DIFFERENTIAL EXPRESSION OF INTERLEUKIN-2 RECEPTOR-ALPHA AND BETA-CHAINS IN RELATION TO NATURAL-KILLER-CELL SUBSETS AND AEROBIC FITNESS

Immunophenotyping by dual parameter flow cytometry was used to compare the expression of interleukin-2 receptor alpha and beta chains on lymphocyte subsets in the peripheral blood of 7 trained and 6 untrained volunteers (respective VO(2)max 57.0 +/- 6.1 and 39.O +/- 4.5 ml.kg(-1).min(-1)). Venous blood samples were collected at least 36 h after the most recent exercise session. The trained subjects had higher circulating counts (10(9).1(-1)) of total leukocytes (5.80 +/- 0.83 vs. 4.63 +/- 0.21, p < 0.05), granulocytes (3.14 +/- 0.72 vs. 1.90 +/- 0.30, p < 0.05), and NK cells (CD16(+), 0.32 +/- 0.14 vs. 0.16 +/- 0.05, p < 0.05; CD56(+), 0.41 +/- 0.14 vs. 0.21 +/- 0.03, p < 0.01), but lower lymphocyte counts than their sedentary peers (1.90 +/- 0.22 vs. 2.26 +/- 0.25, p < 0.05). Counts for T cells (CD3(+)) and B cells (CD19(+)), and the CD4(+)/CD8(+) ratio did not differ between the two subject groups. The p55-IL-2 receptor alpha expression (CD25(+): 0.63 +/- 0.11 vs. 0.69 +/- 0.17) was unrelated to training, but the p70-75-IL-2 receptor beta expression was higher in the active group (p70/Mik-beta(1)(+): 0.42 +/- 0.09 vs. 0.20 +/- 0.06, p < 0.001; p75/TU27(+): 0.36 +/- 0.08 vs. 0.17 +/- 0.07, p < 0.005). Beta chain co-expression was also higher on NK cell subsets (p < 0.001) in trained than in sedentary subjects. Aerobic power was strongly correlated with IL-2R beta expression (r = 0.914, p < 0.001 for Mik-beta(1); r = 0.884, p < 0.005 for TU27). We conclude that physical conditioning is associated with an increase in IL-2 receptor beta expression on lymphocytes as assessed by the proportion of circulating p70-75-IL-2R beta positive NK cells. Such changes could enhance protection against both infectious diseases and cancer. Longitudinal studies are now needed to explore the causal nature of this association.