High Sensitivity of CD4+CD25+ Regulatory T Cells to Extracellular Metabolites Nicotinamide Adenine Dinucleotide and ATP: A Role for P2X7 Receptors

Abstract

Although regulatory lymphocytes play an important role in the immune system, the regulation of their functions is poorly understood and remains to be elucidated. In this study we demonstrate that micromolar concentrations of the common cell metabolite NAD induce death in murine forkhead/winged helix transcription factor gene-expressing CD4+CD25+ regulatory T cells with high efficiency and within minutes. Similar, but less dramatic, effects are demonstrable with ATP and its nonhydrolysable derivative, benzoylbenzoyl-ATP. Other T cell subsets are more resistant, with CD8 cells being the least sensitive and CD4 cells expressing intermediate sensitivity. The higher sensitivity of CD4+CD25+ cells is demonstrable in vivo. Injection of NAD or benzoylbenzoyl-ATP causes preferential induction of a cell death signal in CD4+CD25+ cells. Transmission of the death signal requires functional P2X7 receptors, pointing to a role for these receptors in regulation and homeostasis of CD4+CD25+ regulatory T cells. Consistent with this, P2X7R gene-deleted mice possess increased levels of forkhead/winged helix transcription factor gene-expressing CD4+CD25+ cells.

Purinergic signaling in inflammatory cells: P2 receptor expression, functional effects, and modulation of inflammatory responses

“…The extent to one or another of both actions depends on the level of P2X7 receptor cell surface expression in the T cell subtype; CD4+ CD25+ T regulatory cells are particularly sensitive to ATP-induced cell death and this high sensitivity correlates with a high expression level of the P2X7 receptor. T helper cells showed intermediate sensitivity to ATP, whereas cytotoxic T cells are the least sensitive and showed the lowest expression of the P2X7 receptor [177].…”

“…Similarly, Blanchard et al provided evidence that ATP is released from cytotoxic T cells during antigen presentation, and that IFN-γ-activated macrophages underwent necrosis [173].Besides the induction of cell death in the cytotoxic T lympocytes' target cells, also the T cells themselves are reported to undergo ATP-mediated cell death [175]. Unlike cytotoxic T cells and T helper cells, it is the T regulatory cells that are reported to be particularly sensitive to undergo cell death accompanied by CD62L shedding in response to ATP [176,177]. As it is well documented that ATP triggers P2X7 receptor-dependent CD62L shedding in lymphocytes [25,178,179] and because it is also known that the release of CD62L form T cells is associated with T cell activation [180], the involvement of this P2 receptor subtype in T cell responses could be suggested.…”

“…ATP also triggers P2X7 receptor-dependent CD62L shedding in lymphocytes [178,179] which is associated with T cell activation. b T regulatory (Treg) cells: CD4+ helper T cells upon stimulation of the TCR and potentiated by the inflammatory cytokine IL-6, increases the synthesis and release of ATP [169] which subsequently induces an autocrine P2X7-mediated signaling in Tregs [169] that inhibits the suppressive potential and stability of Tregs [177], and promotes their conversion to IL-17-secreting T Th17 effector cells [169]. However, TCR stimulation also enhances the expression of CD39 [170] which degrades ATP to ADP and AMP.…”

NAD+-Consuming Enzymes in the Regulation of Lung Immune Responses

“…Recently it has been shown that T cell activation induces down modulation of P2X7 expression and shedding of ART2 by TACE metalloproteinase leading to resistance to NICD [4,7,38]. Alternatively, CD4+Foxp3+ regulatory cells were demonstrated to be highly sensitive to NICD through the ART2-P2X7 pathway [8,39]. This suggests that elimination of part of the naïve and regulatory T cells via ART2-dependent ADP-ribosylation would allow the expansion of Ag-primed T cell populations and thus increase T cell responses.…”

“…It has been shown as well that sensitivity to NICD is high in CD4+CD25+ regulatory T cell. This suggests that NAD+ treatment during the early phase of the immune response could contribute toward improved response through the elimination of naïve and immunosuppressive regulatory T cells [8].…”