Memory-like Natural Killer cells become resident in non-lymphoid tissue to maintain tissue health

Tissue health is dictated by the capacity to respond to perturbations and then return to homeostasis. Mechanisms that initiate, maintain, and regulate immune responses in tissues are therefore essential. Adaptive immunity plays a key role in these responses, with memory and tissue-residency being cardinal features. A corresponding role for innate cells is unknown. Here we have identified a population of innate lymphocytes that we term tissue-resident memory-like natural killer (NKRM) cells. In response to murine cytomegalovirus infection, we show that circulating NK cells were recruited in a CX3CR1-dependent manner to the salivary glands where they formed NKRM cells, a long-lived tissue-resident population that prevented autoimmunity via TRAIL-dependent elimination of CD4+ T cells. Thus, NK cells develop adaptive-like features, including long-term residency in nonlymphoid tissues, to modulate inflammation, restore immune equilibrium and preserve tissue health. Modulating the functions of NKRM cells may provide additional strategies to treat inflammatory and autoimmune diseases. Overall design: Salivary gland NK cells (live CD45+TCRb- CD3-CD19-NKp46+CD49b+CD200r- cells) were sorted from a pool of 12 mice at day 120 post murine cytomegalovirus infection for single cell RNA sequencing