Alterations in Resident Immune Cells in Prenatal Trisomy 21 Lungs.

Respiratory tract infections (RTIs) are amongst the leading causes of hospitalizations in children with Down syndrome (DS). Their elevated susceptibility likely stems from structural differences in the airways and immune system abnormalities. The aim of this study was to characterize immune cells in prenatal Trisomy 21 (T21) lungs, potentially explaining vulnerability to RTIs. Single-cell RNA sequencing was used to profile immune cells in prenatal T21 (n = 5) and non-T21 (n = 4) prenatal lungs. Spatial phenotypes were assessed via fluorescent in situ hybridization and immunofluorescent staining on prenatal lung tissue sections. Gene expression analysis was also performed on isolated immune cells from lung single-cell suspensions. Several major immune cell populations were identified. A total of 84 DEGs were identified in at least 1 of the 14 different clusters. A significant decrease in the percentage of B cells was observed in T21 lungs (FDR = 0.0037, * p < 0.05). Furthermore, qRT-PCR demonstrated B cell markers were significantly decreased in T21, including those associated with B cell maturation (* p < 0.05 and ** p < 0.01). Several of these markers were also decreased at the protein level (i.e., CD20 and CD38; * p < 0.05 and ** p < 0.01). Our data demonstrate changes in the T21 pulmonary immune system in utero, primarily within the B cell population, which may contribute to the increased susceptibility to RTIs observed in children with DS.