Delayed immune aging in diet-restricted B6CBAT6 F1 mice is associated with preservation of naive T cells.

Age-related changes in peripheral blood, spleen, and thymus of ad libitum (AL)-fed and dietary restricted (DR) C57BL/6J x CBA/CaH-T6/J F1 (B6CBAT6 F1) mice at young (3 mo), middle (16 mo), and old (30 mo) ages were studied to define how dietary restriction retards immune aging. Dietary restriction at 25% AL intake level initiated at weaning significantly reduced the rates of age-related declines in peripheral blood T helper cells, naive T helper cells, and naive cytotoxic T lymphocytes (CTLs). As a result, concentrations of these cell types in old DR mice were equivalent to 161%, 176%, and 250% of those in old AL controls. Dietary restriction also abolished age-related splenomegaly and decreased total splenocyte numbers in old DR mice. Dietary restriction did not prevent age-related decline in thymus size, but preserved thymus cellularity in old mice. Old DR mice had twice as many total thymocytes and 2.6 times as many CD4+CD8+ immature thymocytes as old AL controls. The correlations between total immature thymocytes and concentrations of circulating naive T helper cells and naive CTLs increase with age and become significant in old mice. Thus, dietary restriction preserves immature T-cell precursors in the thymus during aging to maintain higher concentrations of circulating T helper and naive T cells in peripheral blood.