title: CD45RA-R0+ subset is the major population of dividing thymocytes in the human.
abstract: CD45, or leukocyte common antigen, is expressed in different isoforms on different subsets of thymocytes, suggesting its involvement in the process of T cell development in the thymus. We report studies on CD45 isoform expression on human thymocytes at various stages of development using three-color flow cytometric analysis and cell cycle analysis. Among CD45R0+ cells 18.4% were in S+G2/M phase and represented more than 80% of the dividing cells in the thymus. Among the CD45R0- cells 10.9% were also in cell cycle. Because the CD45R0+ population is almost exclusively CD45RA-, the CD45RA-R0+ subset constitutes the major portion of dividing cells in the thymus. Both the CD1high and the CD3- populations were actively cycling. However, the former was almost 100% and the latter only 50% CD45RA-R0+. Dividing CD45RA-R0+ cells contain, therefore, many cells that have not yet expressed the CD3/T cell receptor complex and presumably have not yet undergone selective procedures. These results are hard to reconcile with the previously presented hypothesis that CD45R0 represents a marker for cells that are destined to die in the thymus. Instead, these results suggest an alternative possibility that CD45R0+ cells may contain cells that can mature and, thus, also constitute the thymic generative lineage.
authors.affiliation: First Department of Surgery, Osaka University Medical School, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Okumura
authors.forename: Y
authors.initials: Y
authors.lastname: Fujii
authors.forename: K
authors.initials: K
authors.lastname: Inada
authors.forename: K
authors.initials: K
authors.lastname: Nakahara
authors.forename: H
authors.initials: H
authors.lastname: Matsuda
mesh_terms: D015703:Antigens, CD / Q000032:analysis; D018949:Antigens, CD1; D000954:Antigens, Surface / Q000032:analysis; D017252:CD3 Complex / Q000032:analysis; D002453:Cell Cycle; D002455:Cell Division; D006801:Humans; D007223:Infant; D017493:Leukocyte Common Antigens / Q000032:analysis*; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology*
chemical_list: D015703:Antigens, CD; D018949:Antigens, CD1; D000954:Antigens, Surface; D017252:CD3 Complex; D017493:Leukocyte Common Antigens