Immunological tubulo-interstitial deposits in IgA nephropathy

Fifty-one patients with IgA nephritis and tubulo-interstitial lesions of various degrees were studied to define the frequency of tubulo-interstitial immunological involvement and whether or not it may hold any significance for the course of the nephropathy. The follow-up lasted 8 to 15 years from the first clinical sign of nephropathy. By immunofluorescence, tubulo-interstitial deposits involving 10 to 35% of proximal tubules were found in 19 patients, consisting of C3 in all patients, IgG and IgA in two patients, respectively, and IgM in four. Using electron microscopy dense deposits along the tubular membrane were not found in these patients. Mononuclear infiltrates and tubular basement membrane thickening were observed more frequently by light microscopy in patients with tubulo-interstitial deposits, but they did not correlate with glomerular immunofluorescence or with glomerular cellularity or sclerosis. Twenty-one out of the 51 patients studied presented a reduction in renal function at the end of the follow-up. A significant correlation (P less than 0.001) was found between the decrease in renal function and the presence of tubulo-interstitial deposits. Four of these patients progressed toward endstage renal failure in less than 5 years, despite moderate glomerular changes at the first renal biopsy, while severe tubulo-interstitial damage with immunoglobulin and complement deposition was present. Our results suggest that tubulo-interstitial immunological deposits may have a role in the evolution of IgA nephropathy.