Relationship between IL-17_A and pneumococcal carriage in children aged under two years: data from a randomised controlled trial in Vietnam.

OBJECTIVE

Pneumococcal carriage is a prerequisite for invasive pneumococcal disease (IPD). Interleukin (IL)-17 A and IL-17 A-producing cells are involved in the clearance of pneumococcal carriage in adults, but their role in children is unclear. This study aims to examine the relationship between IL-17 A, IL-17 A-related cytokines (IL-22, IL-23, IFNγ) and IL-17 A-producing cells and pneumococcal carriage in children aged under two years.

METHODS

Blood samples (n = 143) collected from unvaccinated children at 18 months (m) of age and nasopharyngeal swabs collected from unvaccinated children at 2, 6, 9, 12, 18, 24 m in the Vietnam Pneumococcal Project (ClinicalTrials.gov, NCT01953510) were included in this analysis. Pneumococcal carriage was previously determined. Plasma cytokine concentrations were measured by multiplex bead array or ELISA. Flow cytometry was used to measure IL-17 A/IFNγ-producing cells in peripheral blood mononuclear cells.

RESULTS

IL-17 A, IL-22, IL-23 and IFNγ plasma cytokine concentrations were 1.7 to 2.6-fold higher among pneumococcal carriers at 18 m of age compared with non-carriers. Two-to four-fold higher IL-17 A, IL-22, IL-23 concentrations were observed in children carrying two or more pneumococcal serotypes at 18 m compared with children who only carried one pneumococcal serotype or non-carriers. Pneumococcal carriers at 18 m of age had 1.6 to 2-fold higher IL-17 A, IL-22, IL-23 compared with carriers at earlier timepoints (≤12 m). No differences in the frequencies of IL-17 A-producing cells were observed between carriers and non-carriers at 18 m of age. IL-17 A and related cytokines at 18 m of age did not appear to influence clearance of pneumococcus at 24 m of age.

CONCLUSION

Pneumococcal carriage is associated with higher plasma IL-17 A, IL-22 and IL-23 concentrations in children aged under two years.