Interleukin-17 activates human renal epithelial cells in vitro and is expressed during renal allograft rejection.

Local production of cytokines plays a critical role in the regulation of pathophysiologic processes leading to rejection of transplanted organs. In the present study, the possible role of interleukin-17 (IL-17), a recently identified cytokine with unique properties, was investigated. IL-17 is specifically produced by activated T cells, whereas biological activities are restricted to the activation of nonhematopoietic cells. In vitro, IL-17 induced primary human proximal tubular epithelial cells, a type of cell regulating local interstitial inflammatory responses, to secrete higher levels of IL-6, IL-8, and monocyte chemoattractant protein-1, but not of the chemokine RANTES. The effect was specific for IL-17, because it was completely abrogated by a neutralizing anti-IL-17 antibody and was demonstrated to be dose- and time-dependent. In addition, IL-17 increased the production of complement component C3 by human proximal tubular epithelial cells, but not of other complement components. Immunofluorescence showed expression of IL-17 in kidney biopsies from patients suffering from graft rejection (8 of 8 positive), whereas pretransplant biopsies and normal kidneys were negative (0 of 6). Analysis of whole kidney isolates confirmed the presence of IL-17 mRNA by reverse transcription-PCR. IL-17 expression could also be found in in vitro cultured and activated graft-infiltrating T cells. These results represent the first demonstration of IL-17 protein expression in pathologic conditions and suggest that IL-17 might be important in the regulation of local inflammatory responses.