Department of Internal Medicine I, Ulm University Hospital, Ulm, Germany.
PLoS One. 2013 Aug 19;8(8):e71746. doi: 10.1371/journal.pone.0071746. eCollection 2013.
Coinhibitory PD-1/PD-L1 (B7-H1) interactions provide critical signals for the regulation of autoreactive T-cell responses. We established mouse models, expressing the costimulator molecule B7.1 (CD80) on pancreatic beta cells (RIP-B7.1 tg mice) or are deficient in coinhibitory PD-L1 or PD-1 molecules (PD-L1(-/-) and PD-1(-/-) mice), to study induction of preproinsulin (ppins)-specific CD8 T-cell responses and experimental autoimmune diabetes (EAD) by DNA-based immunization. RIP-B7.1 tg mice allowed us to identify two CD8 T-cell specificities: pCI/ppins DNA exclusively induced K(b)/A(12-21)-specific CD8 T-cells and EAD, whereas pCI/ppinsΔA(12-21) DNA (encoding ppins without the COOH-terminal A(12-21) epitope) elicited K(b)/B(22-29)-specific CD8 T-cells and EAD. Specific expression/processing of mutant ppinsΔA(12-21) (but not ppins) in non-beta cells, targeted by intramuscular DNA-injection, thus facilitated induction of K(b)/B(22-29)-specific CD8 T-cells. The A(12-21) epitope binds K(b) molecules with a very low avidity as compared with B(22-29). Interestingly, immunization of coinhibition-deficient PD-L1(-/-) or PD-1(-/-) mice with pCI/ppins induced K(b)/A(12-21)-monospecific CD8 T-cells and EAD but injections with pCI/ppinsΔA(12-21) did neither recruit K(b)/B(22-29)-specific CD8 T-cells into the pancreatic target tissue nor induce EAD. PpinsΔA(12-21)/(K(b)/B(22-29))-mediated EAD was efficiently restored in RIP-B7.1(+)/PD-L1(-/-) mice, differing from PD-L1(-/-) mice only in the tg B7.1 expression in beta cells. Alternatively, an ongoing beta cell destruction and tissue inflammation, initiated by ppins/(K(b)/A(12-21))-specific CD8 T-cells in pCI/ppins+pCI/ppinsΔA(12-21) co-immunized PD-L1(-/-) mice, facilitated the expansion of ppinsΔA(12-21)/(K(b)/B(22-29))-specific CD8 T-cells. CD8 T-cells specific for the high-affinity K(b)/B(22-29)- (but not the low-affinity K(b)/A(12-21))-epitope thus require stimulatory help from beta cells or inflamed islets to expand in PD-L1-deficient mice. The new PD-1/PD-L1 diabetes models may be valuable tools to study under well controlled experimental conditions distinct hierarchies of autoreactive CD8 T-cell responses, which trigger the initial steps of beta cell destruction or emerge during the pathogenic progression of EAD.
抑制性 PD-1/PD-L1（B7-H1）相互作用为自身反应性 T 细胞反应的调节提供了关键信号。我们建立了表达共刺激分子 B7.1（CD80）的胰岛β细胞（RIP-B7.1 tg 小鼠）或缺乏共抑制性 PD-L1 或 PD-1 分子的小鼠（PD-L1(-/-) 和 PD-1(-/-) 小鼠）模型，以研究基于 DNA 的免疫接种诱导前胰岛素（ppins）特异性 CD8 T 细胞反应和实验性自身免疫性糖尿病（EAD）。RIP-B7.1 tg 小鼠使我们能够识别两种 CD8 T 细胞特异性：pCI/ppins DNA 仅诱导 K(b)/A(12-21)-特异性 CD8 T 细胞和 EAD，而 pCI/ppinsΔA(12-21) DNA（编码没有 COOH 末端 A(12-21)表位的 ppins）引发 K(b)/B(22-29)-特异性 CD8 T 细胞和 EAD。在肌肉内 DNA 注射靶向的非β细胞中，突变 ppinsΔA(12-21)（而非 ppins）的特异性表达/加工，从而促进了 K(b)/B(22-29)-特异性 CD8 T 细胞的诱导。与 B(22-29)相比，A(12-21)表位与 K(b)分子的结合亲和力非常低。有趣的是，用 pCI/ppins 免疫 Coinhibition 缺陷型 PD-L1(-/-)或 PD-1(-/-)小鼠诱导了 K(b)/A(12-21)-单特异性 CD8 T 细胞和 EAD，但注射 pCI/ppinsΔA(12-21)既没有招募 K(b)/B(22-29)-特异性 CD8 T 细胞进入胰腺靶组织，也没有诱导 EAD。RIP-B7.1(+)/PD-L1(-/-)小鼠中 ppinsΔA(12-21)/(K(b)/B(22-29))介导的 EAD 得到有效恢复，与 PD-L1(-/-)小鼠的区别仅在于β细胞中 B7.1 的 tg 表达。或者，在 pCI/ppins+pCI/ppinsΔA(12-21)共同免疫的 PD-L1(-/-)小鼠中，由 ppins/(K(b)/A(12-21))特异性 CD8 T 细胞引发的β细胞破坏和组织炎症的持续存在，促进了 ppinsΔA(12-21)/(K(b)/B(22-29))特异性 CD8 T 细胞的扩增。针对高亲和力 K(b)/B(22-29)-（而非低亲和力 K(b)/A(12-21)-）表位的 CD8 T 细胞因此需要来自β细胞或炎症胰岛的刺激帮助才能在 PD-L1 缺陷型小鼠中扩增。新的 PD-1/PD-L1 糖尿病模型可能是有价值的工具，可用于在良好控制的实验条件下研究触发β细胞破坏初始步骤或在 EAD 发病进展过程中出现的自身反应性 CD8 T 细胞反应的不同层次。
