In VitroCharacterization of the Microglial Inflammatory Response toStreptococcus suis, an Important Emerging Zoonotic Agent of Meningitis

Abstract

Streptococcus suis is an important swine and human pathogen responsible for septicemia and meningitis. In vivo research in mice suggested that in the brain, microglia might be involved in activating the inflammatory response against S. suis. The aim of this study was to better understand the interactions between S. suis and microglia. Murine microglial cells were infected with a virulent wild-type strain of S. suis. Two isogenic mutants deficient at either capsular polysaccharide (CPS) or hemolysin production were also included. CPS contributed to S. suis resistance to phagocytosis and regulated the inflammatory response by hiding proinflammatory components from the bacterial cell wall, while the absence of hemolysin, a potential cytotoxic factor, did not have a major impact on S. suis interactions with microglia. Wild-type S. suis induced enhanced expression of Toll-like receptor 2 by microglial cells, as well as phophotyrosine, protein kinase C, and different mitogen-activated protein kinase signaling events. However, cells infected with the CPS-deficient mutant showed overall stronger and more sustained phosphorylation profiles. CPS also modulated inducible nitric oxide synthase expression and further nitric oxide production from S. suis-infected microglia. Finally, S. suis-induced NF-B translocation was faster for cells stimulated with the CPS-deficient mutant, suggesting that bacterial cell wall components are potent inducers of NF-B. These results contribute to increase the knowledge of mechanisms underlying S. suis inflammation in the brain and will be useful in designing more efficient anti-inflammatory strategies for meningitis.

Streptococcus suis Capsular Polysaccharide Inhibits Phagocytosis through Destabilization of Lipid Microdomains and Prevents Lactosylceramide-Dependent Recognition

“…To study this objective, we used a CPS Ϫ mutant of S. suis and compared it with its WT encapsulated strain. In previous studies, using quantitative techniques combined with confocal and electron microscopy, we demonstrated that wellencapsulated S. suis is poorly phagocytosed by macrophages, whereas nonencapsulated strains are rapidly ingested and killed by most phagocytes, including J774 macrophages (5,14,27,28,35). First, S. suis was allowed to interact with cells for either 30 min or 1 h, and then lipid microdomains were labeled with cholera toxin.…”

“…Among them, type 2 CPS plays a key role by protecting the pathogen against phagocytosis and by preventing bacterial surface antigen recognition by immune cell receptors (2,14,20,37,41). Surface polysaccharides can also display similarities to host antigens and are often poorly immunogenic (26,39).…”

“…The S. suis type 2 wild-type (WT) virulent strain 31533, isolated from a case of porcine meningitis, and its isogenic nonencapsulated mutant B218 (capsular polysaccharide deficient [CPS Ϫ ]) were used. These strains have largely been used in previous studies of our laboratory (14,27,28). Strains were grown as described previously (14) in Todd-Hewitt broth (THB; Becton Dickinson, MD) or on sheep blood agar plates at 37°C.…”

“…These strains have largely been used in previous studies of our laboratory (14,27,28). Strains were grown as described previously (14) in Todd-Hewitt broth (THB; Becton Dickinson, MD) or on sheep blood agar plates at 37°C. To perform S. suis macrophage interaction studies, isolated colonies were cultured in THB, followed by 8 h of incubation at 37°C with shaking.…”

The Streptococcus suis transcriptional landscape reveals adaptation mechanisms in pig blood and cerebrospinal fluid

“…Studies on meningitis-associated bacteria have shown that a fatal disease outcome can be caused by the host inflammatory response (Dominguez-Punaro et al 2007). Dominguez-Punaro et al (2010) showed that after being stimulated by an SS CPS-deficient mutant, the microglia induced significantly higher levels of proinflammatory mediators than that of the wild-type strain. Here, our results suggest that SS increases CPS as a protective mechanism against phagocytosis and killing in blood and reduces expression of CPS in CSF to expose the cell wall components, thereby facilitating a higher inflammatory response in the brain.…”