Human natural killer cell subsets and acute exercise: a brief review.

Natural killer (NK) cells are the most responsive immune cell to acute exercise. This sensitivity to physiological stress combined with their role in innate immune defences suggests that these cells may be a link between regular physical activity and overall health status. NK cells are a heterogeneous population consisting of at least two distinct subsets based on the expression intensity of CD56. CD56(bright) and CD56(dim) cells exhibit different phenotypical and functional characteristics. In this review, we examine the effects of acute exercise on NK cell subsets, with special reference to potential health implications of the findings. The available evidence suggests a differential mobilization of NK cell subsets in response to acute exercise; CD56(bright) NK cells are less responsive than their CD56(dim) counterparts. During the post-exercise recovery period (up to 1 h), the ratio of CD56(bright):CD56(dim) cells favours the CD56(bright) subset. The potential significance of these findings is discussed in the context of normal physiological adaptation to exercise. We also discuss the potential role of exercise in certain clinical conditions (e.g., multiple sclerosis) as an adjunct therapy to mobilize the CD56(bright) subset. Further investigation into the biology of NK cell subsets and exercise should prove to be a fruitful area for years to come.