopathic membranous nephropathy

Since urine samples more directly reflect kidney alterations and damage than blood samples, we investigated whether urine anti-PLA₂R antibody (uPLA₂R-Ab) could be utilized similarly to serum anti-PLA₂R antibody (sPLA₂R-Ab) as a noninvasive biomarker of idiopathic membranous nephropathy (IMN). In this study, we performed a qualitative analysis using an indirect immunofluorescence test (IIFT) and measured uPLA₂R-Ab and sPLA₂R-Ab concentrations using an enzyme-linked immunosorbent assay (ELISA) in 28 patients with biopsy-proven IMN and 12 patients with secondary membranous nephropathy (SMN). Overall, 64.3% (n=18) of patients with IMN had IIFT-positive sPLA₂R-Ab, 67.9% (n=19) of patients with IMN had IIFT-positive uPLA₂R-Ab, and none of the SMN patients had IIFT-positive sPLA₂R-Ab or uPLA₂R-Ab. The titers of the anti-PLA₂R antibody from the IMN patients in the urine (10.72±22.24 RU/μmol, presented as uPLA₂R-Ab/urine creatinine) and serum (107.36±140.93 RU/ml) were higher than those from the SMN patients (0.51±0.46 RU/μmol, 0.008±0.029 RU/ml, respectively, p<0.05). Statistical analyses indicated that there were positive correlations between uPLA₂R-Ab and gPLA₂R, sPLA₂R-Ab or urinary protein and negative correlations between uPLA₂R-Ab and serum albumin in patients with IMN. In conclusion, uPLA₂R-Ab is a novel biomarker of IMN. sPLA₂R-Ab combined with uPLA₂R-Ab might be more helpful for diagnosis and activity in PLA₂R associated MN.

Variants in the Promoter Region of HLA-DQA1 were Associated with Idiopathic Membranous Nephropathy in a Chinese Han Population

Background:

Idiopathic membranous nephropathy (IMN) is an autoimmune disease and the leading cause of adult nephritic syndrome. HLA-DQA1 had been identified to be associated with IMN in Europeans and the result was replicated in Chinese Han population. In this study, six single nucleotide polymorphisms (SNPs) in the promoter of HLA-DQA1 and other two SNPs with IgA nephropathy were included for the association analysis.

Methods:

The SNPs were genotyped in 509 patients and 601 controls by the MassArray iPLEX. The quantification of anti-phospholipase A2 receptor (PLA2R) antibodies in sera of IMN patients was performed by anti-PLA2R ELISA (IgG) kit.

Results:

After analysis, four SNPs were significantly associated with IMN, with rs2187668 and rs28383345 as the top two signals (P = 8.42×10^-5 and 2.48×10^-5, respectively). Even under dominant model, the two SNPs were still significantly associated with IMN (P = 3.50×10^-3 for rs28383345 and P = 6.55×10^-5 for rs2187668). After conditional study with rs2187668, rs28383345 was the only variant significantly correlated with IMN after Bonferroni correction (P = 0.016). The minor alleles of the two SNPs were also mutually exclusive in our cohort. This indicated that the two SNPs were independently associated with IMN in Chinese Han population. Levels of anti-PLA2R autoantibodies were correlated with the genotypes of the two SNPs, but not significantly (P>0.05).

Conclusions:

Our results revealed that a novel independent variant in the promoter of HLA-DQA1 was associated with IMN in Chinese Han population. The locus possessed regulatory role according to the data of RegulomeDB. The exact role of the SNPs on the expression of HLA-DQA1 needs further investigation.

Treatment of membranous nephropathy: time for a paradigm shift

In patients with membranous nephropathy, alkylating agents (cyclophosphamide or chlorambucil) alone or in combination with steroids achieve remission of nephrotic syndrome more effectively than conservative treatment or steroids alone, but can cause myelotoxicity, infections, and cancer. Calcineurin inhibitors can improve proteinuria, but are nephrotoxic. Most patients relapse after treatment withdrawal and can become treatment dependent, which increases the risk of nephrotoxicity. The discovery of nephritogenic autoantibodies against podocyte M-type phospholipase A2 receptor (PLA₂R) and thrombospondin type-1 domain- containing protein 7A (THSD7A) antigens provides a clear pathophysiological rationale for interventions that specifically target B-cell lineages to prevent antibody production and subepithelial deposition. The anti-CD20 monoclonal antibody rituximab is safe and achieves remission of proteinuria in approximately two-thirds of patients with membranous nephropathy. In those with PLA₂R-related disease, remission can be predicted by anti-PLA₂R antibody depletion and relapse by antibody re-emergence into the circulation. Thus, integrated evaluation of serology and proteinuria could guide identification of affected patients and treatment with individually tailored protocols. Nonspecific and toxic immunosuppressive regimens will fall out of use. B-cell modulation by rituximab and second-generation anti-CD20 antibodies (or plasma cell-targeted therapy in anti-CD20 resistant forms of disease) will lead to a novel therapeutic paradigm for patients with membranous nephropathy.

