A型流感病毒表面蛋白神经氨酸酶抑制抗细菌获得性免疫反应的机制研究

Influenza A viral (IAV) infection predisposes the host to secondary bacterial pneumonia, which is a major cause of mortality during influenza epidemics. The mechanisms underlying the bacterial super-infection remain elusive, which impedes the prevention and control of IAV sequential severe diseases and death. We found that neuraminidase (NA) of IAV in combination with bacteria stimulation of bone marrow derived dendritic cells (BMDC) induced lymphocyte apoptosis. In addition, IAV infection leads to a decrease of Th17 cells, which play an important role in antibacterial immunity. Since intestinal bacteria promoted dendritic cells (DC) to release TGF-β1, the NA of IAV can activate TGF-β1, and the activated TGF-β1 in IAV infected mice can induce apoptosis, it is thus reasonable to hypothesize that during IAV infection, activated TGF-β1 plays a role in promoting secondary bacterial infection by inducing lymphocyte apoptosis and inhibiting the response of Th17 cells. In this study, in vitro bone marrow DC and T cell co-culture experiment as well as in vivo super-infection experiment will be performed to reveal the synergy of IAV and bacteria in inducing secondary bacterial pneumonia. Accomplishment of the proposal will reveal a mechanism of influenza pathology not known before, and provide new crucial information for reducing disease severity and death in influenza pandemic.

继发细菌性肺炎是导致A型流感病毒（IAV）感染病人死亡的主要原因，然而其机制不明。我们发现IAV的神经氨酸酶（NA）与细菌共刺激小鼠骨髓来源的树突细胞（BMDC）导致共培养的脾脏淋巴细胞凋亡。Th17细胞是粘膜的主要T细胞群，在抗细菌黏膜感染中发挥重要作用。小鼠实验发现IAV感染后Th17细胞对细菌的反应显著降低。已知1）肠道细菌诱导DC分泌转化生长因子（TGF-β1）；2）IAV的NA活化TGF-β1； 3）TGF-β1诱导细胞凋亡。由此我们假设：IAV感染时，继发感染的细菌诱导DC表达的TGF-β1被NA活化，促进淋巴细胞凋亡，抑制Th17细胞对细菌感染的免疫应答，导致继发细菌性肺炎。本课题将采用BMDC与T细胞共培养实验和IAV继发细菌感染的小鼠模型，揭示IAV和细菌协同作用于宿主免疫应答的致病机理，阐明TGF-β1在其中的作用，为预防和治疗IAV继发细菌性肺炎提供新靶标。

细菌继发感染是流感爆发造成高死亡率的主要原因。大多数人群在感染A型流感病毒（IAV）之前就已经经历了继发感染中常见细菌的感染，但是在IAV感染患者中通过回忆免疫反应清除细菌似乎无效。确实细菌疫苗的免疫反应在IAV感染后显著降低。因此我们提出假设IAV感染抑制宿主回忆免疫反应有效清除细菌。我们利用小鼠共感染模型和CD4+T细胞过继转移实验证明这一假设，并探究其机制。研究结果包括：1、IAV感染显著抑制肺炎球菌（Sp）特异的Th17细胞回忆免疫反应对宿主的免疫保护作用；2、IAV感染促进干扰素-γ（IFN-γ）表达，增加宿主感染细菌的敏感性。IFN-γ缺失可部分逆转IAV感染对细菌特异Th17细胞回忆反应的抑制作用，部分恢复回忆免疫反应对细菌的清除作用；3、IAV感染通过抑制CD4+T细胞增殖和迁移的方式，抑制Th17细胞回忆反应。这些发现为理解共感染的发病机理提供了另一个视角，并为共感染临床治疗中疫苗设计和提高抗细菌免疫力提供策略。

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