Immunoelectron microscopic localization of fibrin-related antigen in human glomerular diseases.

The distribution of fibrin-related antigen (FRA) in glomeruli was examined by immunoelectron microscopy in 9 patients with idiopathic membranous nephropathy (MN), 8 patients with minimal-change nephrotic syndrome, and 10 patients with IgA nephropathy (IgA-N), using antisera against human gamma--chain, alpha-chain, mu-chain, and fibrinogen. Electron-dense reaction products of FRA were observed in the endothelium, subendothelium, and/or in electron-dense deposits (EDD). Among the three glomerular diseases, the amount of electron-dense reaction products of FRA in the endothelium was highest in MN. This suggests that coagulation occurs on the endothelium in MN. Although the mesangial EDD of IgA-N were intensely stained with reaction products of FRA, the staining was weak in the subepithelial EDD of MN. This suggests that FRA hardly penetrates into the subepithelial EDD in MN.