NK cells are a distinct lymphocyte subset capable of spontaneous cytotoxic (killing) activity against some virally-infected and tumour cells. Exercise is known to influence circulating NK cell number and cytotoxic activity (NKCA) in a complex manner: NKCA is stimulated during but suppressed between 1 and 5 h after intense prolonged exercise. The mechanisms underlying this dual effect have not been clearly elucidated. The purpose of this study was to further investigate possible mechanisms underlying the NK cell response to intense prolonged exercise, in particular whether exercise induces changes in expression of the lymphocyte function-associated antigen (LFA-2; CD2), an adhesion molecule responsible for NK cell binding to the target cell (a necessary step before killing the target cell). Five male runners ran on a treadmill for 60 min at 80% VO2max; venous blood was collected pre- and immediately (0), 1.5, 5 and 24 h post-exercise. To control for diurnal variability, 4 matched male runners acted as control subjects, participating in all procedures except for sitting quietly while the others ran. The standard whole blood 51Cr release assay was used to measure NKCA, and flow cytometry used to quantify NK cell (CD3-/CD16+CD56+) number and LFA-2 (CD2) expression. As expected, compared with pre-exercise values NKCA increased 63% at 0 and decreased 43% 1.5 h post-exercise. When adjusted for changes in NK cell number, NKCA per cell did not change significantly at any time after exercise. The proportion of NK cells expressing LFA-2 (about 70%) did not change significantly at any time after exercise, nor did exercise influence the fluorescence intensity of antibody staining (related to the amount of LFA-2 expressed on each cell). These data suggest that intense prolonged exercise does not influence expression of LFA-2 on NK cells. We conclude that changes in the binding of NK cells to their target cells is not responsible for the delayed suppression of NKCA after exercise; other mechanisms are likely to be involved, such as changes in circulating NK cell number and/or the killing activity of each NK cell.
© Copyright 1999 5th IOC World Congress on Sport Sciences with the Annual Conference of Science and Medicine in Sport 1999. Alle Rechte vorbehalten.