ITP患者树突状细胞内吲哚胺2,3-双加氧酶异常的机制研究

Indoleamine 2,3-dioxygenase (IDO) expression in dendritic cells (DCs) can induce or maintain peripheral immune tolerance. Regulatory DCs expressing high levels of active IDO are important in the generation and maintenance of peripheral tolerance. Impaired IDO-mediated tryptophan catabolism has been observed in Immune thrombocytopenia (ITP). The expression of IDO in DCs of ITP patients was significantly decreased. CTLA-4-Ig significantly increased the expression of functional IDO in DCs of ITP patients. However, the mechanism(s) remain obscure.TLR9 can induce IDO in DCs. IDO induction did not occur in T cell-deficient mice or in mice with defective B7 or programmed death (PD)-1 costimulatory pathways. These data support that constitutive interactions from activated T cells or Tregs and IDO-competent DCs via concomitant CTLA4/B7 and PD-1/PD -ligand signals maintain the default potential to regulate T cell responsiveness via IDO. IL-6 upregulates the expression of ubiquitin mRNA, ubiquitin ligase and SOCS proteins. The SOCS proteins possess a Src homology 2 (SH2) domain, which can anchor the phosphorylated ITIMs of IDO, brings the enzyme close to the E3 ubiquitin complex that ubiquinates and targets IDO for proteasomal degradation. To investigate the reasons and pathologic mechanisms of insufficient IDO in DCs from patients with ITP, we will detect the effects of TLR9, PD-1/PD-L,CTLA-4/B7 signal pathway and proteasome inhibitors on the expression and catabolism of IDO,lymphocyte function and secretion of cytokine in vitro.

表达吲哚胺2,3-双加氧酶（IDO）的调节性DCs在调节免疫、诱导免疫耐受方面具有重要地位。研究发现，在ITP患者存在IDO介导的色氨酸代谢异常及DCs内IDO含量的不足，CTLA-4-Ig可明显促进患者DCs内IDO的表达，其机制目前仍不清楚。TLR9可诱导DCs表达功能性IDO，但需要T细胞及B7或PD-1共刺激通路，说明PD-1/PD-L及B7/CTLA-4共刺激信号在IDO的功能性表达中起了重要作用。IDO在细胞内通过泛素-蛋白酶体途径降解，ITP患者IL-6水平明显升高。IL-6能够促进IDO的降解。本研究拟在前期研究的基础上，重点研究引起ITP患者DCs内IDO含量不足的原因及可能的机制，深入探讨TLR9、PD-1/PD-L、B7/CTLA-4共刺激信号及蛋白酶体抑制剂在IDO诱导及代谢中的作用及机制，为ITP治疗提供新靶点和新思路。

ITP是以血小板破坏伴巨核细胞成熟障碍，导致外周血中血小板减少的出血性疾病，树突状细胞（dendritic cells，DCs）是功能强大的APC，在启动和调节免疫反应中起关键作用。而吲哚胺2,3-双加氧酶（indoleamine 2,3-dioxygenase，IDO）在调节DCs功能方面起了重要作用。表达吲哚胺2,3-双加氧酶（IDO）的调节性DCs在调节免疫、诱导免疫耐受方面具有重要地位。研究发现，在ITP患者存在IDO介导的色氨酸代谢异常及DCs内IDO含量的不足，CTLA-4-Ig可明显促进患者DCs内IDO的表达，其机制目前仍不清楚。TLR9可诱导DCs表达功能性IDO，但需要T细胞及B7或PD-1共刺激通路，说明PD-1/PD-L及B7/CTLA-4共刺激信号在IDO的功能性表达中起了重要作用。.在我们研究中发现，虽然ITP患者的CD4+T和CD8+T淋巴细胞表面PD-1表达明显高于健康对照组，但PD-L1在树突状细胞上表达明显降低；ITP患者的血浆sPD-1浓度明显升高，外周血单个核细胞sPD-1表达量明显升高。PD-L1-Fc融合蛋白可明显升高DCs/淋巴细胞共培养体系中淋巴细胞的凋亡水平，抑制淋巴细胞的活化及增殖，并降低了IL-2及IFN-γ的分泌。以上研究说明，ITP患者存在PD-1/PD-L信号通路的异常，sPD-1表达的增高和/或DCs表面PD-L表达的降低可能抑制了PD-1/PD-L信号通路，增强PD-1/PD-L信号通路可能是治疗ITP的一个新思路。.另外我们研究发现，ITP患者外周血单个核细胞免疫性蛋白酶体亚基LMP2表达明显上升，非特异性蛋白酶体抑制剂（硼替佐米）可以降低ITP患者淋巴细胞的活化及增殖水平，增加凋亡水平，降低细胞因子的分泌，以上结果为ITP治疗提供了新靶点和新思路。