title: Polyclonal MHC Ib-restricted CD8+ T cells undergo homeostatic expansion in the absence of conventional MHC-restricted T cells.
abstract: Naive T cells have the capacity to expand in a lymphopenic environment in a process called homeostatic expansion, where they gain a memory-like phenotype. Homeostatic expansion is dependent on competition for a number of factors, including growth factors and interactions with their selecting self-MHC molecules. In contrast to conventional T cells, it is unclear whether class Ib-restricted CD8+ T cells have a capacity to undergo homeostatic expansion. In this study, we demonstrate that polyclonal MHC Ib-restricted CD8+ T cells can undergo homeostatic expansion and that their peripheral expansion is suppressed by conventional MHC-restricted T cells. The acute depletion of CD4+ T cells in MHC class Ia-deficient Kb-/-Db-/- mice led to the substantial expansion of class Ib-restricted CD8+ T cells. Adoptive transfer of class Ib-restricted CD8+ T cells to congenic lymphopenic recipients revealed their ability to undergo homeostatic expansion in a MHC Ib-dependent manner. To further study the homeostatic expansion of MHC Ib-restricted T cells in the absence of all conventional MHC-restricted T cells, we generated mice that express only MHC Ib molecules by crossing H-2Kb-/-Db-/- with CIITA-/- mice. CD8+ T cells in these mice exhibit all of the hallmarks of naive T cells actively undergoing homeostatic expansion with constitutive memory-like surface and functional phenotype. These findings provide direct evidence that MHC Ib-restricted CD8+ T cells have the capacity to undergo homeostatic expansion. Their peripheral expansion is suppressed under normal conditions by a numerical excess of conventional MHC class Ia- and class II-restricted T cells.
authors.affiliation: Department of Pathology, University of Utah, Salt Lake City, UT 84112, USA.
authors.forename: David C
authors.initials: DC
authors.lastname: Jay
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Reed-Loisel
authors.forename: Peter E
authors.initials: PE
authors.lastname: Jensen
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D049109:Cell Proliferation; D002999:Clone Cells / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D005260:Female; D006183:H-2 Antigens / Q000235:genetics / Q000276:immunology*; D006706:Homeostasis / Q000235:genetics / Q000276:immunology*; D008212:Lymphocyte Depletion; D008231:Lymphopenia / Q000235:genetics / Q000276:immunology / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009687:Nuclear Proteins / Q000172:deficiency / Q000235:genetics; D016176:T-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics
chemical_list: D006183:H-2 Antigens; C024755:H-2K(K) antigen; C032876:H-2Kb protein, mouse; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; D015534:Trans-Activators