The Transcription Factor E4BP4 Is Not Required for Extramedullary Pathways of NK Cell Development

Abstract

NK cells contribute to antitumor and antiviral immunosurveillance. Their development in the bone marrow (BM) requires the transcription factor E4BP4/NFIL3, but requirements in other organs are less well defined. In this study, we show that CD3−NK1.1+NKp46+CD122+ NK cells of immature phenotype and expressing low eomesodermin levels are found in thymus, spleen, and liver of E4BP4-deficient mice, whereas numbers of mature, eomesoderminhigh conventional NK cells are drastically reduced. E4BP4-deficient CD44+CD25− double-negative 1 thymocytes efficiently develop in vitro into NK cells with kinetics, phenotype, and functionality similar to wild-type controls, whereas no NK cells develop from E4BP4-deficient BM precursors. In E4BP4/Rag-1 double-deficient (DKO) mice, NK cells resembling those in Rag-1–deficient controls are found in similar numbers in the thymus and liver. However, NK precursors are reduced in DKO BM, and no NK cells develop from DKO BM progenitors in vitro. DKO thymocyte precursors readily develop into NK cells, but DKO BM transfers into nude recipients and NK cells in E4BP4/Rag-1/IL-7 triple-KO mice indicated thymus-independent NK cell development. In the presence of T cells or E4BP4-sufficient NK cells, DKO NK cells have a selective disadvantage, and thymic and hepatic DKO NK cells show reduced survival when adoptively transferred into lymphopenic hosts. This correlates with higher apoptosis rates and lower responsiveness to IL-15 in vitro. In conclusion, we demonstrate E4BP4-independent development of NK cells of immature phenotype, reduced fitness, short t1/2, and potential extramedullary origin. Our data identify E4BP4-independent NK cell developmental pathways and a role for E4BP4 in NK cell homeostasis.

Cutting Edge: Salivary Gland NK Cells Develop Independently of Nfil3 in Steady-State

“…ILC1s secrete IFN-g, group 2 ILCs produce IL-5 and IL-13, and group 3 ILCs secrete IL-22 and/or IL-17. ILC1s include conventional NK cells, thymic NK cells (21), intestinal intraepithelial ILC1s (13), liver-resident ILC1s (10,11,18), and CD127 + ILC1s present in inflamed mucosae (22). Our study expands the spectrum of ILC1s, identifying SG NK cells as a novel ILC1 subset with several distinctive features.…”

“…1B). These cells likely correspond to the Nfil3-independent ILC1 recently identified in the liver (10,11). We conclude that SGs are a major site for Nfil3-independent NK cells.…”

“…Infection of Nfil3 2/2 mice resulted in the appearance of NK cells that express the m157-specific receptor Ly49H (9), suggesting that combined signals transmitted by Ly49H and proinflammatory cytokines, such as IFN-a/b and/or IL-12, are sufficient to promote the proliferation and survival of virus-specific NK cells. Moreover, Nfil3 2/2 mice retained a subset of VLA1 + NK cells in the liver, even in the absence of MCMV infection (10,11). The development of these liver NK cells also was Eomes independent but T-bet dependent (12).…”

Differential Requirement for Nfil3 during NK Cell Development

“…Despite the essential role for Nfil3 in the development of cNK and thymic NK cells, this and the copublished study by Crotta, et al (37) duction in TRAIL + NK cells. Future studies that determine the direct binding sites of Nfil3 in NK cells will be highly informative.…”

NK Cell Proportion and Number Are Influenced by Genetic Loci on Chromosomes 8, 9, and 17

“…Apart from Il18, the CD3 complex, Thy1, and Cbl, all of which are associated with T cell function, are all encoded within the chromosome 9 locus. These genes could potentially modulate T cell homeostasis, which would have an indirect effect on NK cell number, as NK cells can compete with T cells for growth factors (65,66). Il10ra, Tirap, Esam,and Cxcr5 are just a few of the other candidate genes comprised within this locus that may directly or indirectly affect NK cell number.…”