Background: Although it is widely known that proteinuria in rats with passive Heymann nephritis (PHN) is prevented by treatment with cobra venom factor (CVF), the precise mechanisms of complement-dependent proteinuria have not been fully elucidated. The aim of this study was to evaluate morphologically whether the size of subepithelial electron-dense deposits (EDDs) contributes to the onset of albuminuria.
Methods: The size of subepithelial EDDs and anionic sites in the lamina rarae externa (LRE) overlaid with subepithelial EDDs were evaluated by ruthenium red and compared between PHN and PHN treated with CVF in rats.
Results: Overt albuminuria was present on days 3 and 4 after injection of anti-Fx1A. CVF-treatment of rats with PHN prevented albuminuria (PHN + CVF: n = 6) (53.6 +/- 38.8 vs 1.02 +/- 0.55 mg/day, P < 0.01, on day 4). Rat C3 was detected along the glomerular capillary walls on day 4 post-injection in rats with PHN, but not in rats with PHN + CVF. Subepithelial EDDs were observed in both groups. Quantitative morphometric analysis revealed that CVF-treatment decreased the size of subepithelial EDDs as well as the extent of retraction of glomerular epithelial cells. In both groups the density of anionic sites in the LRE overlaid with EDDs was decreased compared with the LRE without subepithelial EDDs. However, no difference was noted between the two groups.
Conclusions: Depletion of serum complement decreases subepithelial EDDs as well as the number of sites with decreased anionic charge underlying the EDDs. Thus, the size of subepithelial EDDs plays a pivotal role in the onset of albuminuria.