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

呼吸道共感染在现代集约化农业动物生产系统中起着重要作用，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，但对病原体和宿主在共同感染中相互作用的分子机制知之甚少。在动物感染中研究这一点非常困难，因此，重要的是开发尽可能接近地模拟体内情况的合适的体外模型。在本研究计画中，我们将分析猪呼吸道的两种重要病原体猪流感病毒（SIV）和猪链球菌（S suis）对呼吸道上皮细胞的共感染。这两种药物都很重要，因为它们能够诱导人畜共患感染。本研究的目的是探讨流感病毒与链球菌在猪呼吸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。作为S.猪链球菌含有α 2，6-连接的唾液酸，SIV可与S.猪通过病毒表面蛋白血凝素的唾液酸结合活性。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感染在何种条件下以及在何种程度上受到SIV-S的影响。suis互动。这将不仅用永生化猪气管细胞进行研究，而且用两种病原体的实际靶细胞，即用分化的气道上皮细胞进行研究。后者将作为精确切割的肺切片或作为气液界面培养物进行培养。以这种方式，细胞可用于试剂以阐明分子机制，例如通过用神经氨酸酶预处理唾液酸的重要性。除了荚膜唾液酸外，还将分析S. SUI通过增强血凝素的蛋白水解活化来影响流感病毒感染的过程，这是病毒融合活性的先决条件。预期的结果将增加我们对S。在合并感染的情况下，suis影响猪呼吸道中的SIV感染。基于这一知识，将有可能在后续项目中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免疫细胞（如巨噬细胞）中的细胞因子反应。

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.