title: Homeostatic proliferation of a Qa-1b-restricted T cell: a distinction between the ligands required for positive selection and for proliferation in lymphopenic hosts.
abstract: Naive T cells proliferate in response to self MHC molecules after transfer into lymphopenic hosts, a process that has been termed homeostatic proliferation (HP). Previous studies have demonstrated that HP is driven by low level signaling induced by interactions with the same MHC molecules responsible for positive selection in the thymus. Little is known about the homeostatic regulation of T cells specific for class Ib molecules, including Qa-1 and H2-M3, though it has been suggested that their capacity to undergo homeostatic expansion may be inherently limited. In this study, we demonstrate that naive 6C5 TCR transgenic T cells with specificity for Qa-1(b) have a capacity similar to conventional T cells to undergo HP after transfer into sublethally irradiated mice. Proliferation was largely dependent on the expression of beta(2)-microglobulin, and experiments with congenic recipients expressing Qa-1(a) instead of Qa-1(b) demonstrated that HP is specifically driven by Qa-1(b) and not through cross-recognition of classical class I molecules. Thus, the same MHC molecule that mediates positive selection of 6C5 T cells is also required for HP. Homeostatic expansion, like positive selection, occurs in the absence of a Qa-1 determinant modifier, the dominant self-peptide bound to Qa-1 molecules. However, experiments with TAP(-/-) recipients demonstrate a clear distinction between the ligand requirements for thymic selection and HP. Positive selection of 6C5 T cells is dependent on TAP function, thus selection is presumably mediated by TAP-dependent peptides. By contrast, HP occurs in TAP(-/-) recipients, providing an example where the ligand requirements for HP are less stringent than for thymic selection.
authors.affiliation: Department of Pathology and Laboratory Medicine, Emory University School of Medicine, 101 Woodruff Circle, Atlanta, GA 30322, USA.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Sullivan
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Reed-Loisel
authors.forename: Gilbert J
authors.initials: GJ
authors.lastname: Kersh
authors.forename: Peter E
authors.initials: PE
authors.lastname: Jensen
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000502:physiology; D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology*; D002460:Cell Line; D049109:Cell Proliferation; D002999:Clone Cells; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D006706:Homeostasis / Q000235:genetics / Q000276:immunology*; D007156:Immunologic Memory / Q000235:genetics; D016130:Immunophenotyping; D008024:Ligands; D018655:Lymphocyte Count; D008231:Lymphopenia / Q000235:genetics / Q000276:immunology* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D011828:Radiation Chimera / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism / Q000637:transplantation
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D018984:Epitopes, T-Lymphocyte; D015395:Histocompatibility Antigens Class I; D008024:Ligands; C032907:Q surface antigens; C486171:Tap1 protein, mouse; C489516:Tap2 protein, mouse