Resolution-phase macrophage phenotype is determined by cAMP. Macrophages (0.5 × 10⁶) previously classified as either resolution phase (rM) or M1 were treated with modulators of cAMP with or without LPS for 20 hours in triplicate. Using (A,B) TNFα and (C,D) IL-10 as markers of macrophage inflammatory status, it was determined that cAMP elevation in M1 cells triggered IL-10 while also inhibiting TNFα. Changes in (E) COX 2 and (F) iNOS expression in response to cAMP were determined by Western blot analysis using 3 μg M1 and rM cell lysates in each lane. LPS-stimulated J774 macrophage extracts were used as positive controls. n = 6 to 8 mice per group. *P ≤ .05, as determined by ANOVA, followed by Bonferroni t test with data expressed as mean plus or minus SEM.