T-cell subsets, including naïve (NA), central memory (CM), transitional memory (TM), effector memory (EM), and RA + effector memory (EMRA), differ in phenotype and function. T-cells are mobilized by exercise, with differences in the magnitude of mobilization between subsets. However, the response of TM T-cells to exercise has not yet been described. Further, T-cells expressing the late differentiation marker CD57 are known to be highly responsive to exercise, but the relative response of CD57 + and CD57- within T-cell subsets is unknown. We therefore aimed to characterize the exercise-induced mobilization of TM T-cells, as well as to compare the exercise response of CD57 + and CD57- cells within T-cell subsets.MethodsSeventeen participants (7 female; aged 18–40 years) cycled 30 min at 80% of their estimated maximum heart rate. Venous blood obtained pre, post, and 1H post-exercise was analyzed by flow cytometry. CD45RA, CCR7, and CD28 expression within CD4 + and CD8+ T-cells identified NA, CM, TM, EM, and EMRA subsets. CD57 expression within EM, EMRA, and CD28+ T-cells was also quantified. The relative mobilization of each subset was compared by calculating fold change in cell concentration during (ingress, post/pre) and after exercise (egress,1H post/post). Cytomegalovirus (CMV) serostatus was determined by ELISA and was considered in models.ResultsTM CD8+ T-cell concentration was greater post-exercise than pre-exercise (138.59 ± 56.42 cells/µl vs. 98.51 ± 39.68 cells/µl, p < 0.05), and the proportion of CD8 + with a TM phenotype was elevated 1H post-exercise (1H: 32.44 ± 10.38% vs. Pre: 30.15 ± 8.77%, p < 0.05). The relative mobilization during and after exercise of TM T-cells did not differ from NA and CM but was less than EM and EMRA subsets. Similar results were observed within CD4+ T-cells. CD57 + subsets of CD28+ T-cells and of EM and EMRA CD8+ T-cells exhibited a greater relative mobilization than CD57- subsets (all p < 0.05).ConclusionThese results indicate TM CD4 + and CD8+ T-cells are transiently mobilized into the blood with exercise, but not to as great of an extent as later differentiated EM and EMRA T-cells. Results also indicate CD57 identifies highly exercise responsive cells within CD8+ T-cell subsets.
PURPOSE:To determine whether executive function is altered during two variations of simulated microgravity head down tilt protocols. METHODS: 26 healthy volunteers (n=19 females and 7 males; 20.0 ± 1.7 years; 165.6 ± 24.5 cm; 71.1 ± 15.9 kg; mean±SD) took part in two randomly assigned separate simulated microgravity sessions consisting of 1.5 hours at -6° head down tilt (HDT) sessions. Each testing session lasted approximately 2.5 hours. One session consisted of the broadly used -6° HDT facing up (HDT-FU), while the other consisted of a -6° HDT facing down (HDT-FD) modification of the standard method. For each condition, the participant completed a computerized Stroop Color and Word Test during a thirty-minute horizontal position (0 ° tilt) prior to the interventions and again prior to the end of the 1.5-hour HDT protocols. The Stroop Color and Word Test consisted of 3 tasks (60 trials per task) including: 1) a Naming task, 2) an Inhibition task, and 3) an Inhibition/Switching task. To minimize the learning effect, both the HDT-FU and HDT-FD sessions were counterbalanced amongst all participants and were separated by a minimum of 48 hours. RESULTS: Our cognitive reaction time results demonstrate a main effect of time (pre HDT 777.60 ± 18.08ms vs post HDT 749.30 ± 19.11ms, p<0.01) and a main effect of Stroop Test (Naming < Inhibition < Inhibition/Switching, p<0.01). Additionally, we observed that the 1.5-hour protocol selectively improved the Inhibition/Switching reaction times (the most executive component) for both the p=0.02) and p<0.01). CONCLUSION: When executive demand is increased under short-term simulated microgravity head down tilt conditions, regardless of the position (face up or face down), cognitive reaction time is decreased, suggesting an improvement in overall cognitive function.
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