Studies On The Role Of Porcine Dendritic Cells In The Inflammation Storm Caused By Streptococcus Suis Serotype 2 Infection

Streptococcus suis infection is a zoonosis caused by Streptococcus suis. It has a serious harm to the swine industry in many countries of the world. There are 35 serotypes of Streptococcus suis. The virulence of Streptocuccus suis serotype 2 is the strongest.There are two massive outbreaks of Streptococcus suis serotype 2 in our country, one happened in Province of Jiangsu in 1998, another in Province of Sichuan in 2005, in which a large number of pigs and dozens of people died.Streptococcus suis serotype 2 infection caused meningitis, arthritis, pneumonia, and death. Most of research are focused on the pathogenesis of meningitis, it is not clear about the mechanism of inflammation storm caused by Streptococcus suis serotype 2 infection.Dendritic cells(DCs) are the most powerful antigen-presenting cells(APCs). Different cytokine profiles producted by DCs in response to different antigens. These cytokines can regulate inflammation, and direct the differentiation of CD4+T cells. So DCs have an important role in the innate immune response and specific immune response. However,little is know about whether porcine DCs play roles in the inflammation storm.In order to figure out the role of porcine dendritic cells play in the inflammation storm caused by Streptococcus suis serotype 2 infection, this study started with the establish the invitro culture method of porcine peripheral blood monocyte-derived dendritic cells(Mo DCs). Based on features of DCs, target cells were studied about the morphology and phenotype, phagocytic ability, the proliferation of T cells, which results demonstrated that high pure Mo DCs were obtained. After Mo DCs were stimulated by Streptococcus suis serotype 2 strain SC19, cytokines species production of Mo DCs were detected, especially pro-inflammatory cytokines and IL-12. The differentiation of CD4+T cells was also researched, so we can clarify the role of porcine dendritic cells in the inflammation storm caused by Streptococcus suis serotype 2 infection. Main research subject and results are as following:(1) The method of porcine peripheral blood monocyte-derived dendritic cells cultured in vitro was set up. Mononuclear cells from porcine peripheral blood wereobtained by Ficoll-Hypaque density gradient centrifugation, and then CD14+monocytes were isolated by MACS. CD14+monocytes were cultured in RPMI-1640 medium with porcine GM-CSF and IL-4. After 3-5 days, we combined with the morphology and phenotype, phagocytic ability, the proliferation of T cells. The results showed that we obtained a large number and high pure Mo DCs.(2) After Mo DCs stimulated by SC19, the analysis of phenotype showed that the expression of CD1 and CD172 a molecules were decreased, the phagocytic ability was reduced, the ability to stimulate the proliferation of T cells was enhanced. These results suggested that SC19 can accelerate the maturation of Mo DCs, and Mo DCs can mature without any stimulation. After Mo DCs stimulated by SC19, Mo DCs secreted high level of pro-inflammatory cytokines(IL-1β、IL-8、TNF-α、IFN-γ), especially IL-12. IL-8 was dose-dependent. The high level of IL-12 suggested that Mo DCs may induce Th1-type immune response after stimulated by SC19.(3) To confirm that Mo DCs induced Th1-type immune response, Mo DCs were mixed with CD4+T cells, then stimulated by SC19. After 17 hours, the differentiation of Th cells was analyzed by flow cytometry. The result showed that the proportion of Th1 cells was increased. The cytokine quantification about the culture supernatant of mixed cells showed that IFN-γ was increased. These results indicated that Mo DCs stimulated by SC19 induced Th1-type immune response.Our results suggested that by secreting high level of pro-inflammatory cytokines including IL-12, and IL-12 induced Th1 cells and cytokines produced by Th1 cells,porcine Mo DCs play an important role in the inflammation storm caused by Streptococcus suis serotype 2 infection.