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 pigment epithelium (HFRPE)-mediated T-cell death. METHODS. Pure HFRPE cells were isolated and cultured. Normal and interferon (IFN)-γ-activated HFRPE from early and late in vitro passages were incubated with cells from the human T-cell leukemia line Jurkat (Jkt). Cultures were pulsed with [³H]- thymidine to measure Jkt cell proliferation. Jkt cells were evaluated for apoptosis either by staining with an ethidium bromide/acridine orange mixture (AO/EB) or with Annexin V-phycoerythrin. The role 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 signaling. The involvement of the antiapoptotic human gene bcl-x(L) was determined by using Jkt cells that were stably transfected with bcl-x(L). The role of cell-cell contact in the induction of apoptosis was evaluated in a transwell system in the presence or absence of neutralizing antibodies against IFN-γ and tumor necrosis factor (TNF)-α. RESULTS. HFRPE cells inhibited the proliferation of Jkt cells by inducing apoptosis through a FasL-independent pathway. Passaging and IFN-γ activation strengthened the inhibitory effect of HFRPE cells on the proliferation of Jkt cells. At lower HFRPE passages (P2), bcl-x(L), overexpression rescued the HFRPE cell-mediated apoptosis. The separation of the cells by the transwell system did not affect the HFRPE cell-mediated suppression. This suppressive effect was not mediated by the secretion of IFN-γ or TNF-α molecules. CONCLUSIONS. HFRPE cells suppressed the proliferation of Jkt cells by inducing apoptosis. HFRPE cells induced a stronger inhibitory effect on Jkt cells at higher in vitro passages. The HFRPE-induced apoptosis was not mediated through the FasL/Fas pathway or through the secretion of the apoptosis-inducing cytokines IFN-γ and TNF-α. The bcl-x(L) gene may play a role in preventing HFRPE cell-induced apoptosis in Jkt cells. These combined results 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 subretinal space.