PLA2R and THSD7A: Disparate Paths to the Same Disease?

The phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) are the two major autoantigens in primary membranous nephropathy (MN), and define two molecular subclasses of this disease. Both proteins are large transmembrane glycoproteins expressed by the podocyte, and both induce IgG4-predominant humoral immune responses that produce circulating autoantibodies that can be used clinically for diagnostic and monitoring purposes. The biologic roles of these proteins remain speculative, although several features of THSD7A suggest a role in adhesion. PLA2R-associated MN was initially found to associate with risk alleles within HLA-DQA1, but subsequent studies have shifted the focus to the HLA-DRB locus. Three distinct humoral epitope-containing regions have been defined within the extracellular portion of PLA2R, and it appears that the number of targeted epitopes may determine disease severity. Although similar information is not yet available for THSD7A-associated MN, this form of MN may have a unique association with malignancy. Finally, it appears likely that other autoantigens in primary MN exist. Although protocols similar to those that identified PLA2R and THSD7A may be successful in the identification of novel antigenic targets in MN, newer techniques such as laser-capture mass spectrometry or protein arrays may be helpful as well.

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.

Serum anti-PLA2R antibody and glomerular PLA2R deposition in Chinese patients with membranous nephropathy: A cross-sectional study

M-type phospholipase A2 receptor (PLA2R) is the major target antigen in primary membranous nephropathy (PMN). Previous studies have evaluated the diagnostic value of serum anti-PLA2R antibody. However, the correlation of serum anti-PLA2R antibody and glomerular PLA2R deposition, and their association with clinical characteristics need to be further evaluated.A total of 136 patients were involved as inception group because serum anti-PLA2R antibody and glomerular PLA2R antigen were simultaneously measured. We examined serum anti-PLA2R antibody by ELISA and glomerular PLA2R deposition by immunofluorescence assay.Positive serum anti-PLA2R antibody and glomerular PLA2R deposition were seen in 58.8% (80/136) and 95.6% (130/136) patients, respectively (P < .001). Proteinuria, serum total protein, serum albumin, serum creatinine, and estimated glomerular filtration rate (eGFR) had significant differences between patients with serum anti-PLA2R antibody and those without. Serum anti-PLA2R antibody levels were correlated with serum albumin, serum creatinine, eGFR, and proteinuria. Glomerular PLA2R deposition intensities were weakly correlated with proteinuria. Unexpectedly, there was a positive correlation rather than a negative correlation between glomerular PLA2R deposition intensity and eGFR.In conclusion, serum anti-PLA2R antibody is more closely correlated with disease activity and renal function than glomerular PLA2R deposition.

Membranous nephropathy-one morphologic pattern with different diseases

Since the discovery of the phospholipase A₂ receptor 1 (PLA₂R1) and thrombospondin type-1 domain-containing 7A (THSD7A) as endogenous antigens involved in the development of membranous nephropathy (MN) in over 80% of adult patients, substantial progress in the diagnosis, prognosis, and therapy of MN has been made. In most cases of patients with MN, it is now possible to specifically define the responsible pathogenic mechanisms of disease and make a diagnosis even without a renal biopsy. Moreover, the presence of antibodies in the blood and the detection of the antigens in renal biopsies allow the definite diagnosis without the morphologic uncertainties, which now still apply for only about 20% of all renal biopsies showing MN. The discovery that the expression of THSD7A in malignant tumors might serve as the site of primary antigen recognition for the immune system to start MN might lead to a better understanding of not only tumor-associated MN, which accounts for up to 10% of all patients with MN, but also of the pathomechanisms relevant for MN development in general.

