Initiation and regulation of antibacterial innate immunity

描述（由申请人提供）：本提案的目的是解释单一微生物产物：细菌脂多糖（LPS）如何激活多种先天免疫反应途径。虽然TLR4被广泛认为控制对LPS的转录反应，但存在TLR4独立的反应。这些反应的例子包括内吞作用、转录因子NFAT的激活以及caspase-11对非典型炎性小体的激活。这些不同LPS反应之间的关系在很大程度上是未知的，但正如我们将描述的那样，至少一些tlr4非依赖性反应控制了经典定义的tlr4依赖性LPS反应。了解微生物产物如何激活不同的信号转导途径可能允许设计药物或疫苗，可以靶向治疗途径的子集。我们的建议是基于我们最近的发现，lps通过一个不需要功能性TLR4信号（TIR）结构域或任何相关接头蛋白的过程诱导TLR4的内吞作用。相反，TLR4是由lps结合蛋白CD14激活的内吞作用途径的货物。虽然TLR4不直接指导自身的内吞作用，但这一过程对于TLR4诱导来自核内体的trf依赖性信号转导是必不可少的。这一发现为tlr4依赖性和非依赖性对LPS的反应如何相互依赖提供了一个例子。在这项拨款申请中，我们建议1)确定一个共同的信号通路是否被CD14激活以引发多种细胞类型特异性先天免疫反应，2)确定是否存在调节多种LPS诱导信号通路的共同或独特的蛋白质复合物，以及3)确定在感染动物模型中直接响应致病性细菌感染产生的LPS的细胞群。总的来说，这项工作将提供重要的见解，通过哪些手段

DESCRIPTION (provided by applicant): The goal of this proposal is to explain how diverse innate immune response pathways can be activated by a single microbial product: bacterial lipopolysaccharide (LPS). While TLR4 is widely recognized to control transcriptional responses to LPS, TLR4-independent responses exist. Examples of such responses include endocytosis, activation of the transcription factor NFAT, and activation of non-canonical inflammasomes by caspase-11. The relationship between these diverse LPS responses is largely unknown, but as we will describe, at least some TLR4-independent responses control the classically-defined TLR4-dependent responses to LPS. Understanding how microbial products activate distinct signal transduction pathways may permit the design of drugs or vaccines that can target a subset of pathways therapeutically. Our proposal is founded on our recent discovery that LPS-induces the endocytosis of TLR4 by a process that does not require a functional TLR4 signaling (TIR) domain, or any of its associated adaptor proteins. Rather TLR4 is cargo for an endocytosis pathway that is activated by the LPS-binding protein CD14. While TLR4 does not direct its own endocytosis, this process is essential for TLR4 to induce TRIF-dependent signal transduction from endosomes. This discovery provides an example of how TLR4-dependent and -independent responses to LPS can be interdependent. In this grant application, we propose to 1) determine if a common signaling pathway is activated by CD14 to elicit diverse cell type-specific innate immune responses, 2) determine if common or distinct protein complexes exist that regulate diverse LPS inducible signaling pathways, and 3) identify the cell populations that directly respond to LPS produced by pathogenic bacterial infections in animal models of infection. Collectively, this work will provide important insight into the means by which diverse cellular responses to LPS are interconnected.