Host Genetic Variations and Sex Differences Potentiate Predisposition, Severity, and Outcomes of Group A Streptococcus-Mediated Necrotizing Soft Tissue Infections

Abstract

bHost genetic variations play an important role in several pathogenic diseases, and we previously provided strong evidence that these genetic variations contribute significantly to differences in susceptibility and clinical outcomes of invasive group A Streptococcus (GAS) patients, including sepsis and necrotizing soft tissue infections (NSTIs). The goal of the present study was to investigate how genetic variations and sex differences among four commonly used mouse strains contribute to variation in severity, manifestations, and outcomes of NSTIs. DBA/2J mice were more susceptible to NSTIs than C57BL/6J, BALB/c, and CD-1 mice, as exhibited by significantly greater bacteremia, excessive dissemination to the spleen, and significantly higher mortality. Differences in the sex of the mice also contributed to differences in disease severity and outcomes: DBA/2J female mice were relatively resistant compared to their male counterparts. However, DBA/2J mice exhibited minimal weight loss and developed smaller lesions than did the aforementioned strains. Moreover, at 48 h after infection, compared with C57BL/6J mice, DBA/2J mice had increased bacteremia, excessive dissemination to the spleen, and excessive concentrations of inflammatory cytokines and chemokines. These results indicate that variations in the host genetic context as well as sex play a dominant role in determining the severity of and susceptibility to GAS NSTIs. Streptococcus pyogenes or group A streptococci (GAS) are the causative agents of a multitude of human diseases ranging from nonsevere strep throat, pharyngitis, and impetigo to lifethreatening necrotizing soft tissue infections (NSTIs) and streptococcal toxic shock syndrome (STSS) (1-12). The multifaceted nature of invasive GAS infections requires several modes of pathogenic adaptation to evade host immune defenses to successfully colonize and survive in host niches. In addition to the plethora of pathogenic factors contributing to disease severity, variations in the host genetic context play an equally important role in manipulating disease severity, manifestations, and outcomes.The emergence of virulent strains of GAS bacteria in the early 1980s coincided with a remarkable resurgence of severe and often deadly forms of invasive infections associated with STSS and NSTIs (5,6,12,13). One particular strain that emerged during that time is the clonal M1T1 strain that disseminated globally and continues to be one of the most prevalently isolated strains from patients with invasive and/or noninvasive GAS infections (12,(14)(15)(16)(17). This strain produces many secreted and surface-bound virulence factors; most of them are adapted to evade human host defense mechanisms (12, 18). However, previous studies from our laboratory characterized indistinguishable, invasive M1T1 isolates from patients with starkly different disease severity and outcomes (19). These findings underscored the contribution of host factors to the stark differences in severity and outcomes of invasive GAS infections.Indeed, ensuing ...

Genetic Architecture of Group A Streptococcal Necrotizing Soft Tissue Infections in the Mouse

“…In our initial studies with conventional inbred and outbred mouse models [ 24 ] and in this study, the parental strain D2 was more susceptible to GAS NSTIs than was the B6 strain, but interestingly the resistant B6 strain lost more weight and developed larger lesions than did D2. Susceptibility, in terms of the three phenotypic traits based on their relative genotypes, differed greatly among the BXD strains.…”

“…Our laboratory’s preliminary studies of subcutaneous GAS infections of conventional mouse strains determined that D2 mice are more susceptible to GAS NSTIs than are B6 mice; also D2 female mice are more resistant than are males of the same strain [ 24 ]. To further explore the relative contributions of host genetics, sex, and any other covariates to GAS NSTIs, we infected 33 BXD strains along with their ancestral parental strains (B6 and D2) and their F1 strains (B6D2F1) with an equal dose of GAS bacteria.…”

“…Besides, the protein levels of IL-1β were also increased in patient plasma samples and in infected skin models compared to their respective controls ( Fig 13D and 13F ), suggesting that GAS NSTIs susceptibility is associated with an amplified inflammatory response mediated by IL-1β . However, although IL-1β -dependent macrophage immune response has been shown to be protective in an intravenous mouse model of GAS sepsis utilizing 5448AP bacteria [ 46 ], female CD-1 strains were used for these infections and we have shown that these strains are resistant to GAS NSTIs mediated by 5448WT bacteria [ 24 ]. Moreover, similar to what we mentioned earlier, both these studies use two different infection models (sepsis vs. NSTIs) and bacteria (5448AP vs. 5448WT).…”

“…Although GAS causes NSTIs in humans, successful animal models have been developed through the use of conventional inbred and outbred mouse strains; however, mice are generally more resistant to GAS NSTIs than humans and thus require higher initial GAS inoculum than humans to develop NSTIs [ 16 – 23 ]. Our initial studies to understand the role of host genetic context in GAS NSTIs revealed that the DBA/2J (D2) mouse strain is more susceptible than is the C57BL/6J (B6) strain and that sex differences have a possible role in potentiating the severity of NSTIs [ 24 ]. However, the restricted genetic variations in these inbred strains led us to develop a better animal model for use in further in-depth investigations of the host genetic architecture for GAS NSTIs susceptibility.…”

Heterogeneity in FoxP3- and GARP/LAP-Expressing T Regulatory Cells in an HLA Class II Transgenic Murine Model of Necrotizing Soft Tissue Infections by Group A Streptococcus

“…We used the clinical isolate M1 GAS 2006 for the in vivo studies. GAS 2006 was grown under static conditions in Todd-Hewitt broth supplemented with 1.5% yeast extract for 17 h at 37°C (11,24,41). The bacteria were harvested by centrifugation, washed three times with sterile endotoxin-free Dulbecco's phosphate-buffered saline (DPBS), and resuspended in DPBS.…”