Apoptosis and efferocytosis: regulators of immunity to tuberculosis

描述(申请人提供)：持续的艾滋病毒/艾滋病流行和耐多药结核分枝杆菌(Mtb)的传播使结核病在世界各地的人口中持续流行。虽然卡介苗被普遍用作疫苗，但它在预防肺结核方面并不有效。为了抗击这一持续的世界性祸害，开发结核病疫苗是当务之急。细胞凋亡是一种固有的Mφ防御机制，它限制了细菌的复制和结核分枝杆菌的扩散。细胞凋亡也将先天免疫和克隆免疫联系起来。DC将细菌抗原包装在凋亡小泡中提供给T细胞，从而在体内更好地启动和保护T细胞。细胞凋亡是如何被调控的 限制结核分枝杆菌复制，以及是否可以操纵它来加强疫苗接种是这项提案的重点。创新：二十烷类化合物在对分枝杆菌的免疫中的作用在鱼类、小鼠和人类中都是保守的，强调了它们的根本重要性。我们在体外感染的人M-φ和体内感染的小鼠上发表的工作建立了结核分枝杆菌感染的M-φ的凋亡作为一种关键的宿主防御机制来对抗结核病。结核分支杆菌感染M-φ的死亡途径的复杂性直到最近才被认识到。Mtb毒株诱导脂氧素A4(LXA4)，抑制前列腺素E_2(PGE_2)的合成，阻断细胞凋亡，促进坏死性M-φ死亡。相反，PGE2可防止坏死并增加细胞凋亡。为什么细胞凋亡作为一种宿主防御机制还不清楚。在这里，我们提出了一个新的假设，即导致控制的不是细胞凋亡本身，而是结核分枝杆菌感染的凋亡Mφ的吞噬作用是关键事件。我们预测：(1)M-φ的吞噬作用将抑制感染；(2)DC的吞噬作用将导致幼稚T细胞的启动。除了二十聚糖途径外，IL-1？和I型干扰素之间的平衡正在成为影响先天免疫和克隆免疫的第二个轴。我们提出了一个新的模型，在该模型中，Mtb诱导的LXA4和干扰素ç相互作用抑制天然免疫，而PGE2、IL-1ç和肿瘤坏死因子促进抗菌免疫。目的：在目标1中，我们将确定二十烷类化合物如何调节感染的巨噬细胞的激活和诱导细胞内细菌复制的控制。特别是，我们将确定二十烷类化合物如何影响IL-1ü和I型干扰素之间的平衡，I型干扰素正在成为影响先天性免疫和克隆免疫的第二个轴。在第二个目的中，我们将检验这一假设，即不是细胞凋亡本身杀死了结核分枝杆菌-相反，是感染的凋亡M-φ的吞噬作用限制了结核分枝杆菌在细胞内的生长。吞噬凋亡细胞，称为胞吐作用，是M-φ的主要组成部分；然而，人们对其在感染中的作用知之甚少。最后，在第三个目标中，我们将确定二十烷类细胞凋亡与克隆免疫的关系。我们推测，二十烷类化合物的生物合成和细胞信号通路可以通过药理作用促进感染的M-φ细胞的凋亡。通过促进细胞凋亡性死亡，我们希望增加减毒细菌疫苗的安全性和有效性。我们相信，从机制上理解促凋亡疫苗如何诱导更好的免疫力，将有助于开发针对结核病和其他使用分枝杆菌载体的疾病的更好的免疫策略。摘要：更好地了解细胞凋亡和吞噬作用如何影响结核分枝杆菌的天然免疫，最终控制细菌复制和刺激T细胞免疫，将提高我们对结核病发病机制的理解，并将导致新的治疗方法的研究。

DESCRIPTION (provided by applicant): The continuing HIV/AIDS epidemic and the spread of multi-drug resistant Mycobacterium tuberculosis (Mtb) has perpetuated an epidemic of tuberculosis in human populations around the world. While BCG is used universally as a vaccine, it is not effective in preventing pulmonary tuberculosis. To combat this ongoing worldwide scourge, vaccine development for tuberculosis is a priority. Apoptosis is an innate Mφ defense mechanism that limits bacterial replication and restricts dispersal of Mtb. Apoptosis also links innate and clonal immunity. DC present bacterial antigens packaged in apoptotic vesicles to T cells, leading to better T cell priming and protection in vivo. How apoptosis is regulated and restricts Mtb replication and whether it can be manipulated to enhance vaccination is the focus of this proposal. Innovation: The role of eicosanoids in immunity to mycobacteria is conserved in fish, mice and humans, highlighting their fundamental importance. Our published work on in vitro infected human Mφ and on in vivo infected mice establish apoptosis of Mtb infected Mφ as a critically important host defense mechanism against tuberculosis. The complexity of death pathways in Mtb infected Mφ has only recently been appreciated. Virulent Mtb induces lipoxin A4 (LXA4), inhibits prostaglandin E2 (PGE2) synthesis, blocks apoptosis, and promotes necrotic Mφ death. In contrast, PGE2 protects against necrosis and increases apoptosis. Why apoptosis acts as a host defense mechanism is not understood. Here we put forward a new hypothesis that it is not apoptosis per se that leads to control, but instead phagocytosis of Mtb infected apoptotic Mφ that is the crucial event. We predict: (1) phagocytosis by Mφ will contain the infection; and (2) phagocytosis by DC will lead to priming of naïve T cells. In addition to the eicosanoid pathways, the balance between IL-1ß and type I IFN (IFNß) is emerging as a second axis that affects innate and clonal immunity. We propose a new model in which LXA4 and IFNß, both induced by Mtb, interact to inhibit innate immunity, while PGE2, IL-1ß and TNF promote antibacterial immunity. Aims: In Aim 1, we will determine how eicosanoids regulate activation of infected macrophages and induce control of intracellular bacterial replication. In particular, we will determine how eicosanoids affect the balance between IL-1ß and type I IFN (IFNß), which is emerging as a second axis that affects innate and clonal immunity. In the second aim, we will test the hypothesis that it is not apoptosis per se that kills Mtb - rather it is the phagocytosis f infected apoptotic Mφ that restricts intracellular Mtb growth. Phagocytosis of apoptotic cells, termed efferocytosis, is a major constitutive Mφ function; however, little is known about its role during infection. Finally, in the third aim, we will determine the relationship between eicosanoids apoptosis and clonal immunity. We hypothesize that the eicosanoid biosynthetic and cell signaling pathways can be pharmacologically manipulated to enhance apoptosis of infected Mφ. By promoting apoptotic death, we hope to increase the safety and the efficacy of attenuated bacterial vaccines. We believe that a mechanistic understanding of how pro-apoptotic vaccines induce better immunity will lead to the development of better immunization strategies against tuberculosis and other diseases that are using mycobacterial vectors. Summary: A better understanding of how apoptosis and efferocytosis affect innate immunity to Mtb culminating in control of the bacterial replication and stimulation of T cell immunity will improve our understanding of TB pathogenesis and will lead to research into novel therapies.