On the other hand, the prevalence or intensity of other IgG subclasses was identical between the groups. 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 OF-1 prevalence of glomerular PLA2R Ag expression and anti-PLA2R Ab was 84.2%. The prevalence of anti-PLA2R Abs OF-1 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. == Introduction == Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in the adult population. Approximately 75% of cases are idiopathic MN (IMN), and the remainder is secondary MN (SMN) induced by various clinical conditions including systemic lupus erythematosus (SLE), infections (hepatitis, syphilis), cancers, and drug exposure. IMN is an antibody-mediated autoimmune glomerular disease characterized by subepithelial immune deposits. Target antigens for IMN have been extensively explored to date, both experimentally and clinically. In Heymann nephritis, podocyte antigenic targets identified as megalin were shown to be responsible forin situsubepithelial immune complexes [1]. However, this antigen was not expressed in human podocytes. In 2002, Roncos group identified neutral endopeptidase (NEP) as the responsible antigen in a rare form of alloimmune antenatal MN [2]. In 2009 2009, Mouse monoclonal to SMC1 M-type phospholipase A2 receptor (PLA2R), a membrane glycoprotein localized to podocytes, was identified by Salants group as the target antigen in patients with IMN [3]. Studies have demonstrated that anti-PLA2R antibodies (Abs) ranged from 52 to 82% in patients with IMN [4], but were not detected in patients with secondary MN (SMN). During the clinical course of IMN, the degree of proteinuria and declining renal function were significantly associated with the serum anti-PLA2R antibody (Ab) level [510]. Thus, it has been suggested that serum levels of anti-PLA2R Ab are a potentially useful marker for the prediction of diagnosis and for monitoring the treatment response in IMN [510]. Anti-PLA2R Abs are primarily of the IgG4 subclass, which is consistent with the finding that most cases of IMN have IgG4-dominant subepithelial immune complexes. In Japan, the prevalence of anti-PLA2R Abs in IMN patients has been reported to be lower than in other countries [11,12]. The presence of anti-PLA2R Abs has been verified by various methods, including Western blotting, fluorescence immunoprecipitation assay (FIPA), ELISA, and cell-based indirect immunofluorescence assay (CIIFA). Recently, a commercially available ELISA based on purified human recombinant PLA2R and CIIFA utilizing fixed PLA2R-transfected HEK cells on slides as an antigenic substrate, were introduced by EUROIMMUN AG (Lubeck, Germany). Detection of anti-PLA2R Abs using ELISA was reported to have comparable sensitivity and specificity and correlate highly with the results of CIIFA in MN patients [13]. Although analysis for anti-PLA2R Abs is a useful tool for discrimination between IMN and SMN, taking serum samples at an appropriate OF-1 time is important because the Abs can disappear after immunosuppressive therapy or spontaneous remission. On the other hand, histopathological analysis of glomerular PLA2R antigen (Ag) expression would be helpful to identify the PLA2R association at the time of renal biopsy when disease activity is high. Thus, we should consider PLA2R-related MN if patients have either anti-PLA2R Ab or enhanced glomerular PLA2R Ag expression [11]. In this study, we measured anti-PLA2R Abs using two different immunoassays (ELISA and CIIFA) and analyzed glomerular expression of PLA2R Ag in Japanese patients with MN whose sera were sampled at the time of renal.