DIFFERENTIAL-EFFECTS OF THE IMMUNOSUPPRESSIVE MACROLIDES FK-506 AND RAPAMYCIN ON ACTIVATION-INDUCED T-CELL APOPTOSIS

Activation of certain T-cell lines induces, besides lymphokine production, a suicide process (apoptosis) mediated by fragmentation of the cell's genome. This also occurs intrathymically during negative selection of the T-cell receptor (TcR) repertoire. Cyclosporin A (CsA) has been shown to block activation-driven T-cell apoptosis, an effect which may account for the perturbations of TcR repertoire selection caused by this agent in vivo. Recently, the macrolide FK-506 was demonstrated to suppress T-cell activation by inhibiting lymphokine production in a manner apparently similar to CsA. Thus, it seemed important to determine whether FK-506 would also prevent T-cell apoptosis. For the purpose of comparison, we also investigated rapamycin (RAP), a macrolide structurally related to FK-506, but that does not block lymphokine production and antagonizes the immunosuppressive action of FK-506. The DO-11.10 T-cell hybridoma stimulated with ionomycin plus PMA was used as a model system. FK-506 (1.2 nM) totally prevented DNA fragmentation detectable by agarose gel electrophoresis at 16 h of culture. FK-506 still inhibited this phenomenon when added 2 h after the initiation of the cultures but not later. In contrast, concentrations of RAP as high as 1-mu-M failed to block apoptosis. However, RAP (110 nM) reversed the apoptosis-inhibitory effect of FK-506, even if added 1 - 2 h after the latter to the cultures. Consistent with this antagonism, RAP also reversed the binding of a radiolabeled derivative of FK-506 in DO-11.10 cells. Therefore, FK-506 interferes with an early event of T-cell activation that leads to apoptosis whereas RAP does not. Hence, FK-506, but not RAP, may be able to alter intrathymic T-cell differentiation.