title: An immune system switch in T cell lifespan at birth results in extensive loss of naive fetal T cells during the first week of postnatal life.
abstract: Lymphocyte recirculation is critical to maximize the efficiency of immunological surveillance and is an absolute requirement for the development of systemic memory. The consensus view of the lifespan of peripheral T cells holds that naive T cells are long-lived cells and most memory T cells are short-lived cells, although the question of the lifespan of peripheral T cells is not yet fully resolved. We have studied the lifespan of T cells circulating in efferent lymph draining lymph nodes (LN) in the immunologically naive sheep fetus and in postnatal lambs immediately following birth by examining the in vivo incorporation of [3H]thymidine by newly formed T cells during continuous administration of [3H]thymidine. We report that authentically naive fetal T cells are long-lived cells which continue to recirculate between blood and lymph during fetal life. At birth, however, a process is triggered whereby fetal T cells circulating through LN are rapidly lost from the peripheral T cell pool and are replaced by freshly arriving T cells which have been formed since birth. Our results indicate that by the end of the first week of postnatal life, around three-quarters of the T cells circulating through peripheral LN have been formed since birth.
authors.affiliation: Laboratory for Fetal and Neonatal Immunology, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: R N
authors.initials: RN
authors.lastname: Cahill
authors.forename: W G
authors.initials: WG
authors.lastname: Kimpton
authors.forename: E A
authors.initials: EA
authors.lastname: Washington
authors.forename: L
authors.initials: L
authors.lastname: Dudler
authors.forename: Z
authors.initials: Z
authors.lastname: Trnka
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000276:immunology*; D002454:Cell Differentiation / Q000276:immunology; D002465:Cell Movement / Q000276:immunology; D002470:Cell Survival / Q000276:immunology; D005314:Embryonic and Fetal Development / Q000276:immunology*; D007399:Interphase / Q000276:immunology; D008198:Lymph Nodes / Q000166:cytology / Q000276:immunology; D012756:Sheep; D016176:T-Lymphocyte Subsets / Q000166:cytology*