Positive selection of the T cell repertoire: where and when does it occur?
The T cell repertoire is shaped by both positive and negative influences. T lymphocytes that express the V beta 6 variable region are positively selected in the thymus by cells expressing major histocompatibility complex (MHC) class II E molecules. To identify these cells, we have quantitated V beta 6+ T lymphocytes in a set of transgenic mice showing variant patterns of E expression in the thymus. We demonstrate that class II molecules must be expressed on epithelial cells of the cortex for positive selection to occur. Using a direct assay of unmanipulated thymocytes, we show that positive selection is manifest only as a rather late event in thymocyte differentiation, after the maturation of cortical double-positives into single-positives.
Benoist
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Laboratoire de Génétique Moléculaire des Eucaryotes du CNRS, Faculté de Médecine, Strasbourg, France.
Mathis
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D000818:Animals; D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis; D016827:CD8 Antigens; D005434:Flow Cytometry; D000949:Histocompatibility Antigens Class II / Q000235:genetics*; D007135:Immunoglobulin Variable Region / Q000235:genetics; D008198:Lymph Nodes / Q000276:immunology; D051379:Mice; D008822:Mice, Transgenic; D013601:T-Lymphocytes / Q000145:classification / Q000276:immunology*
D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte; D016827:CD8 Antigens; D000949:Histocompatibility Antigens Class II; D007135:Immunoglobulin Variable Region