Mechanisms of Prostaglandin E2 induction by Francisella tularensis

描述(申请人提供)：病原菌和它们的宿主已经进行了数百万年的双向对话。宿主已经发展出复杂的机制来保护自己免受病原体的侵袭，反过来，病原菌也发展了改变和逃避宿主免疫反应的机制。图拉氏方济氏菌是一种兼性胞内生物体，是图拉热症的病原体。由于这种生物的低感染剂量、高发病率和高死亡率，以及它被美国和苏联武器化的事实，它被指定为A类生物恐怖分子。因此，迫切需要了解该生物体的生物学以及图拉氏丝虫改变其宿主免疫系统的潜在分子和细胞机制。最近的研究清楚地表明，图拉氏F菌能够调节宿主的免疫反应，并创造有利于其在宿主体内生存的环境。然而，我们对图拉氏丝虫改变宿主免疫系统的机制知之甚少。图拉氏丝虫通过抑制细胞因子和T细胞反应而明显改变免疫反应。图拉氏丝虫感染导致受感染的抗原提呈细胞(APC)产生前列腺素E2(PGE2)。APC产生的PGE2抑制T细胞的增殖和激活。此外，呼吸性图拉热症期间PGE2的长期诱导抑制了强大的适应性T细胞反应的产生，因此显著延迟了机体的清除。在初步的发现中，我们筛选了一个方济氏菌转座子突变体库，并鉴定了20个与PGE2诱导相关的候选基因。这项提议的第一个目标是确定负责诱导PGE2的效应分子。这将通过利用非极性无标记的候选基因的干净删除以及候选基因的真核表达来实现。第二个目标将是确定负责鉴定图拉氏丝虫产物的真核传感器。这将通过使用酵母双杂交筛选来实现。这种分子相互作用的鉴定和表征可以被用来作为抗菌化疗的靶点。

DESCRIPTION (provided by applicant): Pathogenic bacteria and their hosts have had a two way conversation for millions of years. The host has developed sophisticated mechanisms to protect itself against pathogens and in turn pathogenic bacteria have developed mechanisms to alter and evade the host immune response. Francisella tularensis is a facultative intracellular organism and the causative agent of tularemia. Due to the organism's low infective dose, high morbidity and mortality, and the fact that it was weaponized by both the U.S.A. and the USSR it has been designated a category A bioterrorism agent. Consequently, there is an urgent need to understand the biology of the organism and the underlying molecular and cellular mechanisms by which F. tularensis alters the immune system of its hosts. Recent studies clearly demonstrate that F. tularensis is able to modulate the host immune response and create an environment in favor of its survival in the host. However, we have only sketchy knowledge about the mechanisms by which F. tularensis alters the host immune system. F. tularensis clearly alters the immune response by inhibiting cytokine and T cell responses. F. tularensis infection results in prostaglandin E2 (PGE2) production by infected antigen presenting cells (APC). PGE2 produced by APC inhibits the proliferation and activation of T cells. Furthermore, the prolonged induction of PGE2 during respiratory tularemia dampens the generation of a robust adaptive T cell response and as a result, significantly delays the clearance of the organism. In preliminary findings a Francisella transposon mutant library was screened and 20 candidate genes associated with induction of PGE2 were identified. The first goal of this proposal will identify the effector molecule responsible for the induction of PGE2. This will be done by utilizing nonpolar markerless clean deletions of candidate genes, as well as eukaryotic expression of candidate genes. The second goal will be to determine the eukaryotic sensor responsible for identifying the F. tularensis product. This will be accomplished with the use of a yeast two hybrid screen. The identification and characterization of this molecular interaction could be conceivably exploited for antimicrobial chemotherapy targets.