AbstractBackground: Streptococcus pneumoniae is an important pathogen associated with bronchiectasis, a chronic respiratory condition characterised by dysregulated airway inflammation and recurrent infection. Indigenous Australian children in the Northern Territory experience disproportionally high burden of bronchiectasis. Despite a comprehensive vaccination strategy against pneumococcal disease in the Northern Territory, several vaccine types of S. pneumoniae associated with lower respiratory infection have been identified. The cellular immune response plays a role during S. pneumoniae infection; however no studies have investigated the cellular immune response towards S. pneumoniae in children with bronchiectasis. Hence, this thesis aims to fill the gap in the literature and characterise the S. pneumoniae-driven cellular immune response in children with bronchiectasis and determine if there are differences between the response towards vaccine and non-vaccine serotypes.
Methods: Peripheral blood mononuclear cells (PBMC) from 46 children (age 20-54 months) with recentlydiagnosed bronchiectasis, and 22 age-matched healthy control children were cultured with vaccine (19F, 9V) and non-vaccine (15A, 7C) S. pneumoniae serotypes, clinically isolated from nasopharyngeal samples (9V, 7C) or from lower airway infection (19F, 15A) in Northern Territory children. Cytokines involved in early inflammation (IL-6 and TNFα), and adaptive Th1 (IFN-γ), Th2 (IL-5 and IL-13) and Th17 (IL-17a) responses were quantified from culture supernatant using dissociation-enhanced lanthanide fluorescence immunoassay (DELFIA®). Cytokine production between groups was compared using non-parametric Mann-Whitney U test. PBMC cultured with serotypes 19F and 9V were stained for NK and T cell markers and intracellular adaptive cytokines IL-13, IL-17a and IFN-γ. Cytokine producing CD4+ T cells, CD8+T cells and CD56+ NK cells were assessed by Flow Cytometry.
Results: Compared with healthy control children, PBMC from children with bronchiectasis produced significantly more IL-13 to serotypes 19F (median 7.2pg/mL vs 60.9 pg/ml; p<0.001), 9V (median 6.0 pg/mL vs 40.3 pg/ml; p=0.001) and 15A (median 14.4 pg/ml, 49.4 pg/ml; p=0.002). Whilst IL-5 was
not detected in all cultures, there was a significantly higher proportion of responders in the bronchiectasis group. Minimal differences were observed in IFN-γ, and no significant differences in innate IL-6 and TNF-α production between groups. Furthermore PBMC from children with bronchiectasis produced significantly more IL-5 (p=<0.001), IL-13 (p<0.001) and IFN-γ (p=0.014) in response to nasopharyngeal and non-vaccine type 7C compared to vaccine serotype 9V.
Conclusions: These findings indicate the S. pneumoniae-driven cell-mediated immune response in children with bronchiectasis is likely skewed towards a Th2 phenotype. These data suggest that childhood bronchiectasis in the Northern Territory is associated with a polarised S. pneumoniae-driven cellular immune response. Consequently this thesis will enable further research to investigate the role of S. pneumoniae and the cellular immune response in the pathogenesis of childhood bronchiectasis in the Northern Territory.
|Date of Award||Nov 2019|
|Supervisor||Susan Pizzutto (Supervisor), Gabriela Minigo (Supervisor) & Anne Chang (Supervisor)|