title: The development of T and non-T cell lineages from CD34+ human thymic precursors can be traced by the differential expression of CD44.
abstract: In addition to T-lineage cells, a small proportion of hematopoietic non-T cells are present in the human postnatal thymus. However, the origin of this minor non-T cell thymic compartment is presently unknown. In this study we have analyzed the developmental potential of the earliest human intrathymic precursors, characterized as CD34+ cells expressing intermediate levels of CD44. We show that these CD34+CD44int thymocytes cultured with interleukin 7 were able to develop simultaneously into both T- and non-T (monocytes and dendritic cells) -lineage cells. Both developmental pathways progress through a CD1+CD4+ intermediate stage, currently believed to be the immediate precursor of double positive thymocytes. However, separate progenitors for either T or non-T cells could be characterized within CD1+CD4+ thymocytes by their opposite expression of CD44. Downregulated levels of CD44 identified CD1+CD4+ T-lineage precursors, whereas CD44 upregulation occurred on CD1+CD4+ intermediates that later differentiated into non-T cells. Therefore, commitment of human early intrathymic precursors to either T or non-T cell lineages can be traced by the differential expression of the CD44 receptor.
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Márquez
authors.forename: C
authors.initials: C
authors.lastname: Trigueros
authors.forename: E
authors.initials: E
authors.lastname: Fernández
authors.forename: M L
authors.initials: ML
authors.lastname: Toribio
mesh_terms: D000941:Antigens / Q000276:immunology; D015703:Antigens, CD / Q000276:immunology*; D018952:Antigens, CD34; D002352:Carrier Proteins / Q000096:biosynthesis / Q000276:immunology*; D002478:Cells, Cultured; D002675:Child, Preschool; D003713:Dendritic Cells / Q000276:immunology; D006411:Hematopoiesis, Extramedullary; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000276:immunology*; D006801:Humans; D018960:Hyaluronan Receptors; D007223:Infant; D015851:Interleukin-7 / Q000494:pharmacology; D009000:Monocytes / Q000276:immunology; D010641:Phenotype; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000276:immunology*; D016201:Receptors, Lymphocyte Homing / Q000096:biosynthesis / Q000276:immunology*; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology*
chemical_list: D000941:Antigens; D015703:Antigens, CD; D018952:Antigens, CD34; D002352:Carrier Proteins; D018960:Hyaluronan Receptors; D015851:Interleukin-7; D011956:Receptors, Cell Surface; D016201:Receptors, Lymphocyte Homing