title: Analysis of cell division among subpopulations of lymphoid cells in sheep. I. Thymocytes.
abstract: The number, distribution and surface phenotype of dividing cells in the thymus, and differences between the cell cycle status of thymocyte subpopulations, were studied in fetal and post-natal lambs using double-labelling techniques. Dividing cells were labelled in vivo for various periods with 5-bromo-2-deoxyuridine (BrdU). The proportions of constituent thymocyte subpopulations that had synthesized DNA during the labelling period were measured by flow cytometry or immunohistochemistry using a panel of monoclonal antibodies (mAbs) specific for sheep lymphocyte differentiation antigens and MHC class I and class II antigens in conjunction with an anti-BrdU mAb. The proportion of thymocytes that incorporated BrdU during a 1-hr labelling period varied with age, and levels of 30%, 13% and 9% were measured, respectively, in 40- and 125-day-old fetuses and 8-week-old lambs. Eight percent of the thymocytes in lambs were synthesizing DNA, with 4% entering the G2 phase per hour, and a substantial number of thymocytes (21%) had a G2 + M phase DNA content. A small subset of thymocytes (1-3%) recognized by mAb E-79 localized to the subcapsular region of the cortex and displayed the highest level of BrdU incorporation. Cortical-type thymocytes (CD1+) comprised 50-70% of thymocytes; however, few of these incorporated BrdU and the proportion in the G2 + M phase of the cell cycle was higher than for other thymocyte subpopulations. The 197+CD4-CD8- T cells also showed no evidence of in vivo division.
authors.affiliation: Basel Institute for Immunology, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: McClure
authors.forename: L
authors.initials: L
authors.lastname: Dudler
authors.forename: D
authors.initials: D
authors.lastname: Thorpe
authors.forename: W R
authors.initials: WR
authors.lastname: Hein
mesh_terms: D000818:Animals; D002455:Cell Division; D012756:Sheep; D013601:T-Lymphocytes / Q000145:classification / Q000166:cytology*; D013950:Thymus Gland / Q000166:cytology