Responsiveness of human natural killer cells during acute,incremental exercise up to exhaustion

Abstract Eight healthy male subjects performed a cycle ergometer incremental exercise up to exhaustion to study possible relationships between excess CO₂ production (CO_2-exc) and natural killer (NK) cells, measured in terms of concentration (NK_abs) and as a percentage of lymphocytes in peripheral blood (NK%). A parabola-like regression equation with its vertex downwards best fit the relationship between CO_2-exc at W_max and the difference between NK cell measurements at the maximum workload (W_max) and at the workload corresponding to the anaerobic threshold (W_AT). For NK cell concentration, the best equation was NK_abs (cells/mm³)=248.8413–0.3105 CO_2-exc (ml min^-1)+0.0001 CO_2-exc ² (ml min^-1) (p=0.044). For NK cells expressed as a percentage, the best equation was NK(%)=108.7636–0.1414 CO_2-exc (ml min^-1)+0.00001 CO_2-exc ² (ml min^-1) (p=0.032). Thus, the higher was the CO_2-exc the lower was the increase in both NK cell measurements at W_max with respect to the value observed at W_AT. However, when CO_2-exc reached more elevated values, then the direction of this relationship was inverted. It may be concluded that when strenuous exercise is performed, an anti-inflammatory/performance-preserving event takes place, while recovery towards a pro-inflammatory/anti-infection state tends gradually to re-establish when a subjects anaerobic power becomes too high.