Department of Microbiology and Immunology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117545, Singapore.
Department of Otolaryngology, National University of Singapore, Singapore 119228, Singapore.
Cells. 2019 Aug 26;8(9):975. doi: 10.3390/cells8090975.
During influenza pneumonia, the alveolar epithelial cells of the lungs are targeted by the influenza virus. The distal airway stem cells (DASCs) and proliferating alveolar type II (AT2) cells are reported to be putative lung repair cells. However, their relative spatial and temporal distribution is still unknown during influenza-induced acute lung injury. Here, we investigated the distribution of these cells, and concurrently performed global proteomic analysis of the infected lungs to elucidate and link the cellular and molecular events during influenza pneumonia recovery. BALB/c mice were infected with a sub-lethal dose of influenza H1N1 virus. From 5 to 25 days post-infection (dpi), mouse lungs were subjected to histopathologic and immunofluorescence analysis to probe for global distribution of lung repair cells (using P63 and KRT5 markers for DASCs; SPC and PCNA markers for AT2 cells). At 7 and 15 dpi, infected mouse lungs were also subjected to protein mass spectrometry for relative protein quantification. DASCs appeared only in the damaged area of the lung from 7 dpi onwards, reaching a peak at 21 dpi, and persisted until 25 dpi. However, no differentiation of DASCs to AT2 cells was observed by 25 dpi. In contrast, AT2 cells began proliferating from 7 dpi to replenish their population, especially within the boundary area between damaged and undamaged areas of the infected lungs. Mass spectrometry and gene ontology analysis revealed prominent innate immune responses at 7 dpi, which shifted towards adaptive immune responses by 15 dpi. Hence, proliferating AT2 cells but not DASCs contribute to AT2 cell regeneration following transition from innate to adaptive immune responses during the early phase of recovery from influenza pneumonia up to 25 dpi.
在流感肺炎中，肺部的肺泡上皮细胞是流感病毒的靶标。据报道，远端气道干细胞（DASCs）和增殖的肺泡 II 型（AT2）细胞是潜在的肺修复细胞。然而，它们在流感引起的急性肺损伤期间的相对时空分布仍不清楚。在这里，我们研究了这些细胞的分布，并同时对感染的肺部进行了全局蛋白质组学分析，以阐明和联系流感肺炎恢复过程中的细胞和分子事件。BALB/c 小鼠用亚致死剂量的流感 H1N1 病毒感染。从感染后 5 天到 25 天（dpi），对小鼠肺进行组织病理学和免疫荧光分析，以探测肺修复细胞的全球分布（使用 P63 和 KRT5 标志物检测 DASCs；使用 SPC 和 PCNA 标志物检测 AT2 细胞）。在 7 和 15 dpi，还对感染的小鼠肺进行蛋白质质谱分析，以进行相对蛋白质定量。从 7 dpi 开始，DASCs 仅出现在肺部受损区域，在 21 dpi 时达到峰值，并持续到 25 dpi。然而，到 25 dpi 时，没有观察到 DASCs 分化为 AT2 细胞。相比之下，AT2 细胞从 7 dpi 开始增殖以补充其数量，尤其是在感染肺的受损和未受损区域之间的边界区域。质谱和基因本体分析显示，在 7 dpi 时存在明显的先天免疫反应，到 15 dpi 时则转向适应性免疫反应。因此，增殖的 AT2 细胞而不是 DASCs 有助于在流感肺炎恢复的早期阶段从先天免疫反应向适应性免疫反应过渡后 AT2 细胞的再生，直至 25 dpi。
