title: A central role for thymic emigrants in peripheral T cell homeostasis.
abstract: After initial seeding by thymic emigrants, homeostatic regulation of the T cell pool has been thought to occur entirely within the periphery. Here we report that the degree of thymic emigration directly affects the number and the CD4/CD8 ratio of peripheral T cells. We demonstrate that the increase in T cell pool size caused by the engraftment of 2, 6, or 9 thymic lobes correlates almost exactly with the number of emigrants exported from those grafts in the previous 3 weeks, regardless of how long the graft has been in place. The extent of the increase supports the concept of a 3-week period after thymic export in which emigrant T cells are exempt from peripheral T cell homeostasis. This apparent exclusion of recent thymic emigrants from the niche-based regulation of peripheral T cell numbers ensures repertoire turnover throughout adult life and provides the basis of a direct and previously unrecognized role for the thymus in the regulation of peripheral T cell homeostasis.
authors.affiliation: Department of Pathology and Immunology, Monash Medical School, Commercial Road, Prahran, Victoria 3181, Australia. berzins@med.monash.edu.au
authors.forename: S P
authors.initials: SP
authors.lastname: Berzins
authors.forename: D I
authors.initials: DI
authors.lastname: Godfrey
authors.forename: J F
authors.initials: JF
authors.lastname: Miller
authors.forename: R L
authors.initials: RL
authors.lastname: Boyd
mesh_terms: D000818:Animals; D017209:Apoptosis; D016516:CD4-CD8 Ratio; D002478:Cells, Cultured; D006706:Homeostasis; D018655:Lymphocyte Count; D051379:Mice; D008810:Mice, Inbred C57BL; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology* / Q000637:transplantation
chemical_list: D016693:Receptors, Antigen, T-Cell, alpha-beta