Reciprocal regulation of the Il9 locus by counteracting activities of transcription factors IRF1 and IRF4

IFN-γ signalling inhibits production of IL-9, the defining cytokine of the Th9 cell subset. Here the authors show that IFN-γ does this by driving IRF1 to compete with IRF4 for Il9 promoter binding and skewing these cells towards a Th1 phenotype, an effect that reduces asthmatic inflammation in mice.