A 3-D perspective on neutrophil migration

趋化性是细胞能够导航到化学诱导剂来源的过程。它对发育、免疫功能和癌细胞的扩散至关重要。它是基于细胞通过其表面高度特异的受体检测趋化物质的能力。值得注意的是，当细胞放置在靠近化学示踪剂来源的地方时，细胞可以确定朝向来源的方向。它既利用了吸引剂变得离源更近这一事实，也利用了它检测周围化学吸引剂浓度的微小差异的能力。然后，细胞朝着化学牵引剂浓度增加的方向迁移。尽管趋化作用很重要，但我们对趋化作用的了解非常有限。很明显，趋化性是由许多成分或亚反应组成。检测化学牵引剂的能力，感知极小距离内化学牵引剂浓度变化的能力，以及对化学吸引剂做出反应(趋化作用)而移动的能力，这反过来又取决于细胞与邻近细胞或表面形成可逆接触的能力。只有了解这些基本成分的反应，才能充分了解趋化作用。在这个项目中，我们将重点放在支持趋化作用的机制上(趋化物质刺激的运动，在我们的分析中，化学牵引剂的浓度通常是均匀的，所产生的迁移是随机的，而不是像趋化作用那样是定向的)，作为趋化作用中的关键事件。我们的目标是了解细胞内允许它们执行这些反应的化学本质(充当信号的分子)和空间组织。中性粒细胞是血液中发现的一种特殊形式的白细胞。它们的主要功能是摄取和杀死细菌和真菌病原体。中性粒细胞利用趋化作用的过程，从血流中迁移到炎症区域，也迁移到病原体的家中。因此，趋化性对于中性粒细胞发挥其正常的健康功能抗击疾病是必不可少的。然而，已知许多长期炎症性疾病是由中性粒细胞过度反应引起的。过多的中性粒细胞聚集在疾病部位，实际上会对宿主组织造成损害，进而导致中性粒细胞进一步聚集。因此，治疗关节炎等炎症性疾病的一个主要目的是减少中性粒细胞向炎症部位的迁移。目前，我们很少有药物能够有效地减少中性粒细胞流入慢性炎症部位，并产生不良副作用，因为我们不知道趋化作用中的哪些步骤是最好的靶点。我们的目标是研究中性粒细胞的趋化运动和趋化作用。最近，在了解中性粒细胞内参与协调趋化作用的事件方面取得了巨大的进展。这是可能的，因为显微镜的发展能够看到活体中性粒细胞运动时的内部，并使用基因工程技术使我们想要在细胞内研究的特定蛋白质发出荧光，从而可以通过显微镜中的特殊照明和检测系统来看到。然而，尽管取得了这些进展，迄今为止，我们对趋化过程中细胞内部的看法一直是非常二维的，就像我们从上面俯视它们一样，不能揭示任何深度(细胞的“侧面”)。通过使用新的成像技术，我们能够开始拍摄许多照片，并将它们组合在一起，给人一种深度感。到目前为止，我们所看到的完全改变了我们对二维图像的解释和对趋化性的空间协调的理解。在这个项目中，我们希望使用数学和计算机来提高我们创建和解释中性粒细胞迁移的3-D图像的能力，并利用这一点来找出调节化学运动和化学趋化的细胞内信号的本质。

Chemotaxis is the process by which cells can navigate towards sources of chemoattractant. It is crucial for development, immune function and the spread of cancer cells. It is based on the ability of cells to detect chemoattractants via highly specific receptors on their surface. Remarkably, when placed near to a source of chemottractant the cell can determine the direction towards its source. It achieves this by using both the fact that the attractant becomes more concentrated nearer the source and its ability to detect tiny differences in the concentration of chemoattractant around it. The cell then migrates in the direction of increasing concentration of chemottractant. Despite its importance our understanding of how chemotaxis works is very limited. It is clear that chemotaxis is made up of many component, or sub, responses. The ability to detect the chemottractant, the ability to sense changes in its concentration across very small distances and the ability to move in response to the chemoattractant (chemokinesis), which is in turn dependent on the ability of the cells to form reversible contacts with neighbouring cells or surfaces. A full understanding of chemotaxis will only emerge from an understanding of these elemental component responses. In this project we focus on the mechanisms underpinning chemokinesis (chemoattractant stimulated movement, in our assays the chemottractants are often uniform in concentration and the resulting migration is random and not directed as in chemotaxis) as a key event in chemotaxis. We aim to understand the chemical nature (the molecules that are acting as the signals) and spatial organisation of the processes inside cells that allow them to perform these responses. Neutrophils are a specialised form of white cell found in the blood. Their primary function is to ingest and kill bacterial and fungal pathogens. Neutrophils use the process of chemotaxis to migrate out of the blood stream towards areas of inflammation and also to home-in on pathogens. Thus chemotaxis is essential for neutrophils to perform their normal healthy function fighting disease. However, many long term inflammatory diseases are known to caused by neutrophils over-reacting. Too many neutrophils accumulate at the site of disease and actually contribute to host tissue damage, which in-turn leads to further accumulation of neutrophils. Hence a major objective in treating inflammatory disease such as arthritis is to reduce neutrophil migration into sites of inflammation. At the moment we have very few drugs that are able to effectively reduce neutrophil influx to sites of chronic inflammation with unwanted side effects because we do not know which steps in chemotaxis to best target. We aim to study neutrophil chemokinesis and chemotaxis. Recently there has been huge progress in understanding the events inside neutrophils that are involved in coordinating chemotaxis. This has been possible through the development of microscopes capable of seeing inside living neutrophils as they move and the use of genetic engineering techniques to make specific proteins we want to study inside cells fluorescent and hence possible to see with special illumination and detection systems in the microscopes. However, despite these advances our views of the inside of cells during chemotaxis has thus far been very 2-dimensional, that is as if we were looking down on them from above, and could not reveal any depth (the 'sides' of the cell). By using new imaging techniques we are able to begin to take many photos and combine them to give a sense of depth. What we have seen so far entirely changes our interpretation of the 2-D images and understanding of the spatial coordination of chemotaxis. In this project we hope to use mathematics and computers to improve our ability to create and interprete 3-D images of migrating neutrophils and to use this to find out the nature of the intracellular signals that regulate chemokinesis and chemotaxis.