TLR2 and the Tubercle Granuloma

描述（由申请人提供）：在本申请中，我们将探讨toll样受体2 （TLR2）是结核性肉芽肿保护和病理特征的主要调节因子的假设。这个假设建立在我们实验室的新发现的基础上。此前我们曾报道，TLR9和TLR2分别在结核分枝杆菌感染的树突状细胞（dc）中诱导促炎性和抗炎性细胞因子，而TLR2在感染的巨噬细胞中诱导促炎性和抗炎性细胞因子。基于这些观察，一个合理的预测是，在结核分枝杆菌感染期间，TLR2触发的先天抗炎反应可能控制Th1效应和记忆T细胞激活的大小。与预期相反，我们发现TLR2的缺失并不影响结核分枝杆菌气溶胶感染后产生的Th1效应反应的强度，也不影响结核分枝杆菌攻击后Th1记忆免疫的诱导。然而，TLR2缺失对宿主抗性的影响在肉芽肿水平上表现出来。受感染的TLR2KO小鼠肺部炎症增强，FoxP3+ T调节细胞（Tregs）浸润减少，而受感染的WT动物肺部炎症消退，出现小而致密的肉芽肿。Tregs已被证明可以阻止宿主对持久性病原体的抗菌反应。令人惊讶的是，尽管缺乏Tregs，与感染的WT小鼠相比，慢性感染的TLR2KO小鼠的肺部表现出更高的细菌负担和肉芽肿完整性的丧失，这表明TLR2在控制肉芽肿体内抗菌反应中的作用迄今尚未得到充分的认识。初步的基因表达研究指出了tlr2诱导的基质金属蛋白酶在调节肉芽肿成熟中的作用。本提案将检验以下具体假设：1)tlr2诱导的MMPs调节肉芽肿成熟；ii)TLR2对巨噬细胞控制结核分枝杆菌的复制和肉芽肿内的遏制至关重要；iii) TLR2诱导Tregs， Tregs主要作为肺免疫病理的抑制剂而不是巨噬细胞抗菌反应的抑制剂；iv) tlr2触发两种不同的信号通路，诱导Mtb感染的巨噬细胞产生促炎性和抗炎性细胞因子，v)信号通路相互交叉调节，Mtb可以操纵这些通路为自己的利益服务。拟议研究的集体发现将提供对结核性肉芽肿中tlr2触发的信号通路的见解，以及可以在治疗中操纵它们的独特方法。

DESCRIPTION (provided by applicant): In this application we will explore the hypothesis that Toll-like receptor 2 (TLR2) is the master regulator controlling both protective and pathologic features of the tubercle granuloma. The hypothesis builds on novel findings made in our laboratory. Previously we had reported that TLR9 and TLR2 induce pro- and anti-inflammatory cytokines, respectively, in M. tuberculosis (Mtb)-infected dendritic cells (DCs), while TLR2 induces both pro- and anti-inflammatory cytokines in infected macrophages. A reasonable prediction, based on these observations, is that during Mtb infection the innate anti-inflammatory response triggered by TLR2 may control the magnitude of Th1 effector and memory T cell activation. Contrary to expectation, we found that the absence of TLR2 did not affect the magnitude of the Th1 effector response generated following aerosol infection with Mtb or the induction of recall Th1 memory immunity in response to Mtb challenge. However, the consequence of TLR2 absence to host resistance was manifested at the level of the granuloma. The infected lungs of TLR2KO mice exhibited enhanced inflammation associated with reduced infiltration of FoxP3+ T regulatory cells (Tregs) into the lung, while lungs from infected WT animals had resolved their inflammation and had small, compact granulomas. Tregs have been shown to thwart host antimicrobial responses against persistent pathogens. Surprisingly, despite the absence of Tregs, lungs from chronically-infected TLR2KO mice exhibited enhanced bacterial burden and loss of granuloma integrity in comparison with infected WT mice indicating a hitherto under-appreciated role for TLR2 in controlling antimicrobial responses in vivo in the granuloma. Preliminary gene expression studies point to the role of TLR2-induced matrix metaloproteinases in regulating granuloma maturation. The following specific hypotheses will be tested in the proposal: I) TLR2-induced MMPs regulate granuloma maturation; ii)TLR2 is essential for macrophage control of Mtb replication and containment within the granuloma; iii) TLR2 induces Tregs which operate primarily as inhibitors of lung immune pathology but not as inhibitors of macrophage antimicrobial responses; iv) TLR2-triggers two distinct signaling pathways for the induction of pro- and anti-inflammatory cytokine production within Mtb- infected macrophages, and v) the signaling pathways cross-regulate each other and Mtb can maneuver the pathways to its own benefit. The collective findings from the proposed studies will provide insights into TLR2-triggered signaling pathways in the tubercle granuloma and unique ways in which they can be manipulated therapeutically. PUBLIC HEALTH RELEVANCE: In this proposal we will study the role of TLR2 in regulating the granuloma, which is a hallmark protective immune response of the host following infection with Mtb.