High-density Association Mapping and Interaction Analysis of PLA2R1 and HLA Regions with Idiopathic Membranous Nephropathy in Japanese

Although recent studies showed anti-PLA2R antibody plays a crucial role in idiopathic membranous nephropathy (IMN), detailed HLA mapping and interaction between the HLA genes and PLA2R1 have not been investigated in IMN. We genotyped across the PLA2R1 gene and the HLA region, using 183 IMN patients and 811 healthy controls. Five SNPs around the PLA2R1 gene were significantly associated with IMN. In addition to the two SNPs previously reported to be strongly associated with IMN, rs3749119 and rs35771982 (OR 3.02 and 2.93, P = 3.24E-14 and 4.64E-14, respectively), two novel intronic SNPs (rs2715928 and rs16844715) were also identified as IMN-associated SNPs (OR = 2.30 and 2.51, P = 3.15E-10 and 5.66E-13, respectively). In the HLA gene analysis, DRB1*1501 and DQB1*0602 were strongly associated with IMN (P = 1.14E-11 and 1.25E-11, respectively). The interaction was strongest between HLA-DRB1*15:01 - HLA-DQB1*06:02 and the intronic SNP rs2715928 (OR = 17.53, P = 4.26E-26). Furthermore, positive interaction was also observed between HLA-DRB1*15:01 - HLA-DQB1*06:02 and the missense SNP rs35771982 (OR = 15.91, P = 2.76E-29), which is in strong linkage disequilibrium with 5′UTR SNP rs3749119, and intronic SNP rs16844715 (OR = 15.91, P = 2.30E-26) for IMN. Neither HLA-DRB1*15:01 nor HLA-DQB1*06:02 was associated with steroid responsiveness, overall survival and renal survival during the observation period of mean 11 years though limited number of analysis.

MHC Class II Risk Alleles and Amino Acid Residues in Idiopathic Membranous Nephropathy

Epitopes of phospholipase A2 receptor (PLA2R), the target antigen in idiopathic membranous nephropathy (iMN), must be presented by the HLA-encoded MHC class II molecules to stimulate autoantibody production. A genome-wide association study identified risk alleles at HLA and PLA2R loci, with the top variant rs2187668 within HLA-DQA1 showing a risk effect greater than that of the top variant rs4664308 within PLA2R1. How the HLA risk alleles affect epitope presentation by MHC class II molecules in iMN is unknown. Here, we genotyped 261 patients with iMN and 599 healthy controls at the HLA-DRB1, HLA-DQA1, HLA-DQB1, and HLA-DPB1 loci with four-digit resolution and extracted the encoded amino acid sequences from the IMGT/HLA database. We predicted T cell epitopes of PLA2R and constructed MHC-DR molecule-PLA2R peptide-T cell receptor structures using Modeler. We identified DRB1*1501 (odds ratio, 4.65; 95% confidence interval [95% CI], 3.39 to 6.41; P<0.001) and DRB1*0301 (odds ratio, 3.96; 95% CI, 2.61 to 6.05; P<0.001) as independent risk alleles for iMN and associated with circulating anti-PLA2R antibodies. Strong gene-gene interaction was noted between rs4664308(AA) and HLA-DRB1*1501/DRB1*0301. Amino acid positions 13 (P<0.001) and 71 (P<0.001) in the MHC-DRβ1 chain independently associated with iMN. Structural models showed that arginine13 and alanine71, encoded by DRB1*1501, and lysine71, encoded by DRB1*0301, facilitate interactions with T cell epitopes of PLA2R. In conclusion, we identified two risk alleles of HLA class II genes and three amino acid residues on positions 13 and 71 of the MHC-DRβ1 chain that may confer susceptibility to iMN by presenting T cell epitopes on PLA2R.

[Idiopathic membranous nephropathy: Evolution in understanding the problem]

The review highlights the evolution of ideas on the. mechanisms responsible for the 'development of membranous nephropathy(MN), glomerulopathy that is the most common cause of nephrotic syndrome in adults. Primary emphasis is placed on the primary form of MN. The important step to understanding the nature of this clinical and morphological form of glomerulonephritis is to create its animal model (Heymann nephritis), then to decipher the mechanisms of immune complex damage (complement activation,a role of cellular immunity), and to identify autoantigens responsible for the development of idiopathic MN in man (podocyteneutral endopeptidase, transmembrane M-type phospholipase A2 receptor, thrombospondin type-1 domain-containing 7A. The findings constituted the basis for developing current methods for the diagnosis and treatment of MN, including the pathogenetically sound inhibition of autoantibody production, as well as a molecular orientation effect on podocyte dysfunction.

