Studies with antibodies to cultured rat glomerular epithelial cells. Subepithelial immune deposit formation after in vivo injection.

To investigate the role of glomerular epithelial cell (GEC) membrane proteins in the in situ formation of subepithelial immune deposits, the authors raised a rabbit antiserum against GEC that had been grown in culture (anti-GEC). By indirect immunofluorescence (IF) on normal rat kidney, anti-GEC stained proximal tubular brush border (BB). After intravenous injection into animals, granular glomerular capillary wall staining for IgG was present by IE and subepithelial immune deposits were identified by standard transmission and immunoelectron microscopy. Using the latter technique, injected anti-GEC IgG was identified beneath slit diaphragms and in endocytic-coated pits and intracellular vesicles of podocytes. Anti-GEC immunoprecipitated gp330 and two other proteins from radiolabeled BB. These proteins also were identified by sheep anti-rat Fx1A, the antiserum responsible for passive Heymann nephritis. Anti-GEC and anti-Fx1A also immunoprecipitated five identical proteins from surface-labeled GEC. Biosynthetically-labeled but not surface-labeled GEC contained immunoprecipitable gp330. Thus, injection into rats of antibodies raised against cultured GEC can produce subepithelial immune deposits, a disease process classically induced by antibodies to BB or its purified components. In addition to gp330, GEC and BB share other antigenic determinants that may contribute to the formation of these immune deposits.