Effect of caffeine ingestion on lymphocyte counts and subset activation in vivo following strenuous cycling.

Caffeine ingestion is associated with increases in the concentration of plasma epinephrine and epinephrine is associated with alterations in immune cell trafficking and function following intensive exercise. Therefore, the purpose of this study was to investigate the effect of caffeine ingestion on plasma epinephrine concentration, lymphocyte counts and subset activation in vivo, as measured by the expression the CD69 surface antigen, before and after intensive cycling. On two occasions, following an overnight fast and 60 h abstention from caffeine containing foods and drinks, eight endurance trained males cycled for 90 min at 70% O(2 max) 60 min after ingesting caffeine (6 mg kg(-1 )body mass; CAF) or placebo (PLA). Venous blood samples were collected at pre-treatment, pre-exercise, post-exercise and 1 h post-exercise. Plasma epinephrine concentrations were significantly higher in CAF compared with PLA at pre-exercise [0.28 (0.05) nmol l(-1) versus 0.08 (0.03) nmol l(-1), P<0.01; mean (SE)] and immediately post-exercise [1.02 (0.16) nmol l(-1) versuss 0.60 (0.13) nmol l(-1), P<0.01]. Compared with pre-treatment, numbers of CD4(+) and CD8(+) cells decreased by 54% and 55%, respectively, in CAF at 1 h post-exercise (both P<0.01) but did not significantly differ in PLA. Compared with PLA, in CAF the percentage of CD4(+)CD69(+) cells was 5-fold higher at post-exercise (P<0.05) and 5.5-fold higher at 1 h post-exercise (P=0.01). Compared with PLA, in CAF the percentage of CD8(+)CD69(+) cells was 2-fold higher at pre-exercise (P<0.05) and 1.7-fold higher at post-exercise (P<0.05). These findings suggest that caffeine ingestion is associated with alterations in lymphocyte subset trafficking and expression of CD69 in vivo following prolonged, intensive exercise.