Insights into kidney diseases from genome-wide association studies

Over the past decade, genome-wide association studies (GWAS) have considerably improved our understanding of the genetic basis of kidney function and disease. Population-based studies, used to investigate traits that define chronic kidney disease (CKD), have identified >50 genomic regions in which common genetic variants associate with estimated glomerular filtration rate or urinary albumin-to-creatinine ratio. Case-control studies, used to study specific CKD aetiologies, have yielded risk loci for specific kidney diseases such as IgA nephropathy and membranous nephropathy. In this Review, we summarize important findings from GWAS and clinical and experimental follow-up studies. We also compare risk allele frequency, effect sizes, and specificity in GWAS of CKD-defining traits and GWAS of specific CKD aetiologies and the implications for study design. Genomic regions identified in GWAS of CKD-defining traits can contain causal genes for monogenic kidney diseases. Population-based research on kidney function traits can therefore generate insights into more severe forms of kidney diseases. Experimental follow-up studies have begun to identify causal genes and variants, which are potential therapeutic targets, and suggest mechanisms underlying the high allele frequency of causal variants. GWAS are thus a useful approach to advance knowledge in nephrology.

Membranous Nephropathy: A Journey From Bench to Bedside

Lessons from an animal model that faithfully resembles human membranous nephropathy (MN) have informed our understanding of the pathogenesis of this organ-specific autoimmune disease and common cause of nephrotic syndrome. After it was established that the subepithelial immune deposits that characterize experimental MN form in situ when circulating antibodies bind to an intrinsic podocyte antigen, it was merely a matter of time before the human antigen was identified. The M-type phospholipase A2 receptor 1 (PLA2R) represents the major target antigen in primary MN, and thrombospondin type 1 domain-containing 7A (THSD7A) was more recently identified as a minor antigen. Serologic tests for anti-PLA2R and kidney biopsy specimen staining for PLA2R show >90% specificity and 70% to 80% sensitivity for the diagnosis of primary MN in most populations. The assays distinguish most cases of primary MN from MN associated with other systemic diseases, and sequential anti-PLA2R titers are useful to monitor treatment response. A positive pretransplantation test result for anti-PLA2R is also helpful for predicting the risk for posttransplantation recurrence. Identification of target epitopes within PLA2R and the genetic association of primary MN with class II major histocompatibility and PLA2R1 variants are 2 additional examples of our evolving understanding of this disease.

Long-Term Exposure to Air Pollution and Increased Risk of Membranous Nephropathy in China

The effect of air pollution on the changing pattern of glomerulopathy has not been studied. We estimated the profile of and temporal change in glomerular diseases in an 11-year renal biopsy series including 71,151 native biopsies at 938 hospitals spanning 282 cities in China from 2004 to 2014, and examined the association of long-term exposure to fine particulate matter of <2.5 μm (PM_2.5) with glomerulopathy. After age and region standardization, we identified IgA nephropathy as the leading type of glomerulopathy, with a frequency of 28.1%, followed by membranous nephropathy (MN), with a frequency of 23.4%. Notably, the adjusted odds for MN increased 13% annually over the 11-year study period, whereas the proportions of other major glomerulopathies remained stable. During the study period, 3-year average PM_2.5 exposure varied among the 282 cities, ranging from 6 to 114 μg/m³ (mean, 52.6 μg/m³). Each 10 μg/m³ increase in PM_2.5 concentration associated with 14% higher odds for MN (odds ratio, 1.14; 95% confidence interval, 1.10 to 1.18) in regions with PM_2.5 concentration >70 μg/m³ We also found that higher 3-year average air quality index was associated with increased risk of MN. In conclusion, in this large renal biopsy series, the frequency of MN increased over the study period, and long-term exposure to high levels of PM_2.5 was associated with an increased risk of MN.

Anti-Phospholipase A2 Receptor (PLA2R) Antibody and Glomerular PLA2R Expression in Japanese Patients with Membranous Nephropathy

The phospholipase A2 receptor (PLA2R) is the major target antigen (Ag) in idiopathic membranous nephropathy (IMN). Recently, several types of immunoassay systems for anti-PLA2R antibody (Ab) have been developed. However, the correlation of serum anti-PLA2R Abs and glomerular expression of PLA2R Ag, and their association with clinicopathological characteristics have yet to be proven in Japanese patients. We examined serum anti-PLA2R Abs by both ELISA and cell-based indirect immunofluorescence assay (CIIFA), and glomerular PLA2R expression by immunofluorescence (IF) in 59 biopsy-proven MN patients including IMN (n = 38) and secondary MN (SMN) (n = 21). In this study, anti-PLA2R Abs were present in 50% of IMN patients, but was absent in SMN patients. The concordance rate between ELISA and CIIFA was 100%. Serum IgG levels were significantly lower in anti-PLA2R Ab-positive patients. Serum albumin levels correlated inversely with serum anti-PLA2R Ab titers. The prevalence and intensity of glomerular staining for IgG4 by IF were significantly higher in anti-PLA2R Ab-positive patients than in -negative patients. Glomerular PLA2 Ag expression evaluated by IF was positive in 52.6% of IMN patients, but was absent in SMN patients. The concordance rate between the prevalence of glomerular PLA2R Ag expression and anti-PLA2R Ab was 84.2%. The prevalence of anti-PLA2R Abs measured by ELISA/CIIFA was equivalent to previous Japanese studies evaluated using Western blotting. These analyses showed an excellent specificity for the diagnosis of IMN, and anti-PLA2R positivity was associated with some clinicopathological features, especially glomerular IgG4-dominant deposition.

