title: Distinct phases in the positive selection of CD8+ T cells distinguished by intrathymic migration and T-cell receptor signaling patterns.
abstract: Positive selection of CD8 T cells in the thymus is thought to be a multistep process lasting 3-4 d; however, the discrete steps involved are poorly understood. Here, we examine phenotypic changes, calcium signaling, and intrathymic migration in a synchronized cohort of MHC class I-specific thymocytes undergoing positive selection in situ. Transient elevations in intracellular calcium concentration ([Ca(2+)]i) and migratory pauses occurred throughout the first 24 h of positive selection, becoming progressively briefer and accompanied by a gradual shift in basal [Ca(2+)]i over time. Changes in chemokine-receptor expression and relocalization from the cortex to medulla occurred between 12 and 24 h after the initial encounter with positive-selecting ligands, a time frame at which the majority of thymocytes retain CD4 and CD8 expression and still require T-cell receptor (TCR) signaling to efficiently complete positive selection. Our results identify distinct phases in the positive selection of MHC class I-specific thymocytes that are distinguished by their TCR-signaling pattern and intrathymic location and provide a framework for understanding the multistep process of positive selection in the thymus.
authors.affiliation: Division of Immunology and Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3200; and.
authors.forename: Jenny O
authors.initials: JO
authors.lastname: Ross
authors.affiliation: Division of Immunology and Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3200; and.
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Melichar
authors.affiliation: Rosalind Russell-Ephraim P. Engleman Medical Research Center for Arthritis, Department of Medicine,Department of Microbiology and Immunology, University of California, San Francisco, CA 94143.
authors.forename: Byron B
authors.initials: BB
authors.lastname: Au-Yeung
authors.affiliation: Division of Immunology and Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3200; and.
authors.forename: Paul
authors.initials: P
authors.lastname: Herzmark
authors.affiliation: Rosalind Russell-Ephraim P. Engleman Medical Research Center for Arthritis, Department of Medicine,Department of Microbiology and Immunology, University of California, San Francisco, CA 94143Howard Hughes Medical Institute, aweiss@medicine.ucsf.edu erobey@berkeley.edu.
authors.forename: Arthur
authors.initials: A
authors.lastname: Weiss
authors.affiliation: Division of Immunology and Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3200; and aweiss@medicine.ucsf.edu erobey@berkeley.edu.
authors.forename: Ellen A
authors.initials: EA
authors.lastname: Robey
mesh_terms: D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D020013:Calcium Signaling / Q000235:genetics / Q000276:immunology*; D002465:Cell Movement / Q000235:genetics / Q000276:immunology*; D060966:Clonal Selection, Antigen-Mediated / Q000235:genetics / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology*
keywords: Zap70; thymic slice; two photon microscopy