It is well recognized that individuals are at an increased risk of illness following an arduous exercise regime. Exercise may affect activation status of cells and play a pivotal role in defense against pathogenic invasion. CD69 is the earliest known expressed cell surface antigen of T-cell activation and is a reliable marker of cell activation status (Green et al. Med. Sci. Sports Exerc. 35, 582-588: 2003). Exercise is known to alter the frequency of senescent cells in the blood expressing the cell surface glycoprotein killer cell lectin-like receptor G1 (KLRG1), and are antigen-experienced and unable to clonally expand upon further antigenic stimulation (Simpson et al. J. Appl. Phys. 103, 396-401:2007), PURPOSE: To examine the contribution of senescent T-cells mobilized by exercise on the overall activation status of the peripheral blood T-cell pool following an acute bout of exercise. METHODS: Ten moderately trained males (age: 24.6 ± 4.8; height: 183.1 ± 6.7cm; mass: 72.8 ± 7.9kg; ; 61.3 ± 5.9 ml.kg-1.min-1) ran at speeds corresponding to 80% until volitional exhaustion (time: 36.1 ± 5.8 minutes). Blood lymphocytes isolated before (PRE), immediately after (POST) and 1 hour after (1HrPOST) exercise were stimulated for 4 hours in culture with and without the mitogen PMA and assessed for KLRG1 and CD69 expression and co-expression on CD3+, CD3+/CD4+ (CD4+) and CD3+/CD8+ (CD8+) lymphocyte subsets using 4-colour flow cytometry. RESULTS: No changes in CD69 GMFI were observed on total CD3+, CD4+ and CD8+ T-cells POST or 1HrPOST exercise. The proportions of KLRG1+ cells among the total CD3+, CD4+ and CD8+ T-cell populations increased by 172%, 107% and 169% respectively POST exercise and fell below baseline values 1h later (p<0.05). At all sample time points, CD69 GMFI was greater on stimulated KLRG1+ T-cells compared to KLRG1- cells (p<0.05). CONCLUSION: We conclude that exercise does not affect the activation status of the total T-cell pool. Instead, the number of senescent cells expressing CD69 is greater than those that are not senescent at all times. This suggests that upon pathogenic invasion post-exercise.



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