Effect of DA on intracellular cAMP in Teffs and in Tregs. Cells were cultured alone (○, control) or in the presence of 1 μM DA (•). Each point is the mean ± SD of 3 separate experiments. *P < .01 versus 0 minutes; §P < .01 versus control at the corresponding time interval. (Inset) Effect of the dopaminergic receptor antagonists SCH 23390 (circles), haloperidol (squares), and spiperone (diamonds) on 1 μM DA–induced increase of cAMP after 4-hour culture. Data are expressed as percentage of the values obtained in the presence of DA alone. Each point is the mean ± SD of 3 separate experiments. See “Results” for IC₅₀ values.