Evidence of sex-based differences in natural killer cell responses to exercise and carbohydrate intake in children.

Distinct natural killer (NK) cell subsets (CD56bright and CD56dim) are mobilized with exercise and these cells may serve adaptive functions. We determined the distribution of NK cell subsets in response to exercise and carbohydrate (CHO) intake in young girls and compared these responses with previous findings in young boys of the same age. Twelve girls (12 years old) cycled for 60 min at 70% VO2max while drinking 6% CHO or flavoured water. Blood was collected at rest, during (30 and 60 min) and following (30 and 60 min) exercise to identify NK cells as CD3-CD56bright or CD3-CD56dim. CD69 expression on total CD3-CD56+ cells was also determined. A trend (P=0.07) was found for a trial x time interaction in CD56dim cell counts, with values lower with CHO than with water. CHO intake did not influence CD56bright responses (P>or=0.39). The CD56bright:CD56dim ratio increased during recovery from exercise (P<0.001), compared to rest, with no effect of CHO intake (P=0.48). CD69 expression was not different between exercise or recovery and rest. Like young boys, girls experience an elevated CD56bright:CD56dim ratio during recovery from exercise and CHO intake attenuates the exercise-induced CD56dim but not CD56bright cell response. Unlike young boys, girls do not experience a CHO-induced increase in the CD56bright:CD56dim ratio during recovery and CD69 expression does not increase on CD3-CD56+ cells during recovery. We conclude that even in young children sex-based differences exist in the NK cell response to exercise and CHO intake.