Streptococcus suis infection: An emerging/reemerging challenge of bacterial infectious diseases?

Feng, Youjun; Zhang, Huimin; Wu, Zuowei; Wang, Shihua; Cao, Min; Hu, Dan; Wang, Changjun

Nearly ten years ago, Gottschalk et al. 161 had observed that cell wall components of S. suis can induce releases of interleukin-1 (IL-1), IL-8, monocyte chemotactic protein-1 (MCP-1) in human brain microvascular endothelial cells (BMEC), which might increase the permeability of the blood-brain barrier. Using the experimental model of CD1 mice, the same group observed that (1) ~20% animals with sudden death exhibit high levels of systemic TNF-α, IL-6, IL-12, IFN-γ, CCL2, CXCL1, and CCL5 24 h after infection; (2) infected mice that survived the early sepsis later developed clinical signs of meningitis present in the transcriptional activation of TLR2, TLR3, CD14, NFκB, IL-1β, CCL2, and TNF-α, mainly in myeloid cells located in affected cerebral structures. 162 Apparently, the inflammatory response plays important roles in S. suis infection of CD1 mice. Similar observation was also reported by Scherk et al. 163 that S. suis infections are correlated with the release of pro-inflammatory cytokines and chemokines (e.g., IL6 and IL8). Gottschalk et al. found that the toll-like receptor 2 (TLR-2)-deficient exhibit significantly reduced production of astrocytes, 164 and proposed that bacterial polysaccharides probably modulates TLR2-dependent recognition of S. suis entry/invasiveness into CD1 mice. 165 Using a transcriptomic approach, de Greeff et al. 166 identified macrophage-specific genes (IL-1-β, MIP-2-α, and TNF-α) with significantly different expression upon S. suis infection, suggesting that MAP-kinase signaling pathway and NFκB signaling are implicated into response of porcine alveolar macrophages to S. suis infections. Additionally, Wu et al. 167 verified that a novel murine ribonuclease, angiogenin inhibitor 1 (AI1) can bind to S. suis hyaluronidase (Hyl), and hypothesized that this interaction between host AI1 partner and bacterial Hyl protein might contribute to S. suis meningitis.