Inhibition of IFN-α production is mediated by P2Y receptors and may involve PKC activation. (A) Influence of nucleotides on CpG ODN uptake by PDCs. PDCs were incubated with Alexa 488–labeled ODN 2216 or ODN 2006 in the absence or presence of 100 μM ATP. ODN uptake was analyzed by fluorescence-activated cell sorting (FACS) analysis after 2 hours. One representative experiment of 2 is shown. (B) Effect of the P2Y receptor antagonist suramin on UDP-mediated inhibition of IFN-α. PDCs were activated with ODN 2216 in the absence or presence of 0.1 μM UDP and suramin. Data represent mean values ± SEM of 3 donors. (C) Effect of ionomycin on IFN-α production. PDCs were activated with CpG ODN 2216 in the absence or presence of 100 ng/mL ionomycin (IM). (D) Effect of PKC activation with PMA on IFN-α production. PDCs were activated with CpG ODN 2216, CpG ODN 2006, influenza virus, or R-848 in the absence or presence of 10 ng/mL PMA. IFN-α levels were measured in the supernatants after 48 hours. Data in panels C,D represent mean values (± SEM) of 4 to 6 donors. *P < .05.