Immune Responses in Children Infected with Streptoccocus A during the Spring 2023 Epidemic in Bulgaria

Abstract

Streptococcus pyogenes, Group A Streptococcus (GAS), is the most common cause of bacterial tonsillitis, scarlet fever, impetigo, etc. in children and adults. Innate and adaptive host immune responses are fundamental for human defence against GAS, but are also important to the clinical manifestations of the infection.

Our aim was to study the humoral and cellular immune responses in children infected with GAS and diagnosed with tonsillitis in the Clinic of Pediatrics in University Hospital “Lozenets”.

The study included 22 infected children and 20 healthy controls. The following immune parameters were investigated: i) Humoral immune response – total serum IgG, IgM, IgA; C3, C4 – complement components, as well as the serum cytokines IFNγ, IL-6, IL-1β, TNFα, IL-17A, IL-10. ii) Cellular immune subsets were tested by immunophenotyping of total T cells, B cells, NK cells, T helper and T cytotoxic subsets.

In this cross-sectional study we found a significant increase in the complement components C3 and C4, increased production of serum IFNγ, IL-6 and IL-10 and decreased levels of IL-17A in infected children with tonsillitis, compared to healthy controls. The cellular immune parameters in infected children showed lymphopenia, reduced total T lymphocytes and T-helper subpopulation, compared to healthy controls.

We assumed that these imbalanced immune responses, found in infected children, are connected with GAS infection and deserved more detailed investigation.