Natural killer (NK) cells are components of innate immunity mediating defense at early times after viral infections. Their cytokine production and cell-mediated cytotoxicity functions overlap those of CD8 T cells elicited later during primary adaptive immune responses, but the populations are distinguished by their basal states and activating receptors as well as the kinetics of their responses. Demonstration of long-lived NK cells has led to speculation on the potential for inducing these to contribute to immunological memory. Conversely, activated CD8 T cells can acquire responses to innate cytokines and, as a result, have the potential to contribute to innate immunity. These observations beg the question: what is required to be a player in innate and adaptive immunity?
