Distinct subsets of tissue-recirculating NK cells revealed by single cell transcriptomic analysis of lymph- and blood-borne cells in sheep 2267560

Introduction Natural Killer (NK) cells are innate effectors that serve as a first line of defense against viral infections and tumors. NK cells are recruited from blood into tissues early following infection and during ontogeny, and can form tissue-specific resident cells, characterized by organ-specific transcriptional profiles in addition to NK subset specific profiles. However, it is unknown whether circulating NK cells that travel through nonlymphoid or lymphoid tissues and egress via lymph exhibit organ-selectivity. Methods To address this, we used single cell RNA-seq based unbiased transcriptional clustering of sorted circulating NK cells from duodenal efferent lymph, skin afferent lymph, and blood of sheep. Results The data revealed more diversity in mesenteric and skin-circulating relative to blood NK cells. Combined analysis showed unexpected cell heterogeneity with 11 distinct NK cell clusters, which were ubiquitous (similar representation in all sites), skin lymph preferential (>2.4fold enrichment relative to other sites) mesenteric lymph-preferential (>2-fold enrichment), all lymph preferential (>2.7fold) or blood preferential (>78-fold enrichment). When compared with signatures of known human NK cells, most tissues circulating NK clusters were high in tissue circulating score, as expected, and several clusters shared signatures with CD56bright NK cells. Conclusion The data support a model in which NK cells while traveling through tissues acquire functional programming and tissue preferences while remaining circulatory, serving as a specialized mobile layer of host defense. Funding Source NIH Topic Categories Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)