Immunopathologic features of de novo membranous nephropathy in renal allografts.

De novo membranous nephropathy (MN) is now one of the most common forms of posttransplant glomerular disease, second only to allograft glomerulopathy. We investigated several immunopathologic and physicochemical properties of the immune complex (IC) or IC components displayed in the sera of patients with de novo MN. The parameters studied included detection of small (9S) preformed IC by monoclonal rheumatoid factor, determination of IC isoelectric point by chromatofocusing, detection of cationic IgG spectrotypes (pI 8.0-9.2), and demonstration of brush border or tubular epithelial/interstitial antibodies in the sera by indirect immunofluorescence. Of 7 de novo MN sera, 5 demonstrated the presence of each of these four immunopathologic features, whereas normal transplant patients, transplant recipients with recurrent focal sclerosis (FSGN), and those with chronic rejection did not display such features. Sera of patients with untreated idiopathic MN revealed immunochemical properties of IC that were similar to those seen in circulating IC of de novo MN. These studies suggest that a strongly nephritogenic internal milieu exists in transplant recipients with de novo MN. Our data indicate that unique immunochemical properties of IC or their components may predispose to subepithelial immune deposit formation and should provide new insights into the pathogenesis of idiopathic human MN.