Recognition of Group B Streptococci by Innate Immune Sensors

工程摘要 B族链球菌（GBS）是一种正常的肠道细菌，存在于约30%的 健康的人类在世界范围内，GBS是前3年肺炎、败血症和脑膜炎的主要原因。 在其他方面健康的新生儿中是最重要的侵入性病原体。而 由于产时使用抗生素，新生儿中GBS诱导疾病的患病率已大大降低， “迟发性”疾病（出生后7-90天）的发病率、死亡率和发病率在2000 - 2001年期间保持不变。 过去几十年里此外，这种疾病仍然是败血症最常见的形式之一， 在发展中国家，阴道GBS携带的脑膜炎筛查不是常规的， 因此，不向母亲提供抗生素预防。定义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途径， 对GBS的反应：TLR 2/MyD 88依赖性通路、IFN α/β通路和NLRP 3 炎性体途径此外，我们小组和其他人最近的工作表明，先天免疫 抗GBS的免疫应答依赖于细胞内胞质DNA传感途径对核酸的识别。DNA 在感染过程中释放到胞质溶胶中或通过转染引入， GMP-AMP合酶（cGAS）。DNA活化的cGAS产生环状二核苷酸，2 '3'-cGAMP，其充当 第二信使，并触发干扰素基因（STING）的蛋白质刺激物。STING反过来激活 TANK结合激酶1（TBK-1）导致IRF 3激活和I型干扰素（IFN）基因表达。 细菌衍生的环状二核苷酸也可以激活STING。 在这个建议中，我们将探讨细菌核酸在激活I型干扰素中的作用 GBS感染时的反应。我们假设GBS DNA激活cGAS，产生cGAMP， 触发STING我们还假设，我们已经证明的细菌c-di-AMP产生于 通过GBS丰度，激活STING。令人惊讶的是，与已知的其他细胞外 革兰氏阳性细菌（例如，肺炎球菌），这种I型IFN对GBS的反应是保护性的。使这件事复杂化 GBS编码两种代谢环状二核苷酸的酶。在少校中使用变种人 磷酸二酯酶（CdnP），我们已经观察到STING依赖性，cGAS非依赖性的I型激活 干扰素应答我们将使用WT、STING科斯和cGAS科斯与相关的GBS突变体组合， 定义塑造对感染的先天免疫反应的关键途径和分子事件。的 这些研究的结果将指导新策略和治疗干预的发展， 改善或预防GBS感染的损害性后遗症。

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.