Table 1.

Alterations in T-Cell Immunity With Aging

Thymus and T-Cell Subsets
Thymus	Atrophy
Frequency of naive CD4+ and CD8+ T cells	Decrease
Frequency of memory CD4+ and CD8+ T cells	Increase
CD4+ T cells
Cell proliferation in response to PMA/ionomycin or PHA	Decrease
IFN-γ and IL-4 production from CD4+ T cells	Variable (no change, decrease, and increase)
Frequency of IL-17–producing Th17 cells in memory CD4+ T cell	Decrease
Frequency of FOXP3+ Treg cells	No change to increase
CD8+ T cells
Proliferation	Decrease
Cytotoxicity	Decrease
Frequency of IL-7Rαlow effector memory CD8+ T cells	Increase
Frequency of CD28− (antigen experienced) and CD57+ CD8+ T cells	Increase
T-cell receptor repertoires	Decrease with oligoclonal CD8+ T-cell expansion

Note: PMA= phorbol myristate acetate; IFN = interferon; IL = interleukin; PHA = phytohemagglutinin.