Group A Streptococcus (GAS) is a preeminent pathogen causing a wide spectrum of human diseases. The propensity of particular GAS strains to produce systemic infection defines its capacity to resist host innate immune clearance mechanisms. A clone of the GAS M1T1 serotype spread globally over the last 40 years as the leading cause of invasive infections. Our lab adopted a multifaceted approach to understanding GAS and host factors explaining diverse outcomes of this host-pathogen interaction, using invasive M1T1 GAS clone as a primary model. Our approach coupled precise, targeted of candidate virulence factor genes with in vitro, ex vivo and in vivo models of disease pathogenesis, including WT and knockout mouse lines. We hypothesized that the outcome of GAS infection is dictated by the action and regulation of these GAS virulence factors in response to selective pressures exerted by host innate immunity. In the first funding period, we examined more than two dozen individual virulence factors of the GAS M1T1 clone and their extra- and intracellular interaction with host neutrophils and macrophages, epithelial and endothelial barriers, and soluble immune effectors including antimicrobial peptides, complement proteins and antibodies. For this first renewal application, a key (originally unanticipated) discovery of the past year serves as the central focus for new investigation: our identification of the long-sought-after molecular genetic basis of the hallmark, species-defining, Lancefield group A cell wall carbohydrate antigen (GAC). Our genetic knowledge allowed us to generate the first, precise isogenic GAS M1T1 mutant lacking the Lancefield epitope, a GlcNAc side chain that extends from the polyrhamnose backbone of the antigen. Previously thought only to play a structural role in cell wall biogenesis, we demonstrated that the GlcNAc side-chain contributes to GAS disease pathogenesis by promoting GAS resistance to cationic defense peptides, serum and neutrophil killing, and a mutant lacking the GlcNAC side chain was markedly attenuated for virulence in vivo. The GlcNAc side-chain of GAC has been implicated in the immunopathogenesis of rheumatic heart disease, and we now have a genetic strategy for its elimination. Here we pursue a comprehensive analysis of the GAC GlcNAc side-chain in colonization and systemic virulence of GAS from different disease-associated serotypes, informed by the enhanced mechanistic understanding provided by studies of the original funding period. We will examine the role of the GAC GlcNAc side chain in GAS epithelial cell adherence and invasion, biofilm formation, intracellular survival, interaction with the autophagy system, resistance to macrophage killing, and modulation of leukocyte activation. In vivo, we will assess its role in GAS colonization, necrotizing skin infection and septicemia. Efficacy and safety of GlcNAc- deficient GAC as a universal vaccine antigen will be examined upon conjugation with three different proteins using an active immunization regimen in three different mouse models of GAS disease, with attention to antibody titers, promotion of opsono-phagocytosis and elimination of human tissue cross-reactivity.
Group A Streptococcus (GAS) is a leading human pathogen and a top 10 infectious killer worldwide. Our collaborative research dissects the molecular basis of GAS virulence to provide new targets for treatment. The current work exploits new discoveries regarding GAS innate immune evasion, and the genetic basis and virulence role of a hallmark GAS antigen that may aid in development of a safe and universal vaccine.
|Rivera-Hernandez, Tania; Pandey, Manisha; Henningham, Anna et al. (2016) Differing Efficacies of Lead Group A Streptococcal Vaccine Candidates and Full-Length M Protein in Cutaneous and Invasive Disease Models. MBio 7:|
|Stewart, Chelsea M; Buffalo, Cosmo Z; Valderrama, J AndrÃ©s et al. (2016) Coiled-coil destabilizing residues in the group A Streptococcus M1 protein are required for functional interaction. Proc Natl Acad Sci U S A 113:9515-20|
|Buffalo, Cosmo Z; Bahn-Suh, Adrian J; Hirakis, Sophia P et al. (2016) Conserved patterns hidden within group A Streptococcus M protein hypervariability recognize human C4b-binding protein. Nat Microbiol 1:16155|
|von KÃ¶ckritz-Blickwede, Maren; Blodkamp, Stefanie; Nizet, Victor (2016) Interaction of Bacterial Exotoxins with Neutrophil Extracellular Traps: Impact for the Infected Host. Front Microbiol 7:402|
|Carey, Alison J; Weinberg, Jason B; Dawid, Suzanne R et al. (2016) Interleukin-17A Contributes to the Control of Streptococcus pyogenes Colonization and Inflammation of the Female Genital Tract. Sci Rep 6:26836|
|DÃ¶hrmann, Simon; Cole, Jason N; Nizet, Victor (2016) Conquering Neutrophils. PLoS Pathog 12:e1005682|
|Secundino, Ismael; Lizcano, Anel; RoupÃ©, K Markus et al. (2016) Host and pathogen hyaluronan signal through human siglec-9 to suppress neutrophil activation. J Mol Med (Berl) 94:219-33|
|Cole, Jason N; Nizet, Victor (2016) Bacterial Evasion of Host Antimicrobial Peptide Defenses. Microbiol Spectr 4:|
|Henningham, Anna; DÃ¶hrmann, Simon; Nizet, Victor et al. (2015) Mechanisms of group A Streptococcus resistance to reactive oxygen species. FEMS Microbiol Rev 39:488-508|
|Lin, Ann E; Beasley, Federico C; Keller, Nadia et al. (2015) A group A Streptococcus ADP-ribosyltransferase toxin stimulates a protective interleukin 1Î²-dependent macrophage immune response. MBio 6:e00133|
Showing the most recent 10 out of 73 publications