Elevated Bcl-2 is not a causal event in the positive selection of T cells.
T cell development is characterized by the induction of apoptosis in most immature thymocytes and the rescue from apoptosis of a small proportion of cells by the process of positive selection.Up-regulation of the anti-apoptotic molecule Bcl-2 is associated with thymocytes undergoing positive selection and a bcl-2 transgene promotes the generation of mature T cells. In contrast,mice transgenic for the pro-apoptotic molecule Bax show impaired T cell maturation. We have used fetal thymic organ culture to determine the action of Bcl-2 and Bax on positive selection of thymocytes. Our data show that Bcl-2 and Bax do not alter the number of thymocytes positively selected by a defined peptide ligand. This implies that Bcl-2 and Bax alter the production of mature T cells in vivo by influencing thymocyte viability rather than by direct action on positive selection. It also presents a solution to the 'chicken-and-egg' scenario relating to Bcl-2 up-regulation and positive selection. The data suggest that the up-regulation of Bcl-2 associated with T cell maturation is a consequence of positive selection rather than a cause of it.
Williams
O
O
Division of Molecular Immunology, Medical Research Council, National Institute for Medical Research, London, GB.
Mok
C L
CL
Norton
T
T
Harker
N
N
Kioussis
D
D
Brady
H J
HJ
D000818:Animals; D002454:Cell Differentiation; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000502:physiology*; D013601:T-Lymphocytes / Q000166:cytology*; D013997:Time Factors; D051028:bcl-2-Associated X Protein
C494827:Bax protein, mouse; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein