Exercise induced alterations in NK-cell cytotoxicity - methodological issues and future perspectives.

With their ability to recognize and eliminate virus-infected and neoplastic cells, natural killer cells (NK-cells) represent an important part of the innate immune system. NK-cells have attracted the attention of exercise scientists for more than thirty years ago. To date, it is widely accepted that NK-cell counts in the peripheral blood are strongly influenced by acute exercise. Additionally, many studies reported effects of both, acute and chronic exercise on NK-cell cytotoxicity. However, these findings are contradictory. The inconsistence in findings may be argued with different exercise paradigms (type, duration, intensity). Moreover, strongly varying methods were used to detect NK-cell cytotoxicity. This review gives an overview of studies, investigating the impact of acute and chronic exercise on NK-cell cytotoxicity in young and old healthy adults, as well as on specific populations, such as cancer patients. Furthermore, different methodological approaches to assess NK-cell cytotoxicity are critically discussed to state on inconsistent study results and to give perspectives for further research in this field.