Bcl-2 expression during T-cell development: early loss and late return occur at specific stages of commitment to differentiation and survival.
During T-cell development CD3-CD4-CD8- (double-negative) thymocytes proliferative and produce an enormous number of CD3loCD4+CD8+ (double-positive) thymocytes which are destined to die intrathymically unless rescued by positive selection. Those which survive become mature CD3hiCD4/8+ (single-positive) cells and are the precursor of peripheral blood lymphocytes. The product of the bcl-2 protooncogene has been implicated in preventing programmed cell death and is required for prolonged lymphocyte survival following maturation. Previously we and others have reported that Bcl-2 protein expression is biphasic, being high in proliferating double-negative stem cells, low in all double-positive thymocytes except for 1-5% of these cells, and restored in mature, single-positive thymocytes. However, it remained unclear which signaling and selection events regulate Bcl-2 during T-cell maturation. Now we have utilized four-color flow cytometry in normal and genetically altered mice for a detailed analysis of Bcl-2 expression as it relates to T-cell receptor (TCR) expression and positive selection. These studies show that (i) expression of a transgenic TCR in double-negative thymocytes does not lead to premature loss of Bcl-2; thus, Bcl-2 downregulation is not solely due to TCR expression; (ii) Bcl-2 expression is lost at the early transitional CD3-/loCD4-CD8+ stage, prior to expression of CD4; (iii) the Bcl-2+ double-positive thymocytes are those which have undergone positive selection; and (iv) upregulation of Bcl-2 during positive selection requires participation of the CD4 or CD8 co-receptor. These results demonstrate that Bcl-2 and TCR expression are regulated independently during T-cell development, and suggest a role for the CD4 or CD8 co-receptor in Bcl-2 induction during positive selection.
Gratiot-Deans
J
J
Department of Internal Medicine, University of Michigan, Ann Arbor 48109.
Merino
R
R
Nuñez
G
G
Turka
L A
LA
D000818:Animals; D000911:Antibodies, Monoclonal; D016923:Cell Death / Q000187:drug effects; D002454:Cell Differentiation; D002470:Cell Survival; D006224:Cricetinae / Q000276:immunology; D003433:Crosses, Genetic; D005260:Female; D005434:Flow Cytometry; D019204:GTP-Binding Proteins / Q000096:biosynthesis; D015870:Gene Expression; D005938:Glucocorticoids / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D019253:Proto-Oncogene Proteins c-bcl-2; D011948:Receptors, Antigen, T-Cell / Q000096:biosynthesis; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000502:physiology; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D015854:Up-Regulation
D000911:Antibodies, Monoclonal; D005938:Glucocorticoids; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011948:Receptors, Antigen, T-Cell; D019204:GTP-Binding Proteins