Phospholipase A2 Receptor Gene Polymorphisms Alter its Functions and Present a Genetic Risk of an Increased Intima-Media Thickness of the Carotid Artery

Aims: Phospholipase A₂ receptor 1 (PLA₂R) has multiple biological functions other than functioning as a receptor for secretory PLA_2s. Two nonsynonymous polymorphisms in the C-type lectin-like domains (CTLD) 1 of PLA₂R gene have been associated with idiopathic membranous nephropathy. This study examined whether the same PLA₂R polymorphisms may alter functions of PLA₂R in cells expressing the variant PLA₂R. In addition, the clinical relevance of the experiment was examined.

Methods: Two nonsynonymous polymorphisms (T/C at rs3749117 and G/C at rs35771982) in CTLD1 of PLA₂R gene were completely linked. HEK293 cells expressing human wild-type PLA₂R (T at rs3749117 and G at rs35771982) or human mutant PLA₂R that had double mutations (C at rs3749117 and C at rs35771982) were constructed.

Results: HEK293 cells expressing mutant PLA₂R had lower migratory and proliferative responses to collagen I compared with cells expressing wild-type PLA₂R. In 580 male patients, PLA₂R gene polymorphisms were associated with an increase in maximum intima-media thickness (maxIMT) of the carotid artery. The multivariate regression model showed that PLA₂R gene polymorphisms were a risk factor of an increased maxIMT that was independent of conventional risk factors (OR = 1.93, 95% CI: 1.17–3.19, p < 0.01).

Conclusions: The nonsynonymous common variants of PLA₂R gene altered biological functions in cells expressing variant PLA₂R. PLA₂R gene polymorphisms present a genetic risk of an increased IMT of the carotid artery in male. The functional changes in the variant PLA₂R may potentially be responsible for its association with an increased IMT of the carotid artery.

Membranous nephropathy: A fairy tale for immunopathologists, nephrologists and patients

This article reviews the considerable progress which has been made in the recent years in the understanding of the pathophysiology of membranous nephropathy, a model of organ-specific auto-immune disease. It shows how experimental models developed more than 30 years ago have led to the identification of several human antigens including neutral endopeptidase in the neonate, phospholipase A2 receptor, and thrombospondin 1 domain 7A in the adult, and cationic bovine serum albumin in children. Thanks to a successful GWAS performed in European Caucasians, the genetics of the disease begins to be understood. These groundbreaking findings already have a major impact on patients' care owing to the development of reliable ELISA and immunofluorescence test for the detection of PLA2R antibodies and of PLA2R antigen screening in biopsies. This review will tell the story from the careful clinical observation of cases to the most recent therapeutic perspectives which have been made possible by these advances. Advances in medical science often proceed by steps which are highly interdependent. New, groundbreaking findings with important clinical implications often result from the combination of faithful experimental models and careful clinical observations. This is well illustrated by the story of membranous nephropathy which started more than 50 years ago. It is remarkable that in this disease, the experimental models predicted the pathophysiology of the human glomerulopathy. The stories that we will tell in this article are aimed at young clinical investigators who are sometimes reluctant to embark on research projects. We hope that they will convince them that bedside research performed with intellectual curiosity and a bit of chance can lead to significant progress in clinical medicine.

Genetic risk variants for membranous nephropathy: extension of and association with other chronic kidney disease aetiologies

Background

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Previous genome-wide association studies (GWAS) of 300 000 genotyped variants identified MN-associated loci at HLA-DQA1 and PLA2R1.

Methods

We used a combined approach of genotype imputation, GWAS, human leucocyte antigen (HLA) imputation and extension to other aetiologies of chronic kidney disease (CKD) to investigate genetic MN risk variants more comprehensively. GWAS using 9 million high-quality imputed genotypes and classical HLA alleles were conducted for 323 MN European-ancestry cases and 345 controls. Additionally, 4960 patients with different CKD aetiologies in the German Chronic Kidney Disease (GCKD) study were genotyped for risk variants at HLA-DQA1 and PLA2R1.

