Abstract
The purpose of the present study was to evaluate the effect of acute bicycle exercise
at different exercise intensities on the immune system. Six healthy volunteers exercised
on a bicycle ergometer for 1 h at 25%, 50% and 75% of V̇O2 max with an interval of 2 to 3 weeks. Blood samples were collected in the basal state,
at the end of exercise and 2 h later. The absolute concentrations of all lymphocyte
subsets increased during and fell after exercise at 50% and 75% of V̇O2 max, but did not change significantly at 25% of V̇O2 max. However, at all exercise levels, the percentage of CD3+ blood mononuclear cells
decreased due to a decline in the fraction of CD4+ cells. This decline was most pronounced
at 75% of V̇O2 max. The fraction of NK cells expressing either the CD16 or the CD56 marker increased
during exercise and declined to prevalues 2 h later, however the changes were most
pronounced at 75% of V̇O2 max. The natural killer (NK) cell and lymphokine activated killer (LAK) cell activities
(lysis per fixed number of mononuclear cells) were increased during all exercise intensities,
but were only suppressed below basal levels after exercise at 75% of V̇O2 max. Indomethacin in vitro abolished the post-exercise suppression of NK cell activity
and the proportion of CD 14+ monocytes increased 2 h after exercise only at 75% of
V̇O2 max. These findings indicate that after exercise NK cell function is inhibited by
prostaglandins released by monocytes. During exercise at 50% and 75% of V̇O2 max the proliferative response of blood mononuclear cells (BMNC) following stimulation
with phytohaemagglutinin A (PHA) decreased, whereas that following stimulation with
interleukin-2 (IL-2) was enhanced. The IL-2 production by BMNC in vitro was markedly
decreased during and after exercise at 75% of V̇O2 max and this inhibition could be abolished by indomethacin in vitro. In conclusion,
the response of the immune system to exercise depends on exercise intensity. In essence,
the response is enhanced during exercie, however, after heavy exercise it is suppressed
due to an increased level of prostaglandins produced by the elevated number of monocytes.
Key words
Exercise - NK cells - lymphokines - lymphocytes - interleukin-2 - blood mononuclear
cells
