IL-15 priming alters the regulation of IFN-γ production in NK cells

Abstract Natural killer (NK) cells are innate lymphocytes important for the control of infections and tumors. Their effector functions can be triggered by inflammatory cytokines or engagement of ITAM-bearing activating receptors. We previously reported that IFN-γ production through ITAM signaling is metabolism-dependent in naïve NK cells. However, cytokine stimulation of naïve cells or priming with high-dose IL-15 prior to ITAM stimulation leads to metabolism-independent IFN-γ production. While both cytokine and receptor stimulation leads to similar IFN-γ protein production, only cytokines upregulate Ifng transcript, suggesting that protein production is translationally regulated in the receptor condition. Based on these observations, we hypothesized that IL-15 priming leads to transcriptional regulation of IFN-γ production in response to ITAM signaling. Indeed, IL-15 primed NK cells strongly upregulated Ifng transcript after receptor stimulation, rendering this receptor stimulation metabolism-independent. Inhibition of glycolysis with 2DG or mTOR with rapamycin during priming inhibited Ifng upregulation upon receptor stimulation and returned metabolism-dependent IFN-γ production. RNA-seq analysis of cytokine-, receptor-stimulated, and IL-15 cultured NK cells identified an association between glycolysis, mTORC1 signaling, and MYC targets with Ifng upregulation. Ongoing work aims to identify how ITAM signaling differs in IL-15 primed versus naïve NK cells. Our studies demonstrate distinct mechanisms of IFN-γ protein production in response to ITAM-mediated signaling between naïve and IL-15 primed NK cells.