title: Engagement of the external domains of CD45 tyrosine phosphatase can regulate the differentiation of immature CD4+CD8+ thymocytes into mature T cells.
abstract: Immature precursor cells are induced in the thymus to express clonotypic T-cell antigen receptors (TCRs) and to differentiate into mature T cells. Perhaps the least understood event which occurs during intrathymic development is the positive selection of immature CD4+CD8+ thymocytes for differentiation into mature CD4+ and CD8+ T cells based on the TCR specificity individual thymocytes express. TCR expression by CD4+CD8+ thymocytes is quantitatively regulated by CD4-mediated activation of p56lck protein-tyrosine kinase whose activity can in turn be regulated by the membrane-bound protein-tyrosine-phosphatase CD45. Here we show that antibody engagement of CD45 external domains enhances Lck tyrosine kinase activity in CD4+CD8+ thymocytes, inhibits TCR expression, and inhibits differentiation of immature CD4+CD8+ thymocytes into mature T cells. Thus, engagement of the external domains of CD45 tyrosine phosphatase can regulate the ability of immature CD4+CD8+ thymocytes to undergo positive selection, suggesting an important regulatory role for intrathymic ligands that are capable of engaging CD45 within the thymus.
authors.affiliation: Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
authors.forename: P
authors.initials: P
authors.lastname: Benveniste
authors.forename: Y
authors.initials: Y
authors.lastname: Takahama
authors.forename: D L
authors.initials: DL
authors.lastname: Wiest
authors.forename: T
authors.initials: T
authors.lastname: Nakayama
authors.forename: S O
authors.initials: SO
authors.lastname: Sharrow
authors.forename: A
authors.initials: A
authors.lastname: Singer
mesh_terms: D000818:Animals; D015704:CD4 Antigens; D016827:CD8 Antigens; D002454:Cell Differentiation; D005434:Flow Cytometry; D051379:Mice; D008810:Mice, Inbred C57BL; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology* / Q000276:immunology; D013950:Thymus Gland / Q000166:cytology
chemical_list: D015704:CD4 Antigens; D016827:CD8 Antigens; D011948:Receptors, Antigen, T-Cell; D017027:Protein Tyrosine Phosphatases