Research on the role of capsular sialic acid in Streptococcus suis activate macrophage TLR2-AKT-NF-κB signaling pathway

Abstract:

[Objective] To explore the mechanism of signaling pathways Streptococcus suis serotype 2 infected monocytes/macrophages leaded, discuss the role of capsular sialic acid component played in Streptococcus suis activate macrophage TLR2-AKT-NF-κB signaling pathway. [Methods] RAW264.7 as the target cell line, RT-PCR, Western blotting, immunofluorescence and ELISA were applied to detect different infection time of wild type strain, sialic acid knockout strain and sialic acid complementary strain on macrophages TLR2 mRNA transcription level, AKT phosphorylation level, NF-κB activation level, as well as TNF-α secretion level. Pretreat with TLR2 blocking agent and PI-3K inhibitor on macrophages, detect the expression level above. [Results] Sialic acid knockout strain activates signal transduction pathways selectively. RT-PCR results show that TLR2 mRNA expression levels began to increase at 1 h, 1.5 h reached its peak then slowly decline. Western blotting showed that TLR2 protein expression level reached its peak at 7 h, 9 h decline. Level of p-AKT is stable at its peak during 1.5?5 h, 7 h decline. Immuno fluorescence showed high level of NF-κB activation-nuclear translocation at 15 min. ELISA results indicate TNF-α secretion level was significantly higher than the other two strains after 10 h. TLR2 blocking agent and PI-3K inhibitor significantly suppressed the activation degree of three strains. [Conclusion] Capsular sialic acid could inhibit activation of the TLR2-AKT-NF-κB signaling pathway to some extent, thus participate in bacteria evading the host immune defense.