Host-Pathogen interactions between Salmonella and Toll-like receptors

描述（由申请人提供）：细菌病原体和宿主先天免疫之间的相互作用通常决定感染的结果。toll样受体（TLRs）诱导抗菌机制，但许多细菌已经进化出毒力策略，使它们能够逃避这种宿主反应的各个方面。TLR对鼠伤寒沙门菌免疫的重要性已通过缺乏TLR或TLR信号成分的细胞或小鼠得到证实。然而，这些研究的一个警告是，由于Nramp-1基因的无功能等位基因，它们通常是在高度易感的近交系小鼠株上进行的。我们假设Nramp-1突变小鼠的极端易感性可能掩盖了沙门氏菌与宿主先天免疫系统之间的宿主-病原体相互作用。因此，我们产生并分析了具有功能性Nramp-1的tlr缺陷小鼠。这些分析得出了一个令人惊讶的发现：TLR的功能是沙门氏菌在巨噬细胞中的存活和复制以及小鼠的毒力所必需的。在缺乏TLR功能的巨噬细胞中，沙门氏菌无法诱导细胞内生存和复制所需的毒力基因。这一要求是基于含吞噬体的沙门氏菌的tlr依赖性酸化。在这个应用中，我们建立在这些发现的基础上，并探讨了TLR激活对沙门氏菌发病机制和宿主反应的影响。在Aim 1中，我们将研究tlr依赖性酸化和Nramp-1功能是否协同调节沙门氏菌毒力基因的诱导。在目标2中，我们将研究哪些细胞类型的TLR信号是沙门氏菌毒力基因诱导所必需的。在目标3中，我们将在tlr缺陷小鼠中验证沙门氏菌毒力不需要细胞内复制的假设。在aims 4中，我们将切换到宿主-病原体相互作用的宿主侧，并研究为什么TLR4在宿主对沙门氏菌感染的反应中发挥如此重要的作用。

DESCRIPTION (provided by applicant): Interactions between bacterial pathogens and host innate immunity often determine the outcome of an infection. Toll-like receptors (TLRs) induce antimicrobial mechanisms, but many bacteria have evolved virulence strategies that allow them to evade aspects of this host response. The importance of TLRs for immunity to Salmonella typhimurium has been demonstrated using cells or mice deficient in TLRs or TLR signaling components. A caveat of these studies, however, is that they are typically performed with highly susceptible inbred mouse strains due to a non-functional allele of the Nramp-1 gene. We hypothesize that the extreme susceptibility of Nramp-1 mutant mice may mask host-pathogen interactions between Salmonella and the host innate immune system. Accordingly, we have generated and analyzed TLR-deficient mice with functional Nramp-1. These analyses have resulted in a surprising finding: TLR function is required for Salmonella survival and replication in macrophages and for virulence in mice. In macrophages lacking TLR function, Salmonella fails to induce virulence genes required for intracellular survival and replication. This requirement is based on TLR-dependent acidification of Salmonella containing phagosomes. In this application, we build on these findings and explore the consequences of TLR activation for Salmonella pathogenesis and for the host response. In Aim 1, we will examine whether TLR-dependent acidification and Nramp-1 function cooperate to regulate induction of Salmonella virulence genes. In Aim 2, we will examine in which cell types TLR signaling is required for Salmonella virulence gene induction in vivo. In Aim 3, we will test the hypothesis that Salmonella virulence does not require intracellular replication in TLR-deficient mice. In Aim 4, we will switch to the host side of the host-pathogen interaction and examine why TLR4 plays such a dominant role in the host response to Salmonella infection.