High-intensity training reduces CD8+ T-cell redistribution in response to exercise.

Purpose: We examined whether exercise-induced lymphocytosis and lymphocytopenia are impaired with high-intensity training.
Methods: Eight trained cyclists (VO(2max) = 64.2 ± 6.5 mL · kg(-1) · min(-1)) undertook 1 wk of normal-intensity training and a second week of high-intensity training. On day 7 of each week, participants performed a cycling task, consisting of 120 min of submaximal exercise followed by a 45-min time trial. Blood was collected before, during, and after exercise. CD8(+) T lymphocytes (CD8(+)TLs) were identified, as well as CD8(+)TL subpopulations on the basis of CD45RA and CD27 expression.
Results: High-intensity training (18,577 ± 10,984 cells per microliter × ~165 min) was associated with a smaller exercise-induced mobilization of CD8(+)TLs compared with normal-intensity training (28,473 ± 16,163 cells per microliter × ~165 min, P = 0.09). The response of highly cytotoxic CD8(+)TLs (CD45RA(+)CD27(-)) to exercise was smaller after 1 wk of high-intensity training (3144 ± 924 cells per microliter × ~165 min) compared with normal-intensity training (6417 ± 2143 cells per microliter × ~165 min, P < 0.05). High-intensity training reduced postexercise CD8(+)TL lymphocytopenia (-436 ± 234 cells per microliter) compared with normal-intensity training (-630 ± 320 cells per microliter, P < 0.05). This was driven by a reduced egress of naive CD8(+)TLs (CD27(+)CD45RA(+)). High-intensity training was associated with reduced plasma epinephrine (-37%) and cortisol (-15%) responses (P < 0.05).
Conclusions: High-intensity training impaired CD8(+)TL mobilization and egress in response to exercise. Highly cytotoxic CD8(+)TLs were primarily responsible for the reduced mobilization of CD8(+)TLs, which occurred in parallel with smaller neuroendocrine responses. The reduced capacity for CD8(+)TLs to leave blood after exercise with high-intensity training was accounted for primarily by naive, and also, highly cytotoxic CD8(+)TLs. This impaired CD8(+)TL redistribution in athletes undertaking intensified training may imply reduced immune surveillance.