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Updated: Aug 24, 2026

Screening Bioactive Nanoparticles in Phagocytic Immune Cells for Inhibitors of Toll-like Receptor Signaling
Published on: July 26, 2017
Toll-like receptor 9 signaling activates NF-kappaB through IFN regulatory factor-8/IFN consensus sequence binding
Hideki Tsujimura1, Tomohiko Tamura, Hee Jeong Kong
1Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Abstract:
Unmethylated CpG DNA binds to the Toll-like receptor 9 (TLR9) and activates NF-kappaB to induce cytokine genes in dendritic cells (DCs). IFN regulatory factor (IRF)-8/IFN consensus sequence binding protein is a transcription factor important for development and activation of DCs. We found that DCs from IRF-8(-/-) mice were unresponsive to CpG and failed to induce TNF-alpha and IL-6, targets of NF-kappaB. Revealing a signaling defect selective for CpG, these cytokines were robustly induced in IRF-8(-/-) DCs in response to LPS that signals through TLR4. IRF-8(-/-) DCs expressed TLR9, adaptor myeloid differentiation factor 88, and other signaling molecules, but CpG failed to activate NF-kappaB in -/- cells. This was due to the selective inability of -/- DCs to activate I-kappaB kinase alphabeta, the kinases required for NF-kappaB in response to CpG. IRF-8 reintroduction fully restored CpG activation of NF-kappaB and cytokine induction in -/- DCs. Together, TLR signals that activate NF-kappaB are diverse among different TLRs, and TLR9 signaling uniquely depends on IRF-8 in DCs.
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