title: Precommitment of CD4+CD8+ thymocytes to either CD4 or CD8 lineages.
abstract: CD4+ and CD8+ mature T cells arise from CD4+CD8+ precursors in the thymus. During this process, cells expressing T-cell receptors (TCRs) reactive with self major histocompatibility complex (MHC) class I or II molecules are positively selected to the CD8 or CD4 lineage, respectively. It is controversial whether lineage commitment of CD4+CD8+ thymocytes is controlled directly by TCR specificity for MHC (instructional model) or, alternatively, by processes that operate independently of TCR specificity (stochastic model). We show here that CD4+CD8+ thymocytes bearing a MHC class I-restricted transgenic TCR can be subject to two alternative developmental fates. One population of CD4+CD8+ cells is positively selected by MHC class I molecules to the CD8 lineage as expected, whereas the other CD4+CD8+ population rearranges endogenous TCR genes and is positively selected by MHC class II molecules to the CD4 lineage. Blocking TCR-MHC class II interactions in vivo does not interfere with the generation of CD4+CD8+ cells expressing endogenous TCRs but does prevent their subsequent maturation to CD4+ cells. These data support a version of the stochastic model in which CD4+CD8+ thymocytes are precommitted to the CD4 or CD8 lineage independently of TCR specificity for MHC and prior to positive selection.
authors.affiliation: Ludwig Institute for Cancer Research, Lausanne Branch, Epalinges, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Crompton
authors.forename: R K
authors.initials: RK
authors.lastname: Lees
authors.forename: H
authors.initials: H
authors.lastname: Pircher
authors.forename: H R
authors.initials: HR
authors.lastname: MacDonald
mesh_terms: D000375:Aging / Q000276:immunology*; D000818:Animals; D000911:Antibodies, Monoclonal; D015704:CD4 Antigens / Q000032:analysis / Q000276:immunology*; D016827:CD8 Antigens / Q000032:analysis / Q000276:immunology*; D002453:Cell Cycle; D003433:Crosses, Genetic; D005260:Female; D005434:Flow Cytometry; D015332:Gene Rearrangement, alpha-Chain T-Cell Antigen Receptor; D015333:Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; D018398:Homeodomain Proteins; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology*; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D015704:CD4 Antigens; D016827:CD8 Antigens; D018398:Homeodomain Proteins; D011506:Proteins; D012333:RNA, Messenger; D016693:Receptors, Antigen, T-Cell, alpha-beta; C064658:RAG-1 protein