Key Laboratory of Diagnostic Medicine Designated by the Ministry of Education, Chongqing Medical University, Chongqing, China.
School of Laboratory Medicine, Chongqing Medical University, Chongqing, China.
Front Immunol. 2018 Aug 2;9:1754. doi: 10.3389/fimmu.2018.01754. eCollection 2018.
Vaccine effectiveness is mainly determined by the mechanism mediating protection, emphasizing the importance of unraveling the protective mechanism for novel pneumococcal vaccine development. We previously demonstrated that the regulatory T cell (Treg) immune response has a protective effect against pneumococcal infection elicited by the live-attenuated pneumococcal vaccine SPY1. However, the mechanism underlying this protective effect remains unclear. In this study, a short synthetic peptide (P17) was used to downregulate Tregs during immunization and subsequent challenges in a mouse model. In immunized mice, increase in immune cytokines (IL-12p70, IL-4, IL-5, and IL-17A) induced by SPY1 were further upregulated by P17 treatment, whereas the decrease in the infection-associated inflammatory cytokine TNF-α by SPY1 was reversed. P17 also inhibited the increase in the immunosuppressive cytokine IL-10 and inflammatory mediator IL-6 in immunized mice. More severe pulmonary injuries and more dramatic inflammatory responses with worse survival in P17-treated immunized mice indicated the indispensable role of the Treg immune response in protection against pneumococcal infection by maintaining a balance among acquired immune responses stimulated by SPY1. Further studies revealed that the significant elevation of active transforming growth factor β (TGF-β)1 by SPY1 vaccination activated FOXP3, leading to increased frequencies of CD4CD25Foxp3 T cells. Moreover, SPY1 vaccination elevated the levels of Smad2/3 and phosphor-Smad2/3 and downregulated the negative regulatory factor Smad7 in a time-dependent manner during pneumococcal infection, and these changes were reversed by P17 treatment. These results illustrate that SPY1-stimulated TGF-β1 induced the generation of SPY1-specific Tregs the Smad2/3 signaling pathway. In addition, SPY1-specific Tregs may participate in protection the enhanced expression of PD-1 and CTLA-4. The data presented here extend our understanding of how the SPY1-induced acquired Treg immune response contributes to protection elicited by live-attenuated vaccines and may be helpful for the evaluation of live vaccines and other mucosal vaccine candidates.
疫苗效力主要取决于介导保护的机制，强调了解新型肺炎球菌疫苗开发的保护机制的重要性。我们之前已经证明，调节性 T 细胞（Treg）免疫反应对活减毒肺炎球菌疫苗 SPY1 引起的肺炎球菌感染具有保护作用。然而，这种保护作用的机制尚不清楚。在这项研究中，短合成肽（P17）用于在小鼠模型中在免疫接种和随后的挑战期间下调 Treg。在免疫接种的小鼠中，SPY1 诱导的免疫细胞因子（IL-12p70、IL-4、IL-5 和 IL-17A）的增加进一步被 P17 处理上调，而 SPY1 引起的感染相关炎症细胞因子 TNF-α 的减少则被逆转。P17 还抑制了免疫接种小鼠中免疫抑制细胞因子 IL-10 和炎症介质 IL-6 的增加。在接受 P17 治疗的免疫接种小鼠中，更严重的肺部损伤和更剧烈的炎症反应导致更差的存活率，这表明 Treg 免疫反应在通过维持 SPY1 刺激的获得性免疫反应之间的平衡来保护免受肺炎球菌感染方面发挥不可或缺的作用。进一步的研究表明，SPY1 疫苗接种引起的活性转化生长因子β（TGF-β）1 的显著升高激活了 FOXP3，导致 CD4CD25Foxp3 T 细胞的频率增加。此外，SPY1 疫苗接种在肺炎球菌感染过程中呈时间依赖性方式升高 Smad2/3 和磷酸化 Smad2/3 的水平，并下调负调节因子 Smad7，而 P17 处理则逆转了这些变化。这些结果表明，SPY1 刺激的 TGF-β1 诱导了 SPY1 特异性 Treg 的产生，这是由 Smad2/3 信号通路介导的。此外，SPY1 特异性 Treg 可能通过增强 PD-1 和 CTLA-4 的表达参与保护作用。这里呈现的数据扩展了我们对 SPY1 诱导的获得性 Treg 免疫反应如何有助于活减毒疫苗引起的保护的理解，这可能有助于评估活疫苗和其他粘膜疫苗候选物。
