EXERCISE-INDUCED ALTERATIONS IN NATURAL-KILLER-CELL NUMBER AND FUNCTION

To study the effects of exercise on natural killer (NK) cell number an d activity (NKCA) healthy male (n = 32) and female (n = 32) subjects w ere randomly assigned to an exercise or control condition. Exercise in volved a continuous incremental protocol consisting of cycling for thr ee periods of 6 min at work rates corresponding to 55%, 70% and 85% pe ak oxygen uptake (VO2peak). Blood samples were drawn at baseline, at 6 min, 12 min and 18 min during exercise, and at 2 h following completi on of exercise. Relative to both baseline and control conditions, exer cise resulted in an increase in the number of circulating lymphocytes. The proportion of T cells (CD3(+)) and B cells (CD19(+)) significantl y decreased, and NK cells (CD3(-)CD16(+)CD56(+)) increased throughout exercise. NKCA increased (P < 0.001) during the initial 6 min of exerc ise with no further changes observed, despite increases (P < 0.001) in the number and proportion of circulating NK cells during exercise at 70% and 85% VO2peak. Plasma epinephrine and norepinephrine increased ( P < 0.001) above baseline at 12 min and 18 min. The changes in NK cell number and function were independent of gender. The results indicate that short-duration low-intensity exercise can significantly increase NK cell number and activity. However, alterations in NK cell number ar e not accompanied by changes of a similar magnitude in NKCA.