A, Adenosine (ADO) augments LPS-stimulated IL-10 production by LPS-activated RAW 264.7 macrophages. Adenosine (100 μM) was added to cells immediately before immunostimulation with 10 μg/ml LPS. IL-10 concentrations were measured from supernatants taken 5 h after stimulation with LPS. B, Effect of the A1 receptor agonist CCPA, A2A receptor agonist CGS-21680 (CGS), nonselective/A2B receptor agonist NECA, and A3 receptor agonist IB-MECA on LPS-induced IL-10 production by RAW cells. Selective agonists were added to cells immediately before immunostimulation with 10 μg/ml LPS. IL-10 concentrations were measured from supernatants taken 5 h after stimulation with LPS. C, The A2B receptor antagonist alloxazine (ALLO) prevents the effect of adenosine on IL-10 production. Alloxazine (10 μM) was administered 30 min before adenosine (100 μM) and LPS (10 μg/ml) followed by a 5-h-long incubation, after which supernatants were taken for IL-10 ELISA. D, Western blot analysis confirms expression of A2B receptors in membrane fractions from RAW 264.7 macrophages. LPS (10 μg/ml) treatment of the cells for 3 h up-regulates A2B receptor expression. β-actin was used as control for protein loading. Results (mean ± SEM) shown are representative of at least three experiments with n = 4 in each experiment, with the exception of D, where n = 2 for each group. **, p < 0.01.