Unilateral ureteral obstruction (UUO) results in tubulointerstitial fibrosis of the obstructed kidney. In this study, we report the contribution of tumor necrosis factor-alpha (TNF-alpha) to the fibrosis that develops after ureteral obstruction. Mice in which individual TNF-alpha receptors TNFR1 or TNFR2 had been genetically knocked out were used, and results were compared with mice of C57Bl/6 background after 5 days UUO. Both kidneys were removed and examined histologically for changes in interstitial volume (Vv(int)), collagen IV deposition, alpha-smooth muscle actin (alpha-SMA) matrix score, nuclear factor-kappaB (NF-kappaB) activity, and TNF-alpha mRNA levels. We found that the Vv(int) of contralateral unobstructed kidneys averaged approximately 7% and was indistinguishable among the three genotypes of mice. Vv(int) of ureteral obstructed kidney of C57Bl/6 mice averaged 33 +/- 3.9% after 5 days of UUO. Vv(int) of obstructed kidneys of TNFR1 mice was significantly reduced to 19.4 +/- 3.1%, whereas that of TNFR2 mice was significantly decreased to 25.4% +/- 4.8%. There was a modest but significant difference between Vv(int) of TNFR1 and TNFR2 (P < 0. 047). Both collagen IV and alpha-SMA matrix scores were decreased significantly in obstructed kidney of TNFR1 mouse compared with that of C57Bl/6 and TNFR2 mice. Nuclear extracts prepared from kidney cortex were found to have a significant increase in NF-kappaB binding activity in obstructed kidney compared with contralateral kidney. Individual knockout of the TNFR1 or TNFR2 genes resulted in significantly less NF-kappaB activation compared with the wild type, with TNFR1 being less than TNFR2 knockout. There was a significant increase in TNF-alpha mRNA in the kidney with ureteral obstruction in all three genotypes. TNFR1 knockout displayed a significant reduction in amount of TNF-alpha mRNA induced compared with wild-type or TNFR2 knockout mice. Treatment of TNFR1 knockout mice with an angiotensin converting enzyme inhibitor further decreased Vv(int) and TNF-alpha mRNA induction, suggesting an interaction of ANG II and TNF-alpha systems. These results suggest that TNF-alpha contributes, in part, to changes in interstitial volume, myofibroblast differentiation, and NF-kappaB activation in the kidney during ureteral obstruction. These changes appear to be mediated through both TNFR1 and TNFR2 gene products with effects through the TNFR1 receptor predominating. Furthermore, ANG II appears to stimulate TNF-alpha pathophysiological events leading to renal fibrosis.