One of the traditional dividing lines separating innate and adaptive immunity was the restriction of immune memory to adaptive immune cells. This paradigm has been challenged by accumulating evidence that memory responses can be evoked in natural killer (NK) cells from experimental animals, including mice and nonhuman primates.
To determine whether human NK cells also exhibit memory responses, Nikzad et al. analyzed NK cells recovered from humanized mice or NK cells found in the viral antigen-challenged skin of adult volunteers who had chickenpox as children. Antigen-specific recall responses by human NK cells were observed in both experimental systems. These findings suggest that human NK memory responses contribute to acquired host protection after either natural infections or vaccine administration.