Strenuous exercise decreases the percentage of type 1 T cells in the circulation

Prolonged strenuous exercise is followed by a temporary functional immune i mpairment. Low numbers of CD4(+) T helper (Th) and CD8(+) T cytotoxic (Tc) cells are found in the circulation. These cells can be divided according to their cytokine profile into type I (Th1 and Tc1), which produce interferon -gamma and interleukin (IL)-2, and type 2 (Th2 and Tc2) cells, which produc e IL-4. The question addressed in the present study was whether exercise af fected the relative balance between the circulating levels of these cytokin e-producing T cells. Nine male runners performed treadmill running for 2.5 h at 75% of maximal oxygen consumption. The intracellular expression of cyt okines was detected following stimulation with ionomycin and phorbol 12-myr istate 13-acetate in blood obtained before, during, and after exercise. The percentage of type I T cells in the circulation was suppressed at the end of exercise and 2 h after exercise, whereas no changes were found in the pe rcentage of type 2 T cells. Plasma epinephrine correlated negatively with t he percentage of circulating CD8(+) T cells producing IL-2, whereas peak IL -6 correlated with the percentage of CD8(+) IL-4-producing T cells in the c irculation. Peak plasma IL-6 correlated with plasma cortisol postrunning. I n conclusion, the postexercise decrease in T lymphocyte number is accompani ed by a more pronounced decrease in type 1 T cells, which may be linked to high plasma epinephrine. Furthermore, IL-6 may stimulate type 2 T cells, th ereby maintaining a relatively unaltered percentage of these cells in the c irculation compared with total circulating lymphocyte number.