Synergistic effect of interleukin-1 and CD40L on the activation of human renal tubular epithelial cells

Background. Renal tubular epithelial cells are a central cell type in tubul ointerstitial inflammation because they can produce inflammatory mediators such as cytokines and chemokines. Several signals derived from either monoc ytes or activated T calls have been reported to regulate the activation of tubular epithelial cells. We studied this regulation in more detail by comb ined treatment with CD40 ligand and the proinflammatory cytokine interleuki n-1 (IL-1) in vitro. Methods. The regulation of cytokine and chemokine production was studied in primary cultures of human proximal tubular epithelial cells (PTECs). PTECs were activated by coculture with CD40L-transfected murine fibroblasts in c ombination with recombinant human cytokines. The production of IL-6, IL-8, monocyte chemoattractant protein-1 (MCP-1), and RANTES were measured by spe cific enzyme-linked immunosorbent assay. Results. The combined activation of PTECs with CD40L and IL-1 resulted in s trong synergistic effects on the production of IL-6, IL-8, and RANTES, wher eas only an additive stimulation of MCP-1 production was observed. The effe cts were specific for IL-I and could be neutralized by the addition of the IL-1R antagonist. Both IL-1 alpha and IL-1 beta showed similar effects on c ytokine production by PTECs. The effects of IL-1 were dose dependent, and k inetic experiments showed that synergistic effects were observed after 24 h ours of activation and remained present for at least five days. Reverse tra nscription-polymerase chain reaction analysis showed that human PTECs could express both IL-1 alpha and IL-1 beta. The activation of PTECs with IL-1 r esulted in an up-regulation of CD40 expression on these cells. Conclusions. A complex network of regulation exists for the production of c ytokines and chemokines by PTECs. The combined treatment results in strong synergistic effects on IL-6, IL-8, and RANTES production. This strengthens the potential role of tubular epithelial cells in inflammatory responses wi thin the kidney.