Effect of Physical Exercise on Blood Mononuclear Cell Subpopulations and in Vitro Proliferative Responses

The present study was designed to examine the effect of physical exercise on subsets and proliferative responses of blood mononuclear cells. Sixteen young, healthy volunteers underwent 60min of bicycle exercise at 75% of maximal oxygen uptake (VO_2max). After an interval of at least 1 week, six of the subjects underwent a 60‐min back muscle training period at up to 30% of VO_2max. Blood samples were collected before and during the last minutes of exercise, as well as 2 and 24 h later. Blood mononuclear cell (BMNC) subpopulations were determined and the proliferate responses after incubation with phytohaemagglutinin (PHA) or purified derivative of tuberculin (PPD), were quantified by [³H]thymidine incorporation. During bicycle exercise the relative blood concentration of T cells (CD3⁺ cells) declined, mainly due to a fall in T helper cells (CD4⁺ cells). The natural killer (NK) cell subset (CD16⁺ cells) increased during work, but reverted after; the monocytes (CD14⁺ cells) increased 2 h after work, whereas the B‐cell subset (CD20⁺ cells) did not change. BMNC subsets were not significantly changed by back muscle exercise. The PHA‐induced proliferative response decreased during bicycle exercise, whereas the PPD‐induced response did not change. No significant changes occurred during back muscle exercise. Investigation of subgroups after incubation with [³H]thymidine showed that the proliferative response per CD4⁺ cell did not change in relation to exercise, but the contribution of the CD4⁺ subgroup to proliferation declined during bicycle exercise due to the decreased proportion of CD4⁺ cells. The suppression of the PHA response during bicycle exercise can be explained in part by a relative fall in CD4⁺ cells. The pool sizes of BMNC subfraction may be elicited by increased catecholamine and cortisol levels.