Introduction: There is currently little information regarding the human immune response to GAS infection. In addition to the M protein, there are shared GAS antigens that have been shown to elicit protective immunity in animal studies. This pilot study aimed to investigate the kinetics and specificity of antibody responses against a panel of GAS antigens in a cohort of school-aged children in Cape Town.
Methods: Thirty-five antigens (10 shared GAS antigens and 25 synthetic M-peptides) were used as ELISA antigens to assess immune responses in participants who provided serum samples and throat swabs at two-monthly follow-up evaluations.
Results: Twenty-nine participants (from the total of 256 enrolled) provided 108 swabs and serum samples. Of these, 19 had at least one GAS-positive culture, 15 of which were successfully emm-typed. We observed four patterns of immune responses: 1) GAS-positive culture with an immune response to at least one shared antigen and the homologous M peptide (N=3), 2) GAS-positive culture with an immune response to at least one shared antigen and a heterologous M peptide (N=13), 3) GAS-positive culture with responses to shared antigens but no response to any of the M peptides tested (N=4) and, 4) GAS-negative culture with antibody responses to shared antigens and M peptides (N=7). Two participants had neither positive culture or antibody responses.
Conclusion: We observed that GAS culture-positive participants displayed high levels of antibodies against shared-antigens and against specific M peptides. Completion of the analysis of immune responses in the entire study cohort may provide important information to inform future vaccine design.