Study On Virulence Factor Of Streptococcus Suis Traversing The Blood Brain Barrier

Streptococcus suis （S.suis） infection is an important emerging disease with high mortalityand morbility. The most important clinical feature associated with S.suis infection in humansis meningitis. At present, the molecular mechanisms of meningitis, especially howStreptococcus suis traverses the blood brain barrier （BBB） into centre nervous system remainunclear.Brain microvascular endothelial cells are the main component of BBB. This researchaimed at to explore how S.suis traverse across the BBB and determine the virulence factoraffected to across the BBB.This paper successfully constructed the model of the human blood brain barrier in vitroby using Millicell Transwell and hCMEC/D3cells and evaluated it.The change of the cellsurface and the adhesion position of the bacterium on hCMEC/D3cells are observated byscaning electron microscopy （SEM） after the interacting between streptococcus suis and thehuman brain microvascular endothelial cells. The bacteria mostly congregating in theintercellular place and the split of intercellular are observed under the SEM. The variation ofthe brain microvascular endothelial tight junction is observated by Transmission electronmicroscopy （TEM） and the intercellular space is found to be increasing causing to thebacteria traversing across the increased space. The interaction of streptococcus suis and thehuman brain microvascular endothelial are analyzed by immunofluorescence and western blot.And the expression of VE-cadherin、ZO-1、Claudin-5in hCMEC/D3are found to bedown-regulated by streptococcus suis.In order to blot virulence factors of affecting streptococcus suis on traversing blood brainbarrier, penetration rate, transendothelial electrical resistance （TEER）, permeability testresults show that SSU05₀272influence streptococcus suis on traversing blood brain barrier.The recombinant protein of SSU05₀272is purified by nickel affinity chromatographyand HiTrap Q HP chromatography sequently. The recombinant protein is up to90%purifiedby SDS-PAGE detection. The expression of β-catenin、Claudin-5、IL-12P40in the humanbrain microvascular endothelial cell of hCMEC/D3are down regulated, whereas theexpression of IL-6、IL-8、TNF-α、IL-1β are up regulated through real time PCR detection. The contents of β-catenin、claudin-5in hCMEC/D3are decreasing due to the down regulatedthrough SSU05₀272by immunofluorescence and western blot detection. And the regulationof SSU05₀272protein is inhibited by addition the inhibitor of TGF-β.In conclusion, Streptococcus suis may paracellularly traverse the blood brain barrier bydestructing tight junction. SSU05₀272affects the ability of streptococcus suis traversing theblood brain barrier, and this process may be through the TGF-β signaling pathways.