Proper immune responses are needed to control pathogen infection at mucosal surfaces. IL-22-producing CD4(+) T cells play an important role in controlling bacterial infection in the gut; however, transcriptional regulation of these cells remains elusive. In this study, we show that mice with targeted deletion of the fourth DNA-binding zinc finger of the transcription factor Ikaros had increased IL-22-producing, but not IL-17-producing, CD4(+) T cells in the gut. Adoptive transfer of CD4(+) T cells from these Ikaros-mutant mice conferred enhanced mucosal immunity against Citrobacter rodentium infection. Despite an intact in vivo thymic-derived regulatory T cell (Treg) compartment in these Ikaros-mutant mice, TGF-?, a cytokine well known for induction of Tregs, failed to induce Foxp3 expression in Ikaros-mutant CD4(+) T cells in vitro and, instead, promoted IL-22. Aberrant upregulation of IL-21 in CD4(+) T cells expressing mutant Ikaros was responsible, at least in part, for the enhanced IL-22 expression in a Stat3-dependent manner. Genetic analysis using compound mutations further demonstrated that the aryl hydrocarbon receptor, but not ROR?t, was required for aberrant IL-22 expression by Ikaros-mutant CD4(+) T cells, whereas forced expression of Foxp3 was sufficient to inhibit this aberrant cytokine production. Together, our data identified new functions for Ikaros in maintaining mucosal immune homeostasis by restricting IL-22 production by CD4(+) T cells.
C2H2 zinc fingers are found in several key transcriptional regulators in the immune system. However, these proteins usually contain more fingers than are needed for sequence-specific DNA binding, which suggests that different fingers regulate different genes and functions. Here we found that mice lacking finger 1 or finger 4 of Ikaros exhibited distinct subsets of the hematological defects of Ikaros-null mice. Most notably, the two fingers controlled different stages of lymphopoiesis, and finger 4 was selectively required for tumor suppression. The distinct defects support the hypothesis that only a small number of genes that are targets of Ikaros are critical for each of its biological functions. The subcategorization of functions and target genes by mutagenesis of individual zinc fingers will facilitate efforts to understand how zinc-finger transcription factors regulate development, immunity and disease.
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