Plasmacytoid dendritic cells and their Toll-like receptor 9 expression selectively decrease with age.

Dendritic cells (DCs) play a crucial role in the initiation of immune responses against infectious particles and tumor cells; however, the impact of age, anthropometric parameters, and gender on the number and the expression of function-associated molecules of human DCs is poorly understood. In this study, blood DCs of 50 volunteers (19-84 years old) with no acute or chronic inflammatory diseases were examined using 4-color flow cytometry. Increasing age was associated with a decrease in blood plasmacytoid, but not myeloid DCs and a selective decrease in Toll-like receptor 9 (TLR9) expression by plasmacytoid DCs. In contrast, gender and body mass index did not impact the number of DC subsets or the expression of function-associated DC molecules. Thus, we demonstrate that age has a selective impact on plasmacytoid DCs and their TLR9 expression. This may contribute to an increased susceptibility to infections and tumors with increasing age.