Recognition of Group B Streptococci by Innate Immune Sensors

项目摘要 B组链球菌(GBS)是一种在肠道和阴道中发现的正常共生菌，约30% 健康的人类。在全球范围内，GBS是前3年肺炎、败血症和脑膜炎的主要原因 在生命的几个月内是最重要的侵袭性病原体，在其他健康的新生儿中。而当 由于产期抗生素的使用，GBS引起的疾病在新生儿中的患病率已大大降低。 晚发性疾病(出生后7-90天)的发病率、死亡率和发病率保持不变。 在过去几十年里。此外，该病仍然是败血症最常见的形式之一， 发展中国家的脑膜炎，在那里产前筛查阴道GBS携带者并不是常规的和 因此，不向母亲提供抗生素预防。确定GBS如何激活先天免疫系统 导致疾病仍然是一个重要的科学和医学挑战。 在过去的十年中，我们报道了三种不同的致炎途径 对GBS的反应：TLR2/MyD88依赖途径、IFNα/β途径和NLRP3 炎症体途径。此外，我们小组和其他人最近的研究表明，先天免疫 抗GBS依赖于细胞内胞浆DNA传感通路对核酸的识别。脱氧核糖核酸 在感染过程中释放到细胞质中或通过转基因引入，结合并激活一种循环酶- GMP-AMP合成酶(CGAS)。DNA激活的cGAS产生环状二核苷酸2‘3’-cGAMP，其作用是 第二个信使，并触发干扰素基因的蛋白质刺激物(STING)。刺痛进而激活 TANK-BINDING KEK1(TBK-1)导致IRF3激活和I型干扰素基因表达。 细菌衍生的环二核苷酸也可以激活刺痛。 在这项建议中，我们将探讨细菌核酸在I型干扰素激活中的作用。 在GBS感染期间的反应。我们假设GBS DNA激活cGAS，产生cGAMP和 触发刺痛。我们还假设细菌c-diamp，我们已经证明了它是在 GBS的丰度，激活了刺痛。令人惊讶的是，与已知的其他细胞外 对于革兰氏阳性细菌(如肺炎球菌)，这种I型干扰素对GBS的反应具有保护性。使这件事复杂化 图片是GBS编码两种代谢环二核苷酸的酶。在主修课程中使用突变体 磷酸二酯酶(CDNP)，我们观察到了依赖刺痛的、非依赖于cGAS的I型激活 干扰素反应。我们将使用WT、STING KOS和cGAS KOS，并结合相关的GBS突变体，以 确定塑造对感染的先天免疫反应的关键途径和分子事件。这个 这些研究的结果将指导开发新的战略和治疗干预措施 改善或预防GBS感染的破坏性后遗症。

Project Abstract Group B streptococci (GBS) is a normal commensal bacterium found in the intestine and vagina of ~30% of healthy humans. Worldwide, GBS is the leading cause of pneumonia, septicemia and meningitis in the first 3 months of life and is the most important invasive pathogen in otherwise healthy newborn infants. While the prevalence of GBS-induced disease has been vastly diminished in neonates due to intrapartum antibiotics, the incidence, mortality, and morbidity of “late” onset disease (7-90 days after birth) has remained unchanged over the last few decades. Furthermore, the disease remains one of the most common forms of sepsis and meningitis in the developing world where prepartum screening for vaginal GBS carriage is not routine and hence antibiotic prophylaxis is not offered to mothers. Defining how GBS activates the innate immune system to cause disease remains an important scientific and medical challenge. During the last decade, we reported on three distinct pathways responsible for the inflammatory response to GBS: a TLR2/MyD88 dependent pathway, an IFNalpha/beta pathway, and the NLRP3 inflammasome pathway. In addition, recent work from our group and others indicates that innate immunity against GBS depends on recognition of nucleic acids by an intracellular cytosolic DNA sensing pathway. DNA released into the cytosol during infection or introduced by transfection binds to and activates an enzyme cyclic- GMP-AMP synthase (cGAS). DNA-activated cGAS produces a cyclic di-nucleotide, 2'3'-cGAMP, which acts as a second messenger and triggers a protein stimulator of interferon genes (STING). STING, in turn, activates TANK-binding kinase 1 (TBK-1) leading to IRF3 activation and type I interferon (IFN) gene expression. Bacteria derived cyclic-di-nucleotides can also activate STING. In this proposal we will explore the role of bacterial nucleic acids in the activation of type I IFN responses during GBS infection. We hypothesize that GBS DNA activates cGAS, generating cGAMP and triggering STING. We also hypothesize that bacterial c-di-AMP, which we have shown is produced in abundance by GBS, activates STING. Surprisingly, and in contrast to what is known about other extracellular Gram-positive bacteria (e.g., pneumococcus), this type I IFN response to GBS is protective. Complicating this picture is that GBS encodes for two enzymes that metabolize cyclic-di-nucleotides. Using mutants in the major phosphodiesterase (CdnP), we have observed STING-dependent, cGAS-independent activation of the type I interferon response. We will use WT, STING KOs and cGAS KOs, in combination with related GBS mutants, to define the key pathways and molecular events that shape the innate immune response to infection. The outcome of these studies will guide the development of novel strategies and therapeutic interventions to ameliorate or prevent the damaging sequelae of GBS infection.