Streptococcus pyogenes (Group A streptococcus, GAS) is an important human pathogen responsible for a wide variety of diseases from uncomplicated tonsillitis to life-threatening invasive infections. GAS secretes EndoS, an endoglycosidase able to specifically cleave the conserved N-glycan on human IgG antibodies. In vitro, removal of this glycan impairs IgG effector functions but its relevance to GAS infection in vivo is unclear. Using targeted mass spectrometry, we were able to characterize the effects of EndoS on host IgG glycosylation during the course of natural infection in human patients. We found substantial IgG glycan hydrolysis locally at site of infection as well as systemically in the most severe cases. Using these findings we were able to set up appropriate model systems to demonstrate decreased resistance to phagocytic killing of GAS lacking EndoS in vitro, as well as decreased virulence in a mouse model of invasive infection. These findings highlight the importance of IgG glycan hydrolysis for streptococcal pathogenesis, offer new insights into the mechanism of immune evasion employed by this pathogen and have clear implications for treatment of severe GAS infections and future efforts at vaccine development.

1.) human and mouse control plasma samples for method validation 2.) plasma and swab samples from patients suffering from GAS infections and controls 3.) plasma and skin homogenates from experimental GAS infections in C57BL/6J mice