Tissue-resident natural killer cells.

Natural killer (NK) cells kill infected and tumor cells and produce cytokines that modulate other immune cells. However, most of our current knowledge is derived from investigations of mouse splenic and human peripheral blood NK cells, "conventional" NK cells. Herein we discuss recent studies indicating that the liver contains two subpopulations of NK cells, one of which is liver-resident and bears distinct markers from another liver subpopulation that resembles conventional NK cells. Thus, the liver and potentially other organs contain tissue-resident NK cells that may differ from conventional NK cells in terms of origin, development, and/or function.