Table 1.

Subset-specific Differences of Human CD4 and CD8 T cells with Age

CD4 T cells	CD8 T cells
Circulating naïve cell number decline moderately	Circulating naïve cell number decline markedly
Distribution of memory cell subsets is stable	Effector memory and TEMRA cells increase, mostly due to stimulation with latent viruses
Central memory cells remain CD45RO positive	Central memory cells revert to CD45RA, masquerading as naïve CD8 T cells
Naïve T cell homeostasis dependent on recognition of MHC class II molecules	Naïve T cell homeostasis dependent on recognition of MHC class I molecules
Decline in TCR richness in naïve cells by 3–5 fold	Decline in TCR richness in naïve cells by 3–5 fold
Minor TCR repertoire oligoclonality in naïve cells	Increased TCR repertoire oligoclonality in naïve cells
CpG methylation changes at >10,000 sites	CpG methylation changes at >40,000 sites
Minor changes in chromatin accessibility in naïve and central memory cells	Naïve and central memory cells exhibit evidence of progressive differentiation in their chromatin accessibility patterns
Normal mitochondrial function (oxygen consumption rates) in naive cells	Impaired mitochondrial function (reduced oxygen consumption rates) in naive cells