THE LONG-TERM EVOLUTION OF IMMUNE DEPOSITS IN PASSIVE HEYMANN NEPHRITIS

1. To study the long term course of passive Heymann nephritis (PHN), 4 2 adult male Wistar rats were injected with rabbit anti-FX1A serum (PH N group) and 42 rats received normal rabbit serum (control group). Two animals from each group were sacrificed 2 weeks after the inoculation and 10 animals each from the control and PHN groups were sacrificed 4 , 13, 25 and 53 weeks later. 2. The PHN group exhibited a significant elevation in 20-h proteinuria which lasted from the first week (contro l group, 9.19 +/- 0.87; PHN group, 25.3 +/- 2.66) to the 25th week (co ntrol group, 22.6 +/- 2.15; PHN group, 66.7 +/- 10.4) except for week 17. From week 29 to week 53 there was no statistical difference betwee n the 2 groups. 3. Light microscopy showed no difference between the k idneys of PHN and control rats. Immunofluorescence microscopy in PHN r ats showed granular deposition of autologous and heterologous IgG on t he glomerular basement membrane (GBM), whose intensity and pattern did not change during 53 weeks of observation. 4. When examined by electr on microscopy the glomeruli of PHN rats showed: a) electron-dense depo sits which were initially subepithelial and homogeneous and later intr amembranous, granular and often surrounded by an electron-transparent halo; b) focal thickening of the GBM at the sites of intramembranous d eposits; c) effacement of podocytes located close to the deposits; d) "penetration" of the podocytes into the GBM associated with the deposi ts; e) presence of osmiophilic granules in the cytoplasm of the podocy te located inside the GBM similar to the granules of the deposits next to them. The association of the penetration of the podocytes into the GBM with the deposits and the presence of the osmiophilic granules in side the foot process have not been described previously in PHN. 5. Th e results suggest that the podocytes play a role in the clearing of in tramembranous deposits in PHN.