Study On The Function Of Streptococcus Suis Serotype 2 IgG Binding Protein

Streptococcus suis(S.suis)is an important swine pathogen that causes a number of pathological conditions,such as fever,meningitis,endocarditis,arthritis,pneumonia, septicemia,neurosis symptom and so on.There are currently 33 serotypes of Streptococcus suis,among which serotype 2 is the most popular and pathogenic.At present,there are more study on SS2,but the mechanism on surviving,reproduce and infection in vivo is poorly understand.S.suis IgG-binding protein(SSPG) was present in all S.suis strains examined.It showed binding activities with IgG from various host species.Little was known about the biological role of this protein,but it was commonly believed that it acted as a virulence factor.Thus the topic purpose of our study is clarifying the relationship between SSPG and the pathogenicity of S.suis by different means.Prokaryotic expression of recombinant SSPG and the study on its immunity characteristicThe interaction between SSPG and immune system in the host may lead to the S.suis infection.Getting purified SSPG and clarifying its immunity characteristic can help explaining the pathogenesis and invasiveness of SS2.In this study,the genes encoding SSPG were amplified respectively from the total DNA of the S.suis serotype 1/2,1,2 and 9 with PCR and expressed in E.coli BL-21 by plasmid pET-28a as vector.The recombinant proteins were first purified with affinity chromatography(Ni-NTA),and further purified by sephadexG-200 gel chromatography. The recombinant SPG proteins were identified to have binding activities with IgG of different host species,and for human and porcine IgG they showed better binding activities.But the SSPG from different serotypes of S.suis showed no great differences in their binding activties with IgG from the same host species.To investigate whether SSPG can influence the immune system as other IgG binding proteins,we stimulated the mouse immunized spleen cells with the SSPG,and analyzed the transcripts of various genes relevant to proinflammatory cytokines by real-time RT-PCR.Mice were also immunized with SSPG,SSPG and SLY mixture,and SSPG with MRP mixture.The results showed that SSPG was not superantigen.Although SSPG surely induced a high antibody lever in vaccinated group,it can not provide immunoprotection,even may play a negative role in the immunity protection. Construction and characterization of SSPG gene knock-out mutant of Streptococcus suis serotype 2It was proved that most IgG binding protein played an important role in the pathogenesis and invasiveness,such as Staphylococcus Protein A.The pathogenic mechanism always related with immune escape.We constrcted SSPG gene knock-out mutant of Streptococcus suis serotype 2 to clarify the relationship.Based on the principle of homologous recombination,we construct gene knock-out mutant of SSPG gene in Streptococcus suis serotype 2(SS2) virulent strain SC-19.PCR analysis confirmed that the coding gene of SSPG was knocked out completely.Analysis of biological characteristics showed that there were no differences in mycelial morphology,hemolytic activity and dyeing properties between the mutant and SC-19,but the wild strain grewed better in their decline phase and had a better cell wall.Virulence assays with murine model confirmed that the mutant is avirulent.However,the deletion of SSPG gene in SS2 may influence its field planting.