Santic Marina, Asare Rexford, Doric Miljenko, Abu Kwaik Yousef
Department of Microbiology and Immunology, University of Louisville College of Medicine, 319 Abraham Flexner Way 55A, Louisville, KY 40202, USA.
Infect Immun. 2007 Jun;75(6):2903-13. doi: 10.1128/IAI.00147-07. Epub 2007 Apr 9.
The Dot/Icm system of Legionella pneumophila triggers activation of caspase-3 during early stages of infection of human macrophages, but apoptosis is delayed until late stages of infection. During early stages of infection of mouse macrophages, the organism triggers rapid caspase-1-mediated cytotoxicity, which is mediated by bacterial flagellin. However, it is not known whether caspase-1 is triggered by L. pneumophila in human macrophages or whether caspase-3 is activated in permissive or nonpermissive mouse macrophages. Using single-cell analyses, we show that the wild-type strain of L. pneumophila does not trigger caspase-1 activation throughout the intracellular infection of human monocyte-derived macrophages (hMDMs), even when the flagellated bacteria escape into the cytoplasm during late stages. Using single-cell analyses, we show that the Dot/Icm system of L. pneumophila triggers caspase-3 but not caspase-1 within permissive A/J mouse bone marrow-derived primary macrophages by 2 to 8 h, but apoptosis is delayed until late stages of infection. While L. pneumophila triggers a Dot/Icm-dependent activation of caspase-1 in nonpermissive BALB/c mouse-derived macrophages, caspase-3 is not activated at any stage of infection. We show that robust intrapulmonary replication of the wild-type strain of L. pneumophila in susceptible A/J mice is associated with late-stage Dot/Icm-dependent pulmonary apoptosis and alveolar inflammation. In the lungs of nonpermissive BALB/c mice, L. pneumophila does not replicate and does not trigger pulmonary apoptosis or alveolar inflammation. Thus, similar to hMDMs, L. pneumophila does not trigger caspase-1 but triggers caspase-3 activation during early and exponential replication in permissive A/J mouse-derived macrophages, and apoptosis is delayed until late stages of infection. The Dot/Icm type IV secretion system is essential for pulmonary apoptosis in the genetically susceptible A/J mice.
嗜肺军团菌的Dot/Icm系统在感染人类巨噬细胞的早期阶段会触发半胱天冬酶-3的激活，但细胞凋亡会延迟到感染后期。在感染小鼠巨噬细胞的早期阶段，该病原体触发由细菌鞭毛蛋白介导的半胱天冬酶-1介导的快速细胞毒性。然而，尚不清楚嗜肺军团菌是否在人类巨噬细胞中触发半胱天冬酶-1的激活，也不清楚半胱天冬酶-3是否在允许或不允许的小鼠巨噬细胞中被激活。通过单细胞分析，我们发现嗜肺军团菌的野生型菌株在人类单核细胞衍生巨噬细胞（hMDM）的整个细胞内感染过程中不会触发半胱天冬酶-1的激活，即使在后期有鞭毛的细菌逃逸到细胞质中也是如此。通过单细胞分析，我们发现嗜肺军团菌的Dot/Icm系统在允许的A/J小鼠骨髓来源的原代巨噬细胞中在2至8小时内触发半胱天冬酶-3而非半胱天冬酶-1的激活，但细胞凋亡会延迟到感染后期。虽然嗜肺军团菌在不允许的BALB/c小鼠来源的巨噬细胞中触发Dot/Icm依赖性的半胱天冬酶-1激活，但在感染的任何阶段半胱天冬酶-3都不会被激活。我们发现嗜肺军团菌野生型菌株在易感的A/J小鼠肺部的强劲复制与后期Dot/Icm依赖性的肺部细胞凋亡和肺泡炎症有关。在不允许的BALB/c小鼠的肺部，嗜肺军团菌不复制，也不会触发肺部细胞凋亡或肺泡炎症。因此，与hMDM类似，嗜肺军团菌在允许的A/J小鼠来源的巨噬细胞的早期和指数增殖阶段不会触发半胱天冬酶-1，但会触发半胱天冬酶-3的激活，并且细胞凋亡会延迟到感染后期。Dot/Icm IV型分泌系统对于基因易感的A/J小鼠的肺部细胞凋亡至关重要。
