A simple method to measure NK cell cytotoxicity in vivo.

Natural killer (NK) cells were discovered in the 1970 s and named after their naturally occurring cytotoxic activity against tumor cells. It has recently become clear that NK cells are not just killers and that malignancy is unlikely to be the selective pressure driving the evolution of NK cells. Indeed, NK cells secrete a host of cytokines and chemokines that contribute to tissue remodeling at the feto-maternal interface and to both innate and adaptive immunity during infection. Moreover, in certain conditions, they cannot deliver functions cell autonomously, as they require priming from other cells, namely dendritic cells. Nevertheless, natural cytotoxicity is still considered an important parameter used to evaluate NK cell biology, both in the clinic and in the research lab. In this chapter we describe a simple method to quantify spontaneous NK cell cytotoxicity in vivo.