Incubation of purified C57BL/6 murine CD4+ T lymphocytes with anti-CD3 mAb serves as a model of TCR-mediated activation and results in increased IFN-γ production and cell surface expression of CD25 and CD69. We demonstrate here that signaling through the TCR causes a rapid (4-h) 5-fold increase in A 2A adenosine receptor (AR) mRNA, which is correlated with a significant increase in the efficacy of A 2A AR-mediated cAMP accumulation in these cells. A 2A AR activation reduces TCR-mediated production of IFN-γ by 98% with a potency order of 4-{3-[6-amino-9-(5-ethylcarbamoyl-3, 4-dihydroxytetrahydrofuran-2-yl)-9H-purin-2-yl] prop-2-ynyl} cyclohexanecarboxylic acid methyl ester (ATL146e; EC 50= 0.19±0.03 nM)> 4-{3-[6-amino-9-(5-cyclopropyl-carbamoyl-3, 4-dihydroxytetrahydrofuran-2-yl)-9H-purin-2-yl] prop-2-ynyl} piperidine-1-carboxylic acid methyl ester (ATL313; 0.43±0.06 nM)> 5′-N-ethylcarboxamidoadenosine (3.5±0.77 nM)> 2-[4-(2-carboxyethyl) phenethylamino]-5′-N-ethylcarboxamidoadenosine (CGS21680; 7.2±1.4 nM)≫ N 6-cyclohexyladenosine (110±33 nM)> 2-chloro-N 6-(3-iodobenzyl)-5′-N-methylcarboxamide (390±160 nM), similar to the potency order to compete for radioligand binding to the recombinant murine A 2A AR but not the A 3 AR. The selective A 2A AR antagonist, 4-(2-[7-amino-2-[2-furyl][1, 2, 4] triazolo [2, 3-a][1, 3, 5] triazin-5-yl-amino] ethyl) phenol (ZM241385), inhibits the effect of ATL146e with ap A 2 of 0.34 nM and also inhibits the effects of N 6-cyclohexyl-adenosine and 2-chloro-N 6-(3-iodobenzyl)-5′-N-methylcarboxamide. In CD4+ T cells derived from A 2A AR−/− and A 2A AR+/− mice, the IFN-γ release response to ATL146e is reduced by 100 and 50%, respectively, indicative of a gene dose effect. The response of T cells to the phosphodiesterase inhibitor, 4-(3′-cyclopentyloxy-4′-methoxyphenyl)-2-pyrrolidone (rolipram), is not affected by A 2A AR deletion. We conclude that the rapid induction of the A 2A AR mRNA in T cells provides a mechanism for limiting T cell activation and secondary macrophage activation in inflamed tissues.