CHRONIC EXERCISE ENHANCES INVIVO AND INVITRO CYTOTOXIC MECHANISMS OF NATURAL IMMUNITY IN MICE

This study investigated the influence of 9 wk of chronic exercise on natural cytotoxicity in male C3H mice. Both in vivo cytotoxicity (pulmonary vasculature) and in vitro cytotoxicity (spleen) were determined for voluntary (wheel running; n = 30) and forced (treadmill running, 15 m/min, 30 min/day; n = 30) exercise protocols. A sedentary control group (n = 30) and a treadmill control group (5 m/min, 5 min/day; n = 30) were also included. After 9 wk of chronic exercise, submaximal exercise 02 uptake was reduced in the wheel-running group relative to that in sedentary or treadmill-trained mice. Maximal citrate synthase activity of soleus muscle was higher in treadmill-trained group compared with that in sedentary or wheel-running mice. Chronic exercise consistently reduced percent retention of CIRAS 3 tumor cells in the lungs of treadmill- (15.3 +/- 1.4) and wheel- (1 7.9 +/- 1.4) trained mice below that of sedentary (29.5 +/-2.7) and treadmill control (25.8 +/- 1.8) groups (P < 0.001). Injection of anti-asialo GM1 (ASGM1) antibody increased tumor cell retention in the lungs for all groups but did not alter the differences between activity conditions. In vitro cytotoxicity was enhanced in treadmill- and wheel-trained mice relative to that in sedentary controls but was not elevated in the treadmill control group. Anti-ASGM1 injection eliminated in vitro cytotoxicity for all groups. Chronic exercise slightly increased the frequency of ASGM1-positive splenocytes in treadmill-trained mice only. These results indicate that chronic exercise enhances natural cytotoxic mechanisms in vivo and in vitro and that this enhancement is present for both forced and voluntary exercise. Finally, to the extent that natural killer cells are involved, potentiation of natural cytotoxicity appears due to functional rather than numerical changes in natural killer cells.