Immunomorphometric studies of proteinuria in individual nephrons of rats.

BACKGROUND

Heterogeneity of proteinuria among nephrons has been directly shown by micropuncture analysis of experimental models. Since the number of nephrons per kidney that are accessible for micropuncture is very small, we have developed a new immunomorphometric method for directly studying proteinuria in a much larger number of individual nephrons. This new method is based on the luminal surfaces of thick ascending limb of the loop of Henle (TAL) cells collectively functioning as an immunoabsorbent column for anti-Tamm-Horsfall protein antibodies that enter the urinary filtrate of that nephron.

EXPERIMENTAL DESIGN

The distribution of luminal IgG deposits formed in TALs after injection of anti-Tamm-Horsfall protein antibodies was studied in three models of experimental proteinuria in rats to define the relationship between the formation of luminal deposits and the overall level of albuminuria and to test the utility of this method in analyzing the heterogeneity of luminal deposits among nephrons in other models.

RESULTS

A close relationship between the magnitude of albuminuria and the distances that luminal IgG deposits extended along the straight course of TALs in individual nephrons of rats injected with rabbit anti-Tamm-Horsfall protein antibodies was established in a model of proteinuria with a uniform pattern of glomerular hemodynamics, heterologous immune complex nephropathy in rats. In models with more heterogeneous glomerular hemodynamics, autologous immune complex nephropathy and aminonucleoside nephrosis, greater heterogeneity in luminal IgG deposit formation among nephrons was demonstrated. The distances that luminal IgG deposits extended along TALs was more variable in these models than in heterologous immune complex nephropathy rats with comparable levels of albuminuria.

CONCLUSIONS

Variability in the distances that luminal IgG deposits extend along TALs reflects heterogeneity among nephrons. The luminal deposit technique provides a new means for direct analysis of variability of dysfunction in many individual nephrons not accessible to micropuncture.