Streptococcus pyogenes M1T1 Variants Induce an Inflammatory Neutrophil Phenotype Including Activation of Inflammatory Caspases

Abstract

Invasive infections due to group A Streptococcus (GAS) advance rapidly causing tissue degradation and unregulated inflammation. Neutrophils are the primary immune cells that respond to GAS. The neutrophil response to GAS was characterised in response to two M1T1 isolates; 5448 and animal passaged variant 5448AP. Co-incubation of neutrophils with 5448AP resulted in proliferation of GAS and lowered the production of reactive oxygen species when compared with 5448. Infection with both strains invoked neutrophil death, however apoptosis was reduced in response to 5448AP. Both strains induced neutrophil caspase-1 and caspase-4 expression in vitro, with inflammatory caspase activation detected in vitro and in vivo. GAS infections involving strains such as 5448AP that promote an inflammatory neutrophil phenotype may contribute to increased inflammation yet ineffective bacterial eradication, contributing to the severity of invasive GAS infections.

Inflammasome activation and IL ‐1β signalling in group A Streptococcus disease

“…These seemingly opposing effects of NLRP3‐mediated inflammation may reflect the impact of cytokine release at different sites and stages of infection. For example, while a host‐adapted covRS mutant M1 GAS strain causes reduced IL‐1β production in a nasopharyngeal infection model (LaRock et al, 2020), the same GAS strain promotes caspase‐1 activation and increased IL‐1β production in an intradermal infection model (Williams et al, 2021).…”

“…A hallmark of inflammation is the chemoattraction of innate immune cells, such as neutrophils. Given that GAS expresses multiple mechanisms to resist neutrophil killing (Ato, Ikebe, Kawabata, Takemori, & Watanabe, 2008; Walker et al, 2007; Williams, Ly, Geraghty, McArthur, et al, 2021), it is possible that in the context of recruited innate immune cells, GAS outcompetes the normal microflora leading to colonisation of the nasopharynx (LaRock et al, 2020).…”

“…While functions for the non‐canonical inflammasome pathway in defence against Gram‐negative bacteria are well characterised, their potential function in GAS infection is less clear. GAS‐induced IL‐1β secretion in murine macrophages is not affected by caspase‐11 deficiency (Hancz et al, 2017), however, increased expression of the human ortholog caspase‐4 is reported during GAS infection in human cells (Agarwal, Agarwal, Jin, Pancholi, & Pancholi, 2012; Williams et al, 2021). Although functions for caspase‐4 in this context are currently unknown, it is possible that caspase‐4 serves inflammasome‐independent functions during GAS infection.…”

Purinergic Signalling in Group A Streptococcus Pathogenesis

“…Collectively, the above studies indicate that the role of P2X7 in GAS infection varies between host cell types. Moreover, other GAS virulence factors, such as M protein and SpyA, can also induce NLRP3 inflammasome activation and IL-1β release in macrophages ( 35 , 36 ), and GAS infection can induce IL-1β release from neutrophils ( 37 , 38 ) but a role for P2X7 in these settings has not been investigated.…”

Playing With Fire: Proinflammatory Virulence Mechanisms of Group A Streptococcus

“…Some of the underlying cost-benefit of SpeB expression is clear from mutants recovered from natural and experimental infections. These include mutations in the two-component regulatory system CovRS (CsrRS) that lead to constitutive speB repression, increased expression of other virulence factors that promote tissue invasion, and shifts in cytokine responses ( Li et al., 2014 ; LaRock et al., 2016 ; Williams et al., 2021 ). Development of these mutations is variable between GAS serotypes, and more rarely, other mutations are found to disrupt speB expression, such as in the positive regulator ropB ( Friaes et al., 2015 ; Feng et al., 2016 ).…”