Effect of physical exercise on cytokines and lymphocyte subpopulations in human peripheral blood

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Abstract
To examine the effect of intensive physical exercise on interleukin 2 (IL‐2), tumor necrosis factor alpha (TNFα) and lymphocyte subsets, eleven elite and well‐conditioned runners were tested in relation to a five‐kilometer race. IL‐2 was significantly decreased (p < 0.01) immediately after the exercise and significantly increased after 24 hours (p < 0.05), compared to the pre‐exercise values taken at steady state. TNFα was significantly increased after 2 hours (p < 0.05), and returned to habitual values after 24 hours. In the steady state at rest, elevation of HLA‐DR+ cells was observed in all runners compared with control subjects (p < 0.05), indicating a persistent activation of lymphoid cells. In connection with exercise a significant increase in NK cells (CD 16+) was observed (p < 0.01). The T‐helper/T‐suppressor (CD4+/CD8+) ratio was significantly reduced in connection with physical activity (p < 0.01). In seven runners the ratio was reduced to a value of less than one. This decrease was observed immediately after the exercise, followed by increased ratios 2 hours later (p < 0.01), due to oppositely directed quantitative changes of the CD4+ and CD8+ cell populations. After 24 hours the ratios returned to habitual levels. Furthermore, we confirmed an increase in the total number of granulocytes in connection with exercise (p < 0.01), and observed a decrease in absolute numbers of lymphocytes two hours after exercise (p < 0.01). We emphasize the importance of obtaining information about physical activity within the previous 24 hours before measuring white blood cell parameters.