Porcine brain microvascular endothelial cell-derived interleukin-8 is first induced and then degraded by Streptococcus suis.

Streptococcus suis is a major pathogen of swine, causing mainly meningitis, and it also represents an emerging zoonotic agent. We investigated its ability to induce the release of pro-inflammatory cytokines and chemokines by porcine brain microvascular endothelial cells (PBMEC). We demonstrated that live S. suis induced a strong release of interleukin (IL)-6 and IL-8 by PBMEC. We showed that the suilysin (hemolysin) was largely responsible for such stimulation, although cell wall components also contribute to cell stimulation but to a considerably lower extent. Interestingly, IL-8 production by PBMEC became undetectable by increasing either the incubation time or bacterial concentration of certain live S. suis strains. We further demonstrated that this decrease of IL-8 levels was probably linked to the production of a serine protease by S. suis. Our results suggest that S. suis can induce an exacerbated release of inflammatory mediators by swine endothelial cells that could cause a massive recruitment of leukocytes and subsequent blood-brain barrier breakdown facilitating the pathogenesis of S. suis-induced meningitis. In addition, S. suis could modulate this response by degrading IL-8 which might delay recruitment of S. suis killer-neutrophils to the site of inflammation, allowing this pathogen to survive upon its arrival to central nervous system.