Apoptotic cell death in human chronic renal allograft rejection

Chronic renal allograft rejection is characterized by gradual progression suggesting persistent low-grade injury. Apoptotic cell death may be initiated by low-grade injury secondary to external factors, making apoptosis a potential pathway of chronic rejection. In the present investigation, protocol kidney biopsies of 20 pediatric renal allograft recipients (12 with chronic rejection and 8 with normal histology), 9 pediatric liver allograft recipients, and 7 children with minimal change nephrotic syndrome were evaluated. The presence of apoptotic cell death was studied by determining apoptosis-induced oligonucleosomal DNA fragmentation in the biopsy specimens using 3' end labeling with terminal transferase, gel fractionation, and Southern blotting. The specific cell types with increased DNA fragmentation were determined by in situ 3' end labeling performed on sections of the biopsies. Significant DNA fragmentation was found only in the specimens from patients with chronic rejection. In situ investigation revealed increased apoptosis of both proximal and distal tubular epithelial cells, but not in the glomeruli or interstitium. The mean number of apoptotic tubular epithelial cells per 400x magnified field was higher in the renal allografts than in kidneys of liver transplant recipients or patients with minimal change nephrotic syndrome (2.3 vs. 0.8, P<0.05, in both cases). Our data provide biochemical evidence of increased apoptotic cell death of renal tubular epithelial cells in patients undergoing chronic renal allograft rejection.