Immunity to Chlamydial Infection

对衣原体感染的免疫力

• 批准号: 6808655
• 负责人: HARLAN D CALDWELL
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6808655
• 关键词: Chlamydia trachomatis; bacteria infection mechanism; bacterial antigens; bacterial genetics; bacterial vaccines; bactericidal immunity; biotechnology; chlamydial disease; disease /disorder model; enzyme activity; functional /structural genomics; gene mutation; genetic strain; laboratory mouse; live vaccine; microorganism metabolism; molecular cloning; mucosal immunity; sexually transmitted diseases; tissue /cell culture; tryptophan synthase; vaccine development; virulence

The purpose of this work is to understand how C. trachomatis infection persists in humans and how persistence contributes to serious post-infection sequelae such as blindness and infertility. To accomplish this goal we have performed functional genomic studies on both reference laboratory strains and clinical isolates focusing on the genes that reside in the pathogen's plasticity zone (PZ); a small polymorphic region that contains cytotoxin genes, phospholipase D genes, and the tryptophan operon (trpRBA) that encodes the last two enzymes (Trp B and Trp A) of the tryptophan biosynthetic pathway. We found that laboratory reference strains of Chlamydia trachomatis differing in infection organotropism correlated with inactivating mutations in the pathogen's Trp A synthase. Our functional genomic studies find that the paradigm established for reference serovars also applies to clinical isolates; specifically, all ocular trachoma isolates tested have inactivating mutations in the synthase, whereas all genital isolates encode a functional enzyme; implicating a functional role for the synthase in the pathogenesis of chlamydial STDs. Moreover, functional enzyme activity was directly correlated to IFN-gamma resistance through an indole rescue mechanism. Hence, a strong selective pressure exists for genital strains to maintain a functional synthase capable of using indole for tryptophan biosynthesis. The fact that ocular serovars (serovar B) isolated from the genital tract were found to possess a functional synthase provided further persuasive evidence of this association. These results argue that there is an important host-parasite relationship between chlamydial genital strains and the human host that determines organotropism of infection and the pathophysiology of disease. We believe that this relationship involves the production of indole by components of the vaginal microbial flora, allowing chlamydiae to escape IFN-gamma mediated eradication and thus establish persistent infections. We have shown that Chlamydiae use Trp A and B to avoid the effect of IFN-gamma on host epithelial cells, a mechanism that allows the pathogen to avoid host defense and establish persistent. To date, vaccination using conventional approaches such as targeted chlamydial recombinant proteins or DNA encoding proteins have failed in eliciting a protective anti-chlamydial immunity at the genital mucosae. Our conclusions are that the antigenic complexity of the chlamydiae, its complex life cycle, and tropism for mucosal epithelial cells constitute overwhelming challenges for the generation of a conventional vaccine. Consequently, we are currently focusing on the generation of live-attenuated vaccine strains. This is being accomplished by the clonal selection of variants that are incapable of synthesizing tryptophan synthase, a key enzyme in the ability of the pathogen to persist in epithelial cells in the presence host defense. Clones whose growth is highly sensitive to IFN-gamma in vitro and that have mutations in the trpRBA genes will be tested in in vivo in pre-clinical primate models of infection for attenuated growth and pathological properties. These studies should yield information important to the development of a highly efficacious and safe vaccine capable of preventing or controlling chlamydial caused STDs in humans.

本工作的目的是了解C.沙眼感染在人类中持续存在，以及持续存在如何导致严重的感染后后遗症，如失明和不育。为了实现这一目标，我们对参考实验室菌株和临床分离株进行了功能基因组学研究，重点是病原体可塑性区（PZ）中的基因;一个小的多态性区域，包含细胞毒素基因、磷脂酶D基因和编码色氨酸生物合成途径最后两种酶（Trp B和Trp A）的色氨酸操纵子（trpRBA）。我们发现，实验室参考菌株沙眼衣原体不同的感染亲器官性与失活突变的病原体的色氨酸A合酶。我们的功能基因组研究发现，为参考血清型建立的范例也适用于临床分离株;具体而言，所有检测的眼沙眼分离株在合酶中具有失活突变，而所有生殖器分离株编码功能性酶;暗示合酶在衣原体性传播疾病发病机制中的功能性作用。此外，功能性酶活性通过吲哚拯救机制与IFN-γ抗性直接相关。因此，生殖株存在强大的选择压力，以维持能够使用吲哚进行色氨酸生物合成的功能性合酶。从生殖道分离的眼血清型（血清型B）被发现具有功能性合酶，这一事实为这种关联提供了进一步有说服力的证据。这些结果表明，生殖道衣原体菌株和人类宿主之间存在重要的宿主-寄生虫关系，决定了感染的器官嗜性和疾病的病理生理学。我们认为，这种关系涉及阴道微生物植物群成分产生吲哚，使衣原体逃避IFN-γ介导的根除，从而建立持续感染。我们已经表明，衣原体使用色氨酸A和B，以避免干扰素-γ对宿主上皮细胞的影响，一种机制，使病原体，以避免宿主防御和建立持久的。迄今为止，使用常规方法如靶向衣原体重组蛋白或DNA编码蛋白的疫苗接种未能在生殖器粘膜处引发保护性抗衣原体免疫。我们的结论是，衣原体的抗原复杂性，其复杂的生命周期，和粘膜上皮细胞的嗜性构成了压倒性的挑战，为传统疫苗的产生。因此，我们目前正集中精力生产减毒活疫苗株。这是通过克隆选择不能合成色氨酸合酶的变体来实现的，色氨酸合酶是病原体在宿主防御存在下在上皮细胞中持续存在的能力的关键酶。将在临床前灵长类动物感染模型中体内测试其生长在体外对IFN-γ高度敏感并且在trpRBA基因中具有突变的克隆的减弱的生长和病理性质。这些研究应产生重要的信息，以开发一种高度有效和安全的疫苗，能够预防或控制衣原体引起的性病在人类。