Interleukin-1, interleukin-8, tumour necrosis factor alpha and interferon gamma stimulate DNA synthesis but have no effect on apoptosis in small-intestinal cell lines.

OBJECTIVES

Cytokines stimulate lymphocyte cell proliferation and affect cell division in several other cell types. Helicobacter pylori-induced gastritis and coeliac disease are characterized by an increased cell proliferation in association with an increased production of proinflammatory cytokines, which could contribute to these cell kinetic changes. Our aim is to examine in vitro whether cytokines usually present in the gastrointestinal mucosa affect DNA synthesis and apoptosis in a rat and a human small-intestinal cell line.

METHODS

IEC-6 and FHs-74 cells were incubated for 24 h with 10(-13)-10(-9) M of tumour necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-8 (IL-8), transforming growth factor-beta (TGF-beta) and interferon gamma (IFN-gamma). IEC-6 cells were also incubated with 10(-13)-10(-9) M of interleukin-1alpha (IL-1alpha) and 10(-8) M of interleukin-1 receptor antagonist (IL-1ra). The cells were labelled with 3H-methyl thymidine for the final 4 hours, and then processed for autoradiography. DNA synthesis was evaluated by the labelling index (LI%). Apoptosis was evaluated in IEC-6 cells by changes in membrane lipid asymmetry using annexin-V binding to externalized phosphatidylserine (flow cytometry) and by estimating the caspase activity.

RESULTS

TNF-alpha, IL-1beta, IL-8 and IFN-gamma significantly and markedly increased the LI, even at low concentrations (P< 0.0001), in both IEC-6 and FHs-74 cells, as did IL-1alpha in IEC-6 cells. TGF-beta significantly reduced the LI in both cell lines (P< 0.0001), whereas IL-2, IL-6 and IL-1ra did not affect DNA synthesis significantly. None of IL-1beta, IL-8, TNF-alpha or IFN-gamma affected apoptosis in IEC-6 cells.

CONCLUSION

TNF-alpha, IL-1alpha, IL-1beta, IL-8 and IFN-gamma stimulated DNA synthesis in a human and a rat small-intestinal cell line. The cytokines exert their mitogenic action directly on the intestinal cells via specific receptors. Our findings indicate that pro-inflammatory cytokines may participate in the regulation of the gastrointestinal epithelial cell proliferation in health and disease.