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Natural killer cell lytic activity and CD56^dim and CD56^bright cell distributions during and after intensive training

¹School of Business Administration, Meiji University, Suginami, Tokyo 168-8555; ²School of Health and Sports Science, Juntendo University, Inba, Chiba 270-1695; ³School of Medicine, Juntendo University, Bunkyo, Tokyo, Japan 113-8421; ⁴Defence Research and Development Canada-Toronto, Toronto M3M 3B9; ⁵Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto M5G 1L5; and ⁶Faculty of Physical Education & Health, Department of Public Health Sciences, University of Toronto, Toronto, Ontario, Canada M5S 1A1

Submitted 14 May 2003 ; accepted in final form 27 January 2004

The purpose of this study was to examine the impact of intensive training for competitive sports on natural killer (NK) cell lytic activity and subset distribution. Eight female college-level volleyball players undertook 1 mo of heavy preseason training. Volleyball drills were performed 5 h/day, 6 days/wk. Morning resting blood samples were collected before training (Pre), on the 10th day of training (During), 1 day before the end of training (End), and 1 wk after intensive training had ceased (Post). CD3^-CD16^brightCD56^dim (CD56^dim NK), CD3^-CD16^dim/-CD56^bright NK (CD56^bright NK), and CD3⁺CD16^-CD56^dim (CD56^dim T) cells in peripheral blood were determined by flow cytometry. The circulating count of CD56^dim NK cells (the predominant population, with a high cytotoxicity) did not change, nor did the counts for other leukocyte subsets. However, counts for CD56^bright NK and CD56^dim T cells (subsets with a lower cytotoxicity) increased significantly (P < 0.01) in response to the heavy training. Overall NK cell cytotoxicity decreased from Pre to End (P = 0.002), with a return to initial values at Post. Lytic units per NK cell followed a similar pattern (P = 0.008). Circulating levels of interleukin-6, interferon-, and tumor necrosis factor- remained unchanged. These results suggest that heavy training can decrease total NK cell cytotoxicity as well as lytic units per NK cell. Such effects may reflect in part an increase in the proportion of circulating NK cells with a low cytotoxicity.

catecholamines; creatine kinase; CD44; CD62l; cytokines

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