Background/Purpose: CD39 and CD73 are so-called ectonucleotidases, surface enzymes expressed by leukocytes and endothelial cells that jut into the extracellular space. There, they mediate the step-wise conversion of the autocrine and paracrine danger signal ATP into anti-inflammatory adenosine. Given the established role of a cell’s “purinergic halo” in maintenance of immune and vascular homeostasis, we hypothesized that ectonucleotidases might play a protective role in lupus.

Methods: Lupus can be modeled by intraperitoneal administration of pristane to mice. Cardinal features of lupus develop over 6-9 months, including anti-ribonucleoprotein (RNP) antibody production and immune-complex nephritis. In this study, we administered either pristane or saline to three groups of female C57BL/6 mice: wild-type (WT), CD39^-/-, and CD73^-/-. After 36 weeks, we characterized serum autoantibodies, splenocyte activation/polarization, neutrophil responses, proteinuria, and endothelial function.

Results:  As both CD39 and CD73 have well-recognized roles in regulatory T cell function, we first assessed adaptive immune responses. In the T-cell compartment, deficiency of either ectonucleotidase led to a 3-fold expansion of autoimmune-promoting T_H17 (but not T_H1) cells. CD39^-/- mice developed marked spenomegaly in response to pristane. Activated B cells and plasma cells were expanded in CD73^-/- mice. Regarding serum autoantibodies, the CD73^-/- mice in particular showed exaggerated anti-RNP production in response to pristane (a 10-fold increase) as compared to WT. As purinergic signaling may also regulate innate immune cells, we assessed an effector function of emerging importance in lupus, neutrophil extracellular trap (NET) release. NETs are pro-inflammatory webs of chromatin extruded from neutrophils. CD73 deficiency resulted in relative neutrophilia in response to pristane, while deficiency of either ectonucleotidase led to exaggerated NET release (a 2-fold increase) as compared to WT. Further, CD73^-/- mice demonstrated heightened levels of plasma cell-free DNA, a surrogate for circulating NETs. Both nephritis and accelerated arterial disease are major causes of morbidity in lupus. Urine protein was elevated in both pristane-treated CD39^-/- and CD73^-/- mice as compared to pristane-treated WT. The administration of pristane to WT mice triggered only subtle dysfunction of the arterial endothelium. In contrast, both CD39^-/- and CD73^-/- mice demonstrated striking dysfunction in response to pristane. This endothelial dysfunction could be rescued by treatment with superoxide dismutase, suggesting a role for oxidative stress in driving the vasculopathy.

Conclusion: These data are the first to link ectonucleotidases with lupus autoimmunity and vascular disease. In particular, they newly implicate purinergic signaling in the regulation of lupus T-cell responses and NET release, and demonstrate that ectonucleotidases protect against endothelial dysfunction in lupus by suppressing oxidative stress. New therapeutic strategies may harness purinergic signaling to limit the damage inflicted by lupus upon organs and blood vessels.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ectonucleotidase-mediated-protection-of-lupus-mice-from-exaggerated-immune-responses-and-arterial-vasculopathy/