Anti-NCR1 monoclonal antibody, clone 30B2.5 [R-PE/CY7®]

Natural killer (NK) cells are cytotoxic innate lymphoid cells (ILCs) that mediate antiviral and antitumor responses and require the transcriptional regulator Eomesodermin (Eomes) for early development, However, the role of Eomes and its molecular program in mature NK cell biology is unclear To address this, we develop a tamoxifen-inducible, type-I -ILC-specific (Ncr1-targeted) cre mouse and combine this with Eomes-floxed mice. Eomes deletion after normal NK cell ontogeny results in a rapid loss of NK cells (but not ILC1s), with a particularly profound effect on penultimately mature stage III NK cells. Mechanisms responsible for stage III reduction include increased apoptosis and impaired maturation from stage II precursors. Induced Eomes deletion also decreases NK cell cytotoxicity and abrogates in vivo rejection of major histocompatibility complex (MHC)-class-I-deficient cells. However, other NK cell functional responses, and stage IV NK cells, are largely preserved. These data indicate that mature NK cells have distinct Eomes-dependent and -independent stages.

The bone marrow hosts NK cells whose distribution, motility and response to systemic immune challenge are poorly understood. At steady state, two-photon microscopy of the bone marrow in Ncr1(gfp/+) mice captured motile NK cells interacting with dendritic cells. NK cells expressed markers and effector molecules of mature cells. Following poly (I:C) injection, RNA-Seq of NK cells revealed three phases of transcription featuring immune response genes followed by posttranscriptional processes and proliferation. Functionally, poly (I:C) promoted upregulation of granzyme B, enhanced cytotoxicity in vitro and in vivo, and, in the same individual cells, triggered proliferation. Two-photon imaging revealed that the proportion of sinusoidal NK cells decreased, while at the same time parenchymal NK cells accelerated, swelled and divided within the bone marrow. MVA viremia induced similar responses. Our findings demonstrate that the bone marrow is patrolled by mature NK cells that rapidly proliferate in response to systemic viral challenge while maintaining their effector functions.