ABSTRACT

Myeloid cells, including antigen-presenting cells (APCs) and myeloid-derived suppressor cells (MDSCs) play opposing roles to orchestrate innate and adaptive immune responses during physiological and pathological conditions. We investigated the role of DNA methylation in regulating the transcription of inhibitory/suppressive molecules in myeloid suppressive cells (identified as CD33⁺HLA-DR^–) in comparison to APCs. We selected a number of immune checkpoints (ICs), IC ligands, and immunosuppressive molecules that have been implicated in MDSC function, including PD-L1, TIM-3, VISTA, galectin-9, TGF-β, ARG1 and MMP9. We examined their mRNA expression levels, and investigated whether DNA methylation regulates their transcription in sorted myeloid cell subpopulations. We found that mRNA levels of PD-L1, TIM-3, TGF-β, ARG1 and MMP9 in CD33⁺HLA-DR^– cells were higher than APCs. However, VISTA and galectin-9 mRNA levels were relatively similar in both myeloid subpopulations. CpG islands in the promoter regions of TGF-β1, TIM-3 and ARG1 were highly unmethylated in CD33⁺HLA-DR^–cells, compared with APCs, suggesting that DNA methylation is one of the key mechanisms, which regulate their expression. However, we did not find differences in the methylation status of PD-L1 and MMP9 between CD33⁺HLA-DR^– and APCs, suggesting that their transcription could be regulated via other genetic and epigenetic mechanisms. The promoter methylation status of VISTA was relatively similar in both myeloid subpopulations. This study provides novel insights into the epigenetic mechanisms, which control the expression of inhibitory/suppressive molecules in circulating CD33⁺HLA-DR^– cells in a steady-state condition, possibly to maintain immune tolerance and haemostasis.

摘要

髓样细胞，包括抗原呈递细胞（APC）和髓样来源的抑制细胞（MDSC），在生理和病理状况下起着协调先天性和适应性免疫反应的相反作用。我们研究了DNA甲基化在调节髓样抑制细胞（识别为CD33 ⁺ HLA-DR ^–）与APC相比。我们选择了许多与MDSC功能有关的免疫检查点（IC），IC配体和免疫抑制分子，包括PD-L1，TIM-3，VISTA，galectin-9，TGF-β，ARG1和MMP9。我们检查了它们的mRNA表达水平，并研究了DNA甲基化是否在分类的髓样细胞亚群中调节其转录。我们发现CD33 ⁺ HLA-DR ^–细胞中PD-L1，TIM-3，TGF-β，ARG1和MMP9的mRNA水平高于APC。但是，在两个髓样亚群中，VISTA和galectin-9 mRNA的水平相对相似。TGF-β1，TIM-3和ARG1启动子区域的CpG岛在CD33 ⁺ HLA-DR中高度未甲基化^–与APCs相比，这提示DNA甲基化是调节其表达的关键机制之一。但是，我们没有发现CD33 ⁺ HLA-DR ^–和APC之间PD-L1和MMP9的甲基化状态存在差异，这表明它们的转录可以通过其他遗传和表观遗传机制进行调控。在两个髓样亚群中，VISTA的启动子甲基化状态相对相似。这项研究为表观遗传机制提供了新的见解，该机制控制稳态状态下循环CD33 ⁺ HLA-DR ^–细胞中抑制/抑制分子的表达，可能维持免疫耐受和止血。