Thymic output in aged mice.
Using GFP to mark recent thymic emigrants (RTEs) in mice carrying a GFP transgene driven by the recombination-activating gene 2 promoter, we demonstrate that RTEs are readily detectable even in 2-year-old mice, despite the fact that the proportion of the peripheral T cell pool comprised of RTEs declines with age. Although the number of RTEs decreases after reaching a peak at 6 weeks of age, thymic output as a function of thymic size is surprisingly age-independent. The CD4:CD8 ratio of RTEs declines with age, partly because of a striking decrease in steady-state proliferation of CD4+ RTEs in older mice. RTEs in aged mice undergo phenotypic maturation in the lymphoid periphery with delayed kinetics compared with young mice. RTEs from aged mice secrete less IL-2, proliferate less well, and achieve only weak expression of early-activation markers compared with more mature naïve peripheral T cells from the same mice. The proportion of GFP- cells in the CD4+ and CD8+ thymic compartments increases with age, partly as a result of leakiness in the aged thymus, allowing reentry of naïve peripheral T cells.
Hale
J Scott
JS
Department of Immunology, University of Washington, Seattle, WA 98195, USA.
Boursalian
Tamar E
TE
Turk
Gail L
GL
Fink
Pamela J
PJ
D000375:Aging / Q000276:immunology*; D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology; D002465:Cell Movement; D049109:Cell Proliferation; D002478:Cells, Cultured; D007113:Immunity, Innate; D007700:Kinetics; D018655:Lymphocyte Count; D051379:Mice; D009929:Organ Size; D010641:Phenotype; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology*