IMMUNOBIOLOGY Extracellular nucleotide signaling by P2 receptors inhibits IL-12 and enhances IL-23 expression in human dendritic cells: a novel role for the cAMP pathway

The interleukin-12 (IL-12) cytokine family plays important roles in the orchestration of innate and adaptive immunity by den-dritic cells (DCs). The regulation of IL-12 expression has been thoroughly studied, but little is known about factors govern-ing the expression of IL-23 and IL-27, 2 novel IL-12 family members acting on memory and naive T cells, respectively. We report that the expression of these cytokines by DCs was critically depen-dent on the mode of activation. DC activa-tion by CD40L predominantly induced IL-12. Ligands of the Toll-like recepto