Membranous glomerulonephritis associated with industrial mercury exposure. Study of pathogenetic mechanisms

The nephrotoxicity associated with mercury may be manifested as either acute tubular necrosis or an immune complex glomerulonephritis, depending upon the conditions under which the patient is exposed to the metal. Two patients with industrial exposure to mercury developed the nephrotic syndrome due to membranous glomerulonephritis. A multidisciplinary approach was used to define more precisely the pathogenetic mechanisms involved in the production of the glomerular lesion. Although glomeruli were normal by light microscopy, immunohistochemical studies demonstrated confluent finely granular epimembranous deposits of IgG and C3. This distribution was confirmed at the ultrastructural level with immunoelectron microscopy. High resolution elemental analysis of electron dense inclusions in tubular epithelial phagolysosomes demonstrated energy dispersion spectra characteristic of coexisting mercury and selenium. Eluates from the biopsy material were not immunoreactive against normal rat or human kidney. There was no immunoreactivity of epimembranous deposits with antibodies having renal tubular epithelial antigen or urinary uromucoid specificity. These observations suggest that a distinctive immunopathologic lesion is associated with mercury-associated membraneous glomerulonephritis, that the role of the metal itself may only be coincidental, and that the involved antigen remains unknown. Prednisone therapy had no documented persistent beneficial influence upon the level of proteinuria in one patient who has been lost to follow-up. In one patient not treated with steroid therapy, withdrawal of exposure to the metal resulted in disappearance of mercury from body fluids and clinical remission.