Publications

Polymorphonuclear neutrophils release ATP in response to stimulation by chemoattractants, such as the peptide N-formyl-methionyl-leucyl-phenylalanine. Released ATP and the hydrolytic product adenosine regulate chemotaxis of neutrophils by sequentially activating purinergic nucleotide and adenosine receptors, respectively. Here we show that that ecto-nucleoside triphosphate diphosphohydrolase 1 (E-NTPDase1, CD39) is a critical enzyme for hydrolysis of released ATP by neutrophils and for cell migration in response to multiple agonists (N-formyl-methionyl-leucyl-phenylalanine, interleukin-8, and C5a). Upon stimulation of human neutrophils or differentiated HL-60 cells in a chemotactic gradient, E-NTPDase1 tightly associates with the leading edge of polarized cells during chemotaxis. Inhibition of E-NTPDase1 reduces the migration speed of neutrophils but not their ability to detect the orientation of the gradient field. Studies of neutrophils from E-NTPDase1 knock-out mice reveal similar impairments of chemotaxis in vitro and in vivo. Thus, E-NTPDase1 plays an important role in regulating neutrophil chemotaxis by facilitating the hydrolysis of extracellular ATP.

The study of T regulatory cells (T reg cells) has been limited by the lack of specific surface markers and an inability to define mechanisms of suppression. We show that the expression of CD39/ENTPD1 in concert with CD73/ecto-5'-nucleotidase distinguishes CD4(+)/CD25(+)/Foxp3(+) T reg cells from other T cells. These ectoenzymes generate pericellular adenosine from extracellular nucleotides. The coordinated expression of CD39/CD73 on T reg cells and the adenosine A2A receptor on activated T effector cells generates immunosuppressive loops, indicating roles in the inhibitory function of T reg cells. Consequently, T reg cells from Cd39-null mice show impaired suppressive properties in vitro and fail to block allograft rejection in vivo. We conclude that CD39 and CD73 are surface markers of T reg cells that impart a specific biochemical signature characterized by adenosine generation that has functional relevance for cellular immunoregulation.

CD39, the endothelial ecto-nucleoside triphosphate diphosphohydrolase (NTPDase), regulates vascular inflammation and thrombosis by hydrolyzing ATP and ADP. Although ecto-NTPDase activities have been used as a marker of epidermal dendritic cells (DCs) known as Langerhans cells, the identity and function of these activities remain unknown. Here we report that Langerhans cells in CD39-/- mice express no detectable ecto-NTPDase activity. Irritant chemicals triggered rapid ATP and ADP release from keratinocytes and caused exacerbated skin inflammation in CD39-/- mice. Paradoxically, T cell-mediated allergic contact hypersensitivity was severely attenuated in CD39-/- mice. As to mechanisms, T cells increased pericellular ATP concentrations upon activation, and CD39-/- DCs showed ATP unresponsiveness (secondary to P2-receptor desensitization) and impaired antigen-presenting capacity. Our results show opposing outcomes of CD39 deficiency in irritant versus allergic contact dermatitis, reflecting its diverse roles in regulating extracellular nucleotide-mediated signaling in inflammatory responses to environmental insults and DC-T cell communication in antigen presentation.

CD39, or vascular adenosine triphosphate diphosphohydrolase, has been considered an important inhibitor of platelet activation. Unexpectedly, cd39-deficient mice had prolonged bleeding times with minimally perturbed coagulation parameters. Platelet interactions with injured mesenteric vasculature were considerably reduced in vivo and purified mutant platelets failed to aggregate to standard agonists in vitro. This platelet hypofunction was reversible and associated with purinergic type P2Y1 receptor desensitization. In keeping with deficient vascular protective mechanisms, fibrin deposition was found at multiple organ sites in cd39-deficient mice and in transplanted cardiac grafts. Our data indicate a dual role for adenosine triphosphate diphosphohydrolase in modulating hemostasis and thrombotic reactions.