Results

In GWAS, lead variants in known loci [rs9272729, HLA-DQA1, odds ratio (OR) = 7.3 per risk allele, P = 5.9 × 10^-27 and rs17830558, PLA2R1, OR = 2.2, P = 1.9 × 10^-8] were significantly associated with MN. No novel signals emerged in GWAS of X-chromosomal variants or in sex-specific analyses. Classical HLA alleles (DRB1*0301-DQA1*0501-DQB1*0201 haplotype) were associated with MN but provided little additional information beyond rs9272729. Associations were replicated in 137 GCKD patients with MN (HLA-DQA1: P = 6.4 × 10^-24; PLA2R1: P = 5.0 × 10^-4). MN risk increased steeply for patients with high-risk genotype combinations (OR > 79). While genetic variation in PLA2R1 exclusively associated with MN across 19 CKD aetiologies, the HLA-DQA1 risk allele was also associated with lupus nephritis (P = 2.8 × 10^-6), type 1 diabetic nephropathy (P = 6.9 × 10^-5) and focal segmental glomerulosclerosis (P = 5.1 × 10^-5), but not with immunoglobulin A nephropathy.

Conclusions

PLA2R1 and HLA-DQA1 are the predominant risk loci for MN detected by GWAS. While HLA-DQA1 risk variants show an association with other CKD aetiologies, PLA2R1 variants are specific to MN.

Immunology of membranous nephropathy: from animal models to humans

Membranous nephropathy (MN), the leading cause of nephrotic syndrome in adults, is characterized by the deposition of subepithelial immune deposits that consist mainly of immunoglobulin (Ig)G and complement. Most of the cases are primary or idiopathic (iMN), while only approximately 25% of the cases are secondary to some known disease such as systemic lupus erythematosus, hepatitis B, drugs and malignancies. Most of our knowledge on the pathogenesis of iMN has relied upon old experimental models (i.e. Heymann nephritis) that have shown that immune deposits are formed in situ by the reaction of autoantibodies against the respective podocyte antigen. Recent findings indicate that podocyte proteins also act as an autoantigen in human iMN. The M-type phospholipase A2 receptor (PLA2R) has been identified as the main target antigen, as it can be found in approximately 70% of iMN patients but only rarely in other glomerulonephritides. Podocytes damage in the experimental model of Heymann nephritis is complement-mediated. In humans, the presence of complement within the subepithelial deposits is well established, but IgG4, which does not activate complement by classical or alternative pathways, represents the predominant subclass of IgG anti-PLA2R. Some evidence suggests that IgG4 anti-PLA2R autoantibodies can bind mannan-binding lectin (MBL) and activate the lectin complement pathway. A genetic background for iMN has been demonstrated by genome-wide association studies that have shown highly significant associations of the PLA2R1 and the human leucocyte antigen (HLA)-DQA1 loci with iMN. In addition to their diagnostic value, anti-PLA2R antibodies may be useful to monitor disease activity and predict response to treatment.

Antiphospholipase A2 Receptor Autoantibodies: A Step Forward in the Management of Primary Membranous Nephropathy

Since the identification of PLA2R (M-type phospholipase A2 receptor) as the first human antigenic target in primary membranous nephropathy (MN), perpetual progress has been made in understanding the pathogenesis of this disease. Accumulating clinical data support a pathogenic role for the anti-PLA2R antibodies (PLA2R ABs), but confirmation in an animal model is still lacking. However, PLA2R ABs were related to disease activity and outcome, as well as to response therapy. Accordingly, PLA2R ABs assay seems to be promising tool not only to diagnose MN but also to predict the course of the disease and could open the way to personalize therapy. Nevertheless, validation of a universal assay with high precision and definition of cut-off levels, followed by larger studies with a prolonged follow-up period, are needed to confirm these prospects.

Actualizing the Benefits of Genomic Discovery in Pediatric Nephrology

The discovery of genetic variation associated with pediatric kidney disease has shed light on the biology underlying these conditions and, in some cases, has improved our clinical management of patients. We are challenged to continue the momentum of the genomic era in pediatric nephrology by identifying novel disease-associated genetic variation and translating these discoveries into clinical applications. This article reviews the diverse forms of genetic architecture that have been found to be associated with kidney diseases and traits. These include rare, fully penetrant variants responsible for Mendelian forms of disease, copy number variants, and more common variants associated with increased risk of disease. These discoveries have provided us with a greater understanding of the molecular mechanisms underlying these conditions and highlighted key pathways for potential intervention. In a number of areas, the identification of rare, fully penetrant variants is immediately clinically relevant, whether in regard to diagnostic testing, prediction of outcomes, or choice of therapies and interventions. This article discusses limitations in the deterministic view of rare, putatively causal mutations, a challenge increasing in importance as sequencing expands to many more genes and patients. This article also focusses on common genetic variants, using those found to be associated with focal segmental glomerulosclerosis in African-Americans, IgA nephropathy, chronic kidney disease (CKD), and estimated glomerular filtration rate (eGFR) as examples. Identifying common genetic variants associated with disease will complement other areas of genomic inquiry, lead to a greater biological understanding of disease, and will benefit pediatric nephrology patients.

