Neutralization of Apx toxicity as an alternative to antibiotics for control of contagious porcine pleuropneumonia.

传染性胸膜肺炎是一种严重的急性疾病，会导致许多生猪死亡，并对存活下来的猪的肺部造成终身损伤。这会影响生产系统的盈利能力。养猪场经常使用抗生素来控制这种疾病，因为可以使用的抗生素很少。在建议兽医对猪单位减少抗生素的使用之前，我们需要它们的替代品。除了改善饲养方法，如增加通风和减少牲畜的数量外，几乎没有什么可以提供的。这是一个世界性的问题，也是整个欧洲在猪身上使用处方抗生素的主要原因之一。在英国，没有有效的疫苗，因为这些疫苗不能保护猪免受疾病的侵害，或者疫苗本身有毒。生产农场疫苗（紧急疫苗）的努力未能解决这一问题，因为它们无效，而且为了避免灾难性损失，在饲料、水中和注射中使用了抗生素。该病是由胸膜肺炎放线杆菌引起的，这种细菌产生三种不同蛋白毒素中的两种（ApxI、II和III）。病原体产生这些毒素是疾病过程的关键。从疾病中恢复的猪有抗体，可以中和毒素，证据表明这对保护猪免受疾病的侵害至关重要。它需要在一种成功的疫苗中复制。然而，仅仅使用这种毒素作为疫苗并不能保护猪。尽管刺激产生抗体，但这些抗体不是毒素中和抗体。似乎这些细菌已经进化到合成具有不相关但高度免疫原性区域的毒素分子，以将免疫反应转移到毒素的错误部分，从而使抗体反应无效，从而使细菌传播和疾病继续下去。在这个项目中，我们将消除毒素中那些分散免疫反应的部分，这些部分似乎导致毒素分子在用作疫苗时无法产生中和反应。这些小片段将被连接到载体蛋白，修饰白喉毒素。这将增强免疫反应，使抗原足够大，可以被猪的免疫系统识别为疫苗抗原。我们将用这些修饰的毒素对猪进行免疫，并测量免疫反应和对活性毒素的中和作用。为了改进毒素的检测方法和中和抗体的效果，我们将建立猪皮肤水肿模型并进行试验。这将用于确定用于猪胸膜肺炎模型的最佳疫苗抗原。然后，我们将对猪进行免疫接种，并通过对猪进行毒性病原体的实验性攻击来测试疫苗接种的效果。如果这一假设是正确的，并且对毒素片段的免疫反应是有效的，这可能是生产有效的胸膜肺炎疫苗所需的步骤，并且最终有机会为养猪业提供抗生素的替代品，从而显着减少用于控制猪呼吸道疾病的这些药物的数量。

Contagious pleuropneumonia is a severe acute disease that kills many growing pigs and causes lifelong damage to the lungs of those that survive. This impacts on the profitability of the production system. Pig farms regularly use antibiotics to control this disease because there is very little that can otherwise be used.Before the advising veterinary surgeon on a pig unit can reduce the use of antibiotics, we need alternatives for them to use. Apart from improving husbandry practices such as increasing ventilation and reducing the number of animals held together, there is little that can be offered. This is a problem throughout the world and is one of the primary reasons for using prescription antibiotics in pigs throughout Europe. In the UK, there is no effective vaccine because these have failed to protect pigs from disease, or the vaccine was itself toxic. Efforts to make on-farm vaccines (emergency vaccines) have not solved the problem because they are not efficacious and antibiotics, in feed, in water and by injection, are used in an attempt to avoid catastrophic losses.The disease is caused by a bacterium, Actinobacillus pleuroneumoniae, which produces two of three different protein toxins (ApxI, II and III). Production of these toxins by the pathogen is key to the disease process. Pigs that recover from disease have antibodies which neutralize the toxins and evidence suggests this is crucial in protecting pigs from the disease. It needs to be replicated in a successful vaccine. However, simply using the toxin(s) as a vaccine does not protect pigs. Despite stimulating production of antibodies these are not toxin-neutralizing antibodies. It appears that these bacteria have evolved to synthesise toxin molecules with irrelevant but highly immunogenic regions to distract the immune response to the wrong part of the toxin so that the antibody response is ineffective allowing the bacteria to spread and the disease continue.In this project we will eliminate those parts of the toxin that are distracting the immune response and which appear to be causing failure of the toxin molecules to generate a neutralizing response when used as a vaccine. These small fragments will be joined to a carrier protein, modified diphtheria toxin. This will enhance the immune response and make the antigen large enough to be recognised by the pigs' immune system as a vaccine antigen. We will immunize pigs with these modified toxins and measure the immune response and the neutralizing effect against the active toxins. To improve the method of testing the toxins and the effect of neutralizing antibody, we will develop and test a pig model of dermal oedema. This will be used to indicate the best vaccine antigens for use in the pig model of pleuropneumonia. We will then proceed to immunize pigs and test the efficacy of the vaccination by experimental challenge of the pigs with the virulent pathogen.If this hypothesis is correct, and the immune response to the toxin fragment is effective, this could be the step needed for production of an effective vaccination against pleuropneumonia and the opportunity, finally, to offer the pig industry an alternative to antibiotics which would markedly reduce the quantity of these drugs used in controlling pig respiratory disease.