Selective IL-10 inhibition of HLA-DR expression in IFN-gamma-stimulated human retinal pigment epithelial cells

Purpose. Human RPE cells express HLA-DR antigens, bind leukocytes via ICAM-1, and secrete IL-8 and MCP-I, which attract and activate leukocytes. Since little is known concerning endogenous cytokines that may alter ocular immunologic and inflammatory mechanisms; we investigated whether IL-IO, an immunosuppressive cytokine, modulates these HRPE features. Methods. IL-10 effects on HLA-DR and ICAM-1 were examined by HRPE exposures to: (I) IFN-gamma (10-1000 U/ml) + IL-10 (1-100 U/ml) and (2) IL-10 pre-incubation followed by IFN-gamma + IL-10. Immunohistochemistry for HLA-DR and ICAM-1 was graded by masked observers. Flow cytometric analysis quantitated HRPE HLA-DR and ICAM-1. Effects of IL-10 on IL-IP (0.2 or 2 ng/ml)-, or TNF-alpha (0.2 or 2 ng/ml)-induced IL-8 and MCP-1 secretion and gene expression were assessed using enzyme-linked immunosorbent assay (ELISA) and Northern blot analysis. Results. HLA-DR expression, detected by immunohistochemistry and flow cytometric analysis, showed dose-dependent increases to IFN-gamma IL-10 pre-/co-incubation, but not co-incubation alone, markedly reduced HLA-DR expression, but did not modulate constitutive or IFN-gamma-induced ICAM-1. IL-10 alone did not induce MCP-1 or IL-8 secretion or steady-state mRNA expression, nor modulate IL-1 beta-, TNF-alpha- or IFN-gamma-induced IL-8 or MCP-1. Conclusions. This study suggests that HRPE HLA-DR antigens are-selectively inhibited by IL-IO, but the timing of IL-10 exposure may be crucial.