探索在小鼠肺炎模型中肺炎链球菌诱导免疫细胞亚群产生IL-17的抗感染机制

Streptococcus pneumoniae (S.pn) is the leading cause of community-acquired pneumonia. The incidence of pneumococcal pneumonia is greatest at the extremes of age and in individuals with medical comorbidity. Human immunity to pneumococcal infections has been assumed to depend on anticapsular antibodies. However, recent findings from murine models suggest that alternative mechanisms, dependent on T helper cells, are also involved. Especially, the interleukin-17 (IL-17) was shown to represent a key component in pneumococcal immunity in mice, and the proposed mechanism was IL-17-dependent neutrophil killing of pneumococci. Our Preliminary study found that the production of IL-17 in serum and bronchoalveolar lavage fluid were increased in murine models of pneumococcal colonization. However, little is known about the cellular source of IL-17 and the precise role of IL-17 in pneumococcal infection and immunity. Therefore, in the present study, by bead sorting of CD4 + αβ T, CD8 + αβ T, NK, γδ T cells and antigen presenting cells from mouse lymph nodes or spleen, we will investigate S.pn modulate the activation of dendritic cells to release IL-17-production related cytokines and chemokines which can further prompt CD4 + αβ T, CD8 + αβ, TNK and γδ T cells to generate IL-17 in vitro, respectively. Using intracellular staining with flow cytometry and selective inhibitors, we further investigate the underlying intracellular signaling mechanisms regulating the expression of the target cell surface receptors and activation of the transcription factor. Using respective specific neutralizing antibodies, we establish the mice depleted of CD4 + αβT, CD8 + αβT, NK or γδ T cells respectively, to determinate the effects of IL-17 generated from these IL-17-producing cells in pneumococcal infection and immunity. This study therefore provide a new insight into the anti-infection effects of IL-17 from IL-17-producing cells mediated by distinct intracellular signal transductions in pneumococcal infection and a new idea and direction on the immune prevention and treatment of S.pn infection.

肺炎链球菌（S.pn）是一种引起儿童及成人细菌性肺炎的主要致病菌，也是社区获得性肺炎最主要的致病菌。目前研究发现宿主不仅通过体液免疫产生抗体清除S.pn，还可通过IL-17招募和活化中性粒细胞清除S.pn。本课题组前期研究显示:小鼠鼻腔感染S.pn后，血清和支气管肺泡灌洗液中的IL-17含量明显升高，但IL-17的细胞来源及其在抗感染免疫中的具体机制尚不清楚。本研究以S.pn感染小鼠和小鼠体内分别缺失CD4+ αβ T、CD8+ αβ T、NK和γδ T细胞为动物模型，以IL-17的产生及其在S.pn肺炎中所起的效应作用为切入点，探讨S.pn如何诱导CD4+ αβ T、CD8+ αβ T、NK和γδ T细胞产生IL-17的相关细胞因子、趋化因子和受体的表达，以及下游信号分子的活化情况，加深对S.pn与宿主细胞相互作用机理的认识，为免疫预防和治疗s.pn感染性疾病提供新的方向和思路。

肺炎链球菌是一种引起儿童及成人细菌性肺炎的主要致病菌，也是社区获得性肺炎最主要的致病菌。研究发现宿主不仅通过体液免疫产生抗体清除致病菌，还可通过IL-17招募和活化中性粒细胞清除致病菌，但IL-17家族相关细胞因子在调节肺部免疫和炎症方面的作用机制尚不清楚。本研究中，我们发现社区获得性肺炎患者中，无论是成人还是儿童，其血清IL-17B的水平均高于正常对照，并且IL-17B的升高水平与IL-8的浓度显著正相关。体外实验显示，IL-17B通过激活Akt、P38 MAPK、ERK和NF-κB途径诱导人支气管上皮细胞(BEAS-2B)表达IL-8，IFN-γ可抑制IL-17B对BEAS-2B的刺激，TNF-α则能促进IL-17B的作用；但是IL-17B对肺成纤维细胞无此作用。在用肺炎链球菌等致病菌构建的小鼠支气管肺炎模型中，小鼠支气管肺泡灌洗液和血清中的IL-17含量明显升高，进一步研究显示了IL-17B的升高水平与IL-8的浓度正相关。综上所述，肺炎会引起IL-17B的释放增加，进而介导支气管上皮细胞分泌IL-8以调节肺部免疫和炎症。本研究加深了IL-17家族细胞因子对气道炎症作用机理的认识，为免疫预防和治疗肺部炎症性疾病提供新的方向和思路。