EXPRESSION AND FUNCTION OF FAS (CD95) ON HUMAN RENAL TUBULAR EPITHELIAL-CELLS

Renal transplant rejection is characterized by an influx of mononuclea r cells in the tubulointerstitial area. Recent studies indicate that t ubular damage during graft rejection is dependent, at least in part, o n apoptosis. It is thought that apoptosis may be induced by the mononu clear cell infiltrate via the perforin/granzyme or the Fas/Fas ligand pathway. Fas is a 43-kD member of the tumor necrosis factor receptor f amily, and ligation results in apoptosis of the Fas-bearing cell. The present study analyzes whether Fas is expressed on human tubular epith elial cells in situ and in vitro. It was found that 50 to 70% of the t ubules in renal tissue exhibited a positive staining for Fas. To furth er study the occurrence of Fas on tubular cells, eight different prima ry proximal tubular epithelial cell (PTEC) lines were analyzed for Fas expression. More than 90% of the PTEC were positive for Fas, and trea tment with IFN-gamma resulted in an even higher expression. To determi ne whether Fas ligation resulted in apoptosis of PTEC in culture, PTEC were incubated with two different anti-Fas antibodies, which were abl e to induce apoptosis in Jurkat cells. No apoptotic PTEC were observed after Fas ligation, as determined by morphological staining and termi nal deoxynucleotidyl transferase-mediated dUTP nick end labeling analy sis. Simultaneous CD40 and Fas ligation, or treatment with IFN-gamma b efore Fas ligation, also did not result in the induction of apoptosis. Fas ligation did not result in proliferation or activation of PTEC, a s measured by interleukin-8 production. Apoptotic PTEC could only be d etected when the cells were incubated with both anti-Fas antibodies an d cycloheximide, resulting in up to 92% apoptotic cells. This study de monstrates that although renal tubular epithelial cells express Fas, t hey appear to be resistant to Fas-mediated apoptosis, suggesting that Fas-mediated apoptosis does not play a role in the induction of apopto sis during renal transplant rejection.