Antigens in membranous nephropathy: discovery and clinical implications

Membranous nephropathy is an autoimmune disease that results in an accumulation of antigen–antibody (IgG) immune complexes along the subepithelial region of the glomerular basement membrane and is the most common cause of nephrotic syndrome in adults. The diagnosis of membranous nephropathy is based on the presence of granular IgG on immunofluorescence microscopy and subepithelial electron dense deposits along the glomerular basement membrane on electron microscopy. Prior to 2009, the target antigen within the immune complexes was unknown. However, in the past 15 years, and in particular the past 5 years, several target antigens have been identified. These target antigens include PLA2R, THSD7A, EXT1 and EXT2, NELL1, SEMA3B, NCAM1, CNTN1, HTRA1, FAT1, PCDH7, NTNG1, PCSK6, NDNF and MPO. Several rare putative antigens have also been reported. These findings have transformed our understanding of membranous nephropathy from that of an idiopathic disease, which results from an autoimmune response to an unknown target antigen, to a disease in which a target antigen can be identified in ~80% of cases. Improved understanding of the distinctive clinical association, pathology and prognostic findings of each target antigen will have implications for clinical evaluation and therapeutic targeting in patients with membranous nephropathy. Since the discovery of PLA2R, several target antigens associated with membranous nephropathy have been identified. This Review describes the distinct clinical associations, pathology and prognostic findings associated with each of the identified target antigens and implications for the reclassification of membranous nephropathy.