Glomerular basement membrane expansion in passive Heymann nephritis. Absence of increased synthesis of type IV collagen, laminin, or fibronectin

The distribution and synthetic rate of glomerular basement membrane components was examined in the Passive Heymann Nephritis model of experimental membranous nephropathy. The extensive tissue injury that developed included subepithelial electron-dense deposits, podocyte foot process effacement, and expansion of the glomerular basement membrane. Levels of mRNA for type IV collagen, laminin, and fibronectin from isolated glomeruli was quantitated by slot-blot analysis and showed no change in experimental animals as compared to controls at either 1 week, 3 weeks, or 3 months after disease induction. Immunoelectron microscopy with gold-labeled anti-laminin IgG revealed no difference in the number of particles bound to the glomerular basement membrane of experimental animals and controls. Immunofluorescence with both type IV collagen antisera and anti-laminin antibody showed no difference in the intensity or pattern of staining. Despite extensive glomerular damage and glomerular basement membrane thickening, no evidence was found for either an increase in the synthetic rate of type IV collagen, laminin, or fibronectin or for an accumulation of basement membrane laminin within the damaged glomeruli. Alternate processes, such as diminished density of matrix components or accumulation of other unmeasured matrix constituents, presumably account for the expansion of the glomerular basement membrane seen in experimental membranous nephropathy.