Essential Role for IKKβ in Production of Type 1 Interferons by Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs) are characterized by their ability to produce high levels of type 1 interferons in response to ligands that activate TLR7 and TLR9, but the signaling pathways required for IFN production are incompletely understood. Here we exploit the human pDC cell line Gen2.2 and improved pharmacological inhibitors of protein kinases to address this issue. We demonstrate that ligands that activate TLR7 and TLR9 require the TAK1-IKK beta signaling pathway to induce the production of IFN beta via a pathway that is independent of the degradation of I kappa B alpha. We also show that IKK beta activity, as well as the subsequent IFN beta-stimulated activation of the JAK-STAT1/2 signaling pathway, are essential for the production of IFN alpha by TLR9 ligands. We further show that TLR7 ligands CL097 and R848 fail to produce significant amounts of IFN alpha because the activation of IKK beta is not sustained for a sufficient length of time. The TLR7/9-stimulated production of type 1 IFNs is inhibited by much lower concentrations of IKK beta inhibitors than those needed to suppress the production of NF kappa B-dependent proinflammatory cytokines, such as IL-6, suggesting that drugs that inhibit IKK beta may have a potential for the treatment of forms of lupus that are driven by self-RNA and self-DNA-induced activation of TLR7 and TLR9, respectively.