Physical Activity Modifies the Metabolic Profile of CD4+ and CD8+ T-Cell Subtypes at Rest and Upon Activation in Older Adults.

T-cell metabolism is a key regulator of immune function. Metabolic dysfunction in T cells from young mice results in an aged phenotype, accelerating immunosenescence. Physical activity (PA) maintains T-cell function and delays immunosenescence in older adults, but the underlying mechanisms are poorly understood. We investigated the effects of PA on the metabolic and functional profiles at a single-cell resolution of resting and stimulated T cells from young adults (N = 9, 23 ± 3 years) and physically active older adults clustered between higher PA (HPA, N = 9, 75.5 ± 4.7 years) or lower PA levels (LPA, N = 10, 76.4 ± 2.1 years). Compared to young donors, HPA older adults had higher mitochondrial dependence (MD) and lower glucose dependence (GD) in unstimulated naïve, central memory (CM) and effector memory (EM) CD4⁺ and EM CD8⁺ T cells, while LPA older adults had higher overall protein synthesis in naïve and EM CD4⁺ and CD8⁺. In response to PMA and Ionomycin stimulation, there was a similar increase in GD and a reduction in MD across groups for most T-cell subsets. Although LPA and HPA underwent a higher increase in protein synthesis upon activation compared to the young subjects, HPA did not exhibit the excessive increase in the percentage of IL-6⁺ T cells observed in the LPA group compared to young subjects. Taken together, our data provide evidence of a higher energy demand, impaired metabolic flexibility, and hyperinflammatory responses in aged T cells, and PA reduces metabolic demand in these cells, potentially through increased MD and improved metabolic flexibility.