Group A Streptococcus Infection of the Nasopharynx Requires Proinflammatory Signaling Through the Interleukin-1 Receptor

Abstract

22Group A Streptococcus (GAS) is the etiologic agent of numerous high morbidity and high 23 mortality diseases which commonly have a highly proinflammatory pathology. One factor 24 contributing to this inflammation is the GAS protease SpeB, which directly activates the 25 proinflammatory cytokine interleukin-1β (IL-1β), independent of the canonical inflammasome 26 pathway. IL-1β drives neutrophil activation and recruitment that limits bacterial growth and 27 invasion during invasive skin and soft tissue infections like necrotizing fasciitis. GAS also causes 28 pharyngitis (strep throat), and the upper respiratory tract is its primary nidus for growth and 29 transmission. Since the fitness selection for the species is likely primarily for this site, we 30 examined the process of IL-1β activation in the murine nasopharynx. SpeB still activated IL-1β, 31 which was required for neutrophil migration, but this inflammation instead increased GAS 32 replication. Inhibiting IL-1β or depleting neutrophils, which both promote invasive infection, 33 prevented GAS infection of the nasopharynx. Prior antibiotic exposure increased GAS growth in 34 the murine nasopharynx, and antibiotics were sufficient to reverse the attenuation previously 35 observed when IL-1β, neutrophils, or SpeB were not present to drive inflammation. Therefore, 36 the same fundamental mechanism has opposing effects on virulence at different body sites. 37 Invasive disease may be limited in part due to specific adaptations for inducing host 38 inflammation that are beneficial for pharyngitis. 39 IMPORTANCE 40Our previous reports showed that Group A Streptococcus (GAS) protease SpeB directly activates 41 the host proinflammatory cytokine IL-1β and this restricts invasive skin infection. The upper 42 respiratory tract is the primary site of GAS colonization and infection, but the host-pathogen 43 interactions at this site are still largely unknown. We provide the first evidence that IL-1β-44 3 mediated inflammation promotes upper respiratory tract infection. This provides experimental 45 evidence that the notable inflammation of strep throat, which presents with significant swelling, 46 pain, and neutrophil influx, is not an ineffectual immune response, but rather is a GAS-directed 47 remodeling of this niche for its pathogenic benefit. 48 49 50 Group A Streptococcus (GAS, Streptococcus pyogenes) is a top cause of infectious mortality and 51 responsible for over half a million annual deaths (1). Death is primarily due to invasive diseases, 52 including sepsis, necrotizing fasciitis, and toxic shock syndrome, or autoimmune diseases, most 53 prominently acute rheumatic fever and rheumatic heart disease. The nasopharyngeal mucosa and 54 associated lymphoid tissues is the most common site for infection (strep throat pharyngitis) and 55 the primary carriage site for dissemination of GAS between individuals and to other sites of the 56 body (2). Humans are transiently colonized by GAS throughout childhood but can be culture-57 positive at any point in ...

Colonization of the Murine Oropharynx by Streptococcus pyogenes Is Governed by the Rgg2/3 Quorum Sensing System

“…Congruent with our findings, a previous report showed that an insertional disruption in rgg2 decreased the survival of mice in a model of intraperitoneal infection, indicating that this system may be broadly important for the host-pathogen interaction [35]. Recent evidence has shown that the RopB-SIP quorum sensing system and its cysteine protease product SpeB also contributes to GAS pharyngeal colonization in the nasopharynx [36,37], indicating that cell-cell communication systems are important for this niche.…”

“…6D). IL-1β has been shown to promote nasopharyngeal infection by GAS in the mouse model, and LaRock et al suggest that this initial immune response and recruitment of neutrophils may be crucial for overcoming microbial interference [37]. The lack of activation of IL-1β in the Δrgg2 bacteria lends credence to the hypothesis that QS-off bacteria are eliminated before eliciting MyD88-dependent activation of neutrophil migration to the NALT.…”

The Pseudomonas aeruginosa protease LasB directly activates IL-1β

“…Eight-to-ten week old male or female C57Bl/6 and isogenic caspase-1/−11 −/− mice (000664 and 016621, Jackson labs) were assigned to experimental groups, each using 15 mice broken into three independent experiments containing five mice each; none were excluded from analysis. Sample size is based on power function of effect size established in our previous studies [ 34 , 35 ]. The effect size (difference in means) and variance in data was expected to be consistent with this prior work, since similar biological processes were being examined.…”

“…No cross-reactivity between cytokines and neutralising antibodies was observed. After 18 h, reporter cell supernatants were analysed for secreted alkaline phosphatase activity using HEK-Blue Detection reagent (Invivogen) as previously [35] . Cytokines were quantified by enzyme-linked immunosorbent assay following the manufacturer's protocol (DY400, DY401, DY410, DY453 DY406; R&D Systems).…”

Playing With Fire: Proinflammatory Virulence Mechanisms of Group A Streptococcus

“…During GAS infection of the murine nasopharynx (a model of strep throat), neutrophils, T cells, and the proinflammatory cytokine IL-1b all promote GAS growth (Zeppa et al, 2017;LaRock et al, 2020), despite conventionally having vital antimicrobial roles in immunity and acting to counter GAS invasion at other body sites (LaRock et al, 2016;Pinho-Ribeiro et al, 2018). In antibiotic-treated mice, neutrophils and IL-1b are no longer essential for GAS colonization of the nasopharynx, suggesting this immune axis may be necessary for overcoming interference from antibiotic-sensitive members of the resident microbiota (LaRock et al, 2020).…”