Light and electron microscopical changes seen in acute tubular necrosis in renal allografts

Seven renal biopsy specimens taken from three renal-allografted patients clinically suspected of having acute tubular necrosis were examined by light microscopy and five of these specimens were also examined by electron microscopy. The common findings in these three patients were as follows: The tubular lumina in all parts were dilated and the tubular epithelia were flat. Large vacuoles were occasionally observed within the tubular epithelial cell cytoplasm. These alterations were prominent in proximal convoluted tubules. Electron microscopically, the microvilli of the brush border of proximal convoluted tubules were loose and relatively short. The basal infoldings of proximal convoluted tubules were reduced or had disappeared. It could not be confirmed whether the large intracytoplasmic vacuoles apparent by light microscopic observation were intracytoplasmic or widened lateral intercellular spaces upon electron microscopy. In the most markedly damaged allograft of the three, a grayish hematoxylinophilic substance, which corresponded to autophagosomes with electron-dense round bodies upon electron microscopy, was often observed in the tubular epithelia. In addition, immature or regenerative tubular epithelia were observed. Most of these alterations were similar to those of acute ischemic change seen in non-renal transplantation.