• Nicola M Tomas, Laurence H Beck, Catherine Meyer-Schwesinger, Barbara Seitz-Polski, Hong Ma, Gunther Zahner, Guillaume Dolla, Elion Hoxha, Udo Helmchen, Anne-Sophie Dabert-Gay, Delphine Debayle, Michael Merchant, Jon Klein, David J Salant, Stahl Rolf A K RAK Institut de Pharmacologie Moléculaire et Cellulaire, UMR7275, Centre National de la Recherche Scientifique and Université de Nice Sophia Antipolis, Val, and Gérard Lambeau.
• Institut de Pharmacologie Moléculaire et Cellulaire, UMR7275, Centre National de la Recherche Scientifique and Université de Nice Sophia Antipolis, Valbonne, France (N.M.T., B.S.-P., G.D., A.-S.D.-G., D.D., G.L.); University Medical Center Hamburg-Eppendorf, Hamburg, Germany (N.M.T., C.M.-S., G.Z., E.H., U.H., R.A.K.S.); Boston University School of Medicine, Boston (L.H.B., H.M., D.J.S.); and the University of Louisville (M.M., J.K.) and Robley Rex Veterans Affairs Medical Center (J.K.) - both in Louisville, KY.
• N. Engl. J. Med. 2014 Dec 11; 371 (24): 2277-2287.

BackgroundIdiopathic membranous nephropathy is an autoimmune disease. In approximately 70% of patients, it is associated with autoantibodies against the phospholipase A2 receptor 1 (PLA2R1). Antigenic targets in the remaining patients are unknown.MethodsUsing Western blotting, we screened serum samples from patients with idiopathic membranous nephropathy, patients with other glomerular diseases, and healthy controls for antibodies against human native glomerular proteins. We partially purified a putative new antigen, identified this protein by means of mass spectrometry of digested peptides, and validated the results by analysis of recombinant protein expression, immunoprecipitation, and immunohistochemical analysis.ResultsSerum samples from 6 of 44 patients in a European cohort and 9 of 110 patients in a Boston cohort with anti-PLA2R1-negative idiopathic membranous nephropathy recognized a glomerular protein that was 250 kD in size. None of the serum samples from the 74 patients with idiopathic membranous nephropathy who were seropositive for anti-PLA2R1 antibodies, from the 76 patients with other glomerular diseases, and from the 44 healthy controls reacted against this antigen. Although this newly identified antigen is clearly different from PLA2R1, it shares some biochemical features, such as N-glycosylation, membranous location, and reactivity with serum only under nonreducing conditions. Mass spectrometry identified this antigen as thrombospondin type-1 domain-containing 7A (THSD7A). All reactive serum samples recognized recombinant THSD7A and immunoprecipitated THSD7A from glomerular lysates. Moreover, immunohistochemical analyses of biopsy samples from patients revealed localization of THSD7A to podocytes, and IgG eluted from one of these samples was specific for THSD7A.ConclusionsIn our cohort, 15 of 154 patients with idiopathic membranous nephropathy had circulating autoantibodies to THSD7A but not to PLA2R1, a finding that suggests a distinct subgroup of patients with this condition. (Funded by the French National Center for Scientific Research and others.).

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