Moderate physical activity associated with a higher naive/memory T-cell ratio in healthy old individuals: potential role of IL15

Introduction: ageing is accompanied by impairments in immune responses due to remodelling of the immune system (immunesenescence). Additionally, a decline in habitual physical activity has been reported in older adults. We have recently published that specific features of immunesenescence, such as thymic involution and naive/memory T-cell ratio, are prevented by maintenance of a high level of physical activity. This study compares immune ageing between sedentary and physically active older adults. Methods: a cross-sectional study recruited 211 healthy older adults (60-79 years) and assessed their physical activity levels using an actigraph. We compared T- and B-cell immune parameters between relatively sedentary (n = 25) taking 2,000-4,500 steps/day and more physically active older adults (n = 25) taking 10,500-15,000 steps/day. Results: we found a higher frequency of naive CD4 (P = 0.01) and CD8 (P = 0.02) and a lower frequency of memory CD4 cells (P = 0.01) and CD8 (P = 0.04) T cells in the physically active group compared with the sedentary group. Elevated serum IL7 (P = 0.03) and IL15 (P = 0.003), cytokines that play an essential role in T-cell survival, were seen in the physically active group. Interestingly, a positive association was observed between IL15 levels and peripheral CD4 naive T-cell frequency (P = 0.023). Discussion: we conclude that a moderate level of physical activity may be required to give a very broad suppression of immune ageing, though 10,500-15,000 steps/day has a beneficial effect on the naive T-cell pool.