a Department of Health Technology and Informatics , The Hong Kong Polytechnic University , Kowloon , Hong Kong , China.
Virulence. 2018 Jan 1;9(1):185-196. doi: 10.1080/21505594.2017.1373925. Epub 2017 Oct 4.
Legionella pneumophila, the causative agent of Legionnaires' disease, is widely distributed throughout natural and artificial water systems and can replicate in macrophages and amoebae. Amoebae are the natural hosts of L. pneumophila, whereas macrophages are incidentally infected. The life cycle of L. pneumophila comprises a replicative phase within the Legionella-containing vacuole (LCV) and a transmissive phase during which bacterial cells become motile and are released via killing of the host. Although the host death mechanisms induced by L. pneumophila have been studied, the expression patterns of related L. pneumophila genes have not been reported. The present study compared the expression patterns of host cell death-associated genes in L. pneumophila grown in the human monocytic cell line THP-1 and Acanthamoeba castellanii. Notably, when L. pneumophila was grown in THP-1, expression of the gene flaA, which is involved in the induction of pyroptosis, was downregulated during the course of infection. In contrast, sdhA associated indirectly with host death, was upregulated. Expression of the genes vipD and sidF, which are involved in the induction and suppression of apoptosis, changed by less than 2-fold. Notably, a lower percentage of pyroptotic cells was observed among infected THP-1 cells relative to uninfected cells, and the latter exhibited stronger expression of caspase-1. A different pattern was observed when L. pneumophila was grown in A. castellanii: flaA and vipD were activated, whereas sdhA and sidF were downregulated during the later stage of replication. The percentage of non-viable (annexin-V PI or annexin-VPI) A. castellanii organisms increased with Legionella infection, and the expression of metacaspase-1, which is involved in encystation was up-regulated at late infection time. In summary, L. pneumophila can multiply intracellularly in both amoebae and macrophages to induce cell death and secondary infection, and this characteristic is essential for its survival in water and the lungs. The gene expression profiles observed in this study indicated the increased cytotoxicity of L. pneumophila in A. castellanii, suggesting an increased adaptation of Legionella to this host.
嗜肺军团菌是军团病的病原体，广泛分布于自然和人工水系统中，可以在巨噬细胞和变形虫中复制。变形虫是嗜肺军团菌的天然宿主，而巨噬细胞是偶然感染的。嗜肺军团菌的生命周期包括在含有军团菌的空泡（LCV）内的复制阶段和在该阶段细菌细胞变得运动并通过杀死宿主释放的可传播阶段。虽然已经研究了嗜肺军团菌诱导的宿主死亡机制，但相关嗜肺军团菌基因的表达模式尚未报道。本研究比较了在人单核细胞系 THP-1 和棘阿米巴中生长的嗜肺军团菌中与宿主细胞死亡相关的基因的表达模式。值得注意的是，当嗜肺军团菌在 THP-1 中生长时，参与细胞焦亡诱导的 flaA 基因的表达在感染过程中下调。相比之下，与宿主死亡间接相关的 sdhA 基因上调。参与诱导和抑制细胞凋亡的基因 vipD 和 sidF 的表达变化不到 2 倍。值得注意的是，与未感染的细胞相比，感染的 THP-1 细胞中观察到的细胞焦亡细胞的百分比较低，并且后者表现出更强的 caspase-1 表达。当嗜肺军团菌在棘阿米巴中生长时观察到不同的模式：flaA 和 vipD 被激活，而 sdhA 和 sidF 在复制的后期下调。随着军团菌感染，非存活（膜联蛋白-VPI 或膜联蛋白-VPI）棘阿米巴生物体的百分比增加，并且参与包囊形成的 metacaspase-1 的表达在晚期感染时间上调。总之，嗜肺军团菌可以在变形虫和巨噬细胞中在细胞内增殖，诱导细胞死亡和继发感染，这一特征对于其在水中和肺部的生存至关重要。本研究中观察到的基因表达谱表明嗜肺军团菌在棘阿米巴中的细胞毒性增加，表明军团菌对该宿主的适应性增加。
