The Research On Underlying Mechasiam Of Th17 Immune Response Elicited By Streptococcus Pneumoniae Live Attenuated Vaccine SPY1

Streptococcus pneumoniae is one of the major causes of pneumonia, meningitis, otitis media and sepsis. The damage of Streptococcus pneumoniae to children and elderly is especially dominant. Vaccination is an effective strategy to combat against Streptococcus pneumoniae invasion. We previously reported that SPY1, an attenuated vaccine strain of Streptococcus pneumoniae, which can significantly reduce pneumococcal colonization and protect from Streptococcus pneumoniae infection in mice. Further investigation revealed that Th17 (IL-17A) response plays a central role in SPY1 induced protective immunization. However, the underlying mechanisms that SPY1 elicited Th17 (IL-17A) immune response remain undefined.Antigen-presentation cells such as dendritic cells (DCs) and macrophage play a critical role in innate and adaptive immune responses. In this study, we first cultured bone marrow derived macrophage and dendritic cells from mice, and investigated macrophage response by RT-PCR and ELISA. TLR2 and TLR4 mutant mice were adopted to determine its role in macrophage response induced by SPY1. MAPK, PI3K and NF-kB activation were measured by Western Blot and which was further evidenced by associated inhibitor. Treatment of macrophages with SPY1 caused up-regulation of inflammatory cytokines (like TNF-a and IL-6), which was not mediated by TLR2 or TLR4. Additionally, SPY1-induced macrophage activation was shown to result in MAPK, PI3K and NF-κB activation and drastically abrogated by relevant inhibitor.Next, mice bone marrow derived dendritic cells were infected with SPY1 and co-cultured with homologous CD4+T cells. Our results showed that SPY1 could up-regulate expression of pro-inflammatory cytokines (TNF-a, IL-6, IL-12p40, IL-12p70 and IL-23) and promote DCs maturation with up-regulated expression of co-stimulatory molecules (CD40, CD86 and MHCⅡ). In comparison with its wild strain counterpart D39, SPY1 could efficiently enhance DCs activation and maturation. Moreover, we found SPY1 has much stronger capability to activate MAPK and NF-kB signaling pathways. Further, SPY1 treated DCs could promote Th17 response, and the mice received SPY1-conditioned DCs induce robust Th17 (IL-17A) response.Taken together, our results suggest that SPY1 induced strong innate immune response in macrophage, which through MAPK, PI3K and NF-κB signal pathway, but not depend on TLR2 or TLR4. In experiments of SPY1 interact with DCs, our data demonstrate that Streptococcus pneumoniae attenuated vaccine strain SPY1 promotes Th17 immune response via enhancing DCs activation and maturation. Our studies also support the potential of SPY1 as a novel attenuated pneumococcus whole cell strain, as SPY1-activated dendritic cells could get fully maturation phenotype, initiate an adaptive immune response, and orchestrate Thl and Th17 responses.