Cutting edge: CpG DNA inhibits dendritic cell apoptosis by up-regulating cellular inhibitor of apoptosis proteins through the phosphatidylinositide-3 '-OH kinase pathway

CpG DNA has been recognized as a powerful stimulant of dendritic cells (DCs). In this study, we demonstrate that CpG DNA inhibits spontaneous apoptosis of DCs. CpG DNA up-regulated cellular inhibitor of apoptosis proteins (cIAPs) as well as Bcl-2 and Bcl-x(L), but down-regulated active caspase-3. Although CpG DNA activated p38 mitogen-activated protein kinase, extracellular signal-related kinase, and phosphatidylinositide-3'-OH kinase (PI3K), only the blocking of PI3K inhibited the CpG DNA-induced DC survival. Moreover, while the expression of Bcl-2 and Bel-x(L) depends on both PI3K and p38 mitogen-activated protein kinase, the up-regulation of cIAPs and the down-regulation of active caspase-3 by CpG DNA require PI3K activation, suggesting PI3K-dependent upregulation of cIAPs in the antiapoptotic activity of CpG DNA in DCs. This study indicates that CpG DNA provides a survival signal to DCs, which might be one of mechanisms by which bacterial DNA stimulates and maintains the innate immune responses.