IL-1α stimulated TNFα production by cultured human proximal tubular epithelial cells

Abstract

Tumor necrosis factor alpha (TNFα) production by proximal tubuli was studied by immunoperoxidase staining of 20 renal biopsies from transplant patients. A positive staining for TNFα on proximal tubuli was seen in nine out of 15 patients with interstitial infiltrate, five without clinical significant rejection and four with moderate to severe interstitial rejection. TNFα was only expressed on tubuli within areas of interstitial infiltrate. Expression of TNFα in the mononuclear cell infiltrate was seen only in three patients with interstitial rejection. Absence of TNFα could be seen in biopsies with no renal abnormalities. To obtain more information on the regulation of TNFα production, proximal tubular epithelial cells (PTEC) cultures were established and assessed for production of TNFα. Heterogenicity in production of TNFα was found in 14 tested PTEC lines cultured under serum free conditions. The presence of IL-1α in the cultures induced a time- and dose-dependent enhancement of TNFα production by PTEC. Enhanced production of TNFα was not seen after stimulation with other cytokines such as IL-2 or IFN gamma. Inhibition studies with cycloheximide indicated de novo synthesis of TNFα. Western blot analysis of supernatants of unstimulated and IL-1α stimulated PTEC indicated a 17 kd product, a size similar to that of recombinant TNFα. Northeru blot analysis revealed the presence of a 2.0 kb hybridization signal in total RNA of PTEC cultures and up regulation upon treatment of PTEC with 1 ng/ml of IL-1α. These results show that TNFα is produced by infiltrated mononuclear cells (MNC) and PTEC within areas of interstitial infiltrate, and thus may modulate the immune response during interstitial rejection.