Murine Peritoneal Macrophages Transcriptional Responses Following In Vivo Infection With Streptococcus Suis Type 2

Streptococcus suis type 2 (SS2), a Gram-positive encapsulated coccus, is considered to be an important pathogen of infection in swine, which not only causes septicemia but also affects the central nervous system (CNS) and other tissues, leading to meningitis, endocarditis, pneumonia and arthritis. SS2 does not only cause disease in pigs, but also affects human. In human, the entrance is mainly through skin injuries. The pathogenesis of S. suis infection is poorly elucidated. Animal models are essential to obtain a better understanding for pathogenesis of S. suis. Mice had been used as experimental model for evaluation of virulence of S. suis. Recently, it has been demonstrated that A/J mice were significantly more susceptible to SS2 infection than B6 mice, especially during the acute septic phase of infection. In order to elucidate the genetic basis of differ in susceptibility to SS2 infection, the following researches were took.Illumina mouse GeneChips were used to identify alterations in gene expression of mice injected with SS2. Gene expression analysis with microarrays revealed 3,689 (the differentially expressed genes between control A/J and B6 mice have been eliminated, which were thought to be inherent differentially expressed genes between A/J and B6 mice) genes to be differentially expressed in peritoneal macrophages between SS2 infected A/J and B6 mice.2646 genes were identified to be differentially expressed between SS2 infected and control A/J mice, of which 1469 genes were upregulated and 1177 genes were downregulated.1449 genes were identified to be differentially expressed between SS2 infected and control B6 mice, of which 778 genes were upregulated and 671 genes were downregulated. The reliability of the data obtained from the microarrays was verified by performing quantitative real-time PCR on 20 representative genes. Fold changes of expression of 4 genes (Tlr2, Tnf, Mmp9 and Ptx3) were different between A/J and B6 mice after infected with SS2, which have previously been implicated in the response to S. suis infection. The data produce a set of candidate genes that may influence susceptibility to SS2 infection in the A/J and B6 mouse model. That may provide further validation of this model, which will contribute to understanding of S. suis pathogenic mechanisms.In order to study the function and characteristics of differentially expressed genes, Gene Ontology category, KEGG pathway, Path-net and Signal-net were analyzed for these genes. The results showed that upregulated genes of A/J and B6 mice were involved in immune response, positive regulation of B cell receptor signaling pathway, type I interferon biosynthetic process, defense response and inflammatory response. Downregulated genes of B6 mice played roles in glycolysis, carbohydrate metabolic process, amino acids metabolism, behavior and muscle. Otherwise, upregulated genes of B6 mice after infected with SS2 were also involved in antigen processing and presentation of exogenous peptide antigen, peptide antigen stabilization, regulation of lymphocyte differentiation, positive regulation of monocyte differentiation, antigen receptor-mediated signaling pathway and positive regulation of phagocytosis. These results facilitated the analysis about function of differential genes and genetic basis of susceptibility to SS2 infection.In order to determine the phagocytosis of SS2 by Ana-1 macrophages, expression level of relative genes on Ana-1 cells were analyzed by using RT-PCR. The results showed that the capability of phagocytosis of Ana-1 cells was low and expression of Tlr2, Tnf and Mmp9 were all upregulated. These results demonstrated Tlr2,Tnf and Mmp9 involved in the process of interaction between SS2 and Ana-1 cells.