cAMP inhibits Fc_γ R-mediated phagocytosis in U937 cells. (A) Phagocytosis of E-IgG by U937 cells was performed after preincubation for 48 hours in the presence of the indicated concentrations of 8-bromoadenosine-3′:5′-cyclic-monophosphate and 40 nmol/L PMA. (B) cAMP levels in HIV-1–expressing U937 cells and controls. (C) cAMP levels in the indicated cell lines incubated for 48 hours in the absence or presence of the adenylate cyclase inhibitor, 2′-5′-dideoxyadenosine. (D) Phagocytosis of E-IgG by either U937 or UΔpol cells incubated for 48 hours in the absence or presence of the adenylate cyclase inhibitor, 2′-5′-dideoxyadenosine. Data represent the mean ± SEM of three to six experiments.