Acute aerobic exercise in humans increases cytokine expression in CD27^- but not CD27⁺ CD8⁺ T-cells

Exercise alters the percentage of CD8⁺ T-cells in the bloodstream expressing type I and type II cytokines. It is unknown if this reflects a change in cytokine expression within individual cells, or whether these observations result from the exercise-induced shift in the proportions of early/intermediate (CD27⁺) and late (CD27^-) differentiated cells, which have vastly different cytokine profiles. 16 males cycled for 60min at 95% maximal steady state. Mononuclear cells isolated from blood collected before, immediately after, and 1h after exercise were cultured overnight with and without phytohaemagglutinin stimulation. CD8⁺ T-cells were assessed for differentiation markers and intracellular cytokine expression by flow cytometry. The numbers and percentage of CD27^-CD8⁺ T-cells increased immediately after exercise and fell below pre-exercise values 1h later. At 1h after exercise, an increased number and percentage of CD8⁺ T-cells expressing IL-2, IFN-γ, TNF-α, IL-6, IL-4, and IL-10 was observed in both stimulated and unstimulated cells. The cytokine response to exercise was confined to CD27^-CD8⁺ T-cells, although cytokine expression among CD8⁺ T-cells was highest when the proportion of CD27^-CD8⁺ T-cells was lowest. Moreover, the cytokine response to exercise could be predicted by the number of late cells in resting blood: cytokine expression was highest among those with low resting proportions of late cells. We conclude that exercise-induced changes in the percentage of CD8⁺ T-cells expressing cytokines are not due to proportional shifts in early/intermediate and late differentiated T-cells. Exercise may prime late-differentiated blood CD8⁺ T-cells to initiate effector functions in preparation for their extravasation into the tissues.