Exploring the role of type I interferon in Rickettsia pathogenesis

项目摘要/摘要 立克次体是一组不同的革兰氏阴性、专性细胞内病原体，可引起 人类疾病，包括斑疹伤寒和斑疹伤寒。斑点热群的致病因素中 (SFG)立克次体病在美国，帕氏立克次体已被证明是一种独特的、强大的研究模型 在细胞水平上的致病性，因为它会引起一种非致命性的焦痂相关疾病，因此可以 在生物安全2级条件下生长，便于细胞生物学研究。然而，取得的进展是 发展帕氏杆菌作为研究SFG立克次体感染先天免疫反应的模型 由于缺乏使用突变小鼠的研究，这一研究受到阻碍。因此，关于先天的关键问题 对SFG立克次体的免疫反应仍然没有答案，包括细菌对I型的反应 干扰素(IFN-I)，天然免疫系统的重要细胞因子。我们新的初步数据表明 帕氏杆菌对同时缺乏干扰素-I和干扰素受体的小鼠的皮内感染 在感染和偶尔死亡的地方导致坏死性损害，而小鼠缺乏每一个个体 受体没有表现出症状。这表明了干扰素-I(和干扰素-g)在限制帕氏杆菌生长中的作用。 活着。此外，双重突变体的病理类似于(但比)在 人类感染，这表明它可能代表了一种新的人类疾病动物模型。我们还观察到 干扰素-I严重限制帕氏杆菌在原代小鼠巨噬细胞中的生长，这部分是由于 由干扰素-I调节的基因产物，包括抗菌鸟苷结合蛋白(GBP)。尽管 尽管取得了这些进展，但在认识上仍然存在两个关键差距：(1)尚不清楚干扰素-I是如何限制帕氏杆菌的生长的 在体内的器官/组织/细胞水平；(2)干扰素-I上调的基因产物如何杀死R. 在细胞/分子水平上的帕克里。我们推测，干扰素-I在限制 体内和体外通过上调胞浆抗菌分子生长的立克次体。我们将对此进行测试 假设有两个目的。在目标1中，我们将描述静脉和皮内感染的动力学， 在缺乏这两种受体的小鼠中引起的器官和组织病理以及帕氏杆菌感染的细胞类型 用于干扰素-I/干扰素-g。这些研究将揭示干扰素-I如何在体内限制帕氏杆菌的生长，并将建立一种 用于研究SFG立克次体发病机制的可靠小鼠模型。在目标2中，我们将测试 激活或突变候选抗菌因子(经RNAseq鉴定)对下游细菌的杀灭作用 干扰素-I信号，并将测试Gbps是否在体外和小鼠内皮细胞中抑制帕氏杆菌的生长 活着。我们的发现将揭示干扰素-I如何在体外限制帕氏杆菌和其他微生物的生长。 在活体内。此外，我们还将建立一种新的动物模型来研究帕氏杆菌的致病机制。

PROJECT SUMMARY / ABSTRACT The Rickettsiae are a diverse group of Gram-negative, obligate intracellular bacterial pathogens that cause human diseases, including typhus and spotted fever. Among the causative agents of spotted fever group (SFG) rickettsiosis in the U.S., Rickettsia parkeri has proven to be a uniquely powerful model for studying pathogenicity at the cellular level, because it causes a non-lethal eschar-associated disease and therefore can be grown under biosafety level 2 conditions, facilitating cell biological studies. However, progress toward developing R. parkeri as a model for studying the innate immune response to SFG Rickettsia infection has been hindered by a dearth of studies employing mutant mice. As such, key questions regarding the innate immune response to SFG Rickettsia remain unanswered, including how the bacteria respond to type I interferon (IFN-I), an important cytokine of the innate immune system. Our new preliminary data indicate that intradermal infection of mice lacking both receptors for IFN-I and type II interferon (IFN-g) with R. parkeri results in a necrotic lesion at the site of infection and occasional lethality, whereas mice lacking each individual receptor exhibit no symptoms. This demonstrates a role for IFN-I (and IFN-g) in restricting R. parkeri growth in vivo. Moreover, the pathology of the double mutant is similar to (but more severe than) that occurring during human infection, suggesting it may represent a new animal model of human disease. We have also observed that IFN-I severely restricts R. parkeri growth in primary mouse macrophages, and that this is partially due to killing by the IFN-I regulated gene products, including antimicrobial guanylate binding proteins (GBPs). Despite these advances, there remain two key gaps in knowledge: (1) it is unclear how IFN-I restricts R. parkeri growth at the organ/tissue/cellular level in vivo; and (2) it is not known how gene products upregulated by IFN-I kill R. parkeri at the cellular/molecular level. We hypothesize that that IFN-I plays an important role in restricting Rickettsia growth in vivo and in vitro via the upregulation of cytosolic antibacterial molecules. We will test this hypothesis in two aims. In Aim 1, we will characterize the kinetics of intravenous and intradermal infection, the resulting organ and tissue pathologies, and the cell types infected by R. parkeri in mice lacking both receptors for IFN-I/IFN-g. These studies will reveal how IFN-I restricts growth of R. parkeri in vivo and will establish a robust murine model for investigating SFG Rickettsia pathogenesis. In Aim 2, we will test the effect of activating or mutating candidate antimicrobial factors (identified by RNAseq) on bacterial killing downstream of IFN-I signaling, and will test whether the GBPs restrict R. parkeri growth in endothelial cells in vitro and mice in vivo. Our findings will reveal how IFN-I restricts the growth of R. parkeri, and perhaps other microbes, in vitro and in vivo. Furthermore, we will develop a new animal model to investigate R. parkeri pathogenesis.