Influence of time point of nucleotide exposure on inhibition of IFN-α production. PDCs were exposed to 100 μM ATP either 1 hour before, simultaneously, or up to 6 hours after activation with CpG ODN 2216. CpG-induced IFN-α production in the absence of nucleotides was normalized to 100%. Data represent means of percent changes (± SEM) of 4 different donors. *P < .05.