The paradoxical pro- and anti-inflammatory properties of IL-27. Through ligation of its cognate receptor, IL-27 influences a range of immune cell lineages. This figure summarizes the effects of IL-27 treatment or IL-27 receptor deficiency on mast cells, monocytes, NK cells, NK T cells, CD4+ T cells and CD8+ T cells. References are listed as bracketed citations in the far right column of the figure. IFN, interferon; IL, interleukin; NK, natural killer; TNF, tumor necrosis factor.