Defining the reciprocal interaction between neutrophils and human cytomegalovirus

人类巨细胞病毒（hCMV）是一种高度流行的机会性病毒，可感染高达90%的成年人，并在体内潜伏终生。最初的“原发性”感染通常引起轻微的腺热样疾病，但在某些高危人群中，病毒可引起严重疾病，或在以后重新激活引起“继发性”感染。妊娠期感染可导致新生儿先天性巨细胞病毒感染，导致出生缺陷，在器官移植受者或艾滋病毒感染者等免疫抑制患者中，巨细胞病毒是疾病的主要原因，导致住院率增加，移植器官存活率降低，死亡率升高。据信，这种病毒在骨髓中处于休眠状态，通过劫持宿主自身的细胞机制进行复制来传播，最终导致宿主细胞破裂或裂解，大量传染性病毒颗粒逸出。这种“溶解性”感染在某些白细胞类型（如巨噬细胞）中可见，但在更常见的白细胞（中性粒细胞）中未见。这种类型的细胞保护身体免受大多数细菌和某些病毒的侵害，吞噬并杀死生物体，然后经历一种被称为细胞凋亡的自我毁灭过程，从而引发炎症反应的消退。然而，最近的研究表明，某些病毒和细菌可以逃避中性粒细胞的防御机制，并在其通常不适宜生存的内部环境中生存下来，利用它作为“特洛伊木马”进行复制和传播。在这种情况下，中性粒细胞凋亡甚至可能促进感染，允许活生物体转移到巨噬细胞和其他细胞类型，从而从炎症部位清除凋亡的中性粒细胞。我的初步工作表明，hCMV与纯化的健康中性粒细胞接触，通过抑制凋亡细胞死亡，导致中性粒细胞存活率的显著增加。存活的中性粒细胞不会产生新的病毒，但会释放出对邻近细胞产生深远影响的物质，增加其他中性粒细胞的寿命，并导致巨噬细胞改变其表面信号，使其更容易受到hCMV感染。我将通过确定病毒与中性粒细胞表面的接触点来研究病毒是如何在中性粒细胞中产生这种效应的，以及它是如何触发下游效应来抑制细胞死亡过程的。此外，我将通过分析中性粒细胞释放的物质来确定中性粒细胞在hCMV治疗后产生的活性物质的确切性质，并探索这些物质是如何延长它们的寿命的。最后，我计划探索增加的免疫细胞存活率如何被病毒利用为自己的优势，研究中性粒细胞是否可以将完整的病毒转移到其他细胞类型-“特洛伊木马”模型-或使周围的巨噬细胞更容易感染，在感染时产生更多的病毒。作为一名照顾艾滋病毒感染患者的传染病专科实习生，我亲眼目睹了这种破坏性机会性感染的影响，并寻求找到更好地了解和治疗巨细胞病毒的方法。这个项目有可能揭示hCMV在身体周围传播方式的新见解，这可能使我们将来能够在最危险的人群中对抗其传播。

Human Cytomegalovirus (hCMV) is a highly prevalent opportunistic virus that infects up to 90% of the adult population and persists dormant in the body for life. The initial "primary" infection usually causes a mild glandular fever-like illness, but in certain at-risk populations the virus can cause substantial disease, or reactivate to cause "secondary" infection at a later date. Infection during pregnancy can result in congenital CMV infection in the newborn, leading to birth defects, and in immunosuppressed patients such as organ transplant recipients or HIV-infected individuals CMV is a major cause of disease, leading to increased hospitalisation, reduced survival of transplanted organs, and higher mortality.The virus is believed to lie dormant in the bone marrow, and spreads by hijacking the hosts own cellular mechanisms to replicate, leading ultimately to rupture or lysis of the host cell and escape of large numbers of infectious virus particles. This "lytic" infection has been seen in certain white blood cell types such as the macrophage but not in the more common white blood cell, the neutrophil. This cell type protects the body from most bacteria and certain viruses, engulfing and killing the organisms then undergoing a process of self-destruction known as apoptosis, which triggers resolution of the inflammatory response. Recent research however has shown that certain viruses and bacteria can evade the neutrophil's defence mechanisms and survive its normally inhospitable internal environment, using it as a "Trojan horse" to replicate and spread. In this context, neutrophil apoptosis may even promote infection, allowing the transfer of live organisms to macrophages and other cell types, which remove apoptotic neutrophils from the inflamed site.My preliminary work has shown that contact between hCMV and purified healthy neutrophils causes a profound increase in neutrophil survival by inhibiting apoptotic cell death. The surviving neutrophil does not produce new virus, but does release substances that quite profoundly affect its neighbouring cells, increasing the lifespan of other neutrophils and causing macrophages to alter their surface signals, making them potentially more susceptible to hCMV infection.I will be investigating exactly how the virus produces this effect in the neutrophil, by defining its point of contact with the neutrophil surface and how this triggers a downstream effect to inhibit the cell death process. Additionally, I will determine the precise nature of the active substances that neutrophils produce following treatment with hCMV by analysing the material released by these cells and exploring exactly how these substances act to prolong their lifespan. Finally, I plan to explore how the increased immune cell survival may be used by the virus for its own advantage, investigating whether the neutrophil can transfer intact virus to other cell types - the "Trojan Horse" model - or make surrounding macrophages more susceptible, producing more virus upon infection.As an Infectious Diseases specialist trainee caring for HIV-infected patients I see first-hand the effects of this devastating opportunistic infection, and seek to find ways to better understand and treat CMV. This project has the potential to reveal new insights into the way hCMV spreads around the body, which in the future may enable us to combat its spread in those most at risk.