Department of Microbiology and Immunology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.
PLoS One. 2009 Nov 20;4(11):e7920. doi: 10.1371/journal.pone.0007920.
Francisella tularensis is the causative agent of tularemia and is classified as a Category A select agent. Recent studies have implicated TLR2 as a critical element in the host protective response to F. tularensis infection, but questions remain about whether TLR2 signaling dominates the response in all circumstances and with all species of Francisella and whether F. tularensis PAMPs are predominantly recognized by TLR2/TLR1 or TLR2/TLR6. To address these questions, we have explored the role of Toll-like receptors (TLRs) in the host response to infections with F. tularensis Live Vaccine Strain (LVS) and F. tularensis subspecies (subsp.) novicida in vivo.
METHODOLOGY/PRINCIPAL FINDINGS: C57BL/6 (B6) control mice and TLR- or MyD88-deficient mice were infected intranasally (i.n.) or intradermally (i.d.) with F. tularensis LVS or with F. tularensis subsp. novicida. B6 mice survived >21 days following infection with LVS by both routes and survival of TLR1(-/-), TLR4(-/-), and TLR6(-/-) mice infected i.n. with LVS was equivalent to controls. Survival of TLR2(-/-) and MyD88(-/-) mice, however, was significantly reduced compared to B6 mice, regardless of the route of infection or the subspecies of F. tularensis. TLR2(-/-) and MyD88(-/-) mice also showed increased bacterial burdens in lungs, liver, and spleen compared to controls following i.n. infection. Primary macrophages from MyD88(-/-) and TLR2(-/-) mice were significantly impaired in the ability to secrete TNF and other pro-inflammatory cytokines upon ex vivo infection with LVS. TNF expression was also impaired in vivo as demonstrated by analysis of bronchoalveolar lavage fluid and by in situ immunofluorescent staining.
CONCLUSIONS/SIGNIFICANCE: We conclude from these studies that TLR2 and MyD88, but not TLR4, play critical roles in the innate immune response to F. tularensis infection regardless of the route of infection or the subspecies. Moreover, signaling through TLR2 does not depend exclusively on TLR1 or TLR6 during F. tularensis LVS infection.
弗朗西斯菌是土拉热弗朗西斯菌的病原体，被归类为 A 类选择剂。最近的研究表明 TLR2 是宿主对弗朗西斯菌感染的保护性反应的关键因素，但仍存在一些问题，即 TLR2 信号是否在所有情况下以及所有弗朗西斯菌物种中都占主导地位，以及弗朗西斯菌的 PAMP 是否主要由 TLR2/TLR1 或 TLR2/TLR6 识别。为了解决这些问题，我们探讨了 Toll 样受体 (TLR) 在宿主对弗朗西斯菌活疫苗株 (LVS) 和弗朗西斯菌亚种 (subsp.) novicida 感染的反应中的作用。
方法/主要发现：C57BL/6 (B6) 对照小鼠和 TLR 或 MyD88 缺陷型小鼠经鼻腔 (i.n.) 或皮内 (i.d.) 感染弗朗西斯菌 LVS 或弗朗西斯菌亚种 novicida。B6 小鼠通过两种途径感染 LVS 后可存活>21 天，而 TLR1(-/-)、TLR4(-/-) 和 TLR6(-/-) 小鼠经 i.n. 感染 LVS 的存活率与对照小鼠相当。然而，TLR2(-/-)和 MyD88(-/-) 小鼠的存活率与 B6 小鼠相比显著降低，无论感染途径或弗朗西斯菌亚种如何。TLR2(-/-)和 MyD88(-/-) 小鼠经 i.n. 感染后，肺部、肝脏和脾脏中的细菌负荷也明显高于对照小鼠。MyD88(-/-)和 TLR2(-/-) 小鼠的原代巨噬细胞在体外感染 LVS 后分泌 TNF 和其他促炎细胞因子的能力显著受损。通过分析支气管肺泡灌洗液和原位免疫荧光染色，也证明了 TNF 表达在体内受损。
我们从这些研究中得出结论，TLR2 和 MyD88，但不是 TLR4，在弗朗西斯菌感染的固有免疫反应中发挥关键作用，无论感染途径或亚种如何。此外，在弗朗西斯菌 LVS 感染过程中，TLR2 信号不依赖于 TLR1 或 TLR6。
