title: Human thymocytes become lineage committed at an early postselection CD69+ stage, before the onset of functional maturation.
abstract: Mature functional CD4 or CD8 single positive (SP) thymocytes differentiate from immature CD4+ 8+ double positive (DP) precursors through a process of positive selection and terminal differentiation. To study CD4/CD8 lineage commitment, human postselection CD69+ thymocytes were separated into distinct subpopulations based on the differential expression of CD27, CD1, and CD45RA/RO. We demonstrate that these CD69+ subpopulations represent transitional stages of a common differentiation pathway during which CD69+ thymocytes that are initially CD27- CD1+ CD45RA- will sequentially up-regulate CD27, down-regulate CD1, and eventually acquire CD45RA upon maturation. Examination of CD4 and CD8 expression on these CD69+ subsets identified an early postselection CD69+ CD27- CD4SP population that gives rise to both CD4SP and CD8SP mature T cells when cultured in mouse thymus organs. In addition, a CD4+ 8+ DP population was identified that is CD69+ and CD27+, which only gives rise to CD8SP progeny upon culture. Although these results suggest that development of CD4SP and CD8SP cells may proceed through distinct intermediates, examination of active biosynthesis of CD4 and CD8 by the various subsets demonstrated that cells that have selectively terminated CD4 synthesis are already present in the CD27- CD4SP and CD27+ DP populations before culture. These data support a model of thymocyte differentiation whereby the decision of thymocytes to differentiate into one or the other lineage occurs concomitantly with, or very soon after, acquisition of CD69 and before the cells acquire CD27, down-regulate CD1, or acquire functional properties.
authors.affiliation: University of Gent, Department of Clinical Chemistry, Microbiology and Immunology, University Hospital Gent-Blok A, Belgium.
authors.forename: D
authors.initials: D
authors.lastname: Vanhecke
authors.forename: B
authors.initials: B
authors.lastname: Verhasselt
authors.forename: M
authors.initials: M
authors.lastname: De Smedt
authors.forename: G
authors.initials: G
authors.lastname: Leclercq
authors.forename: J
authors.initials: J
authors.lastname: Plum
authors.forename: B
authors.initials: B
authors.lastname: Vandekerckhove
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000032:analysis / Q000502:physiology*; D018949:Antigens, CD1 / Q000032:analysis; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis / Q000502:physiology*; D017252:CD3 Complex / Q000032:analysis; D015704:CD4 Antigens / Q000032:analysis; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D016827:CD8 Antigens / Q000032:analysis; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D002454:Cell Differentiation / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D018920:Coculture Techniques; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D005333:Fetus; D016654:Genes, RAG-1 / Q000276:immunology; D018398:Homeodomain Proteins; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D037181:Lectins, C-Type; D017493:Leukocyte Common Antigens / Q000032:analysis; D051379:Mice; D016513:Mice, SCID; D009924:Organ Culture Techniques; D013234:Stem Cells / Q000166:cytology / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology*; D013950:Thymus Gland; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7 / Q000032:analysis; D000099192:CD69 Antigens
chemical_list: D015703:Antigens, CD; D018949:Antigens, CD1; D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D015704:CD4 Antigens; D016827:CD8 Antigens; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D037181:Lectins, C-Type; D017493:Leukocyte Common Antigens; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7; D000099192:CD69 Antigens; C064658:RAG-1 protein