Regulation and production of IL‐8 by human proximal tubular epithelial cells in vitro

A number of inflammatory kidney diseases are associated with interstitial nephritis and influx of leucocytes in the renal interstitium. Potentially the influx of neutrophils in the interstitium may be induced by the chemotactic cytokine IL‐8. In the present study we have analysed the production of IL‐8 by cultured human proximal tubular epithelial cells (PTEC) in response to a number of proinflammatory cytokines. Primary cell lines of proximal tubular epithelium obtained from ten different kidneys, and cultured under serum‐free conditions, were found to produce IL‐8 to different degrees from not detectable levels up to 10.8±1.5 ng IL‐8 per 1×105 cells in 72 h. Gel filtration chromatography of PTEC supernatant indicated that the size of IL‐8 of PTEC is 15.1 and 8.1 kD, and is chemotactically active for polymorphonuclear neutrophils (PMN). Addition of 0.5 ng/ml rIL‐1α or 1000 U/ml recombinant tumour necrosis factor‐alpha (TNF‐α) to the culture media of PTEC induced an up‐regulation of IL‐8 production up to 6.3‐fold and 3.0‐fold, respectively. The up‐regulation by IL‐1α and TNF‐α was dose‐ and time‐dependent. In contrast, 500 U/ml recombinant interferon‐gamma (rIFN‐γ) down‐regulated the production of IL‐8 3.4‐fold. Northern blot analysis showed that IL‐1α and TNF‐α increased the expression of IL‐8 mRNA, whereas IFN‐γ reduced IL‐8 mRNA expression. Taken together, these experiments indicate that human PTEC are a potential source of IL‐8 in the kidney, and that IL‐8 produced in the proximal tubule can be induced by various proinflammatory cytokines.