Extracellular purine metabolism and signaling of CD73-derived adenosine in murine Treg and Teff cells

Abstract

CD73-derived adenosine acts as potent inhibitor of inflammation, and regulatory T cells (Treg) have been shown to express CD73 as a novel marker. This study explored the role of endogenously formed adenosine in modulating NF-κB activity and cytokine/chemokine release from murine Treg and effector T cells (Teff) including key enzymes/purinergic receptors of extracellular ATP catabolism. Stimulating murine splenocytes and CD4(+) T cells with anti-CD3/anti-CD28 significantly upregulated activated NF-κB in CD73(-/-) T cells (wild type: 4.36 ± 0.21; CD73(-/-): 6.58 ± 0.75; n = 4; P = 0.029). This was associated with an augmented release of proinflammatory cytokines IL-2, TNF-α, and IFN-γ. Similar changes were observed with the CD73 inhibitor APCP (50 μM) on NF-κB and IFN-γ in wild-type CD4(+) T-cells. Treatment of stimulated CD4(+) T-cells with adenosine (25 μM) potently reduced IFN-γ release which is mediated by adenosine A2a receptors (A2aR). AMP (50 μM) also reduced cytokine release which was not inhibited by APCP. In Teff, A2aR activation (CGS21680) potently inhibited the release of IL-1, IL-2, IL-3, IL-4, IL-12, IL-13, IFN-γ, TNF-α, granulocyte-macrophage colony-stimulating factor (GM-CSF), CCL3, and CCL4. However, in Treg, CGS21680 did not alter cytokine/chemokine release. In summary, CD73-derived adenosine tonically inhibits active NF-κB in CD4(+) T-cells, thereby modulating the release of a broad spectrum of proinflammatory cytokines and chemokines. Downregulation of P2X7 and upregulation of CD73 in Treg after antigenic stimulation may be an important mechanism to maintain the ability of Treg to generate immunosuppressive adenosine.

Autocrine Adenosine Signaling Promotes Regulatory T Cell–Mediated Renal Protection

“…11 A recent study reported that stimulation of the A 2A R during antigen-dependent stimulation enhanced FoxP3 and LAG-3 expression in T cells. 20 In our study, we compared gene expression of known Treg functional molecules in freshly isolated CD4 + CD25 + Tregs from WT and A 2A R KO mice (including FoxP3, IL-10, TGF-b1, CTLA-4, CD73, CD39, or LAG-3) and found no difference in Tregs between the two genotypes of mice.…”

“…[8][9][10][11][12][13] Adenosine generation by Tregs is a recognized mechanism of suppressing adaptive immune responses. [8][9][10]12 To investigate the requirement for adenosine generation by Tregs in suppressing the inflammation that contributes to kidney IRI, we compared the ability of adoptively transferred WTand CD73 KO Tregs to protect from kidney IRI.…”

“…8,9 Tregs highly express CD39 and CD73, cell-surface enzymes that sequentially dephosphorylate extracellular ATP and ADP to AMP and AMP to adenosine, respectively. [8][9][10][11][12] Although the importance of Treg production of adenosine is established in the context of suppressing adaptive immunity, the requirement for adenosine generation in Treg-mediated suppression of innate immunity and/or kidney ischemic injury has not been investigated.…”

“…13 The protective effect of A 2A R agonists required A 2A R expression on bone marrow-derived cells in contrast to kidney parenchymal cells. 14 In addition to proinflammatory leukocytes, Tregs express the A 2A R, 8,11 but the functional significance of this receptor on Tregs is not known.…”

Immune Abnormalities in Patients Meeting New Diagnostic Criteria for Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

“…CD73 + converts AMP to adenosine, regulating the immune response [33]. Abnormal levels in these parameters may alter inflammatory reactions in the CFS/ME patients altering the extent of Treg suppression of other immune cells and immune processes [31].…”