Abstract
Human memory T cells (T(M) cells) that produce IL-17 or IL-22 are currently defined as Th17 or Th22 cells, respectively. These T cell lineages are almost exclusively CCR6(+) and are important mediators of chronic inflammation and autoimmunity. However, little is known about the mechanisms controlling IL-17/IL-22 expression in memory Th17/Th22 subsets. We show that common γ chain (γc)-using cytokines, namely IL-2, IL-7, and IL-15, potently induce Th17-signature cytokine expression (Il17a, Il17f, Il22, and Il26) in CCR6(+), but not CCR6(-), T(M) cells, even in CCR6(+) cells lacking IL-17 expression ex vivo. Inhibition of phosphoinositide 3-kinase (PI-3K) or Akt signaling selectively prevents Th17 cytokine induction by γc-cytokines, as does ectopic expression of the transcription factors FOXO1 or KLF2, which are repressed by PI-3K signaling. These results indicate that Th17 cytokines are tuned by PI-3K signaling in CCR6(+) T(M) cells, which may contribute to chronic or autoimmune inflammation. Furthermore, these findings suggest that ex vivo analysis of IL-17 expression may greatly underestimate the frequency and pathogenic potential of the human Th17 compartment.