Human plasmacytoid dendritic cells express the functional purinergic halo (CD39/CD73)

Area of Science:

• Immunology
• Cell Biology

Background:

• Plasmacytoid dendritic cells (pDCs) are key in antiviral immunity, sensing pathogens via toll-like receptors (TLRs) and releasing type I interferons (IFN-I).
• While pDC inflammatory roles are known, their regulatory mechanisms, particularly involving ectoenzymes CD39 and CD73, remain understudied.
• CD39 and CD73 convert extracellular ATP into adenosine, shifting the immune microenvironment from pro-inflammatory to anti-inflammatory.

Purpose of the Study:

• To investigate the expression and function of the CD39/CD73 purinergic system in human blood pDCs for the first time.
• To determine if TLR-7 stimulation affects CD39 and CD73 expression and activity in pDCs.
• To explore the impact of the CD39/CD73 system on pDC allostimulatory capacity.

Main Methods:

• Flow cytometry was used to assess CD39 and CD73 surface and intracellular expression on human peripheral blood pDCs.
• pDCs were stimulated with a TLR-7 agonist (R848) to evaluate changes in ectoenzyme expression and IFN-α secretion.
• Adenosine generation was measured upon exogenous ATP addition to activated pDCs, with and without CD73 blockade.
• pDC allostimulatory capacity for CD4+ T cells was assessed using co-culture assays.

Main Results:

• Under steady-state conditions, CD39 was expressed on 14.0% of pDCs, while CD73 was intracellularly expressed on 8.0% of pDCs.
• TLR-7 agonist stimulation significantly increased surface CD39 (43.3%) and CD73 (18.6%) expression and enhanced IFN-α secretion.
• Activated pDCs produced more adenosine from exogenous ATP, an effect reduced by CD73 blockade.
• Blocking CD73 diminished adenosine production and improved pDC allostimulatory function for CD4+ T cells.

Conclusions:

• Human blood pDCs express functional CD39 and CD73 ectoenzymes, forming a purinergic system.
• This purinergic system is upregulated upon TLR-7 activation and influences pDC immunoregulatory capacity.
• The findings open new avenues for understanding pDC roles in immune regulation and disease.