Preliminary evidence of reductive stress in human cytotoxic T cells following exercise

This study investigated immunophenotypic differences in intracellular thiol redox state of peripheral blood mononuclear cells (PBMCs) isolated from trained [ n = 9, means ± SD: age 28 ± 5 yr; (body mass index) BMI 23.2 ± 2.6 kg/m²; V̇o_2max (maximal oxygen intake)56.9 ± 6.1 ml·kg^-1·min^-1] and recreationally active (RA, n = 11, means ± SD: age 27 ± 6 yr; BMI 24.2 ± 3.7 kg/m²; V̇o_2max 45.1 ± 6.4 ml·kg^-1·min^-1) participants before and after a maximal aerobic exercise tolerance test. Blood samples were taken before (Pre), during (sample acquired at 70% maximum heart rate), immediately after (Post + 0), and 15 min postexercise (Post + 15). PBMCs were isolated, and reduced thiol analysis [fluorescein-5 maleimide (F5M)] by immunophenotype [cluster of differentiation (CD)3⁺, CD4⁺, and CD8⁺] was performed using flow cytometry. A significant increase in cellular F5M fluorescence was observed in CD3⁺ T cells at Post + 0, with changes driven to a greater extent by CD8⁺ T cells (fold change in both groups CD4: +2.3, CD8: +2.8; P < 0.05). Further analysis revealed a population of highly reduced CD8⁺ T cells (CD8⁺T-reduced⁺) that significantly increased from Pre to Post + 0 in RA participants only (RA: +272 cell/µl, P < 0.05). To understand these results further, CD8⁺T-reduced⁺ and CD8⁺T-reduced^- cells were analyzed for immunophenotype in response to the same exercise protocol ( n = 6, means ± SD: age 24 ± 5 yr; BMI 25.7 ± 4.1 kg·m^-2; V̇o_2max 41.33 ± 7.63 ml·kg^-1·min^-1). CD8⁺T-reduced⁺ had significantly less lymphoid homing potential (chemokine receptor type 7) Post + 0 compared with Pre. This study is the first, to our knowledge, to demonstrate that lymphocyte populations become more reductive in response to acute exercise. NEW & NOTEWORTHY The study presented provides the first evidence to suggest that cytotoxic T cells become transiently reductive in healthy individuals following a single bout of cycling. Detection of these cells was enabled via the use of a flow cytometric assay that incorporates the thiol reactive probe fluorescein-5 maleimide. Using this method, transient reductive stress in viable T cells is permissible and provides the basis for further research in the area of exercise immunology.