Innate immune effectors constitute the first line of host defense against pathogens. However, the roles of these effectors are not clearly defined during Klebsiella pneumoniae (K. pneumoniae) respiratory infection. In the current study, we established an acute pneumonia model of K. pneumoniae respiratory infection in mice and confirmed that the injury was most severe 48 h post infection. Flow cytometric assay demonstrated that alveolar macrophages were the predominant cells in BALF before infection, and neutrophils were quickly recruited after infection, and this was in consistent with the kinetics of chemokine expression. Further, we depleted neutrophils, macrophages, and complement pathways in vivo and challenged these mice with a sublethal dose of K. pneumonia, the result showed that 80%, 60%, and 40% of mice were died in these groups, respectively, while no deaths occurred in the control group. Besides, innate immune effector depleted mice showed higher bacterial burdens in lungs and blood, companied with more severe lung damage and increased levels of cytokine/chemokine expression. These results demonstrated that the innate immune effectors are critical in the early controlling of K. pneumoniae infection, and neutrophils are the most important. Thus, alternative strategies targeting these innate immune effectors may be effective in controlling of K. pneumoniae respiratory infection.

中文翻译：

---

先天性免疫效应因子在肺炎克雷伯菌引起的急性呼吸道感染中起重要作用

先天性免疫效应子构成宿主对抗病原体的第一道防线。然而，在肺炎克雷伯菌（K.pneumoniae）呼吸道感染期间，这些效应子的作用尚不清楚。在当前的研究中，我们建立了小鼠肺炎克雷伯菌呼吸道感染的急性肺炎模型，并证实该损伤在感染后48小时最为严重。流式细胞仪检测表明，肺泡巨噬细胞是感染前BALF中的主要细胞，感染后迅速募集中性粒细胞，这与趋化因子的表达动力学相符。此外，我们在体内耗尽了中性粒细胞，巨噬细胞和补体途径并用亚致死剂量的肺炎克雷伯氏菌攻击这些小鼠，结果显示这些组分别有80％，60％和40％的小鼠死亡，而对照组没有死亡。此外，先天性免疫效应耗竭的小鼠在肺和血液中显示出更高的细菌负担，同时伴有更严重的肺损伤和细胞因子/趋化因子表达水平的升高。这些结果表明，先天性免疫效应子在肺炎克雷伯菌感染的早期控制中至关重要，而中性粒细胞是最重要的。因此，针对这些先天免疫效应子的替代策略可能有效控制肺炎克雷伯菌呼吸道感染。