Quorum sensing by Streptococcus pyogenes induces global inflammatory suppression in host macrophages

Streptococcus pyogenes or Group A Streptococcus (GAS), a significant human pathogen, employs quorum sensing (QS) systems to coordinate its behavior and genetic regulation to enhance survival. Our previous research established that one such QS system, the Rgg2/3 system, can suppress macrophage NFκB activity and production of pro-inflammatory cytokines. Yet, the scope of suppression and the mechanism by which it occurs remain unknown. In this study, transcriptomic and phosphoproteomic approaches were used to address these unanswered questions. It was found that QS-ON GAS broadly suppressed most inflammatory transcriptional pathways, including those of NFκB, type I and type II interferon responses, and intracellular stress responses. Yet, we found that no alternative transcriptional programs were activated after QS-ON GAS infection. Additionally, phosphoproteomics showed no disruption in typical inflammatory pathways such as those related to NFκB and MAPK activation, which was confirmed by western blotting and translocation assays. Instead, the proteomic data highlighted a potential role for epigenetic mechanisms of inflammatory regulation. A role for epigenetic regulation in QS-mediated immunomodulation was validated using pharmacological inhibitors of histone and chromatin modifiers. These findings expand our understanding of QS-mediated suppression and of GAS virulence strategies that appear to employ atypical methods of restricting inflammation. Uncovering this mechanism will offer invaluable insight into GAS itself, as well as into understudied immunological pathways.