Centre for Molecular Microbiology and Infection, Division of Cell and Molecular Biology, Imperial College London, London, United Kingdom.
Infect Immun. 2012 Aug;80(8):2780-90. doi: 10.1128/IAI.00510-12. Epub 2012 May 29.
Legionella pneumophila is a facultative intracellular human pathogen and the etiological agent of severe pneumonia known as Legionnaires' disease. Its virulence depends on protein secretion systems, in particular, the Dot/Icm type IV secretion system (T4SS), which is essential to establish a replication-permissive vacuole in macrophages. The analysis of the role of these systems and their substrates for pathogenesis requires easy-to-use models which approximate human infection. We examined the effectiveness of the larvae of the wax moth Galleria mellonella as a new model for L. pneumophila infection. We found that the L. pneumophila strains 130b, Paris, and JR32 caused mortality of the G. mellonella larvae that was strain, infectious dose, growth phase, and T4SS dependent. Wild-type L. pneumophila persisted and replicated within the larvae, whereas T4SS mutants were rapidly cleared. L. pneumophila strain Lp02, which is attenuated in the absence of thymidine but has a functional T4SS, resisted clearance in G. mellonella up to 18 h postinfection without inducing mortality. Immunofluorescence and transmission electron microscopy revealed that L. pneumophila resided within insect hemocytes in a vacuole that ultrastructurally resembled the Legionella-containing vacuole (LCV) observed in macrophages. The vacuole was decorated with the T4SS effector and LCV marker SidC. Infection caused severe damage to the insect organs and triggered immune responses, including activation of the phenoloxidase cascade leading to melanization, nodule formation, and upregulation of antimicrobial peptides. Taken together, these results suggest that G. mellonella provides an effective model to investigate the interaction between L. pneumophila and the host.
嗜肺军团菌是一种兼性细胞内人类病原体，也是一种严重肺炎的病原体，这种肺炎通常被称为军团病。它的毒力依赖于蛋白质分泌系统，特别是 Dot/Icm 型 IV 型分泌系统（T4SS），这对于在巨噬细胞中建立一个允许复制的空泡是至关重要的。分析这些系统及其在发病机制中的底物的作用，需要易于使用的、接近人类感染的模型。我们研究了蜡螟幼虫作为一种新的嗜肺军团菌感染模型的有效性。我们发现，嗜肺军团菌菌株 130b、巴黎和 JR32 导致蜡螟幼虫死亡，这与菌株、感染剂量、生长阶段和 T4SS 有关。野生型嗜肺军团菌在幼虫体内持续存在并复制，而 T4SS 突变体则迅速被清除。在没有胸苷的情况下衰减但具有功能性 T4SS 的嗜肺军团菌菌株 Lp02 在感染后 18 小时内仍未被清除，也未引起死亡。免疫荧光和透射电子显微镜显示，嗜肺军团菌存在于昆虫血细胞内的一个空泡中，这个空泡的超微结构与巨噬细胞中观察到的军团菌包含的空泡（LCV）相似。该空泡被 T4SS 效应蛋白和 LCV 标记物 SidC 修饰。感染导致昆虫器官严重损伤，并引发免疫反应，包括酚氧化酶级联反应的激活，导致黑化、结节形成和抗菌肽的上调。综上所述，这些结果表明，蜡螟幼虫为研究嗜肺军团菌与宿主的相互作用提供了一个有效的模型。
