Human retinal pigment epithelial (hRPE) cells form a selectively permeable monolayer between the neural retina and the highly permeable choroidal vessels. Thus, hRPE cells bear important regulatory functions and are potential targets of pathogens in vivo. Endogenous bacterial endophthalmitis (EBE) is frequently caused by infections with the Gram-positive bacterium Staphylococcus aureus (S. aureus). Upon microbial infection, interferon gamma (IFN-γ), a major cytokine of the adaptive immune response, induces a broad spectrum of effector molecules, such as the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase-1 (IDO1). We stimulated human RPE (hRPE) cells in vitro with proinflammatory cytokines and analyzed the expression levels and enzymatic activities of IDO1 and inducible nitric oxide synthase (iNOS), another antimicrobial effector molecule. The antimicrobial capacity was analyzed in infection experiments using S. aureus and Toxoplasma gondii (T. gondii). Our aim was to characterize the particular importance of IDO1 and iNOS during EBE. We found that an IFN-γ stimulation of hPRE cells induced the expression of IDO1, which inhibited the growth of T. gondii and S. aureus. A co-stimulation with IFN-γ, interleukin-1 beta, and tumor necrosis factor alpha induced a strong expression of iNOS. The iNOS-derived nitric oxide production was dependent on cell-culture conditions; however, it could not cause antimicrobial effects. iNOS did not act synergistically with IDO1. Instead, iNOS activity inhibited IDO1-mediated tryptophan degradation and bacteriostasis. This effect was reversible by the addition of the iNOS inhibitor N^G-monomethyl-l-arginine. In conclusion, iNOS mediates anti-inflammatory effects in hRPE cells stimulated with high amounts of IFN-γ together with tumor necrosis factor alpha and Interleukin-1 beta and prevents potential IDO1-dependent tissue damage.

中文翻译：

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人视网膜色素上皮细胞中 IDO1 和 iNOS 之间的相互作用。

人视网膜色素上皮 (hRPE) 细胞在神经视网膜和高渗透性脉络膜血管之间形成选择性渗透单层。因此，hRPE 细胞具有重要的调节功能，并且是体内病原体的潜在靶标。内源性细菌性眼内炎 (EBE) 经常由革兰氏阳性菌金黄色葡萄球菌 (S. aureus) 感染引起. 在微生物感染后，作为适应性免疫反应的主要细胞因子的干扰素 γ (IFN-γ) 会诱导广谱效应分子，例如色氨酸降解酶吲哚胺 2,3-双加氧酶-1 (IDO1)。我们用促炎细胞因子在体外刺激了人类 RPE (hRPE) 细胞，并分析了 IDO1 和诱导型一氧化氮合酶 (iNOS)（另一种抗菌效应分子）的表达水平和酶活性。在使用金黄色葡萄球菌和弓形虫（T. gondii）。我们的目标是在 EBE 期间描述 IDO1 和 iNOS 的特殊重要性。我们发现 hPRE 细胞的 IFN-γ 刺激诱导了 IDO1 的表达，从而抑制了弓形虫和金黄色葡萄球菌的生长。与 IFN-γ、白细胞介素 1 β 和肿瘤坏死因子 α 的共同刺激诱导了 iNOS 的强烈表达。iNOS 衍生的一氧化氮产量取决于细胞培养条件；然而，它不能引起抗菌作用。iNOS 与 IDO1 没有协同作用。相反，iNOS 活性抑制了 IDO1 介导的色氨酸降解和抑菌。通过添加 iNOS 抑制剂N ^G -monomethyl- l，这种作用是可逆的-精氨酸。总之，iNOS 在用大量 IFN-γ 以及肿瘤坏死因子 α 和白细胞介素 1 β 刺激的 hRPE 细胞中介导抗炎作用，并防止潜在的 IDO1 依赖性组织损伤。