Adaptive immunity as an indicator of optimum physical loads during 520-day isolation

High stress level in the mechanisms responsible for adaptation to physical work affects the human immune system. Therefore, the effectiveness of countermeasures of reduced physical activity was studied using some parameters of the immune system. Our purpose was to examine how different types of exercises can modify physical performance and immune function in six subjects volunteered for Mars-500 simulation study. During the study, the resistance and cyclic training alternated over the period of about two months. According to the design, training was interrupted twice by an interval of approximately one month. The training plan was developed so that the initial and final stages of isolation could not impair the effectiveness of training. The cyclic training included running on the motorized and non-motorized treadmill and bicycling. Resistance exercises were performed using the MDS multifunctional exercise machine, expanders, and the Galileo 2000 vibration plate. Physical performance was assessed by the criteria of maximal voluntary effort, incremental locomotion, and bicycle exercise tests. Analysis of the quantitative and functional properties of effector cells of both innate and adaptive immunity was employed to investigate the immune status of subjects. Due to the plan of physical training, the level of physical performance in isolation was better than during the baseline data collection, although the intervals caused a considerable decrease in performance. Comparison of immunograms with the baseline ones showed positive changes: the number of naive CD4⁺Т-cells (CD4⁺CD45RA⁺) increased significantly. The functional activity of adaptive immunity did not reduce during isolation; on the contrary, the ability of T cells to express the early activation marker CD69⁺ on the surface was increased. The immune status parameters assessed in the subjects in the second half of the isolation period indicate that the proposed physical loads were adequate. In addition to retention of the baseline level of, or improvement in, physical performance, positive activation of the T component of adaptive immunity was observed.