Can just 15 minutes of moderate-intensity exercise mobilize cytotoxic NK cells into circulation?

Intro: Acute exercise transiently mobilizes natural killer (NK) cells into the bloodstream with the degree of mobilization directly related to the intensity of the exercise. This increase in NK cells is thought to offer a period of heightened immune activity during exercise and is of particular interest to cancer patients as NK cells can kill tumor cells without prior sensitization. Previous work demonstrating the benefits of exercise on NK cells used vigorous bouts of exercise lasting 30 minutes or longer, which may not be attainable for cancer patients. The objective of this study was to determine whether a short bout of moderate-intensity exercise can mobilize activated, cytotoxic NK cells into circulation. We hypothesized that i) a bout of moderate-intensity exercise would significantly increase NK cells in the blood and ii) the exercise-induced NK-cell mobilization would occur rapidly, such that the relative increase in blood NK cells would not differ after 15 minutes of exercise and 30 minutes of exercise. Methods: In this pilot study, ten healthy, non-athletes (4 female; aged 18-40 years) cycled for 30 minutes at 55% of their heart rate reserve. Venous blood was obtained pre-, after 15 minutes, and after 30 minutes of exercise, and was analyzed by flow cytometry. The proportion of NK cells, CD16+ and CD57+ NK-cells were compared between the three time points by repeated measures ANOVA with Greenhouse Geisser corrections. Sidak-corrected post-hoc tests were used to further analyze significant main effects. Results: All subjects successfully completed the exercise (mean ± standard deviation heart rate: 144 ± 2 bpm; rating of perceived exertion: 11 ± 0.25 (of 20)). There was a significant main effect of time on the proportion of NK cells present in the blood (F (1.253, 10.025) = 7.719, p= 0.016). Post-hoc analyses indicate that there was a significant increase at minute 15 relative to baseline (p=.050), with no further increase at minute 30 relative to minute 15 (p=.175). There was no main effect of time on the proportion of CD57+NK cells (F (1.451, 10.159) = 0.335, p= 0.656) or CD16+ NK cells (F (1.154, 9.231) = 3.020, p= 0.113) in our sample. Conclusion: The results from this pilot study indicate that 15 minutes of moderate-intensity cycling mobilizes NK cells into the bloodstream. However, we did not detect significant differences in NK cells with an activated, highly cytotoxic phenotype. While limited by a small sample, these results build upon prior work demonstrating a significant effect of longer-lasting, vigorous-intensity exercise. The current results suggest that a more accessible exercise intervention for individuals with health limitations can also significantly increase NK cells into the blood, but that greater intensity exercise may be required to mobilize particular subsets of NK cells. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.