Mitogenic action of tumour necrosis factor-alpha and interleukin-8 on explants of human duodenal mucosa

Our aim is to examine whether tumour necrosis factor-alpha (TNF-alpha) and interleukin affect the mitotic activity in explants of human duodenal mucosa and to estimate the release of cytokines from explants incubated with TNF-alpha. Biopsy specimens of normal duodenal mucosa were taken from 19 subjects that underwent upper endoscopy for investigation of dyspeptic symptoms or chronic gastrointestinal bleeding. The specimens were processed following guidelines for organ culture technique. Paired biopsy specimens from 12 subjects were cultured for 23 h to achieve steady state and thereafter the explants were incubated 25 h with 10(-13)-10(-9) M of TNF-alpha or IL-8. Mitoses were arrested in the metaphase by adding vincristine sulphate for the last three hours. The explants were then fixed and processed for microdissection. Fifteen crypts were microdissected and the total number of metaphases was determined using the whole crypt as reference volume. The number of metaphases per crypt was also estimated in explants incubated with 10(-10) M TNF-alpha in the presence of anti-IL-8 antibodies. Additional duodenal explants from seven subjects were incubated with 10(-10) M TNF-alpha for 25 h. Thereafter the release of IL-1-beta, IL-6, IL-8 and interferon gamma (IFN-gamma) into the culture medium was measured by enzyme immunoassay and expressed as pg/mg protein. TNF-alpha and IL-8 significantly increased the number of metaphases/crypts (P<0.0001). The addition of anti-IL-8 slightly reduced the number of metaphases/crypt compared to the values observed in the explants incubated with 10(-10) M TNF-alpha alone (P<0.0001). The number of metaphases/crypt in the explants incubated with 10(-10) M TNF-alpha in the presence of anti-IL-8 antibodies was, however, markedly and significantly higher than that of the controls (P<0.000). TNF-alpha induced the release of IL-8 (P<0.01) and IL-6 (P<0.05) from the duodenal explants. TNF-alpha and IL-8 are potent mitogens to human small intestinal crypts. The mitogenic action of TNF-alpha is primarily a direct effect of the cytokine and only to a minor extent mediated by a secondary production of IL-8 in the duodenal explant. Our findings indicate that TNF-alpha and IL-8 may participate in the regulation of cell proliferation in the human small intestinal epithelium.