Genomic Expression Profiling In Streptococcus Suis-Infected Porcine Spleen And The Development Of A New-Style Subunit Vaccine

Streptococcus suis (S. suis) is an important pathogen that causes swine streptococcicosis and leads to pathological conditions, such as meningitis, septicemia, pneumonia, endocarditis and arthritis. Thirty-three serotypes (type 1 to 31,1/2 and 33) have been described based on capsular polysaccharides. Serotype 2 (SS2) is the most frequently isolated and the most virulent bacterial strain associated with swine streptococcicosis. In order to further understand the pathogenesis and the mechanism of the host immune response, the Affymetrix GeneChip Porcine Genome Array was applied to analyse the changes of the transcript profile after SS2 infection. Beside this, some other studies have been done on the SS2 subunit vaccine research. The principal results were described as follows:1. Transcript profiling of pigs infected with S.suis 2.In this study, a highly pathogenic strain 05ZY and the avirulent isogenic strain were used to inoculate pigs, and PBS was used as control. From the differences of the genomic expression profile of spleens between the infected pigs and the mock-infected pigs, we could futher understand the pattern of host immune responses to SS2.104 and 129 unique genes were significantly up-regulated and down-regulated in the spleens of pigs infected with SS2 (WT) compared to the mock-infected pigs. Only a few genes showed significantly differential expression when comparing avirulent isogenic strain with mock-infected samples.The up-regulated genes were principally related to immune response, such as genes involved in inflammatory response; acute-phase/immune response; cell adhesion and response to stress. The down-regulated genes were mainly involved in transcription, transport, material and energy metabolism which were representative of the reduced vital activity of SS2-influenced cells.From the data of genechip and the in vitro stimulation study we found that only TLR2 of the TLR family upregulated. The results indicated that highly pathogenic SS2 could persistently induce cytokines mainly by Toll-like receptor 2 (TLR2) pathway. The another receptor TREM-1 was also upregulated after SS2 infection. In order to understand the function of membrane anchored TREM-1 in primary immune responses after SS2 infection, agents which either activate or block TREM-1 were used in vivo before infection. The results indicated that the activation of TREM-1 one hour before SS2 infection could amplify the inflammatory responses. The amplified inflammation was beneficial for eliminating pathogens and increasing survival. On the contrary, blocking TREM-1 using a recombinant TREM-1 fusion chimera prevented the secretion of pro-inflammatory cytokines in response to SS2, and then SS2 proliferated rapidly and induced persistent high level pro-inflammatory cytokines which might lead to excessive tissue damage and sudden death. This work helps understanding the pathogenesis and the host immune response to SS2.2. Study on SS2 subunit vaccineIn this study, some immunoreactive proteins of SS2 were used to compose different subunit vaccines to evaluate the protective efficiency to SS2. The results indicated that three immunogenic SS2 surface proteins HP 1097, HP 1036 and Enolase mixed together with the oil adjuvant to immunize mice could increase the survival of mice against SS2 infection markedly. In order to futher evaluate the protective efficiency of the proteins in pigs, pigs were vaccinated twice. One week after immunization, specific antibodies to the three proteins could be detected, and two weeks later the other immunization was done. After the second immunization high antibody titers were detected constantly for a few weeks. Three weeks after the second immunization the pigs were challenged with high pathogenic SS2, the survival rate was up to 80%.