Effect of adenosine on MAPK activation in E coli-stimulated macrophages. (A) E coli but not adenosine increases p42/44 activation. Peritoneal macrophages were challenged with E coli in the presence or absence of adenosine for 5, 15, and 30 minutes. p42/44 MAPK activation was determined from cytosolic extracts taken at the end of the 5-, 15-, and 30-minute incubation periods using Western blotting with antibodies raised against the active, doubly phosphorylated form of p42/44. Bands were detected using autoradiography. Relative densities are fold increase vs. control. This figure is representative of 3 separate experiments. (B) Adenosine but not E coli increases p38 activation. Peritoneal macrophages were challenged with E coli in the presence or absence of adenosine for 5, 15 and 30 minutes. p38 MAPK activation was determined from cytosolic extracts taken at the end of the 5-, 15-, and 30-minute incubation periods using Western blotting with antibodies raised against the active, doubly phosphorylated form of p38. Bands were detected using autoradiography. Relative densities are fold increase vs. control. This figure is representative of 3 separate experiments. (C) Inhibition p38 but not p42/44 MAPK prevents the stimulatory effect of adenosine on IL-10 production in E coli–treated macrophages. Peritoneal macrophages were pretreated for 30 minutes with 5 μM SB203580 (p38 inhibitor) or 30 μM PD98059 (p42/44 inhibitor) before adding 100 μM adenosine and heat-killed E coli. After 5 hours, supernatants were harvested and IL-10 levels measured using enzyme-linked immunosorbent assay. Results (mean ± SEM) shown are representative of at least 3 experiments with n = 6 in each experiment. ***P < .001 vs. E coli alone. ^###P < .001 vs. 100 μM adenosine plus E coli.