Human fetal retinal pigment epithelial cells induce apoptosis in the T-cell line Jurkat

PURPOSE. TO investigate the mechanism(s) involved in human fetal retinal pi gment epithelium (HFRPE)-mediated T-cell death. METHODS. Pure HFRPE cells were isolated and cultured. Normal and interferon (IFN)-gamma-activated HFRPE from early and late in vitro passages were inc ubated with cells from the human T-cell leukemia line Jurkat (Jkt). Culture s were pulsed with [H-3]-thymidine to measure Jkt cell proliferation. Jkt c ells were evaluated for apoptosis either by staining with an ethidium bromi de/acridine orange mixture (AO/EB) or with Annexin V-phycoerythrin. The rol e of Fas ligand (FasL) molecule in HFRPE-mediated apoptosis was assessed by using a mutant Jkt cell line (DD3), which is deficient in Fas-mediated sig naling. The involvement of the antiapoptotic human gene bcl-x(L), was deter mined by using Jkt cells that were stably transfected with bcl-x(L). The ro le of cell-cell contact in the induction of apoptosis was evaluated in a tr answell system in the presence or absence of neutralizing antibodies agains t IFN-gamma and tumor necrosis factor (TNF)-alpha. RESULTS. HFRPE cells inhibited the proliferation of Jkt cells by inducing a poptosis through a Fast-independent pathway. Passaging and IFN-gamma activa tion strengthened the inhibitory effect of HFRPE cells on the proliferation of Jkt cells. At lower HFRPE passages (P2), bcl-x(L), overexpression rescu ed the HFRPE cell-mediated apoptosis. The separation of the cells by the tr answell system did not affect the HFRPE cell-mediated suppression. This sup pressive effect was not mediated by the secretion of IFN-gamma or TNF-alpha molecules. CONCLUSIONS. HFRPE cells suppressed the proliferation of Jkt cells by induc ing apoptosis. HFRPE cells induced a stronger inhibitory effect on Jkt cell s at higher in vitro passages. The HFRPE-induced apoptosis was not mediated through the FasL/Fas pathway or through the secretion of the apoptosis-ind ucing cytokines IFN-gamma and TNF-alpha. The bcl-x(L), gene may play role i n preventing HFRPE cell-induced apoptosis in Jkt cells. These combined resu lts suggest that the HFRPE-mediated suppression of primary T cells may also be mediated by the induction of apoptosis. Therefore, the retinal pigment epithelium may play a role in the induction of immune privilege in the subr etinal space.