Dexamethasone induces apoptosis in human T cell clones expressing low levels of Bcl-2

Previous results of ours have demonstrated that the same clonotype can expr ess both a sensitive and a resistant phenotype to Dex-mediated PCD inductio n depending on its cell cycle phase. In particular, we demonstrated that hu man T lymphocytes, arrested in the G0/G1 phase of the cell cycle, are susce ptible, while proliferating T cells are resistant to Dex-mediated apoptosis , In this paper, we have further characterized the sensitive and resistant phenotypes and investigated whether a different expression of the apoptotic genes Pas, Fast, Bcl-2, Bcl-x and Bar is involved in the regulation of Dex -mediated apoptosis, The results show that the amount of Bcl-2 expression, that changes during cell cycle phases, determines susceptibility or resista nce to apoptosis induced by Dex, In fact, undetectable expression of Bcl-2 in sensitive cells favors Dex-mediated apoptosis while high expression of B cl-2 in proliferating cells counterbalances apoptosis induction. Moreover, the addition of exogenous IL-2, in the presence of Dex, fails to up-regulat e Bcl-2 expression and to revert Dex-mediated apoptotic phenomena.