Indoleamine 2,3-dioxygenase (IDO) can promote tryptophan metabolism to kynurenine and modulate regulatory T cells (Tregs), thereby maintains lower efficiency to induce tolerance. Our aim is to investigate the mechanism of tolerance induction by a IDO metabolite named Immutol.

Methods

We established rat heterotopic heart transplantation models and treated them with Immutol, cyclosporine A (CsA) and 1-methyl-DL-tryptophan (1-MT) in vivo. The drugs were administered via gavage to all but the control group one day before surgery. CsA was gavaged continually for 20 days and Immutol for 60 days; after withdrawal of the drugs, the recipients were observed for at least 10 months. Immune cells were analyzed by flow cytometry. The IDO signaling pathway was evaluated by Western blotting, RT-PCR and immunochemical staining. Enzyme-linked immunosorbent assays (ELISAs) were used to detect changes in cytokines.

Results

CsA or Immutol alone prolonged survival but did not induce tolerance after withdrawal. Immutol+CsA inhibited acute rejection, and the grafts survived more than 400 d, with tolerance detected in most rats (13/15). Increased protein IDO and kynurenine could regulate the accumulation of CD4⁺Tregs, CD8⁺Tregs and pDC to induce immune tolerance. I-MT specifically blocked IDO, weakened the expression of IDO and kynurenine, and produced grafts rejection. Additionally, Tregs could down-regulate immune responses through production of the immunosuppressive cytokines IL-10 and TGF-beta, thus induce immune tolerance. CD8⁺ Tregs produce IFN-γ, and tolerance is dependent on both IFN-γ and IDO.

Conclusion

Immutol combined with CsA can control acute rejection and induce tolerance in rats with cardiac allografts after withdrawal. Immutol may become a novel drug for future clinical use.

中文翻译：

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Immutol通过IDO信号通路调控CD4+Tregs、CD8+Tregs和pDCs诱导大鼠心脏移植免疫耐受

吲哚胺 2,3-双加氧酶 (IDO) 可促进色氨酸代谢为犬尿氨酸并调节调节性 T 细胞 (Tregs)，从而维持较低的诱导耐受性。我们的目标是研究一种名为 Immutol 的 IDO 代谢物诱导耐受的机制。

方法

我们建立了大鼠异位心脏移植模型，并在体内用 Immutol、环孢素 A (CsA) 和 1-甲基-DL-色氨酸 (1-MT) 对其进行治疗。手术前一天通过管饲法对除对照组以外的所有人给药。CsA 连续灌胃 20 天， Immutol 灌胃 60 天；停药后，接受者至少观察10个月。通过流式细胞术分析免疫细胞。通过蛋白质印迹、RT-PCR和免疫化学染色评估IDO信号通路。酶联免疫吸附试验 (ELISA) 用于检测细胞因子的变化。

结果

单独使用 CsA 或 Immutol 可延长生存期，但在停药后不会诱导耐受。Immutol+CsA 抑制急性排斥反应，移植物存活超过 400 天，在大多数大鼠中检测到耐受性 (13/15)。增加的蛋白质 IDO 和犬尿氨酸可以调节 CD4 ⁺ Tregs、CD8 ⁺ Tregs 和 pDC 的积累，从而诱导免疫耐受。I-MT特异性阻断IDO，减弱IDO和犬尿氨酸的表达，产生移植排斥。此外，Tregs 可以通过产生免疫抑制细胞因子 IL-10 和 TGF-β 来下调免疫反应，从而诱导免疫耐受。CD8 ⁺ Tregs 产生 IFN-γ，耐受性取决于 IFN-γ 和 IDO。

结论

Immutol联合CsA可控制大鼠心脏停药后的急性排斥反应并诱导耐受。Immutol 可能成为未来临床应用的新型药物。