Diverse and Opposing Roles of IL-27 in Immunity

IL-27 was originally thought to play a pro-inflammatory role in immunity, however it is now clear that IL-27 also exerts potent anti-inflammatory effects. Here, we discuss some of the key studies that have elucidated the diverse and apparently paradoxical roles of IL-27. While IL-27 can promote early Th1 development there is evidence of suppressive effects in later phases of Th1 responses. IL-27 exerts a direct inhibitory effect in Th2 immunity by blocking Th2 cell differentiation. The role of IL-27 in Th17 immune responses is also complex as it seems that while IL-27 can block early Th17 development, fully differentiated Th17 cells may become resistant to the inhibitory effects of IL-27. In the field of cancer biology, IL-27 has been shown to have anti-tumourigenic effects however it acts via both immunogenic and nonimmunogenic mechanisms. Collectively, the studies discussed in this review have demonstrated multiple biological functions and mechanisms of action of IL-27.