A comprehensive phenotypic and functional immune analysis unravels circulating anti-PLA2R antibody secreting cells in membranous nephropathy patients

ABSTRACT Introduction Primary membranous nephropathy (MN) is characterized by the presence of anti-podocyte antibodies, but studies describing phenotypic and functional abnormalities in circulating lymphocytes are limited. Methods We analyzed 68 different B- and T- cell subsets by flow cytometry in 30 MN patients (before initiating immunosuppression) comparing to 31 patients with nonimmune-mediated chronic kidney disease (CKD) and 12 healthy individuals. We also measured 19 serum cytokines in MN patients and in healthy controls. Lastly, we quantified ex vivo production of PLA2R-specific IgG by plasmablasts (measuring antibodies in culture supernatants and by newly developed FluoroSpot assay) and assessed the circulating antibody repertoire by phage immunoprecipitation sequencing (PhIP-Seq). Results After adjusting for multiple testing, plasma cells and regulatory B cells (BREG) were significantly higher (P Conclusion This extensive phenotypic and functional immune characterization shows that autoreactive plasma cells are present in the circulation of MN patients, providing a new therapeutic target and a candidate biomarker of disease activity.