Changes In The Frequency Of Senescent Blood T-cells During 6-months Training Preparation For An Ironman Triathlon

Abstract

It is well-known that athletes are at an increased susceptibility to illness when adhering to arduous training regimens in preparation for endurance events. Senescent T-lymphocytes are antigen-experienced cells that accumulate with age and fail to clonally expand following further antigenic stimulation, thus predisposing the individual to a greater risk of infection. Although acute exercise is known to alter the frequency of senescent T-cells in blood, less is known about the effects of long-term endurance training. PURPOSE: To examine the effects of 6-months training preparation for an Ironman triathlon on the frequency of senescent blood T-cells. METHODS: Ten club-level triathletes (9 males; 1 female: Age: 42.9 ± 3.1 yrs) provided a fasted resting blood sample in the morning at 27 (DEC), 21 (JAN), 15 (MAR), 9 (MAY) and 3 (JUN) weeks before the 2008 Zurich Ironman Triathlon. An additional sample was collected 2-weeks post-competition (AUG). Total training hours completed by the participants over the 6-month period was 284.4 ± 122.9. Isolated blood lymphocytes were labelled with monoclonal antibodies to assess cell surface expression and co-expression of the T-cell senescence markers KLRG1, CD57 and CD28; and the naïve and memory T-cell markers CD45RA and CD45RO on CD3+, CD3+/CD4+ and CD3+/CD8+ T-cells using four-colour flow cytometry. Data was analyzed for time-change using a repeated measures linear mixed model. RESULTS: Compared to DEC, the percentage of CD4+ T-cells expressing KLRG1 increased by 71% (MAR), 20% (MAY) and 71% (AUG). CD4+ T-cells co-expressing KLRG1 and CD57 was 192% greater in AUG compared to DEC. No changes in senescent markers were found on CD8+ T-cells. The proportion of transitional T-cells (CD45RA+/CD45RO+) increased from MAY to JUN by 141% and 115% for CD4+ and CD8+ T-cells respectively. The proportion of memory CD8+ T-cells (CD45RA-/CD45RO+) was 40% (MAY) and 55% (AUG) greater than DEC. CONCLUSION: Adherence to a 6-month training program in preparation for an Ironman triathlon leads to an increased frequency of senescent CD4+ T-cells (KLRG1+/CD57+) and a greater proportion of naïve to memory transitional CD4+ and CD8+ T-cells in blood. These changes could have important implications for athlete infection risk during periods of arduous training.