title: T cell development and activation in Jak3-deficient mice.
abstract: Jak3, a member of the Janus family of tyrosine kinases, participates in signaling through cytokine receptors that contain the common gamma-chain, including the receptors for interleukin (IL)-2, IL-4, IL-7, IL-9, and IL-15. Jak3- and gamma c-deficient mice have pleiotropic defects that can be attributed to their inability to respond to multiple specific cytokines. A great deal of recent work has focused on the T cell defects in these mutant mice. Specifically, Jak3- and gamma c-deficient mice have small thymuses revealing a defect in T cell development, and in addition, have functionally unresponsive peripheral T cells with an activated/memory cell phenotype. The thymic defect in these mutant mice strongly resembles that seen in IL-7 and IL-7 receptor knockout mice, suggesting that the lack of IL-7 receptor signaling accounts for this defect in Jak3-/- and gamma c- mice. To characterize this defect further, we have examined the earliest stages of T cell development in adult and fetal Jak3-/- thymuses. These studies identify two discrete developmental defects at the CD4-CD8- stage of T cell maturation. Analyses of peripheral T cells in Jak3-/- and gamma c- mice have also revealed a number of abnormalities. All of the T cells in these mutant mice have an activated phenotype and a large fraction of them are proliferating in vivo. In addition, Jak3-/- and gamma c- T cells are more prone to undergo apoptosis than wild-type T cells. Together, these features account for the decreased IL-2 secretion by in vitro-stimulated Jak3-/- T cells. Overall, many of the lymphoid defects of Jak3- and gamma c-deficient mice can be accounted for by the lack of IL-7R and IL-2R signaling; however, other cytokine systems must also be involved in maintaining peripheral T cell homeostasis.
authors.affiliation: Department of Pathology, University of Massachusetts Medical Center, Worcester 01655, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Baird
authors.forename: D C
authors.initials: DC
authors.lastname: Thomis
authors.forename: L J
authors.initials: LJ
authors.lastname: Berg
mesh_terms: D000818:Animals; D006801:Humans; D053616:Janus Kinase 3; D008213:Lymphocyte Activation / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D011505:Protein-Tyrosine Kinases / Q000172:deficiency*; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology* / Q000502:physiology*
chemical_list: D011505:Protein-Tyrosine Kinases; C507933:JAK3 protein, human; C507935:Jak3 protein, mouse; D053616:Janus Kinase 3