Frequency of lower respiratory tract infections in relation to adaptive immunity in children with Down syndrome compared to their healthy siblings

Aim: Children with Down syndrome (DS) experience respiratory tract infections (RTIs) more frequently than healthy children. We investigated whether this is related to different immunological characteristics associated with DS. Methods: The study group consisted of 22 children with DS and 22 of their healthy, age-range matched siblings. Data were collected on infections and hospitalizations because of lower RTIs. Immunoglobulin and IgG subclass levels in blood, as well as lymphocyte and T cell (subset) counts, were determined. Results: The children with DS had a significantly higher frequency of lower RTIs and related hospitalization than their siblings. We also found significantly reduced IgG2 levels as well as significantly lower counts of total lymphocytes, CD4+ T lymphocytes, CD4+ invariant natural killer (iNKT) cells and regulatory T cells in the DS group. Conclusion: In children with DS, reduced levels of IgG2, total lymphocytes, T lymphocytes, iNKT cells and regulatory T cells might contribute to their higher susceptibility to lower RTIs.