Glomerular epithelial cell endocytosis of immune deposits in human lupus nephritis

Sixteen human renal biopsies taken from patients suffering from systemic lupus erythematosus nephritis were examined using an immunohistochemical method which allows the localisation of IgG at both light and electron-microscopical levels. The tissue was embedded in the hydrophilic resin lowicryl K4M and sections were stained using gold-labelled antibodies. On routine light microscopical examination the biopsies were diagnosed as: 1 case of WHO type II, 3 type III, 9 type IV, 2 type V, and 1 type III/V. Using light microscopy, IgG was localised in the glomerulus using the IGSS staining method. In some cases staining was seen within the glomerular epithelial cell cytoplasm. At the ultrastructural level the presence of IgG was demonstrated within vesicles in the cytoplasm of the epithelial cells in 0/1 type II, 2/3 type III, 8/9 type IV, 1/2 type V, and 1/1 type III/V cases: in some vesicles deposits of immune material were electron-dense but in others immune material was electron-lucent. Our results suggest that the human glomerular epithelial cell can endocytose IgG and that this may be part of a clearance mechanism acting within the glomerulus.