Background:
The current lack of knowledge about acquired immunity against S. pyogenes in humans is a barrier to developing safe and effective vaccines. Specifically, much is unknown about how immune responses develop and could be protective at sites of mucosal infection.
Methods:
To address this knowledge gap, we collected tonsil tissue from 25 children with and without microbiologically confirmed S. pyogenes infection. We used flow cytometry and single cell sequencing to analyse memory B cell responses against leading conserved GAS vaccine antigens (SpyCEP, SpyAD, SCPA, SLO).
Results:
Colonized tonsils exhibited higher frequencies of memory B cells specific to all studied antigens. In uncolonized tonsils, antigen-specific memory B cells were in a quiescent resting state, whereas in colonized tonsils they displayed phenotypes associated with activation, including germinal center and antibody-secreting cell responses. Sequencing the B cell receptor repertoires of thousands of antigen-specific cells revealed that the B cell response diversifies and evolves in response to colonization, enhancing antibody affinity.
Conclusion:
Our data reveal that localized humoral immunity is generated within the tonsils of children following S. pyogenes encounter, with B cells undergoing activation and differentiation in situ. These findings highlight that asymptomatic colonization with S. pyogenes is immunologically active and demonstrate the immunogenicity of several conserved vaccine antigens during natural mucosal infection. Together, our results provide new insights into the development of immunity against S. pyogenes in mucosal tissues.