Natural Killer (NK) cells are recruited into circulation in response to physiological stress such as exercise. In adults, NK deployment and receptor expression are proportional to exercise intensity, and the cytotoxic CD56dim NK subset is preferentially deployed compared to immunoregulatory CD56bright subset. We know much less about the NK response to different exercise stimuli in children; however, pre-pubertal children are less responsive to acute exercise and recover faster than post-pubertal children and adults. The aims of this study were to (1) investigate the effects of exercise intensity and structure on NK recruitment and receptor expression, (2) compare the response among pre-pubertal and post-pubertal children, and (3) assess if factors such as fitness and physical activity were correlated with the magnitude of NK cell response. Healthy, recreationally active, pre- and post-pubertal boys and girls were recruited from the Hamilton community (N=11; 5 pre-pubertal, 6 post-pubertal). At the initial study visit, participants completed an aerobic fitness test to determine V̇O2peak and ventilatory threshold. At the subsequent visits, participants performed one of four cycling structures in a randomized, counterbalanced order, including: high-intensity continuous (HI-CONT), high-intensity intermittent (HI-INT), moderate-intensity continuous (MI-CONT), or moderate-intensity intermittent (MI-INT) exercise. Blood was collected pre-, post-exercise, 30- and 60-minutes into recovery. NK cells, CD56dim, and CD56bright NKs, activating (NKG2D and DNAM1) and inhibitory receptors (NKG2A and KIR2DL2/DL3) were quantified via flow cytometry. Participants were also outfitted with an accelerometer to measure physical activity. Three-way mixed ANOVA were used to examine effects of time, exercise and puberty on NK parameters, with Tukey’s HSD post hoc where appropriate. Pre-pubertal children showed no significant increase in the NK concentration in response to any of the exercise stimuli. Post-pubertal children, increased their NK cell concentration PRE to POST in all exercise stimuli except MI-CONT. Greater increases in NK concentration were seen POST HI-INT (124723 +/- 91596 cells/mL) and MI-INT (109644 +/- 84664 cells/mL), compared to HI-CONT (19931 +/- 1492 cells/mL) and MI-CONT (17082 +/- 9516 cells/mL), respectively (p < 0.001). Only increases in the expression of NKG2A were observed during REC1 (63.6 +/- 13.7 %), and REC2 (64.2 +/- 12.8 %) compared to PRE (57.9 +/- 13.4%) (p < 0.01). However, the density of NKG2D, NKG2A and DNAM1 were all significantly increased at REC2 compared to PRE. Fitness (R2= - 0.742) but not moderate-to-vigorous physical activity (R2= 0.098) or sedentary time (R2= 0.621) were significantly negatively associated with the magnitude of NK cell response. We demonstrated that an acute bout of intermittent cycling (5 min of exercise) leads to greater NK recruitment and a more immunoregulatory NK environment than continuous cycling in post-pubertal children. Contrarily, we showed that pre-pubertal children are not responsive to acute exercise of 30-minutes or shorter. Across our cohort, exercise also upregulated the density of expression of both activating and inhibitory receptors. Future research should examine if the NK cell response to acute exercise is maintained with repeated exercise exposures or exercise training. / Thesis / Master of Science (MSc) / This study looked at how exercise can be used to change the behavior of Natural Killer cells. These are cells that are part of the immune system and help protect people from viruses and cancer cells by quickly detecting cells that don’t belong in our bodies. They can also produce messenger chemicals to make other protective cells in the body aware of invaders. In this study children came into the lab and completed a different cycling exercise every time. In total, they completed four cycling exercises that included: 1) very hard cycling for 30 minutes; 2) very hard cycling in intervals, with 15 seconds of pedalling as hard and as fast as possible followed by a 1 minute rest, and repeating this for a total of 20 times; 3) comfortable cycling for 30 minutes; and 4) comfortable cycling in intervals. During each visit blood was collected from participants in order to count the number of natural killer cells there were before and after exercise as well as 30- and 60-minutes after the participants stopped cycling. Our study showed that in younger kids (8 to 10 years old), exercise doesn’t change how many natural killer cells are in the blood. However, in teens (14 to 18 years old) we showed that pedaling in intervals increased the number of natural killer cells in the blood more than riding a bicycle for 30 minutes straight. Our research helps us understand how exercise can be used to make our immune system stronger.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/25831 |
| Date | January 2020 |
| Creators | Ushcatz, Inna |
| Contributors | Obeid, Joyce, Medical Sciences |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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