Department of Molecular Preventive Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Immunology. 2018 Feb;153(2):253-267. doi: 10.1111/imm.12840. Epub 2017 Oct 24.
The immune system including antigen-specific CD8 T cells, which are cytotoxic T lymphocytes (CTLs), can acquire the potential for more effective elimination of the pathogen at re-infection. As memory CTLs could exert protective immunity after the next response, we aimed to elucidate the substantial change of repetitively infected memory CTLs. Currently, DNA methylation status in repetitively infected memory CTLs is unknown, so we performed next-generation sequencing to evaluate methylation status and transcriptional regulation of naive, primary and secondary memory CD8 T cells on the basis of transcription start sites (TSS). Notably, total CpG sites in the entire regions of all genes were significantly unmethylated in primary memory CTLs (young memory CTLs) and even more unmethylated in secondary memory CTLs (old memory CTLs). However, total proximal regions from TSS, which cover transcriptional promoters, were steadily methylated with repeated infections. In contrast, distal regions from TSS, which are the majority of entire regions and include transcriptional enhancers, were extensively unmethylated by infections. In association between transcriptional and methylation changes, accompanied by genes characteristic of the immune response, natural killer cell signature genes, known to be expressed in senescent CD8 T cells, were transcriptionally up-regulated and unmethylated in young memory CTLs, and more so in old memory CTLs, whereas ribosomal proteins were transcriptionally down-regulated and methylated in proximal region from the TSS by infections. Our results suggest that epigenetically augmented enhancers and suppressed promoters, which could consequently lead to global decline of transcription and translation, could represent the senescence of memory CTLs.
免疫系统包括抗原特异性 CD8 T 细胞，即细胞毒性 T 淋巴细胞 (CTL)，可在再次感染时获得更有效地清除病原体的潜力。由于记忆 CTL 在下次反应后可发挥保护免疫作用，因此我们旨在阐明反复感染的记忆 CTL 的实质性变化。目前，反复感染的记忆 CTL 中的 DNA 甲基化状态尚不清楚，因此我们基于转录起始位点 (TSS) 进行了下一代测序，以评估幼稚、原发性和次级记忆 CD8 T 细胞的甲基化状态和转录调控。值得注意的是，在原发性记忆 CTL（年轻记忆 CTL）中，所有基因的整个区域的总 CpG 位点明显呈非甲基化状态，在继发性记忆 CTL（老年记忆 CTL）中甚至更非甲基化。然而，随着重复感染，TSS 附近区域（覆盖转录启动子）的总近端区域逐渐被甲基化。相比之下，TSS 远端区域（占整个区域的大部分，包括转录增强子）则在感染过程中广泛非甲基化。在转录和甲基化变化之间的关联中，伴随着免疫反应特征的基因、自然杀伤细胞特征基因（已知在衰老 CD8 T 细胞中表达）在年轻记忆 CTL 中被转录上调且非甲基化，在老年记忆 CTL 中更是如此，而核糖体蛋白则在感染过程中在 TSS 的近端区域被转录下调且甲基化。我们的研究结果表明，增强的增强子和抑制的启动子的表观遗传修饰，可能导致转录和翻译的全面下降，这可能代表记忆 CTL 的衰老。
