This family includes four members: PAR-1, PAR-3 and PAR-4 are receptors for thrombin, trypsin or cathepsin G, while PAR-2 is resistant to thrombin, Ruboxistaurin mouse but can be activated by trypsin, mast cell tryptase [30, 34–36]. Since the heat-inactivated SspA still possessed the capacity to induce cytokine secretion in macrophages, the involvement of PARs could be ruled out. We thus investigated whether the SspA may induce cytokine secretion through activation of MAP kinases. More specifically, there

are three major groups of MAPK in mammalian cells: the extracellular signal-regulated protein kinase (ERK), the p38 MAPK and the c-Jun NH2-terminal kinase (JNK) [31]. Our results obtained by including kinase inhibitor during stimulation of macrophages with the recombinant SspA suggested that the production of CCL5 and CXCL8 was regulated by p38 MAPK while the production of IL-6 was mostly regulated by JNK. MAPK are known as key regulators for the synthesis of numerous cytokines, chemokines, and other inflammatory mediators [31]. Previous studies also suggested a similar involvement of the MAPK regulatory pathway

in inflammatory responses induced by S. suis [37–39]. In agreement with our observations, the cysteine proteinases of Porphyromonas gingivalis was also reported to use the MAPK transduction pathway to induce cytokine MRT67307 supplier secretion in macrophages [40] and fibroblasts [41]. Our data showed that the amounts of CCL5 in the conditioned medium of macrophages

stimulated with the heat-inactivated recombinant SspA was higher compared to that detected following stimulation with the active SspA. This suggests that SspA may degrade this cytokine. Using ELISA, we clearly showed the capacity of the recombinant SspA to degrade dose-dependently CCL5. Since CCL5 possesses chemotactic activity for immune cells, its inactivation by the SspA may allow Exoribonuclease S. suis to avoid and delay neutrophil attraction and activation. Cytokine degradation by proteases is a phenomenon well described in group A streptococci. Sumby et al., reported the ability of Streptococcus pyogenes SpyCEP to reduce neutrophil activity though cleavage and inactivation of the human chemokine granulocyte chemotactic protein 2 (GCP-2) [42]. In addition, the protease of S. pyogenes was reported to cleave CXCL8 [42, 43]. Moreover, Bryan et al., showed that Streptococcus agalactiae CspA, inactivates the CXC chemokines GRO-alpha, GRO-beta, GRO-gamma, neutrophil-activating peptide 2 (NAP-2), and GCP-2 [44]. Lastly, the subtilisin-like protease SufA of Finegoldia magna, that shares many properties with the SspA of S. suis, has been shown to degrade the chemokine MIG/CXCL9 [45]. Degradation of CXCL8 by S. suis has been previously reported [46].