Membranous Nephropathy (MN) is an auto-immune kidney disease and a common cause of nephrotic syndrome. About 30% of MN patients progress to end-stage kidney disease (ESKD) while 30% undergo spontaneous remission. The phospholipase A2 receptor (PLA2R1) is the major auto-antigen in idiopathic MN. Anti-PLA2R1 autoantibodies are found during the active phase of MN [2,3]. Predictors of disease progression include high titers of anti-PLA2R1 autoantibodies and serum creatinine levels at presentation, as well as decline in renal function during the first six months of follow-up. Investigators identified new prognostic factors in a cohort of 41 idiopathic MN patients with nephrotic syndrome and anti-PLA2R1 autoantibodies at the time of presentation. During a follow-up of at least 36 months, 21 patients had a persistent nephrotic syndrome (group A) and 20 showed partial or total remission (group R). We first measured the cross-reactivity of their sera at the time of presentation to human, rabbit and mouse recombinant PLA2R1 by western blot. All patients exhibited reactivity against human and rabbit PLA2R1, but only some of them did against mouse PLA2R1. These results suggest the presence of distinct epitopes that are differentially conserved among PLA2R1 orthologs. We then set-up three parallel ELISAs using human, rabbit and mouse recombinant PLA2R1. All 41 MN patients showed activity in human and rabbit ELISAs at presentation but only 32 of them (78%) in mouse ELISA.