Campylobacter phase variation and its impact on immunity and vaccine development.

弯曲杆菌是英国细菌性食物中毒最常见的原因。人类最常见的感染源之一来自食用未煮熟的家禽或在食物制备过程中被未煮熟的肉类交叉污染。主要的问题是弯曲杆菌可以很容易地在家禽体内大量繁殖而不会引起疾病，而人类摄入少量细菌会导致严重的胃肠炎。这些感染可能导致并发症，因为细菌与人体免疫系统相互作用，导致肠易激综合征和格林-巴利综合征，这是对患者神经的影响，导致瘫痪。控制家禽中的弯曲杆菌预计将显著减少人类感染病例。实现这一目标的途径之一是接种疫苗。疫苗诱导针对细菌特定表面成分的抗体。这些抗体与细菌细胞结合，干扰这些细胞在细菌宿主中定植的能力。弯曲杆菌的疫苗是可用的，但在防止细菌在鸡体内定植方面具有不同的功效。这种方法存在问题的一个原因是，弯曲杆菌自然诱导产生针对其表面成分的抗体，但这些抗体不能阻止细菌的定植或从鸟类中清除细菌。鉴于产生了一系列抗体反应，令人惊讶的是，这些适应性免疫反应并没有清除细菌。这表明细菌必须有一种避免抗体介导控制的方法。我们相信弯曲杆菌可以通过“关闭”关键表面分子的表达来避开抗体，这样它们就不会被鸡的抗体识别。这些开关可以在称为相位变化的过程中以高频率发生，这在细菌物种中广泛存在，并且通常与表面成分相关。在弯曲杆菌中，相位变化由细菌DNA中的重复序列介导，其在细菌复制期间经历高于正常频率的突变，并导致基因被“打开”或“关闭”。如果抗体作用于这些时相可变基因之一的产物，则这通过时相变化产生对组分变化的选择，从而促进弯曲杆菌在鸟类中的持续存在。这个过程是可逆的，允许细菌在抗体消失时恢复基因的功能。关于弯曲杆菌感染鸡时这一过程是如何工作的，只有有限的数据。该项目将确定这些开关的频率以及抗体的产生如何影响免疫系统对相位变体的选择。具体而言，我们将调查是否相位变化涉及在自然感染和接种疫苗后避免抗体。我们将评估一些新的候选疫苗，我们有证据表明，相位变化可能会干扰诱导抗体的有效性，并将修改一些基因，使它们不能关闭。这些数据不仅对了解这种病原体如何在家禽中生存非常重要，而且对了解这种病原体在人类中的生存也非常重要，因为人类的表面成分在疾病中起着重要作用。该项目产生的数据将有助于开发有效的疫苗，以保护动物和人类免受这种细菌的感染。

Campylobacter is the commonest cause of bacterial food poisoning in the UK. One of the most frequent sources of infection for humans comes from eating undercooked poultry or cross contamination by uncooked meat during food preparation. The main problem is that Campylobacter can readily colonise poultry to very high levels without causing disease while ingestion of small amounts of bacteria by humans leads to severe gastroenteritis. These infections can result in complications as the bacterium interacts with the human immune system to cause irritable bowl syndrome and Guillain-Barré syndrome, which is an effect on the nerves of patients causing paralysis. Control of Campylobacter in poultry is predicted to significantly reduce human cases of infection. One route to achieve this is by vaccination. Vaccines induce antibodies to specific surface components of bacteria. These antibodies bind to the bacteria cells and interfere with the ability of these cells to colonise the bacterial hosts. Vaccines for Campylobacter are available but have a variable efficacy in preventing the bacterium from colonising chickens. One reason this approach is a problem is because Campylobacter naturally induces the production of antibodies against its surface components but these antibodies do not prevent colonisation or clear the bacteria from birds. Given that a range of antibody responses are generated, it is surprising that these adaptive immune responses do not clear the bacteria. This suggests that the bacteria must have a way of avoiding antibody-mediated control. We believe that Campylobacter can avoid antibodies by switching 'off' the expression of key surface molecules so that they are not recognised by the chicken's antibodies. These switches can occur at high frequencies in a process known as phase variation, which is widespread in bacterial species and is usually associated with surface components. In Campylobacter, phase variation is mediated by repeat sequences in the DNA of the bacteria which undergo a higher than normal frequency of mutation during replication of the bacteria and result in genes being switched 'on' or 'off'. If an antibody acts against the product of one of these phase variable genes, this generates selection for a change in the component by phase variation facilitating persistence of the Campylobacter in the birds. This process is reversible allowing the bacteria to recover the function of the gene when the antibodies dissipate. There is only a limited amount of data on how this process works when Campylobacter infects chickens. This project will identify the frequency of these switches and how the production of antibody impacts on selection of phase variants by the immune system. Specifically, we will investigate whether phase variation is involved in avoidance of antibodies during natural infections and following vaccination. We will assess some novel vaccine candidates for which we have evidence that phase variation may interfere with the effectiveness of induced antibodies and will modify some genes so they cannot switch 'off'. This data will not only be important in understanding how this pathogen survives in poultry but also in humans where the surface components play a major role in disease. The data generated in this project will aid in the development of effective vaccines to protect both animals and man against infections by this bacterium.