Coupling aging immunity with a sedentary lifestyle: has the damage already been done?--a mini-review

The elderly population is at an unprecedented risk of infectious diseases and malignancy due to apparently inevitable age-related declines in immunity. The 'immune risk profile' (IRP) is an array of biomarkers that has been used to predict morbidity and mortality in older adults. As it is generally accepted that middle-aged and elderly individuals who habitually participate in moderate-intensity exercise are less likely to incur an infection than their sedentary counterparts, this review addresses current knowledge on the effects of regular exercise on aspects of adaptive immunity as they relate to the IRP. Findings from cross-sectional studies mostly show enhanced immunity in physically active compared to sedentary older adults. These include greater T-cell responsiveness to mitogens in vitro, a reduced frequency of antigen-experienced and senescent T-cells (i.e. CD45RO+/KLRG1+/CD57+/CD28-), enhanced IL-2 production and T-lymphocyte expression of the IL-2 receptor, longer chromosome telomere lengths in blood leukocytes and in vivo immune responses to vaccines and recall antigens. In contrast, the evidence from the available longitudinal studies that have used an exercise training intervention in previously sedentary elderly to improve similar immune responses is less compelling. Although this might indicate that exercise has limited immune restorative properties in previously sedentary elderly, there are still relatively few studies that have addressed specific IRP criteria and the large variation in experimental design among the longitudinal studies complicates the juxtaposition of these results. It is clear that a more substantial and focused research approach is required before physical exercise can be used in earnest as an effective immune restorative strategy in the elderly. This mini-review summarizes the major findings of these studies and proposes future avenues of research to investigate the effects of regular exercise on aspects of adaptive immunity in the elderly as they relate to the IRP.