The role of chromatin extracellular traps in host defence of fish against pathogens.

染色质是DNA、RNA和蛋白质的复合物，是构成细胞核的物质，用于储存遗传信息。然而，越来越多的证据表明，它还有第二种功能，特别是作为防御细菌和其他微生物的武器。在哺乳动物和无脊椎动物中，一些参与炎症的专用免疫细胞以受控和调节的方式将其染色质排出细胞外部以响应微生物的存在。然后，它像云一样滚滚而出，形成一个网，捕获病原体，并通过细胞质中的小抗生素蛋白质将它们杀死，这些蛋白质散布在纤维上。简单地说，这是一个细胞死亡过程，使免疫细胞即使在死亡后也能继续对抗感染因子。本项目旨在研究鱼类的这一过程，因为尽管它被广泛认为是人类和其他哺乳动物的一种重要免疫策略，但尚未在鱼类健康和预防感染的背景下加以考虑。疾病是鱼类养殖中的一个大问题。它给生产者造成重大的经济损失，并给鱼类带来不希望的痛苦。随着气候变化导致海水温度上升，疾病问题也可能恶化。尽管近几十年来一直在努力开发鱼类疫苗，但许多疫苗并不能完全保护鱼类免受感染。这是因为病原体中的菌株变异性和鱼类免疫系统中负责产生长寿抗体的“记忆”成分的结构。相反，鱼类严重依赖炎症或“先天”（即先天）过程，如吞噬作用（食菌）和天然抗生素蛋白的产生来保护自己。因此，鱼类的先天系统是预防和控制感染的重要靶点。拟议的研究将针对大西洋鲑鱼，因为这是英国的主要水产养殖物种，许多渔场位于苏格兰。这项工作将使用体外（即细胞培养）方法来评估鲑鱼中哪些炎症细胞部署染色质来杀死病原体，这些细胞的反应有多强以及病原体在染色质网上被杀死的效率。在这些实验中将使用一系列已知会在其库存动物中引起严重和对生产者来说是毁灭性疾病的鱼类病原体。这些病原体还包括不同微生物组的代表性类型，因此应该有可能发现一些病原体是否能够阻断、逃避或逃脱染色质截留。为了研究水温对鱼类宿主防御这方面的可能影响，这项工作将比较染色质释放反应的强度和从适应9至19摄氏度不同水温的鱼类中取样的细胞杀死病原体的效率。这一范围内的最高值涵盖了苏格兰一些海水温度已经上升的地点养殖鲑鱼所经历的温度，但如果沿海水温上升2摄氏度，就会更常见，正如一些气候变化模型所预测的那样。该项目的这一部分将有助于告诉我们，在未来的气候条件下，养殖鱼类是否会变得更容易受到疾病的影响。这项研究将产生关于鱼类高度新颖的免疫过程重要性的新信息，从而使我们能够更好地了解病原体及其宿主如何相互作用。这项工作可能进一步支持新化合物、饲料添加剂或限制水产养殖疾病问题的策略的开发。

Chromatin, a complex of DNA, RNA and protein, is the material that makes up the nucleus of a cell and serves to store genetic information. However, strong evidence has accumulated that it also has a second function, remarkably as a weapon in defence against bacteria and other microbes. In both mammals and invertebrates, some dedicated immune cells involved in inflammation, expel their chromatin in response to the presence of microbes in a controlled and regulated way to the exterior of the cell. It then billows out, like a cloud, to form a mesh that traps pathogens and kills them by virtue of small antibiotic proteins from the cell cytoplasm that become studded on the fibres. Put simply it is a cell death process that enables an immune cell to continue combatting infectious agents even after it has died. The present project aims to investigate this process in fish, as, despite it being widely regarded as an important immune strategy in humans and other mammals, it has not yet been considered in the context of fish health and protection against infection. Disease is a huge problem in fish farming. It causes significant financial losses to the producers and undesirable suffering for the fish. The problem of disease is also likely to worsen as sea temperature rises through climate change. Despite efforts to develop vaccines for fish over recent decades, many do not provide full protection against infections. This is because of strain variability in the pathogens and the structure of the 'memory' component of the fish's immune system that is responsible for producing long-lived antibodies. Instead, fish rely heavily on inflammation, or 'innate' (i.e. inborn) processes, such as phagocytosis (bacteria-eating) and production of natural antibiotic proteins, to protect themselves. Therefore the innate system of fish is an important target for preventing and controlling infection. The proposed research will be directed at Atlantic salmon, as this is the major aquaculture species in the UK, with many fish farms located in Scotland. The work will use in vitro (i.e. cell culture) methods to assess which inflammatory cells in salmon deploy chromatin to kill pathogens, how strong the responses of these cells are and how efficiently pathogens are killed on the chromatin nets. A range of fish pathogens known to cause serious and, for the producers, devastating, diseases in their stock animals will be used in these experiments. These pathogens also include representative types of different microbial groups, so it should be possible to discover if some are able to block, evade or escape chromatin entrapment. To investigate the likely impact of water temperature on this aspect of the fish host defences, the work will compare the strength of the chromatin release response and the efficiency of pathogen killing by cells sampled from fish that have been acclimated to different water temperatures ranging from 9 to 19 degrees Celsius. The highest value in this range covers temperatures experienced by farmed salmon at some sites in Scotland where sea temperatures have already risen, but will be more commonly encountered if coastal water temperatures increase by 2 degrees Celsius, as predicted by some climate change models. This part of the project will help to inform us if farmed fish will become more susceptible to disease under future climatic conditions. The research will generate new information about the importance of a highly novel immune process in fish and thus enable us understand better how pathogens and their host interact. The work may further underpin the development of new compounds, feed additives or strategies to limit the problem of disease in aquaculture.