Membranous Nephropathy Associated With Immunological Disorder-Related Liver Disease: A Retrospective Study of 10 Cases

The association between membranous nephropathy (MN) and immunological disorder-related liver disease has not been extensively investigated, and the specific features of this uncommon association, if any, remain to be determined.We retrospectively identified 10 patients with this association. We aimed to describe the clinical, biological, and pathological characteristics of these patients and their therapeutic management. The possible involvement of the phospholipase A2 receptor (PLA2R) in these apparent secondary forms of MN was assessed by immunohistochemistry with renal and liver biopsy specimens.The mean delay between MN and liver disease diagnoses was 3.9 years and the interval between the diagnosis of the glomerular and liver diseases was <1.5 years in 5 patients. MN was associated with a broad spectrum of liver diseases including primary biliary cirrhosis (PBC), autoimmune hepatitis (AIH), and primary sclerosing cholangitis (PSC). AIH whether isolated (n = 3) or associated with PBC (n = 2) or PSC (n = 2) was the most frequent autoimmune liver disease. Circulating PLA2R antibodies were detected in 4 out of 9 patients but the test was performed under specific immunosuppressive treatment in 3 out of 9 patients. Seven of the 9 patients with available renal tissue specimens displayed enhanced expression of PLA2R in glomeruli whereas PLA2R was not expressed in liver parenchyma from these patients or in normal liver tissue. The study of immunoglobulin (Ig) subclasses of deposits in glomeruli revealed that the most frequent pattern was the coexistence of IgG1 and IgG4 immune deposits with IgG4 predominating.Detection of PLA2R antibodies in glomeruli but not in liver parenchyma is a common finding in patients with MN associated with autoimmune liver disease, suggesting that these autoantibodies are not exclusively detected in idiopathic MN.

Changing the concepts of immune-mediated glomerular diseases through proteomics

Standard classification of glomerular diseases is based on histopathologic abnormalities. The recent application of proteomic technologies has resulted in paradigm changes in the understanding and classification of idiopathic membranous nephropathy and membranoproliferative glomerulonephritis. Those examples provide evidence that proteomics will lead to advances in understanding of the molecular basis of other glomerular diseases, such as lupus nephritis. Proof of principle experiments show that proteomics can be applied to patient renal biopsy specimens. This viewpoint summarizes the advances in immune-mediated glomerular diseases that have relied on proteomics, and potential future applications are discussed.

Pathophysiological advances in membranous nephropathy: time for a shift in patient's care

Membranous nephropathy is a major cause of nephrotic syndrome of non-diabetic origin in adults. It is the second or third leading cause of end-stage renal disease in patients with primary glomerulonephritis, and is the leading glomerulopathy that recurs after kidney transplantation (occurring in about 40% of patients). Treatment with costly and potentially toxic drugs remains controversial and challenging, partly because of insufficient insight into the pathogenesis of the disease and absence of sensitive biomarkers of disease activity. The disease is caused by the formation of immune deposits on the outer aspect of the glomerular basement membrane, which contain podocyte or planted antigens and circulating antibodies specific to those antigens, resulting in complement activation. In 2002, podocyte neutral endopeptidase was identified as an antigenic target of circulating antibodies in alloimmune neonatal nephropathy, and in 2009, podocyte phospholipase A2 receptor (PLA2R) was reported as an antigenic target in autoimmune adult membranous nephropathy. These major breakthroughs were translated to clinical practice very quickly. Measurement of anti-PLA2R antibodies in serum and detection of PLA2R antigen in glomerular deposits can now be done routinely. Anti-PLA2R antibodies have high specificity (close to 100%), sensitivity (70-80%), and predictive value. PLA2R detection in immune deposits allows for retrospective diagnosis of PLA2R-related membranous nephropathy in archival kidney biopsies. These tests already have a major effect on diagnosis and monitoring of treatment, including after transplantation.

