Th17 cell differentiation proceeds independently of IRF8.

The transcriptional repressor/activator interferon regulatory factor 8 (IRF8) modulates the differentiation of a multitude of hematopoietic lineages. However, the role of IRF8 in CD4(+) T-cell development is less well defined, with a recent study implicating IRF8 as an intrinsic repressor of interleukin-17 (IL-17) expressing T helper type 17 (Th17) cell differentiation. Using an IRF8-EGFP reporter strain we have confirmed that IRF8 is expressed in all T helper lineages, including Th17 cells. The loss of IRF8 did not affect Th17 differentiation in vitro, beyond a small increase in IL-22 expression. Moreover, IRF8 deficiency did not enhance the Th17 immune response in experimental T-cell transfer colitis. Together, these results suggest that IRF8 does not play an essential intrinsic role in Th17 cell differentiation.