| Streptococcus suis (S. suis) is an important swine pathogen which causes an economical problem in the swine industry. The manifestations of S. suis infection in swine are meningitis, arthritis, endocarditis and septicemia. Thirty-three serotypes (types1-31,33and1/2) have been described on the basis of the capsular polysaccharides, and S. suis serotype2(SS2) is most commonly associated with diseases in pigs in worldwide. Moreover, it's also the causative agent of serious infections in humans. From the first infection case reported in Demark, more than700infection cases were reported at least20countries all over the world. Although S. suis infection has attracted great attention from the scientific community and the popular press, our current understanding of the S. suis pathogenesis remains limited. The attachment of bacteria to host cells and tissues and their subsequent invasion and spreading are key processes during pathogenesis. Interactions between the bacteria and host cells are responsible for these processes. In this study, we try to provide the theoretical basis to explain the pathogenesis of S. suis by identifying the surface protein-protein interactions between the S. suis and host cells. In the other hand, the surface proteins of pathogenic bacteria which could interact with the host cells play important roles in the pathogenesis of bacteria. Therefore, in the present study, we also want to identify more surface interacting proteins (SIPs) of S. suis by an interactomics method. And the identified proteins could be applied as the candidate proteins to further indentify their pathogenic functions in infection processes. Based on the results, we would screen the SIPs to develop the novel vaccine. And it would be benefit to infection control. The principal results were described as follows:1. The interactions between the protective antigen HP0197and host cellsIn previous works, the protective antigen HP0197had been identified as a virulence-involved protein. However, the biological functions of HP0197remain unknown, and its roles in infection processes need to be further identified. In the present study, we try to indentify the interactions between the HP0197and host cells. And it would help us to define the biological functions of HP0197. First, we confirmed that HP0197could adhere to the surface of Hep-2cells by indirect immunofluorescence assays. The further studies indicate that the interactions between HP0197and Hep-2cells could be inhibited completely by heparin and trypsin. Therefore, it suggests that the heparin-like saccharide would be the receptor of HP0197on the host cells. In addition, the interaction between HP0197and glucose was also confirmed, suggesting that HP0197may involve in the carbon metabolism of S. suis. To proof the supposition, we compare the activity of HPr in Ahp0197strain and parent strain. The results indicate that the phosphorylation of HPr was changed when the hp0197gene was deleted, and it would further affect the biological activity of CcpA.2. Identification of the interactions between the surface proteins of S. suis and the surface molecules of host cellsProtein-protein interactions between bacteria and their hosts are responsible for all types of infection processes. The investigation of the bacteria-host crosstalk can provide a comprehensive understanding of the pathogenesis of bacterial disease. Despite scattered efforts in this field, a systematic identification of interactions between host and bacterial proteins remains unavailable. Here, we develop ACSP (Affinity Chromatography-based Surface Proteomics), which combines affinity chromatography and shotgun proteomics (LC-MS/MS), to investigate the interactions on a large-scale. Using ACSP, the potential surface interacting proteins (SIPs) of SS2were captured by the chromatographic resin which was immobilized with the native surface molecules of Hep-2cells. And then40potential SIPs were identified from the preys by LC-MS/MS, including3SIPs that have been previously reported in the literature. We selected8important SIPs and confirmed their ability to adhere to Hep-2cells. Additionally,3newly identified SIPs, or their polyclonal antibodies, were found to significantly inhibit the adherence of SS2to Hep-2cells, indicating their essential role in the interaction between SS2and Hep-2cells. Using this example, we show that ACSP represents a new valuable tool for investigating the bacteria-host interactions.3. Evaluation of the protective efficacy of a novelly identified immunogenic protein, HP0272, of Streptococcus suisSS2infection is a major cause of sudden death in pigs and is of concern for humans as it has strong zoonotic capabilities. Developing novel effective vaccines would be beneficial to control SS2infection. HP0272is a novel immunogenic surface protein; its protective efficacy remains to be evaluated. The present mouse model found that the purified recombinant HP0272could elicit a significant humoral antibody response, and to confer complete protection against a lethal dose of SS2infection. In addition, real-time PCR confirmed that in vivo-induced antigen existed in most SS2field pathogenic strains, and in half of all reference strains of different serotypes of S. suis. The results indicate that HP0272has the potential as an effective component of a new vaccine.
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