牡蛎疱疹病毒（OsHV-1）逃逸宿主铁蛋白介导营养免疫的机制研究

OsHV-1 disease causes mass mortalities of molluscs worldwide. In recent years, the events of OsHV-1 infection mainly occurred in ark clams, Scapharca broughtonii in China. The limited cognition of the interaction between OsHV-1 and mollusc hosts restricts the effective prevention and control of OsHV-1 disease. Many proteins referring to essential life process need iron to function, such as ribonucleotide reductase, DNA primase and DNA helicase. Competing for necessary iron nutrient forms a hot issue of pathogen-host interaction. The rapid replication of OsHV-1 in the host requires an adequate iron environment. Previous experiments showed that the co-incubation of iron chelating agents and ark clam hemocytes can significantly inhibit the increase of OsHV-1 copies in the hemocytes. As an important iron storage protein, ferritin plays an important role in host nutritional immunity to limit available iron to pathogens. Many studies have shown that the expression of ferritin sharply increased in response to pathogen invading. However, our previous studies showed that OsHV-1 infection led to the reduction of the ferritin content in ark clams, and weakened the immune protective effect of ferritin. This project will use modern molecular biological and immunological methods to explore the defence process of ferritin in ark clams against OsHV-1 infection firstly. Then analyze how OsHV-1 infection leads to the reduction of ferritin content in ark clams at transcription and post transcription levels. At last, clarify the the evading mechanism of OsHV-1 against ark clam ferritin mediating nutritional immunity. Above results would further rich the knowledge of marine invertebrate immunology, provide theoretical guidance for effective prevention and control of OsHV-1 disease.

OsHV-1疫病频繁导致了全球多个国家贝类群体大规模死亡，近些年该病毒在我国多见于魁蚶中。目前，对OsHV-1与宿主相互作用的有限认知，制约了对该病毒疫病的有效防控。铁是诸多功能蛋白的辅基，对铁元素的竞争已成为研究病原与宿主相互作用的热点内容。我们前期实验结果表明，OsHV-1在宿主中复制需要充足的铁离子环境，铁离子螯合剂可显著抑制魁蚶血细胞中该病毒拷贝数的增加。作为重要的铁储蛋白，铁蛋白在介导宿主营养免疫，限制病原对宿主铁元素利用过程中发挥重要作用。前期实验显示OsHV-1感染降低了魁蚶铁蛋白含量，弱化了铁蛋白的防御保护作用。本项目将首先探究铁蛋白在魁蚶抗OsHV-1感染中的防御作用过程；其次在转录和转录后水平，深入解析该病毒感染导致魁蚶铁蛋白含量降低的关键原因，进而阐明该病毒逃逸魁蚶铁蛋白介导营养免疫的机制。相关研究结果将丰富海洋无脊椎动物免疫学知识，为有效防控该病毒疫病提供理论指导。

OsHV-1是贝类中广泛流行的病毒性病原，对贝类产业具有巨大的潜在危害性。铁蛋白做为一类应激蛋白，在贝类抗病原感染过程中发挥重要作用。我们研究发现，重组铁蛋白可显著提高OsHV-1感染宿主的存活率。在细胞水平上，重组铁蛋白处理后可显著降低细胞内OsHV-1 DNA拷贝数。在个体水平上，重组铁蛋白能一定程度抑制病毒拷贝数增加，但与对照组不具有显著性差异。铁蛋白在检测的各魁蚶组织和血清中均有分布，且重组铁蛋白与血细胞孵育后可再次定位到血细胞中，表明魁蚶中铁蛋白具备转运载体的特性，可穿梭于细胞间。血细胞膜表面分子半乳凝集素（SbGal）和清道夫受体（SbSR）与铁蛋白存在直接相互作用，可能介导了胞外铁蛋白锚定到细胞上。胞外铁蛋白可通过NF-κB信号通路一定程度增强自身基因表达，以及其他免疫效应分子的表达水平。此外，胞外铁蛋白还促进了血细胞对特定细菌的吞噬作用，明确了铁蛋白在魁蚶免疫调理过程中发挥的重要作用。随后，我们进一步阐明了在OsHV-1感染宿主后会上调铁调蛋白表达量，增强了铁调蛋白与铁蛋白mRNA中调控元件IRE的结合能力，抑制了铁蛋白的转录后翻译，削弱了铁蛋白对宿主的保护作用。