Reduced numbers of plasmacytoid dendritic cells in aged blood donors

Dendritic cells (DC) play essential functions in both innate and adaptive immune responses. Peripheral blood DCs are divided into two major subsets, named conventional DC (cDC) and plasmacytoid DC (pDC), which play specific functions in the immune response. The absolute numbers of DCs (and their subsets) in peripheral blood may suffer variations due to physiological or pathological reasons, and therefore the enumeration of DC subsets in blood samples may be of clinical interest. However, to date this enumeration has produced controversial rather than consistent results. Here, using a two-tube platform approach, peripheral blood DCs have been enumerated in samples from healthy blood donors aged 18–65 years old. The results obtained showed a significant age-related decrease in pDC numbers, whilst cDC numbers remained unaltered. The different protocols used to define and enumerate DC subsets from blood samples may account for the controversial results reported before, thus emphasizing the importance of a general consensus to enumerate DCs. Reduced pDC numbers may be related to the higher susceptibility to infection and deficient response to vaccination often observed in aged individuals.