Expression of Local Immunosuppressive Factor, Indoleamine 2,3-dixygenase, in Human Coreal Cells

Purpose: To identify the localization of indoleamine 2,3-dioxygenase (IDO) in human corneal cells and to evaluate its ability to act as a local immunosuppressive factor. Methods: The expression profile of IDO was obtained with RT-PCR and Western blot of in a primary culture of human corneal cells (fibroblasts, epithelial cells and endothelial cells). In order to investigate the immunosuppressive function of IDO, immune cells were cultured in a human corneal cell-conditioned medium, and their prolifleration was identified by the MTT assay. Moreover, apoptotic effects of IDO in immune cells treated with IFN-γ were also investigated with apoptosis ELISA. Results: Among the three different types of human corneal cells analyzed, mRNA and protein expression of IDO was observed only in human corneal fibroblasts. Immune cells cultured in a human corneal fibroblast-conditioned medium showed inhibited proliferation. Moreover, IFN-γ-induced expression of IDO significantly enhanced apoptotic ability in a dose-depandant manner. Conclusions: Our results suggest that human corneal fibroblasts are relatively immuno-resistant and that expression of IDO may be one of the factors involved in the immune tolerance observed in corneal grafts.