IL-18 stimulates the proliferation and IFN-gamma release of CD4+ T cells in the chicken: conservation of a Th1-like system in a nonmammalian species.
The phylogeny of Th1 and Th2 subsets has not been characterized mainly due to the limited information regarding cytokines in nonmammalian vertebrates. In this study, we characterize a Th1-like regulatory system focusing on the IL-18- regulated IFN-gamma secretion. Stimulation of splenocytes with chicken IL-18 induced high levels of IFN-gamma secretion. Depletion of either macrophages or CD4(+) T cells from the splenocyte cultures caused unresponsiveness to IL-18. In contrast, PBL were unresponsive to IL-18 in the presence or absence of macrophages, but IFN-gamma secretion was stimulated by suboptimal anti-TCR cross- linking combined with IL-18. Splenocytes from five different chicken lines responded equally well to the IL-18 treatment. LSL chicken splenocytes, however, responded only to IL-18 when stimulated either with optimal TCR cross-linking alone or suboptimal TCR cross-linking combined with IL-18. IL-18 not only induced IFN-gamma secretion, but also stimulated splenocyte proliferation. This IL-18-induced proliferation was compared with the effects observed with IL-2. Both cytokines activated the splenocytes as demonstrated by increased size and MHC class II Ag up-regulation in the case of IL-18. Phenotypic analyses following 6 days of culture revealed that IL-2 mainly affected the proliferation of CD8(+) cells, whereas IL-18 had an opposite effect and stimulated the proliferation of CD4(+) cells. Taken together, these results demonstrate the conservation of Th1-like proinflammatory responses in the chicken; they characterize IL-18 as a major growth factor of CD4(+) T cells and identify two distinct mechanisms of IL-18- induced IFN-gamma secretion.[1]References
- IL-18 stimulates the proliferation and IFN-gamma release of CD4+ T cells in the chicken: conservation of a Th1-like system in a nonmammalian species. Göbel, T.W., Schneider, K., Schaerer, B., Mejri, I., Puehler, F., Weigend, S., Staeheli, P., Kaspers, B. J. Immunol. (2003) [Pubmed]
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