Oral Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Sugar-Coated or Protein-Packed? How antigen type shapes the B cell response against Streptococcus pyogenes in humans (118522)

Holly A Fryer 1 , Catherine Pitt 1 , Hannah R Frost 2 , Nitika Kandhari 1 , Sean Byars 1 , Pailene Lim 3 , Kaneka Chheng 2 , Natalie Caltabiano 2 , Alana Whitcombe 4 , Nicole Moreland 4 5 , Isaak Quast 1 , Marcus Robinson 1 , Stephen Scally 3 , Melanie Neeland 6 7 , Shivanthan Shanthikumar 6 7 8 , Joshua Osowicki 2 7 8 , David M Tarlinton 1 , Andrew C Steer 2 7 8 , Michelle J Boyle 9 10 11 , Danika L Hill 1
  1. Department of Immunology, Monash University, Melbourne, Victoria, Australia
  2. Tropical Diseases Research Group, Murdoch Children's Research Institute, Melbourne, VIC, Australia
  3. Walter and Eliza Hall Institute, Melbourne, VIC, Australia
  4. Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, Auckland, New Zealand
  5. School of Medical Sciences, University of Auckland, Auckland, New Zealand
  6. Infection, Immunity and Global Health Theme, Murdoch Children's Research Institute, Melbourne, Australia
  7. Department of Paediatrics, University of Melbourne, Melbourne, VIC, Australia
  8. Royal Children's Hospital , Melbourne , VIC, Australia
  9. Monash University, Melbourne, VICTORIA, Australia
  10. Burnet Institute, Melbourne, VIC, Australia
  11. Department of Infectious Disease, University of Melbourne, Melbourne, VIC, Australia

Anti-carbohydrate antibodies (Abs) are crucial in pathogen control and believed to form through a distinct pathway from protein-targeting responses, emerging early without T cell interactions. Group A Carbohydrate (GAC) from S. pyogenes is a key candidate antigen for multi-component vaccines. However, the development and maturation of glycan and protein antigen antibody responses in humans, particularly in mucosal tissues, remain poorly understood. We used flow cytometry and single-cell sequencing to study S. pyogenes glycan (GAC) and protein (SpyCEP)-specific B cells in adult blood, spleen, tonsils, and human challenge cohorts. Our findings show that age and infection shift GAC and SpyCEP-specific B cell responses from IgM to IgG and IgA isotypes. Contrary to existing beliefs, glycan-specific B cells showed germinal center (GC) passage, typically seen only for protein antigens. GAC and SpyCEP-specific B cell receptors underwent mutation, clonally expansions and affinity maturation within the GC. However, GAC-specific cells expressed a unique transcriptional signature consistent with reduced ability to recruit or receive T cell help, resulting in fewer antibody-secreting cells. These insights reveal how multiple S. pyogenes encounters shape the quantity, quality and durability of B cell responses in systemic circulation and mucosal tissues. Our findings have broader implications for understanding anti-carbohydrate antibody responses to pathogens, while also illuminating how the memory responses recalled by vaccination differ dramatically between children and adults.