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Toll-like receptor 9 binds single-stranded CpG-DNA in a sequence- and pH-dependent manner
Mark Rutz1, Jochen Metzger, Tanja Gellert
1Institute for Medical Microbiology, Hygiene and Immunology, Munich, Germany.
European Journal of Immunology
|August 13, 2004
Summary
Toll-like receptor 9 (TLR9) directly binds CpG-DNA in endosomes. This interaction, crucial for immune response, is blocked by autoimmune disease drugs, suggesting a novel therapeutic mechanism.
Area of Science:
- Immunology
- Molecular Biology
- Pharmacology
Background:
- Toll-like receptors (TLRs) are key in innate immunity, recognizing pathogen components.
- The precise mechanism of TLR9 binding to its ligand, CpG-DNA, remains incompletely understood.
- TLR9 activation is implicated in autoimmune diseases.
Purpose of the Study:
- To elucidate the direct interaction between TLR9 and CpG-DNA.
- To identify the molecular basis for TLR9-CpG-DNA binding.
- To investigate the effect of autoimmune disease therapeutics on TLR9 activity.
Main Methods:
- Sequence-specific binding assays for TLR9 and CpG-DNA.
- Site-directed mutagenesis to identify the TLR9 binding domain.
- Inhibition assays using chloroquine and quinacrine.
Main Results:
- TLR9 directly and sequence-specifically binds unmethylated CpG-DNA with a phosphodiester backbone.
- Binding occurs under acidic endosomal/lysosomal pH conditions.
- A specific TLR9 domain was identified as critical for CpG-DNA binding and NF-kappaB activation.
- Chloroquine and quinacrine inhibit TLR9-CpG-DNA interaction, but not TLR2-Pam3Cys binding.
Conclusions:
- TLR9 directly interacts with CpG-DNA in an acidic endosomal environment.
- The therapeutic effects of chloroquine and quinacrine in autoimmune diseases may stem from their role as TLR9 antagonists.
- Inhibition of endosomal acidification is a potential mechanism for these drugs.