Carbohydrate consumption during cycling increases in vitro NK cell responses to IL-2 and IFN-γ

Introduction. Exercise has been shown to lower blood natural killer cell concentration and activity for up to 24-h after exercise; however, the mechanism underlying this effect is not clearly defined. We have speculated that an exercise-induced change in T-cell control of NK cells is at least partly responsible for the post-exercise suppression. As a follow-up to our previous research, the purpose of this study was to examine the T and NK cells responses during and following moderate/high-intensity endurance exercise. Methods. Eight male subjects (20 +/- 1 y; VO2peak = 67.22 +/- 2.79 mL-kg(-1)mL(-1)) were recruited to complete two 1-h (75-80% VO2peak) cycling trials in a random counterbalanced order: carbohydrate (CHO) and placebo (PLA). Venous blood samples were collected before (PRE), immediately (POST), 2-h (2H), and 4-h (4H) after exercise. NK (CD3(-)/56(+)) and activated NK (CD3(-)/56(+)/69(+)) number were measured using flow cytometry. NK cell activity (NKCA) was determined using both a Cr-51 release assay (NKCA-51) and activated NK cell number (NKCA-69). Whole blood samples were stimulated with IL-2, IFN-gamma, IL-4, IL-12, and no stimulation for 12-h and then analyzed for NK cell activity using a Cr-51 release assay (NKCA-51). Results. Leukocyte counts and unstimulated NKCA were not different between CHO and PLA; however, exercise significantly increased NKCA (P < .05). Fold change in IL-2, IFN-gamma, and IL-2 + IFN-gamma-stimulated NKCA were significantly greater in CHO compared to PLA (P < .05). No effect of drink was found for IL-4, IL-12, and IL-4 + IL-12-stimulated NKCA. Discussion. The fold change in IL-2-stimulated NKCA is consistant with our previous published work. The drink effect for Th1 (but not Th2) cytokines suggests they may play a more significant role in modulating NKCA following a strenuous bout of aerobic exercise when CHO is consumed. (c) 2006 Elsevier Inc. All rights reserved.