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.