STAT4 promotes Bhlhe40 induction to drive protective IFN-g from natural killer cells during viral infection [IL18R1KO RNA-seq]
NK cells represent a cellular component of the mammalian innate immune system, and mount rapid responses against viral infection, including the secretion of the potent anti-viral effector cytokine IFN-g. Following mouse cytomegalovirus (MCMV) infection, Bhlhe40 was the most highly induced transcription factor in NK cells among the basic helix-loop-helix family. Bhlhe40 upregulation in NK cells depended upon IL-12 and IL-18 signals, with the promoter of Bhlhe40 enriched for STAT4 and the permissive histone H3K4me3, and STAT4-deficient NK cells showing an impairment of Bhlhe40 induction and diminished H3K4me3. Transcriptomic and protein analysis of Bhlhe40-deficient NK cells revealed a defect in IFN-g production during MCMV infection, resulting in diminished protective immunity following viral challenge. Finally, we provide evidence that Bhlhe40 directly promotes IFN-g by binding throughout the Ifng loci in activated NK cells. Thus, our study reveals how STAT4-mediated control of Bhlhe40 drives protective IFN-g secretion by NK cells during viral infection. Overall design: To investigate the transcriptional changes of NK cells during early MCMV infection with and without intact IL18R1, we performed RNA-seq using NK cells from WT and IL18R1-/-(KO) mice. RNA-seq was performed on FACS sorted Ly49H+ NK cells at d0 and d2 in vivo MCMV infection, where WT and IL18R1KO NK cells are paired per replicate for given infection time point (for example, D0 WT rep3 is paired with D0 KO rep3, but not D2 WT rep 3).