The relationship between aerobic fitness and natural killer cell cytotoxicity in healthy children and adolescents

Abstract

Natural killer (NK) cells are lymphocytes that can identify and destroy infected or cancerous cells without prior sensitization. Acute exercise increases total NK cytotoxic activity (NKCA) in peripheral blood. However, this may be due to the increase in NK cells in circulation post-exercise, not an improvement in the function of each cell. Interestingly, adults with higher aerobic fitness demonstrate higher NKCA/cell. The only available study in children reported lower total NKCA at baseline, but a greater increase in total NKCA with exercise in swimmers vs. non-swimmers. This study examined (1) the change in NKCA/cell following exercise in children, and (2) the relationship between aerobic fitness, pubertal status, and NKCA/cell at rest and post-exercise. Seven healthy pre- and post-pubertal children completed an aerobic fitness test on a cycle ergometer. At a second visit, participants completed a high-intensity interval cycling protocol. Blood samples were collected at rest, immediately after exercise, and after 30- and 60-minutes recovery. NKCA against a cancer cell line (K562) was quantified using flow cytometry. There was a main effect of time for NKCA/cell with a significant increase occurring between post-exercise (0.07±0.05 lysed K562 per NK) and 30-minutes recovery (0.16±0.08, p=0.014). Neither fitness nor pubertal status predicted NKCA/cell at baseline or post-exercise. The trends observed were expected, but limitations including small sample size and exclusion of elite athletes may have impacted results. This study provides a basis for future research and suggests exercise can alter NKCA/cell in children; however, the importance of aerobic fitness for NK function remains unclear.