Abstract
The multifunctional cytokine interleukin-18 (IL-18) is an important mediator in intestinal inflammatory processes. The aim of this study was to evaluate the constitutive expression of IL-18 and its receptors (IL-18Rα and IL-18Rβ) in intestinal epithelial cells (IEC) stimulated by tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). In addition, cellular proliferation and evaluation of brush border enzymes as differentiation markers were studied. Nontransformed rat intestinal epithelial IEC-6 cells were grown on an extracellular matrix (ECM) in medium with or without TNF-α, IFN-γ, or a combination of both. Gene expression of IL-18, its receptors and apoptotic markers was evaluated using real-time PCR. Expression of IL-18Rα protein was demonstrated by flow cytometry and Western blot. Enzymatic activities of brush border enzymes and caspase-1 were determined. The constitutive expression of IL-18, IL-18Rα and IL-18Rβ mRNAs and proteins were detected in IEC-6 cells. The biologically active form of IL-18 was released in response to TNF-α and IFN-γ treatment. Exogenous IL-18 had no effect on cellular proliferation, brush border enzyme activities, and gene expression of apoptotic markers. However, the addition of IL-18 stimulated production and release of the chemokine IL-8. These data suggest that IEC-6 cells may be not only a source of IL-18 but also a target for its action.