Viral-bacterial co-infections:Effect of Streptococcus suis on influenza virus infections in differentiated porcine airway epithelial cells

呼吸道合并感染在现代农业动物集约化生产系统中发挥着重要作用，特别是在猪中。控制合并感染是一项具有挑战性的任务，因为与单一感染相比，发病机制要复杂得多。虽然这已经知道了很多年，但对于共同感染中病原体和宿主之间相互作用的分子机制知之甚少。在动物感染中进行研究是非常困难的，因此，开发尽可能接近体内情况的合适的体外模型非常重要。在本项目中，我们将分析两种重要的猪呼吸道病原体：猪流感病毒（SIV）和猪链球菌（S suis）对气道上皮细胞的共同感染。这两种病原体都很重要，还因为它们能够引起人畜共患感染。本项目旨在阐明流感病毒与链球菌在猪气道上皮细胞共感染过程中的相互作用。这是一个非常集中的项目，因此，我们将只分析细菌病原体如何影响病毒感染。由于猪链球菌的荚膜多糖含有α 2,6-链唾液酸，SIV可以通过病毒表面蛋白血凝素的唾液酸结合活性与猪链球菌结合。我们将通过比较两种药物的不同菌株和变体来确定这些相互作用的变化。此外，还将分析SIV-S在哪些条件下以及在多大程度上影响SIV-S的感染。是交互。这不仅将在永生化猪气管细胞上进行研究，而且还将在两种病原体的实际靶细胞上进行研究，即分化的气道上皮细胞。后者将被培养为精确切割的肺片或气液界面培养。通过这种方式，试剂可以通过神经氨酸酶预处理来阐明分子机制，例如唾液酸的重要性。除了荚膜唾液酸外，还将分析猪链球菌的蛋白酶是否通过增强血凝素的蛋白水解活性来影响流感病毒的感染过程，而血凝素是病毒融合活性的先决条件。预期的结果将增加我们对猪链球菌如何影响猪呼吸道SIV感染的共同感染情况的理解。基于这些知识，在后续项目中有可能研究一种病原体对另一种病原体的间接影响，例如通过诱导上皮细胞或巨噬细胞等免疫细胞的细胞因子反应。

Co-infections in the respiratory tract play an important role in modern intensive production systems of agricultural animals, especially in pigs. Control of co-infections is a challenging task, since pathogenesis is much more complex as compared to mono-infections. Though this has been known for many years, little is known about the molecular mechanisms of interactions between pathogens and the host in co-Infections. It is very difficult to study this in animal infections and, therefore, it is important to develop suitable in vitro models which mimic the in vivo situation as closely as possible. In the proposed project, we will analyze the co-infection of airway epithelial cells by two important pathogens of the porcine respiratory tract: swine influenza viruses (SIV) and Streptococcus suis (S suis). Both agents are important also because of their ability to induce zoonotic infections. Aim of the project is to elucidate the interactions between influenza viruses and streptococci during co-infections of porcine airway epithelial cells. This a very focussed project, and thus, we will analyze only how the bacterial pathogen affects the virus infection. As the capsular polysaccharide of S. suis contains alpha2,6-linked sialic acid, SIV can bind to S. suis via the sialic acid-binding activity of the viral surface protein, haemagglutinin. We will determine the variations in these interactions by comparing different strains and variants of the two agents. Furthermore, it will be analyzed under which conditions and to what extent, the SIV-infection is affected by the SIV-S. suis interaction. This will be investigated not only with immortalized porcine tracheal cells but also with the actual target cells of the two pathogens, i.e. with differentiated airway epithelial cells. The latter will be cultivated as precision-cut lung slices or as air-liquid-interface cultures. In this way, the cells are accessible for reagents to elucidate molecular mechanisms such as the importance of sialic acid by pretreatment with neuraminidase. Apart from the capsular sialic acid, it will also be analyzed whether proteases of S. suis affect the course of the influenza virus infection by enhancing the proteolytic activation of the haemagglutinin which is a prerequisite of the viral fusion activity. The expected results will increase our understanding how S. suis affects in a co-infection scenario the SIV infection in the porcine respiratory tract. Based on this knowledge it will be possible to investigate in a follow-up project the indirect effects of one pathogen on the other, e.g. by inducing cytokine reactions in epithelial cells or immune cells like macrophages.