The Role of LPS and Toll-like Receptors in Plague

革兰氏阴性菌鼠疫耶尔森氏菌是鼠疫的病原体。鼠疫杆菌和其他一些病原体能够修改其脂多糖(LPS) /脂质A中的酰基链，以最小化toll样受体4 （TLR4）信号。因此，鼠疫菌在37C时产生tlr4激活能力差的四酰基LPS，而在26C时合成有效的六酰基脂质。我们已经证明，通过产生一种修饰的菌株，在37℃下合成六酰化的tlr4激活LPS，从而在37℃下通过外周途径逃避先天免疫反应是鼠疫杆菌毒力所必需的。改良菌株含有LpxL，这是一种来自大肠杆菌的脂质a生物合成酶，在鼠疫杆菌中不存在，它的毒力降低了100多万倍。我们的主要假设是，逃避LPS-TLR4信号对于鼠疫菌的毒力至关重要，而脂质a结构的严格调控是这种逃避发生的必要条件。我们建议利用产生修饰LPS的鼠疫杆菌菌株来研究鼠疫杆菌逃避和激活先天免疫。我们的模型系统似乎非常适合描述针对鼠疫杆菌的有效先天免疫机制，我们的长期目标是定义这种机制和细菌对策。1)鼠疫菌表达LpxP，这是一种脂质a生物合成基因，可能是在较低温度下产生六酰基tlr4激活LPS所必需的。我们建议研究在37℃时对LpxP表达的调控，因为调控似乎是毒力的必要条件。2)我们还希望研究LPS-TLR4信号在鼠疫杆菌从其最近的祖先假结核杆菌（Y. ptb）进化为高毒力病原体的过程中所起的作用，假结核杆菌仅可能引起轻度胃肠炎。有趣的是，结核分枝杆菌含有一个LpxL基因。我们建议研究Y. ptb LpxL的功能，包括Y. ptb LpxL在鼠疫菌中的表达，以及研究LPS的活性和结构。3)初步结果表明，白细胞介素-1 （IL-1）的释放和信号传导在清除鼠疫杆菌- lpxl感染中的作用比TNF和I型IFN更有效。我们将在体外和体内分析鼠疫杆菌被IL-1诱导和控制的机制。

The gram-negative bacterium Yersinia pestis is the causative agent of plague. Y. pestis and some other pathogens have the ability to modify the acyl chains in their lipopolysaccharide (LPS) /lipid A in order to minimize Toll-like receptor 4 (TLR4) signaling. Consequently, Y. pestis produces a tetra-acyl LPS with poor TLR4-activating ability at 37C, while synthesizing a potent hexa-acyl lipid at 26C. We have shown that the resulting evasion of innate immune responses at 37C is necessary for Y. pestis virulence via the peripheral route, by generating a modified bacterial strain synthesizing a hexa-acylated TLR4-activating LPS also at 37C. The modified strain contained LpxL, a lipid A biosynthesis enzyme from E. coli, that is absent in Y. pestis, and has more than a million-fold reduced virulence. Our main hypothesis is that evasion of LPS-TLR4 signaling is essential for the virulence of Y. pestis, and that a tight regulation of lipid A structure is necessary for this evasion to occur. We propose to use Y. pestis strains that generate modified LPS to study evasion and activation of innate immunity by the plague bacillus. Our model system appears well suited to describe efficient innate immune mechanisms against Y. pestis, and our long-term goal is to define such mechanisms and bacterial countermeasures. 1) Y. pestis expresses LpxP, a lipid A biosynthesis gene that likely is necessary for the production of a hexa-acyl TLR4-activating LPS at lower temperatures. We propose to study regulation of LpxP expression at 37C, as regulation appears necessary for virulence. 2) We also wish to study the role of evasion of LPS-TLR4 signaling in the evolution of Y. pestis to a highly virulent pathogen from its closest ancestor, Y. pseudotuberculosis (Y. ptb), which only may cause a mild gastroenteritis. Interestingly, Y. ptb harbors an LpxL gene. Our proposal suggests studies of Y. ptb LpxL function, this will include expression of Y. ptb LpxL in Y. pestis, and study LPS activity and structures. 3) Preliminary results indicate that interleukin-1 (IL-1) release and signaling is effective in clearing infection with Y. pestis-LpxL, more so than TNF and type I IFN. We will analyze mechanisms by which Y. pestis induces and is controlled by IL-1, in vitro and in vivo.