title: Early progression of thymocytes along the CD4/CD8 developmental pathway is regulated by a subset of thymic epithelial cells expressing transforming growth factor beta.
abstract: Precursor cells differentiate into mature CD4+ and CD8+ T cells in the inductive environment of the thymus by undergoing a series of distinct developmental steps marked by expression of the coreceptor molecules CD4 and CD8. Among the earliest cells to enter the CD4/CD8 developmental pathway are CD4-CD8lo precursors cells that differentiate into CD4+CD8+ thymocytes. Here we show that differentiation of precursor cells into CD4+CD8+ thymocytes requires at least one cell division and that their progression through a cell cycle is specifically retarded in the thymus by interaction with thymic epithelial cells that express transforming growth factor beta (TGF-beta) proteins. We also demonstrate that TGF-beta proteins, either in solution or bound to cell membranes, can regulate cell cycle progression and differentiation of CD4-CD8lo precursor cells into CD4+CD8+ thymocytes. The regulatory effect of TGF-beta is specific for CD4-CD8lo precursor cells as TGF-beta proteins do not regulate the earlier generation of CD4-CD8lo precursor cells from CD4-CD8- thymocytes. Finally, we demonstrate that TGF-beta proteins are expressed in vivo in the intact thymus on subcapsular and cortical thymic epithelium where they can contact developing CD4-CD8lo precursor cells. Thus, thymic epithelial cells expressing TGF-beta proteins can actively regulate the rate at which CD4+CD8+ thymocytes are generated from CD4-CD8lo precursor cells.
authors.affiliation: Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Y
authors.initials: Y
authors.lastname: Takahama
authors.forename: J J
authors.initials: JJ
authors.lastname: Letterio
authors.forename: H
authors.initials: H
authors.lastname: Suzuki
authors.forename: A G
authors.initials: AG
authors.lastname: Farr
authors.forename: A
authors.initials: A
authors.lastname: Singer
mesh_terms: D000818:Animals; D015704:CD4 Antigens; D016827:CD8 Antigens; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D004847:Epithelial Cells; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D013234:Stem Cells / Q000166:cytology; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000096:biosynthesis*
chemical_list: D015704:CD4 Antigens; D016827:CD8 Antigens; D016212:Transforming Growth Factor beta