Differential Expression of Interleukin-2 Receptor Alpha and Beta Chains in Relation to Natural Killer Cell Subsets and Aerobic Fitness

Abstract

Immunophenotyping by dual parameter flow cytometry was used to compare the expression of interleukin-2 receptor α and β chains on lymphocyte subsets in the peripheral blood of 7 trained and 6 untrained volunteers (respective V̇O₂max 57.0±6.1 and 39.0±4.5ml·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 (10⁹ · 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 α expression (CD25⁺: 0.63±0.11 vs. 0.69±0.17) was unrelated to training, but the p70-75-IL-2 receptor β expression was higher in the active group (p70/Mik-β₁ ⁺: 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-2Rβ expression (r = 0.914, p<0.001 for Mik-β₁; r = 0.884, p<0.005 for TU27). We conclude that physical conditioning is associated with an increase in IL-2 receptor β expression on lymphocytes as assessed by the proportion of circulating p70-75-IL-2Rβ 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.

Key words

Aerobic power - cytokines - cancer - immune function - natural immunity - training