Different subpopulations of developing thymocytes are associated with adherent (macrophage) or nonadherent (dendritic) thymic rosettes.
Thymic rosettes (ROS), structures consisting of thymic lymphoid cells attached to a central stromal cell, were isolated from mouse thymus by collagenase digestion and unit-gravity elutriation. The ROS were then separated into those where the stromal cells were either macrophage-like (M-ROS) or dendritic cell-like (D-ROS), on the basis of the differences in adherence properties or in the level of MAC-1 surface antigen. The ROS were then dissociated and the thymocyte content analyzed by immunofluorescent staining and flow cytometry. M-ROS and D-ROS differed in thymocyte composition, although the major component of both was the CD4+CD8+ cortical thymocyte. D-ROS were enriched in thymocytes expressing high levels of surface T-cell antigen receptor (TcR) and the associated CD3 complex, and these included both CD4+CD8-CD3++ and CD4-CD8+CD3++ mature thymocytes. M-ROS were enriched in CD4-CD8- thymocytes and had a reduced content of thymocytes expressing high TcR-CD3 levels; they nevertheless contained some mature thymocytes, but only of the CD4+CD8-CD3++ category. Several lines of evidence indicated that the mature thymocytes in ROS were cells recently formed in the cortex, and were not from the medullary pool. ROS-associated mature thymocytes expressed lower levels of H-2K than free, mature thymocytes. The CD4+CD8+CD3++ subpopulation, believed to be a developmental intermediate between cortical thymocytes and mature T cells, was present in both ROS populations. Further, late intermediates leading to both mature T-cell categories were evident in D-ROS, but only those leading to CD4+CD8-CD3++ T cells were evident in M-ROS. The results are compatible with a role for ROS in TcR-specificity selection and in the final maturation steps in the thymic cortex.
Shortman
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Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia.
Vremec
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D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis; D017252:CD3 Complex; D015704:CD4 Antigens / Q000032:analysis; D016827:CD8 Antigens / Q000032:analysis; D005260:Female; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D016177:Macrophage-1 Antigen / Q000032:analysis; D008264:Macrophages / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL / Q000276:immunology; D008808:Mice, Inbred CBA / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000032:analysis; D012397:Rosette Formation; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology
D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D015704:CD4 Antigens; D016827:CD8 Antigens; D016177:Macrophage-1 Antigen; D011948:Receptors, Antigen, T-Cell