Group 3 innate lymphoid cells (ILC3s) expressing the transcription factor (TF) RORγt are important for the defense and homeostasis of host intestinal tissues. The zinc finger TF Ikaros, encoded by Ikzf1, is essential for the development of RORγt+ fetal lymphoid tissue inducer (LTi) cells and lymphoid organogenesis, but its role in postnatal ILC3s is unknown. Here, we show that small-intestinal ILC3s had lower Ikaros expression than ILC precursors and other ILC subsets. Ikaros inhibited ILC3s in a cell-intrinsic manner through zinc-finger-dependent inhibition of transcriptional activity of the aryl hydrocarbon receptor, a key regulator of ILC3 maintenance and function. Ablation of Ikzf1 in RORγt+ ILC3s resulted in increased expansion and cytokine production of intestinal ILC3s and protection against infection and colitis. Therefore, in contrast to being required for LTi development, Ikaros inhibits postnatal ILC3 development and function to regulate gut immune responses at steady state and in disease.
Ikaros is necessary for the development of fetal lymphoid tissue inducer cells, but its role in postnatal ILC3s is unknown. Zhou and colleagues demonstrate that Ikaros negatively regulates ILC3 development and function by suppressing Ahr transcriptional activity. These findings indicate that Ikaros-mediated regulation of gut immunity occurs in a cell-type-specific manner.