title: The SspA subtilisin-like protease of Streptococcus suis triggers a pro-inflammatory response in macrophages through a non-proteolytic mechanism.
abstract: BACKGROUND
  Streptococcus suis is a major swine pathogen worldwide that causes meningitis, septicemia, arthritis, and endocarditis. Using animal models, a surface-associated subtilisin-like protease (SspA) has recently been shown to be an important virulence factor for S. suis. In this study, we hypothesized that the S. suis SspA subtilisin-like protease may modulate cytokine secretion by macrophages thus contributing to the pathogenic process of meningitis.
  
  
  RESULTS
  Phorbol 12-myristate 13-acetate-differentiated U937 macrophages were stimulated with recombinant SspA prior to monitor cytokine secretion by ELISA. Our results indicated that the recombinant SspA was able to dose-dependently induce IL-1β, IL-6, TNF-α, CXCL8 and CCL5 secretion in macrophages. The heat-inactivated protease was still able to induce cytokine secretion suggesting a non-proteolytic mechanism of macrophage activation. Using specific kinase inhibitors, evidence were bought that cytokine secretion by macrophages stimulated with the recombinant SspA involves the mitogen-activated protein kinase signal transduction pathway. While stimulation of macrophages with low concentrations of recombinant SspA was associated to secretion of high amounts of CCL5, the use of recombinant SspA at a high concentration resulted in low amounts of CCL5 detected in the conditioned medium. This was found to be associated with a proteolytic degradation of CCL5 by SspA. The ability of SspA to induce cytokine secretion in macrophages was confirmed using a mutant of S. suis deficient in SspA expression.
  
  
  CONCLUSIONS
  In conclusion, this study identified a new mechanism by which the S. suis SspA may promote central nervous system inflammation associated with meningitis.
authors.affiliation: Groupe de Recherche en Écologie Buccale, Faculté de médecine dentaire, Université Laval, Quebec City, Quebec, Canada.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Bonifait
authors.forename: Daniel
authors.initials: D
authors.lastname: Grenier
mesh_terms: D001426:Bacterial Proteins / Q000276:immunology*; D002460:Cell Line; D002470:Cell Survival; D018946:Chemokine CCL5 / Q000276:immunology / Q000378:metabolism; D016207:Cytokines / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011994:Recombinant Proteins / Q000276:immunology; D017011:Streptococcus suis / Q000201:enzymology / Q000276:immunology* / Q000472:pathogenicity; D013381:Subtilisins / Q000276:immunology* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C483024:CCL5 protein, human; D018946:Chemokine CCL5; D016207:Cytokines; D047428:Protein Kinase Inhibitors; D011994:Recombinant Proteins; D013381:Subtilisins