EFFECTS OF MAXIMAL EXERCISE ON NATURAL KILLER (NK) CELL ACTIVITY AND RESPONSIVENESS TO INTERFERON-?? IN YOUNG AND OLD 905

Abstract

Recent evidence suggests that acute exercise alters NK cell number and function in the peripheral blood of young subjects. However, it is not known if these effects occur in the elderly, a group that manifests age-altered NK responsiveness. We investigated the effects of a graded maximal exercise treadmill test (modified Balke protocol) on NK cell activity and responsiveness to IFN-α in young (22.5±2.2 years, n=7) and elderly (64±3.5 years, n=12) sedentary subjects. VO2peak for young and old subjects was 47±9.6 and 25.8±5.2 mL O2/kg/min, respectively (p<0.05). Blood samples were collected before and immediately after exercise. NK cell cytotoxicity (NKCC) was determined from Ficoll purified peripheral blood mononuclear cells (PBMC's) using a 51Cr release assay against NK-sensitive (K562) and NK-insensitive (Daudi) target cells at various effector:target ratios (i.e. 50, 25, and 12.5:1). In addition, PBMC's were incubated with rhulFN-α(125 and 250u/mL) for 2 hrs before addition to the 51Cr release assay. Results revealed significantly (p<0.05) lower NKCC vs. K562 in the aged when compared to the young at rest (40±5 vs. 55±2% @ 50:1), despite significantly (p=0.04) higher NK cell numbers (26±3 in old vs. 11.6±2% in young) as determined by CD56 immunofluorescence staining. Acute maximal exercise significantly increased NKCC vs. K562 (66±6 and 80±4% respectively in young and old post-exercise @ 50:1) and Daudi targets in both young and old when compared to pre-exercise values (see above). IFN-α increased NKCC vs. both targets regardless of age and this effect was not altered by exercise. Acute exercise increased the percentage of CD56+ NK cells in the PBMC population in both young (25±5%) and old (43±4%) when compared to pre-exercise values (see above). Therefore, acute maximal exercise increases NK cell number and NKCC in both young and elderly subjects. Furthermore, NK responsiveness to IFN-α is not altered by acute exercise as measured by K562 cytotoxicity.