Streptococcus anginosus Activates the NLRP3 Inflammasome to Promote Inflammatory Responses from Macrophages

Chronic inflammation and oral dysbiosis are common features of oral squamous cell carcinoma (OSCC). The commensal streptococci, S. anginosus, is increased in oral diseases including OSCC. Our previous work revealed that S. anginosus promotes inflammatory responses from macrophage cell lines, however the molecular mechanism by which S. anginosus interacts with macrophages to instigate this response remains to be investigated. Here, we expand on our previous findings by investigating the effects of S. anginosus infection of primary bone marrow derived macrophages (BMMs) and during in vivo infection. We found S. anginosus activated primary BMMs, which presented an enlarged cellular area, increased NF-{kappa}B activation and downstream inflammatory cytokines TNF, IL-6 and IL-1{beta} at 24 hours post infection. S. anginosus viability was dispensable for NF-{kappa}B activation, but essential for the induction of downstream inflammatory proteins and cytokines. S. anginosus persisted intracellularly within BMMs and induced the expression of inflammasome sensors AIM2, NLRC4 and NLRP3. Further, BMMs lacking the inflammasome adapter protein ASC (Asc-/-) had significantly diminished IL-1{beta} production compared to wild type BMMs, indicating that S. anginosus activated the inflammasome. S. anginosus primarily triggered the inflammasome through NLRP3 as S. anginosus-infected Nlrp3-/- BMMs and NLRP3 inhibitor (MCC950)-treated wild type BMMs displayed diminished IL-1{beta} production compared to wild type controls. Lastly, S. anginosus-infected Asc-/- and Nlrp3-/-mice displayed reduced weight loss compared to C57BL/6 mice. These overall findings indicate that S. anginosus replicates within macrophages and promotes a proinflammatory response in part through activation of the NLRP3 inflammasome. brief summary sentence: S. anginosus replicates intracellularly within macrophages and is sensed by the NLRP3 inflammasome to promote proinflammatory response.