Tuning of Natural Killer Cell Reactivity by NKp46 and Helios Calibrates T Cell Responses

Abstract

Natural killer (NK) cells are lymphocytes involved in antimicrobial and antitumoral immune responses. Using N-ethyl-N-nitrosourea mutagenesis in mice, we identified a mutant with increased resistance to viral infections because of the presence of hyperresponsive NK cells. Whole-genome sequencing and functional analysis revealed a loss-of-function mutation in the Ncr1 gene encoding the activating receptor NKp46. The down-regulation of NK cell activity by NKp46 was associated with the silencing of the Helios transcription factor in NK cells. NKp46 was critical for the subsequent development of antiviral and antibacterial T cell responses, which suggests that the regulation of NK cell function by NKp46 allows for the optimal development of adaptive immune responses. NKp46 blockade enhanced NK cell reactivity in vivo, which could enable the design of immunostimulation strategies in humans.

A point mutation in the Ncr1 signal peptide impairs the development of innate lymphoid cell subsets

“…18,21 We show that expression of Ncr1 mRNA was similar in NK cells of both wild-type, Ly5.1 C14R mouse strains suggesting that the gene is effectively transcribed but that alterations occur after this stage. The Noé strain also showed poor cell surface expression of NKp46, and like the NKp46 C14R NK cells, displayed no change in mRNA expression.…”

“…When NK cells were cross-linked through NK1.1, they showed a trend towards increased degranulation which was not statistically significant on the whole NK cell population (Figure 4A), but was statistically significant when restricted to the immature NK cell subset (SI Appendix, Figure S5), consistent with previous findings on Noé mice. 18 Regardless of this point, however, the in vitro anti-tumor NK cell cytolytic capacity was intact in NK cells from Ly5.1 C14R mice (Figure 4B and SI Appendix, Figure S5). Combined, these data suggest that NKp46 C14R NK cells are functionally competent and can induce cell lysis through multiple pathways but exhibit defects in vitro when recognition requires engagement of NKp46.

10.1080/2162402X.2018.1475875-F0004Figure 4.Ly5.1 C14R NK cells cells show altered sensitivity to stimuli in vitro but fail to control melanoma tumor development in vivo .

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“…Various strains of mice have been generated that either lack Ncr1 or exhibit mutations that have been chemically induced. 12,17,18 These lines ( Ncr gfp/gfp , Ncr1 Noe/Noe and Ncr1 iCre/iCre ) exhibit different phenotypes, possibly as a consequence of their difference in NKp46 protein expression. For example, Ncr1 Noe/Noe and Ncr1 iCre/iCre strains harbor modest gene changes but preserve the protein while Ncr1 gfp/gfp mice, 17 and Ncr1 gfp/gfp Klrk1 −/- double knockout mice which have defects in both NKp46 and NKG2D expression, 19 lack exons 5–7 resulting in a complete disruption of the protein.…”

“…Narni-Mancinelli et al 18 first described the effect of the point mutation W32R in a colony of C57BL/6J mice carrying N-ethyl-N-nitrosourea (ENU)–induced mutations (called Noé mice). These mice had normal numbers of NK cells but showed an impaired expression of NKp46 on the cell surface.…”

“…Noé NK cells were hyper responsive to various stimuli in vitro and Noé mice were more resistant to infection with mouse cytomegalovirus. 18 Glasner et al . 20 further characterized the effect of the Noé mutation clarifying that the NKp46 W32R protein could reach the surface of NK cells, but in a slow and unstable manner.…”