The effect of IL-18 on IL-12-induced CD30 expression and IL-4 and IFN-γproduction by allergen and PPD specific T cells

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Abstract
CD30 is expressed on activated T cells that, as has been suggested, preferentially produce IFN-γ. Interleukin 12 increases antigen-induced CD30 expression on T cells and IFN-γ production. Synthesis of IFN-γ can be augmented further by IL-18. The aim of our study was to investigate whether IL-18 affects the IL-12 induced CD30 expression and cytokine production by allergen or PPD specific T cells. Mononuclear cells of healthy or atopic volunteers were stimulated with PPD or allergen, respectively, to obtain specific T cell lines. T cells were restimulated with appropriate antigen and antigen-presenting cells in the presence of IL-12, IL-18 or a combination of these cytokines. After 3 days, expression of CD30 was investigated on CD4 and CD8 T cells and IFN-γ and IL-4 cytokine production was estimated in the culture supernatants. Flow cytometric analyses showed no effect of IL-18 on CD30 expression during IL-12 co-stimulation. At the same time after the optimal stimulation for CD30 expression, the levels of IFN-γ were high in PPD-stimulated cell lines but have not been up-regulated by IL-18. IFN-γ levels were much lower in allergen-stimulated T cells and although they were up-regulated by IL-12 there was no additional or synergistic effect from IL-18. IL-18, however, increased production of IL-4 in allergen-stimulated cell lines. Our studies provide new information about IL-18 activity on human cells and question its exclusive role in Th1 mediated responses.