The characterisation and lifespan of human plasmacytoid dendritic cells
2Division of Medicine, University College London
3Department of Infectious Disease, Imperial College London
4Institute for Infection and Immunity, University of London
Introduction: Human dendritic cells (DC) consist of two principal subsets: plasmacytoid DC (pDC) and conventional DC (cDC). pDC are unique sentinel cells expressing both myeloid and lymphoid-associated antigens. They play a key role in antiviral immunity by producing large amounts of type I interferons. Despite their role in immune defence, the mechanisms regulating their generation and differentiation—key processes for understanding homeostasis and immunity—remain unclear.
Materials and methods: To characterise human pDC, a membrane marker screen was performed, analysing 378 membrane markers using the MACS® Marker Screen kit (Miltenyi Biotec) in combination with the downstream InfinityFlow analysis. To determine the lifespan of pDCs, healthy volunteers received a pulse of deuterium-labelled glucose (6,6-²H₂-glucose). pDC were sorted at several time points over a 25-day period, and non-exchangeable DNA deuterium incorporation was quantified using gas chromatography-mass spectrometry.
Results and discussion: The InfinityFlow pipeline identified several novel cell-surface markers that are uniquely expressed on pDC compared to other mononuclear phagocyte subsets examined. Surprisingly, analysis of the deuterium incorporation, revealed that pDC emerge from the bone marrow much later than other circulating DC e.g. AXL+Siglec6+DCs (ASDC) or cDC. This highlights the variance between the cDC and pDC families. Competing mathematical models of pDC lifespan were assessed and the most appropriate model was adopted. pDC exhibit a protracted bone marrow dwell time of ~7.2 days before transiting to the bloodstream. The mean circulating lifespan of pDC was just under ~2 days before cells left the circulation.
Conclusions: In this study, we conducted an in-depth characterisation of human pDCs during healthy homeostasis. Unlike the fleeting nature of cDC and ASDC in the bone marrow, pDC lingered in the BM for around seven days prior to entering circulation. Future studies will help define the ontology and maturation of these cells.