Immunoelectron microscopic observation of membranous nephropathy in children using protein A-gold complex method

The ultrastructural localization of immunoglobulins (IgG, IgA, IgM), complement component (C3c), or fibrinogen-related antigen (FRA) was investigated on 5 biopsy samples from 5 children with idiopathic MN or lupus nephritis using proteinA-gold (PAG) complex method. The immunoreactivity of IgG was essentially confined to the mesangial and subepi-thelial electron-dense deposit (EDD) in all of 5 children, and more intense staining of IgG was observed in 3 children with stage II of MN than those with stage I and stage III of MN. Double immunocytochemical staining showed the same distribution of both IgG and IgM or both IgG and FRA in subepithelial EDD in 2 of 5 children. These findings suggest that IgG deposits are associated with the formation of subepi-thelial EDD in MN, and raise the possibility that IgM and FRA deposits may result from entrapment and/or immunological reaction.