Demonstration of C3d deposits in membranous nephropathy.

An immunoperoxidase technique for light microscopy was carried out in 16 patients with idiopathic membranous nephropathy in order to determine the role of the complement system in glomeruli. Although C3 deposits are found in 50% of the cases, C3d deposits are identified in all cases in association with IgG deposits. This suggests that C3 deposits are degraded and dissociated from immune complexes. Patients with glomerular C3 deposits showed more proteinuria than those without glomerular C3 deposits. The presence of C3 deposits indicates the importance of proteinuria in human membranous nephropathy.