Ochoa-Repáraz Javier, Sentissi Jami, Trunkle Theresa, Riccardi Carol, Pascual David W
Veterinary Molecular Biology, Montana State University, P.O. Box 173610, Bozeman, MT 59717-3610, USA.
Infect Immun. 2007 Dec;75(12):5845-58. doi: 10.1128/IAI.00901-07. Epub 2007 Sep 24.
Coxiella burnetii is a highly infectious obligate intracellular bacterium. The phase I form is responsible for Q fever, a febrile illness with flu-like symptoms that often goes undiagnosed. The attenuated C. burnetii phase II (having a truncated "O" chain of its lipopolysaccharide) does not cause disease in immunocompetent animals; however, phase II organisms remain infectious, and we questioned whether disease could be produced in immunodeficient mice. To study C. burnetii phase II infections, febrile responses in gamma interferon knockout (IFN-gamma(-/-)), BALB/c, Toll-like receptor 2 knockout (TLR2(-/-)), and C57BL/6 mice were measured using the Nine Mile phase II (NMII) strain of C. burnetii. Immunocompetent mice showed minimal febrile responses, unlike those obtained with IFN-gamma(-/-) and TLR2(-/-) mice, which showed elevated rectal temperatures that were sustained for approximately 15 days with transient increases in splenic weights. Reinfection of IFN-gamma(-/-) and TLR2(-/-) mice with C. burnetii NMII 30 days after primary infection protected mice as evident by reduced febrile responses and a lack of splenic inflammation. Although minimal detection of Coxiella in TLR2(-/-) mouse spleens was observed, greater colonization was evident in the IFN-gamma(-/-) mice. Cytokine analysis was performed on infected peritoneal macrophages isolated from these mice, and immunocompetent macrophages showed robust tumor necrosis factor alpha, IFN-gamma, and granulocyte-macrophage colony-stimulating factor (GM-CSF) but no interleukin-12 (IL-12) responses. IFN-gamma(-/-) macrophages produced elevated levels of IL-6, IL-10, and IL-12, while TLR2(-/-) macrophages produced GM-CSF, IL-12, and minimal IL-10. To distinguish immunity conferred by innate or adaptive systems, adoptive transfer studies were performed and showed that immune lymphocytes obtained from immunocompetent mice protected against a subsequent challenge with NMII, indicating that adaptive immunity mediates the observed protection. Thus, our data show that NMII is capable of eliciting disease in immunocompromised mice, which may help in evaluation of vaccine candidates as well as the study of host-pathogen interactions.
伯纳特柯克斯体是一种极具传染性的专性胞内细菌。I 期形式可引发 Q 热，这是一种伴有流感样症状的发热性疾病，常常未被诊断出来。减毒的 II 期伯纳特柯克斯体（其脂多糖的“O”链截短）在免疫功能正常的动物中不会引发疾病；然而，II 期生物体仍具有传染性，我们质疑其是否能在免疫缺陷小鼠中引发疾病。为了研究 II 期伯纳特柯克斯体感染，使用伯纳特柯克斯体的九里 II 期（NMII）菌株测量了γ干扰素基因敲除（IFN-γ(-/-)）、BALB/c、Toll 样受体 2 基因敲除（TLR2(-/-)）和 C57BL/6 小鼠的发热反应。免疫功能正常的小鼠表现出最小的发热反应，这与 IFN-γ(-/-)和 TLR2(-/-)小鼠不同，后两者表现出直肠温度升高，持续约 15 天，同时脾脏重量有短暂增加。在初次感染 30 天后用 NMII 再次感染 IFN-γ(-/-)和 TLR2(-/-)小鼠，可使小鼠得到保护，这表现为发热反应降低且无脾脏炎症。虽然在 TLR2(-/-)小鼠脾脏中观察到对柯克斯体的检测极少，但在 IFN-γ(-/-)小鼠中明显有更多的定植。对从这些小鼠分离出的感染腹膜巨噬细胞进行细胞因子分析，免疫功能正常的巨噬细胞表现出强烈的肿瘤坏死因子α、IFN-γ和粒细胞-巨噬细胞集落刺激因子（GM-CSF）反应，但没有白细胞介素-12（IL-12）反应。IFN-γ(-/-)巨噬细胞产生升高水平的 IL-6、IL-10 和 IL-12，而 TLR2(-/-)巨噬细胞产生 GM-CSF、IL-12 和少量的 IL-10。为了区分先天或适应性系统赋予的免疫力，进行了过继转移研究，结果表明从免疫功能正常的小鼠获得的免疫淋巴细胞可保护小鼠免受随后 NMII 的攻击，这表明适应性免疫介导了观察到的保护作用。因此，我们的数据表明 NMII 能够在免疫受损小鼠中引发疾病，这可能有助于评估候选疫苗以及研究宿主-病原体相互作用。
