Memory responses of innate lymphocytes and parallels with T cells.

Natural killer (NK) cells are classified as innate immune cells, given their ability to rapidly respond and kill transformed or virally infected cells without prior sensitization. Recently, accumulating evidence suggests that NK cells also exhibit many characteristics similar to cells of the adaptive immune system. Analogous to T cells, NK cells acquire self-tolerance during development, express antigen-specific receptors, undergo clonal-like expansion, and can become long-lived, self-renewing memory cells with potent effector function providing potent protection against reappearing pathogens. In this review, we discuss the requirements for memory NK cell generation and highlight the similarities with the formation of memory T cells.