STAT4 promotes Bhlhe40 induction to drive protective IFN-g from natural killer cells during viral infection [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 function of Bhlhe40 in NK cells during homeostasis and acute MCMV infection, we generated mixed bone marrow chimera from WT and Bhlhe40-/- mice into irradiated hosts. RNA-seq was performed on FACS sorted Ly49H+ NK cells at d0 and d2 in vivo MCMV infection, where WT and Bhlhe40-/- NK cells are paired per replicates.