Morphology in the Digital Age: Integrating High-Resolution Description of Structural Alterations With Phenotypes and Genotypes

Conventional light microscopy has been used to characterize and classify renal diseases, evaluate histopathology in studies and trials, and educate renal pathologists and nephrologists. The advent of digital pathology, in which a glass slide can be scanned to create whole slide images (WSIs) for viewing and manipulating on a computer monitor, provides real and potential advantages compared with conventional light microscopy. Software tools such as annotation, morphometry, and image analysis can be applied to WSIs for studies or educational purposes, and the digital images are available globally to clinicians, pathologists, and investigators. New ways of assessing renal pathology with observational data collection may allow better morphologic correlations and integration with molecular and genetic signatures, refinements of classification schema, and understanding of disease pathogenesis. In multicenter studies, WSIs, which require additional quality assurance steps, provide efficiency by reducing slide shipping and consensus conference costs, and they allow slide viewing anytime and anywhere. Although validation studies for the routine diagnostic use of digital pathology still are needed, this is a powerful tool currently available for translational research, clinical trials, and education in renal pathology.

Loss of heterozygosity at the human leukocyte antigen locus in thymic epithelial tumors

Background

To study the relationship between loss of heterozygosity (LOH) at the human leukocyte antigen (HLA) locus and the pathogenicity and clinicopathological features of thymic epithelial tumors (TET).

Methods

Tumor and adjacent normal tissues were isolated from 36 TET patients. Five microsatellite loci (D6S1666, D6S265, D6S273, DS6276, and D6S291) within the HLA locus were amplified by polymerase chain reaction. DNA sequencing was used to measure the frequency of microsatellite LOH.

Results

LOH was identified in at least one locus in 83.6% of TET patients. LOH frequency at D6S1666, D6S265, D6S273, D6S276, and D6S291 was 44.4%, 16.7%, 30.5%, 38.9%, and 36.1% respectively. There was no significant association between LOH frequency in TET with tumor severity, or in the presence or absence of myasthenia gravis.

Conclusions

D6S1666, D6S265, D6S273, DS6S276, and D6S29 are sensitive loci for studying microsatellite LOH in TET. LOH within the HLA complex is implicated in the occurrence and development of TET, with the HLA-DQA1 gene likely involved. However, an understanding of the relationship between LOH and the clinicopathological features of TET requires a larger sample size than that of the present study.

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

Rituximab induces nephrotic syndrome (NS) remission in two-thirds of patients with primary membranous nephropathy (MN), even after other treatments have failed. To assess the relationships among treatment effect, circulating nephritogenic anti-phospholipase A2 receptor (anti-PLA2R) autoantibodies and genetic polymorphisms predisposing to antibody production we serially monitored 24-hour proteinuria and antibody titer in patients with primary MN and long-lasting NS consenting to rituximab (375 mg/m(2)) therapy and genetic analyses. Over a median (range) follow-up of 30.8 (6.0-145.4) months, 84 of 132 rituximab-treated patients achieved complete or partial NS remission (primary end point), and 25 relapsed after remission. Outcomes of patients with or without detectable anti-PLA2R antibodies at baseline were similar. Among the 81 patients with antibodies, lower anti-PLA2R antibody titer at baseline (P=0.001) and full antibody depletion 6 months post-rituximab (hazard ratio [HR], 7.90; 95% confidence interval [95% CI], 2.54 to 24.60; P<0.001) strongly predicted remission. All 25 complete remissions were preceded by complete anti-PLA2R antibody depletion. On average, 50% anti-PLA2R titer reduction preceded equivalent proteinuria reduction by 10 months. Re-emergence of circulating antibodies predicted disease relapse (HR, 6.54; 95% CI, 1.57 to 27.40; P=0.01), whereas initial complete remission protected from the event (HR, 6.63; 95% CI, 2.37 to 18.53; P<0.001). Eighteen patients achieved persistent antibody depletion and complete remission and never relapsed. Outcome was independent of PLA2R1 and HLA-DQA1 polymorphisms and of previous immunosuppressive treatment. Therefore, assessing circulating anti-PLA2R autoantibodies and proteinuria may help in monitoring disease activity and guiding personalized rituximab therapy in nephrotic patients with primary MN.

Recent advances in the understanding of immune-mediated nephrotic syndrome: diagnostic and prognostic implications

Glomerular diseases with severe defects in glomerular permeability give rise to heavy proteinuria and can present as nephrotic syndrome. There are many different causes of the nephrotic syndrome and a renal biopsy is nearly always needed to elucidate the underlying disease. During the last decade, substantial advances have occurred in the understanding of the pathophysiological mechanisms involved in immune-mediated glomerular diseases. Here, we review the diagnostic and prognostic implications of recent progress on the understanding of membranous nephropathy, minimal change disease, focal segmental glomerulosclerosis, amyloidosis, IgA nephropathy and membranoproliferative glomerulonephritis.