EFFECTS OF MAXIMAL EXERCISE ON NATURAL-KILLER (NK) CELL CYTOTOXICITY AND RESPONSIVENESS TO INTERFERON-ALPHA IN THE YOUNG AND OLD

me investigated the effects of a graded maximal exercise treadmill tes t on natural killer (NK) cell number activity, and responsiveness to i nterferon-alpha (IFN-alpha) in young (22 +/- 0.7 yrs) and elderly (65 +/- 0.8 yrs) sedentary subjects. NK cell cytotoxicity (NKCC) was deter mined using Ficoll Purified peripheral blood mononuclear cells (PBMCs) by a Cr-51 release assay against NK-sensitive (K562) and NK-insensiti ve (Daudi) target cells at various effector:target (E:T) ratios before and immediately after exercise. PBMCs were incubated with rhuIFN-alph a (125 and 250u/10(6) PBMCs) or without for 2 hrs before addition to t he Cr-51 release assay. There were no differences in unstimulated NKCC against K562 or Daudi targets between the old and the young despite s ignificantly (p = .01) higher percentages of CD56(+) NK cells (21.1 +/ - 2.3% in old vs 12.5 +/- 2.5% in young, pre-exercise). IFN-alpha incr eased NKCC versus both targets, and NK cells from old subjects were hy poresponsive to IFN-alpha stimulation; this was especially evident at low E:T ratios versus Daudi cells. Maximal exercise significantly incr eased (50-200%) unstimulated NKCC versus K562 and Daudi targets simila rly in both young and old and increased the percentage of CD56(+) cell s in the PBMC fraction to 33.3 +/- 3.7% and 23.3 +/- 3.6% in old and y oung, respectively. me found a significant correlation between %CD56and basal NKCC versus K562s and Daudi cells in the young (i.e., r = .5 5; p = .02 vs K562s) but nor the old (i.e., r = .20; p = .29 vs K562s) subjects. This indicates that, in the young, part of the exercise-ind uced increase in NKCC is due to an increase in NK cell number. Maximal exercise did not affect unstimulated per cell killing of K562s, but t ended to increase per cell killing of Daudis. These results indicate t hat CD56(+) cells from old subjects have an intrinsic defect in their ability to perform cytolysis and respond to IFN-alpha Furthermore, a s ingle bout of maximal exercise increases NKCC and CD56(+) cell number similarly in both young and old subjects regardless of the target cell used.