title: Constitutive activation of integrin alpha 4 beta 1 defines a unique stage of human thymocyte development.
abstract: Our understanding of thymocyte development and of the positive and negative selection events involved in shaping the repertoire of mature T lymphocytes has been greatly facilitated by the use of transgenic and gene knockout animals. Much less is known about the factors that control the homing and population of the thymus by T cell precursors and the subsequent migration of developing thymocytes through the thymic architecture. As the integrins represent a candidate group of cell surface receptors that may regulate thymocyte development, we have analyzed the expression and function of alpha 4 beta 1 and alpha 5 beta 1 on human thymocytes. A major portion of double positive (CD4+ CD8+) human thymocytes express alpha 4 beta 1 in a constitutively active form and adhere to fibronectin and vascular cell adhesion molecule 1. alpha 4 beta 1 expression is similar on adherent and nonadherent populations, thus, activity reflects the receptor state and not simple expression. The adherent cells are immature, expressing high levels of CD4/CD8 and low levels of CD3 and CD69. In contrast, nonadherent cells possess the phenotype of thymocytes after positive selection, expressing intermediate levels of CD4 and/or CD8 and high levels of CD3 and CD69. The adherent population fails to respond to activation with anti-CD3 and fibronectin, whereas nonadherents exhibit an alpha 5 beta 1-dependent proliferation. Differential regulation of alpha 4 beta 1 and alpha 5 beta 1 receptors may provide a mechanism controlling cellular traffic, differentiation, and positive selection of thymocytes.
authors.affiliation: Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: D R
authors.initials: DR
authors.lastname: Salomon
authors.forename: C F
authors.initials: CF
authors.lastname: Mojcik
authors.forename: A C
authors.initials: AC
authors.lastname: Chang
authors.forename: S
authors.initials: S
authors.lastname: Wadsworth
authors.forename: D H
authors.initials: DH
authors.lastname: Adams
authors.forename: J E
authors.initials: JE
authors.lastname: Coligan
authors.forename: E M
authors.initials: EM
authors.lastname: Shevach
mesh_terms: D000906:Antibodies / Q000276:immunology; D015703:Antigens, CD / Q000276:immunology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology; D017252:CD3 Complex / Q000276:immunology; D015704:CD4 Antigens / Q000276:immunology; D016827:CD8 Antigens / Q000276:immunology; D002448:Cell Adhesion; D002455:Cell Division; D002675:Child, Preschool; D005353:Fibronectins / Q000494:pharmacology; D006801:Humans; D007223:Infant; D039041:Integrin alpha4beta1; D016023:Integrins / Q000276:immunology*; D037181:Lectins, C-Type; D013234:Stem Cells / Q000166:cytology / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology; D000099192:CD69 Antigens
chemical_list: D000906:Antibodies; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D015704:CD4 Antigens; D016827:CD8 Antigens; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D037181:Lectins, C-Type; D000099192:CD69 Antigens