Toxoplasma sporozoite genes that determine environmental resistance and invasion of host cells.

项目摘要 寄生虫弓形虫可导致免疫功能低下的患者和胎儿发生严重疾病， 是美国食源性死亡的第二大原因。感染开始后，摄入的卵囊脱落， 猫粪便或摄入被组织囊肿污染的肉类后。卵囊在水中非常稳定， 环境，抵抗大多数灭活程序，并且具有高度传染性。因为牲畜 被来自卵囊的子孢子感染，基于子孢子或子孢子蛋白质的疫苗可以 有效地保护牲畜和人类。目前，唯一可用的疫苗是减毒活疫苗 只允许用于羊。然而，这种疫苗作为疫苗的遗传基础存在严重缺陷。 衰减是未知的，这会带来逆转风险，并且一旦生产就需要立即使用 因为它是基于活的速殖子，而速殖子在宿主细胞外不能存活很长时间。尽管是一个关键的 弓形虫传播步骤，卵囊内的子孢子研究不足，主要是因为它们不是 可在体外培养且难以在体内获得。因此，迫切需要鉴定子孢子基因， 这些产品对于其入侵宿主细胞至关重要，这可能导致发现疫苗靶点。 此外，如果子孢子极端环境抗性的遗传基础是已知的， 可能利用这一点使其他弓形虫生命阶段，如速殖子，或其他病原体更多 活的细胞外，这可以提高基于活寄生虫的疫苗的保质期。我们的整体 目的是鉴定弓形虫基因，这些基因特异性地参与环境抗性， 子孢子的感染性。我们的中心假设是：1）子孢子特异性微线蛋白（MIC） 对于它们侵入宿主细胞是关键的; 2）晚期胚胎发生丰富蛋白（LEA），其是已知的 提供对环境胁迫如干旱、高盐和冰冻的抗性， 微生物，确定子孢子对环境应激源的抗性。在我们的第一个目标中，我们将确定 LEA在保护子孢子免受环境压力中的作用。在我们的第二个目标中，我们将测试 假设在子孢子中特异性表达的MIC参与宿主细胞的侵袭。 子孢子在宿主细胞外存活和附着/入侵中的作用基因的鉴定 细胞，将为设计预防人类和动物弓形虫感染的疫苗铺平道路。

Project Summary The parasite Toxoplasma gondii can cause severe disease in immunocompromised patients and fetuses and is the second leading cause of foodborne deaths in the USA. Infection starts after ingestion of oocysts shed in cat feces or after ingestion of meat contaminated with tissue cysts. Oocysts are extremely stable in the environment, resistant to the most inactivation procedures, and highly infectious. Because livestock get infected by sporozoites derived from oocysts, a vaccine based on sporozoites or sporozoite proteins could be effective in protecting livestock and humans. Currently, the only vaccine available is a live attenuated vaccine only approved for use in sheep. However, this vaccine has serious shortcomings as the genetic basis for the attenuation is not known, which poses reversion risks, and it needs to be used immediately once produced because it is based on live tachyzoites, which are not viable for long outside host cells. Despite being a critical step for Toxoplasma transmission, sporozoites inside oocysts are under-studied, largely because they are not cultivatable in vitro and difficult to access in vivo. There is, therefore, a critical need to identify sporozoite gene products that are critical for its invasion of host cells, which could lead to the discovery of vaccine targets. Furthermore, if the genetic basis for the extreme environmental resistance of sporozoites was known it might be possible to exploit this to make other Toxoplasma life stages, such as tachyzoites, or other pathogens more viable extracellularly, which could enhance the shelf-life of vaccines based on live parasites. Our overall objectives are to identify Toxoplasma genes that are specifically involved in the environmental resistance and infectivity of sporozoites. Our central hypotheses are that 1) sporozoite-specific micronemal proteins (MICs) are critical for their invasion into host cells; 2) late embryogenesis abundant proteins (LEAs), which are known to provide resistance to environmental stresses such as drought, high salinity, and freezing in a variety of organisms, determine sporozoite resistance to environmental stressors. In our first aim we will determine the role of LEAs in the protection of sporozoites against environmental stressors. In our second aim we will test the hypothesis that MICs that are specifically expressed in sporozoites are involved in the invasion of host cells. The identification of sporozoite genes that play a role in extracellular survival and attachment/invasion of host cells, will pave the way for designing vaccines that can prevent Toxoplasma infection of humans and animals.