Deciphering the Physiological Interaction between the Mosquito Immune and Circulatory Systems

蚊子通过强大的免疫反应来对抗感染，这种免疫反应是由血细胞介导的。在体腔或血腔内，血细胞要么与血淋巴（昆虫血液）一起循环，要么作为无根细胞（附着在组织上）存在。早期的实验表明，在感染过程中，病原体会积聚在成年蚊子的心脏表面。心包检查显示，一小群无梗血细胞存在于心脏瓣膜侧面的区域（骨膜区域），这些血细胞很容易吞噬病原体。感染诱导额外的血细胞募集到骨膜区域，这些血细胞通过吞噬、黑化和溶解迅速杀死病原体。目前，关于血淋巴循环对免疫反应的影响以及在控制感染中的作用的数据缺乏。因此，在了解昆虫血中病原体抗性的时空动态方面存在重大空白。这项研究将探索蚊子新发现的一种免疫组织（骨膜血细胞）的生物学特性，这种免疫组织基本上依赖于心脏的机制来杀死病原体。更具体地说，这个项目将研究感染诱导的血细胞聚集在昆虫心脏表面的分子、空间和时间基础。该项目将对昆虫的抗病原体反应产生重要见解，并将这些信息整合到昆虫免疫、生理学和发育的广泛概念框架中。此外，这项研究将在蚊子中进行，蚊子是一种社会和生态上重要的昆虫群体，因为它们是害虫和病原体的传播者。因此，该项目产生的数据可有助于制定新的病虫害控制战略。此外，首席研究员将与高尔小学（纳什维尔大都会公立学校）合作，向小学生介绍昆虫生物学。该项目有四个主要目标，共同旨在破译蚊子免疫系统和循环系统之间的生理相互作用。目的1将采用分子和成像方法来确定驱动感染诱导的血细胞迁移到心脏表面的途径。目的2将依靠分子和生化方法来测试在感染过程中血细胞产生的因子如一氧化氮是否调节心脏生理。目的3将确定在蚊子发育过程中免疫系统和循环系统之间的相互作用是否被保留。具体来说，因为在成虫和幼虫的生命阶段，总体的身体结构和血淋巴的流动有明显的不同，所以目标3将采用有机和成像的方法来评估幼虫的免疫系统和循环系统在感染过程中是否也相互作用。如果他们这样做，交互的性质将被定义。最后，目的4将通过定量测量这种反应在多种昆虫物种中的发生来评估周膜血细胞聚集是否是一种普遍特征。预计本研究将揭示昆虫免疫系统和循环系统之间的基本生理相互作用。

Mosquitoes fight infection by mounting powerful immune responses that are mediated by cells called hemocytes. Within the body cavity, or hemocoel, hemocytes either circulate with the hemolymph (insect blood) or exist as sessile cells (attached to tissues). Earlier experiments revealed that during the course of an infection, pathogens accumulate on the surface of the heart of adult mosquitoes. Examination of the pericardium then showed that a small population of sessile hemocytes exists in the regions that flank the valves of the heart (the periostial regions), and that these hemocytes readily phagocytose pathogens. Infection induces the recruitment of additional hemocytes to the periostial regions, and these hemocytes rapidly kill pathogens via phagocytosis, melanization and lysis. Currently there is a paucity of data on the effect of hemolymph circulation on immune responses, and on the role sessile hemocytes play in controlling infection. Thus, significant gaps exist in understanding the spatial and temporal dynamics of pathogen resistance in the insect hemocoel. This research will explore the biology of a newly discovered immune tissue in mosquitoes (periostial hemocytes) that fundamentally relies on the mechanics of the heart for pathogen killing. More specifically, this project will investigate the molecular, spatial, and temporal bases of infection-induced hemocyte aggregation on the surface of the insect heart. The project will yield critical insight into the anti-pathogen responses of insects, and will integrate this information into a broad conceptual framework on insect immunity, physiology, and development. Furthermore, this research will be carried out in mosquitoes, a socially and ecologically important insect group because of their role as pests and pathogen transmitters. Thus, data arising from this project could contribute to the development of novel pest and disease control strategies. In addition, the principal investigator will partner with Gower Elementary School (Metropolitan Nashville Public Schools) to introduce elementary school students to insect biology.This project has four primary objectives that collectively aim to decipher the physiological interaction between the mosquito immune and circulatory systems. Objective 1 will employ molecular and imaging methodologies to determine the pathways that drive the infection-induced migration of hemocytes to the surface of the heart. Objective 2 will rely on molecular and biochemical approaches to test whether during the course of an infection hemocyte-produced factors such as nitric oxide modulate cardiac physiology. Objective 3 will determine whether the interaction between the immune and circulatory systems is conserved during mosquito development. Specifically, because the general body plan as well as the flow of hemolymph are markedly different in the adult and larval life stages, objective 3 will employ organismal and imaging approaches to assess whether the immune and circulatory systems of larvae also interact during the course of an infection. If they do, the nature of that interaction will be defined. Finally, objective 4 will assess whether periostial hemocyte aggregation is a general feature by quantitatively measuring the occurrence of this response in a wide variety of insect species. It is expected that this research will uncover fundamental physiological interactions between the immune system and the circulatory system of insects.