Activation of Th1 and Tc1 cell adenosine A2A receptors directly inhibits IL-2 secretion in vitro and IL-2-driven expansion in vivo

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Abstract
To evaluate the direct effect of adenosine on cytokine-polarized effector T cells, murine type 1 helper T cells (Th1) and type 1 cytotoxic T lymphocytes (Tc1) and Th2/Tc2 cells were generated using an antigen-presenting cell (APC)-free method. Tc1 and Tc2 cells had similar adenosine signaling, as measured by intracellular cyclic AMP (cAMP) increase upon adenosine A2A receptor agonism by CGS21680 (CGS). CGS greatly reduced Tc1 and Tc2 cell interleukin 2 (IL-2) and tumor necrosis factor α (TNF-α) secretion, with nominal effect on interferon γ (IFN-γ) secretion. Tc2 cell IL-4 and IL-5 secretion was not reduced by CGS, and IL-10 secretion was moderately reduced. Agonist-mediated inhibition of IL-2 and TNF-α secretion occurred via A2A receptors, with no involvement of A1, A2B, or A3 receptors. Adenosine agonist concentrations that abrogated cytokine secretion did not inhibit Tc1 or Tc2 cell cytolytic function. Adenosine modulated effector T cells in vivo, as CGS administration reduced CD4+Th1 and CD8+Tc1 cell expansion to alloantigen and, in a separate model, reduced antigen-specific CD4+ Th1 cell numbers. Remarkably, agonist-mediated T-cell inhibition was abrogated by in vivo IL-2 therapy. Adenosine receptor activation therefore preferentially inhibits type I cytokine secretion, most notably IL-2. Modulation of adenosine receptors may thus represent a suitable target primarily for inflammatory conditions mediated by Th1 and Tc1 cells. (Blood. 2005;105: 4707-4714)